In order to understand the users and what their activity actually consists of we proceeded with organising the user sessions in all three companies. Sessions consisted of two phases: (1) observation; (2) semi-structured interviews. Observation was focused on identifying characteristics of the working activity performed by the worker, his/her behaviour and usage of PPE. Semi-structured interviews were done both with workers to understand the level of perception about the risk and what they find as motivating or demotivating about wearing the PPE, and employers with a purpose to understand how the question about providing and wearing the PPE in this kind of environment is regulated, and in both cases we wanted to understand whether they are positive about introducing advanced technology based on monitoring in their ambit. In this session, all 20 workers were engaged in the period between December 2015 and January 2016. The user session was essential for this research because it was necessary to get to know the users well, their behaviour, if their activity is supposed to take place in coating cabin and with an aspiration system or not and typology of PPE that they are provided. Findings about the PPE show that the workers are generally provided with two different types of masks: (1) Disposable Protective Mask (with a small valve that helps the respiration) and (2) Reusable Half Mask with carbon filters (solid or liquid particles gas and vapour); the selection of these is certainly dependent on technical and chemical parameters such as: Typology of coating, Typology of pollution, Density of Coating Powder. The mask has its expiry date and it is dependent on its typology. Disposable masks last one day and have to be immediately thrown away, while the reusable ones have temporary bodies and filters that are interchangeable and last no more than 1 month. The filter expiring frequency is not dictated only by the hours of wearing but also whether it was protected in the box or exposed

objective.

3.1. Participants

54 Wearable Technologies

ing of metals, polymers, wood and steel were chosen.

3.2. Identifying the users and general problematics

the mask, wearable device equipped with a sensor able to detect breathing and heart rate parameters and provide information through a Mobile App. Moreover, they would like to know when it is necessary to wear the mask (hazardous condition). They would like to know about daily data (environment and personal health) but also seasonal ones [32–37].

Among all the elements of the system, the Protective Mask was the most diversified one not only on a technological level but also on a formal level; the general idea was to introduce padded fabric instead of rubber material in order to increase comfort and provide more transpiration between skin and mask and perhaps introduce a new mode of use. Beside these design requirements, the mask was supposed to contain temperature and humidity sensor for human-presence detection. Based on these three concepts for the mask that were generated, the first concept represents familiar architecture of the protective mask with a rigid central part and soft structure around the face. Here the proposed improvement is in the material that is in contact with a face that is designed to be in spacer textile. The mode of use is as in traditional masks with standard regulation laces. Beside the rigid part in front of the nose is provided the space for sensor mounting. Second concept is principally focused on suggesting completely new mode of use that is using a lateral Velcro® closing of the mask body and regulation of laces with a small rotating wheel which makes mask regulation more immediate without a need of taking it off. Here the biggest part of the mask is designed in spacer fabric, leaving rigid part for sensor and filter mounting. The spacer is taught to be coupled with a polymeric membrane in order to isolate from outer hazard agents. The third concept puts major focus on the comfort and here we are proposing a mask completely made in thermoformed laminated spacer textile. The idea is to exploit the process of fabric thermoforming, its possibilities to create the space for sensor and filter cartridges mounting. Besides making the structure lighter and providing more comfort, the filter cartridge mounting facilitation by creating the slide-in system was also thought of here.

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For Electronic Nose Device, three solutions based on different visual interactions—graphical form of the information—were generated. The information about air quality is communicated in the following way: (1) Concept 2: very simple with two phases of communication that consider only turning on and alarm; (2) Concept 1: more complex solution based on three phases that are turning on, warning and alarm; (3) and the last one—Concept 3—where there are also three phases as turning, warning and alarm but shaped in the form of a face expressing the emotions from happiness to sadness. All devices combine vibration and LED response. Different modes of use were studied for each device from the point of general wearability (harmony with the human body) that considers putting on and taking off the device and visibility of the feedback due to its position on the clothes or body (see Figure 2). Hypothesis about the mode of use of device was based also on the sensitiveness of the body part because beside the visibility of the feedback it is also important that the user feels vibration. Concepts propose the device be positioned in the zone of abdomen in particular arms and chest or making a more flexible form that can adjust to

Figure 2. Three concepts of the system.

#### 3.3. Delineating project requirements

Results gathered from the user analysis showed a few facts that are very important for project development: (1) Workers prefer not to wear the mask because the environment is not perceived as dangerous, except in some cases where the smell of paint is too evident. (2) Another reason that is influencing sparse wearing of mask is that workers state that generally the mask is uncomfortable. (3) Beside being pessimistic towards existing PPE, workers claimed that they would like to know more about their health condition, activity and working environment. There are some characteristics of the working activity that are to be respected when designing for these users, such as moving easily, having a good and vide visibility, sweating less and maintaining concentration. Thus, the most important factor for the workers was comfort.

Related to previously described points, design requirements were defined in the following way: (1) Form has to respond to the anatomical characteristics of the users, considering dimensions that are supposed to remain relatively small; (2) Apply materials that are breathable, anti-allergic and light; (3) Consider to provide filtered air (mask) and (4) Design the device, portable preferably, able to monitor, sense and eventually alert the user.

Making hypothesis about the potential appearance of the monitoring system, we must consider the possibility of designing a small portable device or apparel, or even integrate both. It seems like the only possibility to protect respiration is in the form of mask but integrating sensor inside it and its modus operandi may have different application possibilities. Information provided to the worker should be simple and comprehensive in order to gain motivation and reduce frustration factor. The principal tasks and requirements for designing wearable system were imposed with the intention to raise motivation about wearing PPE in workers by exploiting persuasive technologies, which also considered in improving comfort and providing real-time information about those that can be defined work-related risks, as in this case air quality and personal health condition.

#### 3.4. Ideation phase and focus group

The objectives enhancing the user's consciousness and providing better comfort considered designing the wearable system based on requirements able to satisfy these needs. Related to this were suggested a few strategies as those that consider creating the natural interaction language between the user and device funded on comprehension and engagement able to influence motivation and perception related to personal health. For this purpose, three concepts were generated and each of these was approached by following imposed requirements and design brief regarding materials and technology (soft technology, smart textiles, electronics, etc.). These concepts were studied trough Mock-ups and as a system rather than separate parts (see Figure 2).

Among all the elements of the system, the Protective Mask was the most diversified one not only on a technological level but also on a formal level; the general idea was to introduce padded fabric instead of rubber material in order to increase comfort and provide more transpiration between skin and mask and perhaps introduce a new mode of use. Beside these design requirements, the mask was supposed to contain temperature and humidity sensor for human-presence detection. Based on these three concepts for the mask that were generated, the first concept represents familiar architecture of the protective mask with a rigid central part and soft structure around the face. Here the proposed improvement is in the material that is in contact with a face that is designed to be in spacer textile. The mode of use is as in traditional masks with standard regulation laces. Beside the rigid part in front of the nose is provided the space for sensor mounting. Second concept is principally focused on suggesting completely new mode of use that is using a lateral Velcro® closing of the mask body and regulation of laces with a small rotating wheel which makes mask regulation more immediate without a need of taking it off. Here the biggest part of the mask is designed in spacer fabric, leaving rigid part for sensor and filter mounting. The spacer is taught to be coupled with a polymeric membrane in order to isolate from outer hazard agents. The third concept puts major focus on the comfort and here we are proposing a mask completely made in thermoformed laminated spacer textile. The idea is to exploit the process of fabric thermoforming, its possibilities to create the space for sensor and filter cartridges mounting. Besides making the structure lighter and providing more comfort, the filter cartridge mounting facilitation by creating the slide-in system was also thought of here.

For Electronic Nose Device, three solutions based on different visual interactions—graphical form of the information—were generated. The information about air quality is communicated in the following way: (1) Concept 2: very simple with two phases of communication that consider only turning on and alarm; (2) Concept 1: more complex solution based on three phases that are turning on, warning and alarm; (3) and the last one—Concept 3—where there are also three phases as turning, warning and alarm but shaped in the form of a face expressing the emotions from happiness to sadness. All devices combine vibration and LED response. Different modes of use were studied for each device from the point of general wearability (harmony with the human body) that considers putting on and taking off the device and visibility of the feedback due to its position on the clothes or body (see Figure 2). Hypothesis about the mode of use of device was based also on the sensitiveness of the body part because beside the visibility of the feedback it is also important that the user feels vibration. Concepts propose the device be positioned in the zone of abdomen in particular arms and chest or making a more flexible form that can adjust to

Figure 2. Three concepts of the system.

the mask, wearable device equipped with a sensor able to detect breathing and heart rate parameters and provide information through a Mobile App. Moreover, they would like to know when it is necessary to wear the mask (hazardous condition). They would like to know about

Results gathered from the user analysis showed a few facts that are very important for project development: (1) Workers prefer not to wear the mask because the environment is not perceived as dangerous, except in some cases where the smell of paint is too evident. (2) Another reason that is influencing sparse wearing of mask is that workers state that generally the mask is uncomfortable. (3) Beside being pessimistic towards existing PPE, workers claimed that they would like to know more about their health condition, activity and working environment. There are some characteristics of the working activity that are to be respected when designing for these users, such as moving easily, having a good and vide visibility, sweating less and maintaining concentration. Thus, the most important factor for the workers was comfort.

Related to previously described points, design requirements were defined in the following way: (1) Form has to respond to the anatomical characteristics of the users, considering dimensions that are supposed to remain relatively small; (2) Apply materials that are breathable, anti-allergic and light; (3) Consider to provide filtered air (mask) and (4) Design the

Making hypothesis about the potential appearance of the monitoring system, we must consider the possibility of designing a small portable device or apparel, or even integrate both. It seems like the only possibility to protect respiration is in the form of mask but integrating sensor inside it and its modus operandi may have different application possibilities. Information provided to the worker should be simple and comprehensive in order to gain motivation and reduce frustration factor. The principal tasks and requirements for designing wearable system were imposed with the intention to raise motivation about wearing PPE in workers by exploiting persuasive technologies, which also considered in improving comfort and providing real-time information about those that can be defined work-related risks, as in this case air

The objectives enhancing the user's consciousness and providing better comfort considered designing the wearable system based on requirements able to satisfy these needs. Related to this were suggested a few strategies as those that consider creating the natural interaction language between the user and device funded on comprehension and engagement able to influence motivation and perception related to personal health. For this purpose, three concepts were generated and each of these was approached by following imposed requirements and design brief regarding materials and technology (soft technology, smart textiles, electronics, etc.). These concepts were studied trough Mock-ups and as a system rather than separate

device, portable preferably, able to monitor, sense and eventually alert the user.

daily data (environment and personal health) but also seasonal ones [32–37].

3.3. Delineating project requirements

56 Wearable Technologies

quality and personal health condition.

3.4. Ideation phase and focus group

parts (see Figure 2).

any part of the clothes. The first concept (see Figure 2 on left) proposes a flexible clip that can be put anywhere from the T-shirt to the pockets of pants, that can fit to any kind of working uniform. The feedback for this device is in the form of LED that is blinking as alarm passes through four LED colours. Second and third concept (see Figure 2 on right) are thought to be positioned and fixed on the T-shirt by a push button in order to take it off when the uniform has to be washed. These two are not versatile; they stay always in the same position. Second concept is showing the interface based on mood expression as happy, not so happy and sad as a way to immediate the information related to the air quality that is equal to good, becoming hazardous and hazardous. The last concept is not using specific interface but just colour and vibration. In this case, the device adopts to the protective mask in sense of formal language. Even though the last concept is the one where the system language is empathised, other concepts are also adopting more or less formally to the protective masks next to which they are represented.

Technological principle is the same for each proposed device which consider Volatile Organic Compound (VOC) sensor, vibration motor and RGB LED. All of them have four steps of feedback where the first one indicates ignition signal and then passes to air quality detection that shows three levels: good air quality (green), air starting to be polluted (yellow) and hazardous air (red). Also, the vibration is set on three levels that correspond to LED signal for which when it is yellow the vibration is lower while when red it gets strong. It is possible to stop the alarm by pressing the delay button on device.

questionnaire to evaluate their experience with each part of the system. During the session,

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Figure 3. Two concepts of the application for the workers (left); the application for the employer (on the right).

During the session workers were able to give general comments and discussed with each other. The difficult part of the session was related to the evaluation of the Mobile App that was provided in form of screen's graphics and it was explained to them step-by-step. Nevertheless, they were also able to validate the App in the given questionnaire. After the session concluded, we gathered results and organised it in order to detect more easily and precisely the main strengths and constrains of proposed concepts. As it was accented previously, the main objective was defining the final concept and the starting point for final design definition. Since concepts proposed for protective mask also integrated application of textile, it was particularly important to have a feedback from workers on whether they liked it or not. Figure 5 shows the

The Mobile Application that workers preferred was Concept 2 because they found it the most comprehensive and simple to use. For the mask they indicated in each concept something that was adequate but the most liked one was Concept 1. One of the most important parameters for the mask designing was the aspect of comfort and it was evaluated very well for Concept 1 and Concept 2, while Concept 3 was generally evaluated with lower points. General image of concept evaluation is given in the charts below. The figure does not show results of the smart shirt because it was not appreciated as a solution, so we decided to eliminate the undershirt and leave just a band because it was something that was already familiar to users and

participants' voices were recorded and photos were taken (see Figure 4).

preferences that workers expressed for all concepts.

considered as more comfortable.

Figure 4. Some pictures from the Focus Group.

Initially, a T-Shirt with textile sensors on the inner part was thought of for the breathing and heart rate measuring. Two solutions were proposed where in the first one T-Shirt was tightened in the zone of chest in order to adhere better and in the second one was proposed undershirt with textile sensors that were supposed to be worn under the clothes or uniform.

Information gathered from the protective mask and electronic nose device are stored in the last part of the system that is the Mobile Application for which are showed three different concepts. Two of these are designed for workers and one for employer (see Figure 3). The idea of proposing few solutions, as in the case of Electronic Nose Device, is in the possibility to understand the level of technological and information engagement of users, starting from the basic communication to more complex one. Here were included options of personalisation of the Mobile App profile and various settings related to the working environment for the more complex interaction (Concept 1), while for the simple one, only parameters that are results of monitoring are represented (Concept 2).

The generated concepts were also realised in form of mock-ups for the user session. Those mock-ups were presented since the early stage of the design development both to engage the user in design process, understand the overall dimension of the product and evaluate its wearability. Indeed, all of these were tested and evaluated by the users. We wanted to investigate how created concepts satisfy needs of users related to previously mentioned parameters. Objective of the session was defining the solution that will be a starting point for final design development. Workers were invited to evaluate each part of the system, for each concept, on a scale from one to five for different objects' qualities, funded on parameters such as aesthetics, function, comfort, mode of use, comprehension of interaction. User session took a place in the same companies where our analysis started, and it was organised with a group of workers and employers that were wearing and trying all mock-ups after which they were given a Wearable Technology as a Tool to Motivate Health Behaviour: A Case Study http://dx.doi.org/10.5772/intechopen.77002 59

Figure 3. Two concepts of the application for the workers (left); the application for the employer (on the right).

questionnaire to evaluate their experience with each part of the system. During the session, participants' voices were recorded and photos were taken (see Figure 4).

During the session workers were able to give general comments and discussed with each other. The difficult part of the session was related to the evaluation of the Mobile App that was provided in form of screen's graphics and it was explained to them step-by-step. Nevertheless, they were also able to validate the App in the given questionnaire. After the session concluded, we gathered results and organised it in order to detect more easily and precisely the main strengths and constrains of proposed concepts. As it was accented previously, the main objective was defining the final concept and the starting point for final design definition. Since concepts proposed for protective mask also integrated application of textile, it was particularly important to have a feedback from workers on whether they liked it or not. Figure 5 shows the preferences that workers expressed for all concepts.

The Mobile Application that workers preferred was Concept 2 because they found it the most comprehensive and simple to use. For the mask they indicated in each concept something that was adequate but the most liked one was Concept 1. One of the most important parameters for the mask designing was the aspect of comfort and it was evaluated very well for Concept 1 and Concept 2, while Concept 3 was generally evaluated with lower points. General image of concept evaluation is given in the charts below. The figure does not show results of the smart shirt because it was not appreciated as a solution, so we decided to eliminate the undershirt and leave just a band because it was something that was already familiar to users and considered as more comfortable.

Figure 4. Some pictures from the Focus Group.

any part of the clothes. The first concept (see Figure 2 on left) proposes a flexible clip that can be put anywhere from the T-shirt to the pockets of pants, that can fit to any kind of working uniform. The feedback for this device is in the form of LED that is blinking as alarm passes through four LED colours. Second and third concept (see Figure 2 on right) are thought to be positioned and fixed on the T-shirt by a push button in order to take it off when the uniform has to be washed. These two are not versatile; they stay always in the same position. Second concept is showing the interface based on mood expression as happy, not so happy and sad as a way to immediate the information related to the air quality that is equal to good, becoming hazardous and hazardous. The last concept is not using specific interface but just colour and vibration. In this case, the device adopts to the protective mask in sense of formal language. Even though the last concept is the one where the system language is empathised, other concepts are also adopting more or less formally

Technological principle is the same for each proposed device which consider Volatile Organic Compound (VOC) sensor, vibration motor and RGB LED. All of them have four steps of feedback where the first one indicates ignition signal and then passes to air quality detection that shows three levels: good air quality (green), air starting to be polluted (yellow) and hazardous air (red). Also, the vibration is set on three levels that correspond to LED signal for which when it is yellow the vibration is lower while when red it gets strong. It is possible to

Initially, a T-Shirt with textile sensors on the inner part was thought of for the breathing and heart rate measuring. Two solutions were proposed where in the first one T-Shirt was tightened in the zone of chest in order to adhere better and in the second one was proposed undershirt with textile sensors that were supposed to be worn under the clothes or uniform. Information gathered from the protective mask and electronic nose device are stored in the last part of the system that is the Mobile Application for which are showed three different concepts. Two of these are designed for workers and one for employer (see Figure 3). The idea of proposing few solutions, as in the case of Electronic Nose Device, is in the possibility to understand the level of technological and information engagement of users, starting from the basic communication to more complex one. Here were included options of personalisation of the Mobile App profile and various settings related to the working environment for the more complex interaction (Concept 1), while for the simple one, only parameters that are results of

The generated concepts were also realised in form of mock-ups for the user session. Those mock-ups were presented since the early stage of the design development both to engage the user in design process, understand the overall dimension of the product and evaluate its wearability. Indeed, all of these were tested and evaluated by the users. We wanted to investigate how created concepts satisfy needs of users related to previously mentioned parameters. Objective of the session was defining the solution that will be a starting point for final design development. Workers were invited to evaluate each part of the system, for each concept, on a scale from one to five for different objects' qualities, funded on parameters such as aesthetics, function, comfort, mode of use, comprehension of interaction. User session took a place in the same companies where our analysis started, and it was organised with a group of workers and employers that were wearing and trying all mock-ups after which they were given a

to the protective masks next to which they are represented.

58 Wearable Technologies

stop the alarm by pressing the delay button on device.

monitoring are represented (Concept 2).

on the Electronic Nose Device design. For the reason of comfort and versatility that we want to obtain, the form of device changed and the form of the graphical feedback as well. We simplified even more the product by creating the abstract graphical representation that excluded the facial expression as a communication and maintained colours because both culturally and perceptually it communicates desired information. The new system consists of a Smart Personal Protective Reusable Mask, a wearable alert device called Electronic Nose

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In order to encourage workers to wear the Protective Mask, its re-design followed the user requirements about aesthetic and wearability. Hereafter, we can see a comparison between the

In the traditional mask, the parts in direct contact with the user's face are made in rubber that causes the mask to be uncomfortable and not worn regularly by the workers. In our new product, the rubber is substituted by a thermoformed spacer textile padded with soft foam. Spacer textile has a structure that is forming exactly to the face and its property to be transpired has the value of preventing from sweating even during the summer days. The Spacer textile chosen for this application has smooth external surface that is very pleasant in contact with skin. Since the spacer textile has a smooth surface, there was necessity to create more friction between the skin and the material surface. This was resolved by printing the silicon pattern in the zone of nose, chin and cheekbone. The layer of the silicon pattern is so thin that it is almost imperceptible, but it is giving enough adherence and friction. Workers were indeed

very positive about the idea to replace traditional materials with textile.

Device, a Chest Band t and a Mobile Application.

traditional mask and our new design (Figure 8).

Figure 6. System refinement.

Figure 7. New wearable system prototype.

Figure 5. System evaluation.

Concept 1 of Electronic Nose Device was appreciated the most for its mode of use, while Concept 3 for the mode of interaction by being the more comprehensive one.

About the Mobile App, the most liked one was the Concept 2. Mobile App for employers showed approval as being retained as very useful. All workers were positive on wearing the more comfortable mask regularly and being informed about the air quality. These factors may help not only in personal protection but also in controlling the ventilation and aspiration system, considering the employers' plants. After studying new forms, functions and communication, we came up with reviewing the previous concept and created the mask with new formal features, with an outer shell in spacer textile and filters made in thermoformed nonwoven textile with a purpose to make the mask lighter. Electronic Nose Device gained a simpler form with a flexible silicon clip. Since the Mobile App was very comprehensible to the users, we maintained the same concept and added the App for employer based on showing the results about the air quality in time and percentage of mask wearing during the day. Since the data about the mask wearing are strictly personal, employers cannot see who is not wearing it but have a general image about the mask wearing expressed in percentage scale.

Once we defined these details and developed new prototypes (Figure 6), we organised another focus group session with users after which they approved the final concept and showed rather positive about a possibility to have this kind of devices.

#### 3.5. Developing phase

Further, we proceeded with engineering parts and the prototype of the system (Figure 7) which brought us to reviewing again some parts of the project. In particular, we intervened on the Electronic Nose Device design. For the reason of comfort and versatility that we want to obtain, the form of device changed and the form of the graphical feedback as well. We simplified even more the product by creating the abstract graphical representation that excluded the facial expression as a communication and maintained colours because both culturally and perceptually it communicates desired information. The new system consists of a Smart Personal Protective Reusable Mask, a wearable alert device called Electronic Nose Device, a Chest Band t and a Mobile Application.

In order to encourage workers to wear the Protective Mask, its re-design followed the user requirements about aesthetic and wearability. Hereafter, we can see a comparison between the traditional mask and our new design (Figure 8).

In the traditional mask, the parts in direct contact with the user's face are made in rubber that causes the mask to be uncomfortable and not worn regularly by the workers. In our new product, the rubber is substituted by a thermoformed spacer textile padded with soft foam. Spacer textile has a structure that is forming exactly to the face and its property to be transpired has the value of preventing from sweating even during the summer days. The Spacer textile chosen for this application has smooth external surface that is very pleasant in contact with skin. Since the spacer textile has a smooth surface, there was necessity to create more friction between the skin and the material surface. This was resolved by printing the silicon pattern in the zone of nose, chin and cheekbone. The layer of the silicon pattern is so thin that it is almost imperceptible, but it is giving enough adherence and friction. Workers were indeed very positive about the idea to replace traditional materials with textile.

Figure 6. System refinement.

Concept 1 of Electronic Nose Device was appreciated the most for its mode of use, while

About the Mobile App, the most liked one was the Concept 2. Mobile App for employers showed approval as being retained as very useful. All workers were positive on wearing the more comfortable mask regularly and being informed about the air quality. These factors may help not only in personal protection but also in controlling the ventilation and aspiration system, considering the employers' plants. After studying new forms, functions and communication, we came up with reviewing the previous concept and created the mask with new formal features, with an outer shell in spacer textile and filters made in thermoformed nonwoven textile with a purpose to make the mask lighter. Electronic Nose Device gained a simpler form with a flexible silicon clip. Since the Mobile App was very comprehensible to the users, we maintained the same concept and added the App for employer based on showing the results about the air quality in time and percentage of mask wearing during the day. Since the data about the mask wearing are strictly personal, employers cannot see who is not wearing it but have a general image about the mask wearing expressed in percentage scale.

Once we defined these details and developed new prototypes (Figure 6), we organised another focus group session with users after which they approved the final concept and showed rather

Further, we proceeded with engineering parts and the prototype of the system (Figure 7) which brought us to reviewing again some parts of the project. In particular, we intervened

positive about a possibility to have this kind of devices.

3.5. Developing phase

Figure 5. System evaluation.

60 Wearable Technologies

Concept 3 for the mode of interaction by being the more comprehensive one.

Figure 7. New wearable system prototype.

Mobile Application is based on simple graphical representation of three parameters that are comparable in time: breathing rate, air quality (related to the level of VOC) and mask-wearing frequency. Application provides the worker with a complete image of the condition at the working place and frequency of his/her mask wearing and possibility to compare these data in sense of understanding whether the mask was worn when the air was hazard and how physiological parameters were respect to this event. Mobile application was designed to organise data on daily basis and provide weekly and monthly statistics as a sort of archive. Statistical data are intended to increase the visible benefits in wearing the Protective Mask: the worker can see the health progress made thanks to the wearing of the mask. Indeed, he/she will realise (see following section) how his/her breathing frequency improves while wearing the mask. This way, we created a wearable system with several useful features: (1) real-time sensing of the environment; (2) monitor the user respiration giving feedback useful to increase awareness about personal health; (3) show statistical data of the Mask-wearing frequency in relation to the presence of dangerous particles. Nowadays the use of PPEs in dangerous working environments is the only way for workers to prevent serious disease. Existing

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Figure 9. Electronic nose device feedback.

Figure 10. Chest band and its configuration.

Figure 8. Comparison between traditional mask and new design.

In our re-design, the thermoformed fabric has been chosen for two specific parts (both grey in the image): the part that adheres between the mask's body and the user's face and the laces staying around the user's head. In our intention, in addition to improving the wearability of the mask, the thermoformed fabric will also reduce the risk of skin irritation.

The laces around the head are traditionally manufactured in plastic with strong edges while we decided to use the thermoformed fabric because it is softer and smoother even in contact with the head. Moreover, we used non-woven thermoformed fabric for the filters that are then welded to the mask's base. This choice was aimed at decreasing the mask's weight reducing the use of plastic pieces. The mask is equipped with a temperature and humidity sensor aimed at monitoring the user 's breath (humidity and respiration frequency) but also to check if the mask is worn or not: if the mask comes in contact with the face, the sensor automatically detects the human temperature, or rather presence, and this information goes to Mobile App. User has a real-time feedback about the quality of the air in coating plant trough the Electronic Nose Device. This function is executed with a sensor that is giving objective data about pollution, which are not perceivable by the human nose. The sensor used for Electronic Nose Device (USM-MEMS-VOC) monitors the level of VOCs. While sensing the environment, the Electronic Nose gives three different feedback to the user: (1) green LED on: the sensor is operative and the air contains an acceptable VOCs' level; (2) yellow LED on and low vibration: the level of VOC is starting to exceed acceptable value; (3) red LED on and strong vibration: VOCs concentration in the air is risky for the user health (Figure 9).

The real-time feedback alerts the user when there is an urgent need to wear the Protective Mask. This might be the first step in increasing the benefits of wearing the mask regularly. Indeed, in the third-use case, if the user properly feels the vibration, he/she should press the button on the Electronic Nose and wear the mask. Therefore, the nose stops vibrating but in the meanwhile the air quality parameters are constantly monitored and transmitted to the Mobile Application via Bluetooth. Finally, the Chest Band (provided by the Company Comftech) monitors through the working day the user's breathing frequency. It is a textile band sensor that is worn under the T-Shirt (Figure 10).

Breathing frequency values are transmitted to Mobile Application to let the user be aware about his/her health every time (when he wears or not the mask). The Mobile Application is a storage of the system; it collects and organises data from the device, mask and chest band. The Mobile Application is based on simple graphical representation of three parameters that are comparable in time: breathing rate, air quality (related to the level of VOC) and mask-wearing frequency. Application provides the worker with a complete image of the condition at the working place and frequency of his/her mask wearing and possibility to compare these data in sense of understanding whether the mask was worn when the air was hazard and how physiological parameters were respect to this event. Mobile application was designed to organise data on daily basis and provide weekly and monthly statistics as a sort of archive. Statistical data are intended to increase the visible benefits in wearing the Protective Mask: the worker can see the health progress made thanks to the wearing of the mask. Indeed, he/she will realise (see following section) how his/her breathing frequency improves while wearing the mask. This way, we created a wearable system with several useful features: (1) real-time sensing of the environment; (2) monitor the user respiration giving feedback useful to increase awareness about personal health; (3) show statistical data of the Mask-wearing frequency in relation to the presence of dangerous particles. Nowadays the use of PPEs in dangerous working environments is the only way for workers to prevent serious disease. Existing

Figure 9. Electronic nose device feedback.

In our re-design, the thermoformed fabric has been chosen for two specific parts (both grey in the image): the part that adheres between the mask's body and the user's face and the laces staying around the user's head. In our intention, in addition to improving the wearability of

The laces around the head are traditionally manufactured in plastic with strong edges while we decided to use the thermoformed fabric because it is softer and smoother even in contact with the head. Moreover, we used non-woven thermoformed fabric for the filters that are then welded to the mask's base. This choice was aimed at decreasing the mask's weight reducing the use of plastic pieces. The mask is equipped with a temperature and humidity sensor aimed at monitoring the user 's breath (humidity and respiration frequency) but also to check if the mask is worn or not: if the mask comes in contact with the face, the sensor automatically detects the human temperature, or rather presence, and this information goes to Mobile App. User has a real-time feedback about the quality of the air in coating plant trough the Electronic Nose Device. This function is executed with a sensor that is giving objective data about pollution, which are not perceivable by the human nose. The sensor used for Electronic Nose Device (USM-MEMS-VOC) monitors the level of VOCs. While sensing the environment, the Electronic Nose gives three different feedback to the user: (1) green LED on: the sensor is operative and the air contains an acceptable VOCs' level; (2) yellow LED on and low vibration: the level of VOC is starting to exceed acceptable value; (3) red LED on and strong vibration:

The real-time feedback alerts the user when there is an urgent need to wear the Protective Mask. This might be the first step in increasing the benefits of wearing the mask regularly. Indeed, in the third-use case, if the user properly feels the vibration, he/she should press the button on the Electronic Nose and wear the mask. Therefore, the nose stops vibrating but in the meanwhile the air quality parameters are constantly monitored and transmitted to the Mobile Application via Bluetooth. Finally, the Chest Band (provided by the Company Comftech) monitors through the working day the user's breathing frequency. It is a textile

Breathing frequency values are transmitted to Mobile Application to let the user be aware about his/her health every time (when he wears or not the mask). The Mobile Application is a storage of the system; it collects and organises data from the device, mask and chest band. The

the mask, the thermoformed fabric will also reduce the risk of skin irritation.

Figure 8. Comparison between traditional mask and new design.

62 Wearable Technologies

VOCs concentration in the air is risky for the user health (Figure 9).

band sensor that is worn under the T-Shirt (Figure 10).

Figure 10. Chest band and its configuration.

personal equipment are "static" products. We instead developed an interactive system made up of "dynamic" products empowered with sensors and technology.

#### 3.6. Testing phase

The testing of the prototype was framed into two phases: Phase 1: The observation of the Practical Use of the System in two steps: (1) the workers were asked to wear the chest band and then to use the electronic nose for 30 min, this was useful to figure out if they understood how the electronic nose works; (2) They wore both the electronic nose and the mask; Phase 2: An unstructured Interview aimed at understanding: (1) Comfort and wearability of the overall system (Mask and Nose); (2) System Feedback Understanding; (3) Application Understanding; and (4) P\_O\_D\_ Efficacy. The user session was organised as a general observation coupled with sensor data collected in the working space and was carried out in May of 2017 on five workers. For the test, we choose the first one of the three companies analysed during the first user session because we met a very open-minded owner willing to innovate, experiment and to use the results of the project afterwards. Moreover, the workers of this company were the most collaborative and proactive ones.

Firstly, workers were given the prototypes and they were supposed to work with it on. This user session had two objectives. The first one was testing the products with users and the second was to understand the accuracy of the system in sense of monitoring data, both vital and environmental. In the image below, we can see the users in the painting cabin wearing the prototype (Figure 11).

> respect to the user's needs defined in the beginning of the project, raised the benefits related to the wearing of the mask and by this the willingness of workers. Giving a real-time feedback showed that when there is the visible input about the risk, they remember to wear the mask and their belief in the air quality changes. Having the data in Mobile App certainly impact motivation

Wearable Technology as a Tool to Motivate Health Behaviour: A Case Study

http://dx.doi.org/10.5772/intechopen.77002

65

A high number of respiratory diseases related to working environment are mostly present in sectors such as agriculture, manufacturing and transportation. Data coming from INAIL show that the manufacturing sector is the most dangerous among these where just in 2014 were detected 5172 cases. The best method of prevention and general increment of health in this case is wearing of PPEs. Results from our user analysis, obtained from three coating plants, approve that the workers are not willing to wear the mask. What we suggested as a solution to this problem was to encourage the workers to wear PPE by raising work-related risk awareness which they often undertake. This was thought to be executed by exploitation of persuasive technologies. Persuasive technologies may be defined as a tool able to influence or indeed change people's attitudes and behaviours [2]. Fogg [21] believes that successful products, the ones user will continue to use after the novelty, will be those that incorporate "hot triggers" to help people change their behaviours for the better. Behavioural Model developed

of workers by showing the progress of wearing the mask in time.

Figure 12. Simulation measurement of air quality and vital parameters.

4. Conclusions and further development

Figure 11. Users engaged in the final testing of the product.

At the same time, while workers were performing their activity we were controlling the parameters about the breathing rate and air quality through Apps on the mobile phone. Electronic part of the product showed as accurate, the quality of the air was changing respect to the presence of the overspray and distance from the object that is painted. It was giving a feedback to the user in real-time and the user found it quite comprehensive. The same is for breathing data; they were changing with respect to the level of presence of overspray and whether the mask was on or off. In the image below are shown the results obtained from air quality measurement and heart and breathing parameters (Figure 12).

After the observation in Coating Plant, users were engaged through an unstructured interview where they explained what they experienced while working with a P.O.D. system and if we succeeded in improving the wearability of the system. Workers were rather positive about the new mask; they appreciated the application of spacer textile instead of rubber and said that they were willing to wear it. They also appreciated Electronic Nose Device very much; the workers appreciated the possibility to wear it a versatile way: on the pants' pocket, on the shirt's collar, on the shirt's sleeves; the feedback and its general functioning was clear to them. They did not complain about the comfort of chest band, they found it unobtrusive and easy to use. In the end, they were given the Mobile App simulation to try to use it. Workers found it simple to use, the complexity of the app was proportional to their level of operating with this kind of medium and the graphical representation was immediate for them. Moreover, the employer showed interest in the system, but in particular he found very useful Electronic Nose Device and his Mobile App. Finally, observing the system as a whole, we can conclude that the improvement of the mask Wearable Technology as a Tool to Motivate Health Behaviour: A Case Study http://dx.doi.org/10.5772/intechopen.77002 65

Figure 11. Users engaged in the final testing of the product.

personal equipment are "static" products. We instead developed an interactive system made

The testing of the prototype was framed into two phases: Phase 1: The observation of the Practical Use of the System in two steps: (1) the workers were asked to wear the chest band and then to use the electronic nose for 30 min, this was useful to figure out if they understood how the electronic nose works; (2) They wore both the electronic nose and the mask; Phase 2: An unstructured Interview aimed at understanding: (1) Comfort and wearability of the overall system (Mask and Nose); (2) System Feedback Understanding; (3) Application Understanding; and (4) P\_O\_D\_ Efficacy. The user session was organised as a general observation coupled with sensor data collected in the working space and was carried out in May of 2017 on five workers. For the test, we choose the first one of the three companies analysed during the first user session because we met a very open-minded owner willing to innovate, experiment and to use the results of the project afterwards. Moreover, the workers of this company were the

Firstly, workers were given the prototypes and they were supposed to work with it on. This user session had two objectives. The first one was testing the products with users and the second was to understand the accuracy of the system in sense of monitoring data, both vital and environmental. In the image below, we can see the users in the painting cabin wearing the

At the same time, while workers were performing their activity we were controlling the parameters about the breathing rate and air quality through Apps on the mobile phone. Electronic part of the product showed as accurate, the quality of the air was changing respect to the presence of the overspray and distance from the object that is painted. It was giving a feedback to the user in real-time and the user found it quite comprehensive. The same is for breathing data; they were changing with respect to the level of presence of overspray and whether the mask was on or off. In the image below are shown the results obtained from air

After the observation in Coating Plant, users were engaged through an unstructured interview where they explained what they experienced while working with a P.O.D. system and if we succeeded in improving the wearability of the system. Workers were rather positive about the new mask; they appreciated the application of spacer textile instead of rubber and said that they were willing to wear it. They also appreciated Electronic Nose Device very much; the workers appreciated the possibility to wear it a versatile way: on the pants' pocket, on the shirt's collar, on the shirt's sleeves; the feedback and its general functioning was clear to them. They did not complain about the comfort of chest band, they found it unobtrusive and easy to use. In the end, they were given the Mobile App simulation to try to use it. Workers found it simple to use, the complexity of the app was proportional to their level of operating with this kind of medium and the graphical representation was immediate for them. Moreover, the employer showed interest in the system, but in particular he found very useful Electronic Nose Device and his Mobile App. Finally, observing the system as a whole, we can conclude that the improvement of the mask

quality measurement and heart and breathing parameters (Figure 12).

up of "dynamic" products empowered with sensors and technology.

3.6. Testing phase

64 Wearable Technologies

most collaborative and proactive ones.

prototype (Figure 11).

Figure 12. Simulation measurement of air quality and vital parameters.

respect to the user's needs defined in the beginning of the project, raised the benefits related to the wearing of the mask and by this the willingness of workers. Giving a real-time feedback showed that when there is the visible input about the risk, they remember to wear the mask and their belief in the air quality changes. Having the data in Mobile App certainly impact motivation of workers by showing the progress of wearing the mask in time.

#### 4. Conclusions and further development

A high number of respiratory diseases related to working environment are mostly present in sectors such as agriculture, manufacturing and transportation. Data coming from INAIL show that the manufacturing sector is the most dangerous among these where just in 2014 were detected 5172 cases. The best method of prevention and general increment of health in this case is wearing of PPEs. Results from our user analysis, obtained from three coating plants, approve that the workers are not willing to wear the mask. What we suggested as a solution to this problem was to encourage the workers to wear PPE by raising work-related risk awareness which they often undertake. This was thought to be executed by exploitation of persuasive technologies. Persuasive technologies may be defined as a tool able to influence or indeed change people's attitudes and behaviours [2]. Fogg [21] believes that successful products, the ones user will continue to use after the novelty, will be those that incorporate "hot triggers" to help people change their behaviours for the better. Behavioural Model developed by Fogg, (FBM), is funded on the thought that any target behaviour occurs only if the person has sufficient motivation, ability and effective trigger; and these are supposed to occur at the same time. This model suggests that the motivation is a trigger of an action or behaviour. Motivation as a characteristic of human action is stimulating to act and demonstrate one kind of behaviour and not the other. It is not always oriented towards positive but also towards negative or not acting decision. Motivation is certainly the reason of our actions and it shapes behaviour with respect to what is desired or how much willingness we have for acting. We use our motives as inner factors that are directing towards action [23]. In the field of working environment, we faced the behaviour problem related to the responsibility and the willingness of wearing the protective equipment. We had few questions to answer: Could an individual approach like self-motivation generate consciousness about risks the workers are at? How the sense of hazards and injuries could let them understand health risks and change behaviour? To answer these questions, we proposed a Wearable System able to address the main problem of "motivating" by improving the comfort and wearability of the system and raising selfawareness about health issues. Besides the theoretical literature, the analysis on the direct user brought to the development of a system composed of four devices: a smart mask, two devices that are monitoring physiological parameters and one dedicated to the environmental monitoring of working place and real time alerting about the level of hazards in the surrounding (i.e. visual and tactile feedback when the environment is hazardous). The system suggested in this research consists of three wearable devices and Mobile Application. In such a system, the motivation starts from a new mask (equipped with temperature sensor) redesigned with attention to the wearability and comfort, evaluated as high by the workers, while the Electronic Nose Device maintains the motivation of the user through information, or alert, about air quality (gas, CO2), and even though the user generally does not want to wear the mask, he/ she will be more encouraged to do it by changing the perception about the risk and by this also the behaviour. Beside environmental monitoring and alerting, also physiological parameters have a purpose to inform the user about the health condition when exposed and not to hazards, and here Chest Band has an important role. Data gathered from all devices are organised in mobile app and are communicated through simple graphical information: if the mask is worn or not; the level of air quality; and the quality of breathing. Seeing how these parameters are related will impact one's self-awareness and increase consciousness. This kind of system operates during the time, by giving knowledge and—as a result of it—conscious behaviour, that on long distances improves health condition. The results of the performed user test are promising: they gave us a first confirmation that the designed system could be an acceptable and effective proposal. Nevertheless, more research is required to demonstrate both that the behaviour change by workers will last longer than the duration of an observation session and that the improved mask's wearability will be enough also after several hours and days of usage. We are currently working on the research project follow-up in collaboration with a SME based in the northern area of Milan that develops and sells respiratory protection products; the collaboration is aimed at improving the system. The company is interested in testing the entire system on a wider population of users not only in Italy but also in Spain and Netherlands where it has other companies' branches. The company also wants to test it in different working environments such as body shops, agriculture, and restoration and is very committed to translating the prototyped system into a commercial product.

Acknowledgements

Conflict of interest

Author details

References

April 26–29

2014 Annual Meeting

ship. 2010;38(3):5-14

[8] Cross N. Design thinking. Berg; 2011

working with them, that could influence our research.

Venere Ferraro\*, Mila Stepanovic and Silvia Ferraris

\*Address all correspondence to<EMAIL_ADDRESS>Department of Design, Politecnico di Milano, Milan, Italy

San Francisco, CA: Morgan Kaufmann; 2003

Interactive Technology. 1st ed. London: Springer-Verlag; 2007

2015. Aesthetics of interaction: Dynamic, multisensory, wise. 2015

[6] Brown T. Design thinking. Harvard Business Review. 2008;86(6):84

Development.

We acknowledge funding provided by INAIL in the context of the SAF€RA under the ERA-NET actions of the 7th Framework Programme for European Research and Technological

Wearable Technology as a Tool to Motivate Health Behaviour: A Case Study

http://dx.doi.org/10.5772/intechopen.77002

67

In accordance with our ethical obligation as researchers, we declare that we have no financial, commercial, legal or professional relationship with other organisations, or with the people

[1] Fogg BJ. Creating. Persuasive Technologies: An Eight-Step Design Process. Persuasive '09,

[2] Fogg BJ. Persuasive Technology: Using Computers to Change What We Think and Do.

[3] Gill SP. Cognition, Communication and Interaction: Transdisciplinary Perspectives on

[4] Hendrik NJ, Schifferstein, Özcan E, Rozendaal MC. Towards the maturation of design: From smart to wise products. Design and semantics of form and movement in DeSForM

[5] Motti V, Caine K. Human factors considerations in the design of wearable devices. HFES

[7] Leavy B. Design thinking—A new mental model of value innovation. Strategy & Leader-

### Acknowledgements

by Fogg, (FBM), is funded on the thought that any target behaviour occurs only if the person has sufficient motivation, ability and effective trigger; and these are supposed to occur at the same time. This model suggests that the motivation is a trigger of an action or behaviour. Motivation as a characteristic of human action is stimulating to act and demonstrate one kind of behaviour and not the other. It is not always oriented towards positive but also towards negative or not acting decision. Motivation is certainly the reason of our actions and it shapes behaviour with respect to what is desired or how much willingness we have for acting. We use our motives as inner factors that are directing towards action [23]. In the field of working environment, we faced the behaviour problem related to the responsibility and the willingness of wearing the protective equipment. We had few questions to answer: Could an individual approach like self-motivation generate consciousness about risks the workers are at? How the sense of hazards and injuries could let them understand health risks and change behaviour? To answer these questions, we proposed a Wearable System able to address the main problem of "motivating" by improving the comfort and wearability of the system and raising selfawareness about health issues. Besides the theoretical literature, the analysis on the direct user brought to the development of a system composed of four devices: a smart mask, two devices that are monitoring physiological parameters and one dedicated to the environmental monitoring of working place and real time alerting about the level of hazards in the surrounding (i.e. visual and tactile feedback when the environment is hazardous). The system suggested in this research consists of three wearable devices and Mobile Application. In such a system, the motivation starts from a new mask (equipped with temperature sensor) redesigned with attention to the wearability and comfort, evaluated as high by the workers, while the Electronic Nose Device maintains the motivation of the user through information, or alert, about air quality (gas, CO2), and even though the user generally does not want to wear the mask, he/ she will be more encouraged to do it by changing the perception about the risk and by this also the behaviour. Beside environmental monitoring and alerting, also physiological parameters have a purpose to inform the user about the health condition when exposed and not to hazards, and here Chest Band has an important role. Data gathered from all devices are organised in mobile app and are communicated through simple graphical information: if the mask is worn or not; the level of air quality; and the quality of breathing. Seeing how these parameters are related will impact one's self-awareness and increase consciousness. This kind of system operates during the time, by giving knowledge and—as a result of it—conscious behaviour, that on long distances improves health condition. The results of the performed user test are promising: they gave us a first confirmation that the designed system could be an acceptable and effective proposal. Nevertheless, more research is required to demonstrate both that the behaviour change by workers will last longer than the duration of an observation session and that the improved mask's wearability will be enough also after several hours and days of usage. We are currently working on the research project follow-up in collaboration with a SME based in the northern area of Milan that develops and sells respiratory protection products; the collaboration is aimed at improving the system. The company is interested in testing the entire system on a wider population of users not only in Italy but also in Spain and Netherlands where it has other companies' branches. The company also wants to test it in different working environments such as body shops, agriculture, and restoration and is very

66 Wearable Technologies

committed to translating the prototyped system into a commercial product.

We acknowledge funding provided by INAIL in the context of the SAF€RA under the ERA-NET actions of the 7th Framework Programme for European Research and Technological Development.

### Conflict of interest

In accordance with our ethical obligation as researchers, we declare that we have no financial, commercial, legal or professional relationship with other organisations, or with the people working with them, that could influence our research.

### Author details

Venere Ferraro\*, Mila Stepanovic and Silvia Ferraris

\*Address all correspondence to<EMAIL_ADDRESS>
Department of Design, Politecnico di Milano, Milan, Italy

### References

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**Chapter 4**

**Provisional chapter**

**Wearable Neuromodulators**

**Wearable Neuromodulators**

DOI: 10.5772/intechopen.76673

In neuromodulation, by delivering a form of stimulus to neural tissue the response of an associated neural circuit may be changed, enhanced or inhibited (i.e., *modulated*) as desired. This powerful technique may be used to treat various medical conditions as outlined in this chapter. After a brief introduction to the human nervous system, key example applications of electrical neuromodulation such as cardiac pacemakers, devices for pain relief, deep brain stimulation, cochlear implant and visual prosthesis and their respective methods of deployment are discussed. Furthermore, key features of wearable neuromodulators with reference to some existing devices are briefly reviewed. This chapter is concluded by a case study on design and development of a wearable device with non-invasive electrodes for treating lower urinary tract dysfunctions after spinal

In neuromodulation by applying a form of stimulus to neural tissue, the response of the underlying neural circuits is modulated and a response is evoked. In this chapter, we solely focus on electrical stimulation of neural tissue. Neuromodulation is used to suppress pain, assist locomotion, treat various conditions and rehabilitate patients. Current neuromodulators are primarily used for medical purposes. Neuromodulators may be classified as invasive, where a form of surgical operation is required to implement the technique, or non-invasive, where surface electrodes are used. Due to the risks associated with surgery and high cost, non-invasive solutions are more desirable. Both classes of neuromodulators may be controlled by the user

**Keywords:** lower urinary tract, electrical stimulation, nervous system, neuromodulation, spinal cord injury, TENS, transcutaneous stimulation

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Arsam N. Shiraz, Brian Leaker and

Arsam N. Shiraz, Brian Leaker and

http://dx.doi.org/10.5772/intechopen.76673

Andreas Demosthenous

Andreas Demosthenous

**Abstract**

cord injury.

**1. Introduction**

#### **Chapter 4 Provisional chapter**

#### **Wearable Neuromodulators Wearable Neuromodulators**

Arsam N. Shiraz, Brian Leaker and Andreas Demosthenous Arsam N. Shiraz, Brian Leaker and Andreas Demosthenous

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76673

#### **Abstract**

In neuromodulation, by delivering a form of stimulus to neural tissue the response of an associated neural circuit may be changed, enhanced or inhibited (i.e., *modulated*) as desired. This powerful technique may be used to treat various medical conditions as outlined in this chapter. After a brief introduction to the human nervous system, key example applications of electrical neuromodulation such as cardiac pacemakers, devices for pain relief, deep brain stimulation, cochlear implant and visual prosthesis and their respective methods of deployment are discussed. Furthermore, key features of wearable neuromodulators with reference to some existing devices are briefly reviewed. This chapter is concluded by a case study on design and development of a wearable device with non-invasive electrodes for treating lower urinary tract dysfunctions after spinal cord injury.

DOI: 10.5772/intechopen.76673

**Keywords:** lower urinary tract, electrical stimulation, nervous system, neuromodulation, spinal cord injury, TENS, transcutaneous stimulation

#### **1. Introduction**

In neuromodulation by applying a form of stimulus to neural tissue, the response of the underlying neural circuits is modulated and a response is evoked. In this chapter, we solely focus on electrical stimulation of neural tissue. Neuromodulation is used to suppress pain, assist locomotion, treat various conditions and rehabilitate patients. Current neuromodulators are primarily used for medical purposes. Neuromodulators may be classified as invasive, where a form of surgical operation is required to implement the technique, or non-invasive, where surface electrodes are used. Due to the risks associated with surgery and high cost, non-invasive solutions are more desirable. Both classes of neuromodulators may be controlled by the user

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

or be completely autonomous and this depends on the application. Most of them are portable and may be on the person while they go about their daily life. Invasive neuromodulators may not be removed when desired. However, if they are composed of external and implanted units, the external part may be detached from the patient if needed. While connectivity can be readily incorporated in such devices, this is not at this stage a fundamental part of such solutions.

Soma houses cell genes and proteins are synthesized in it. A soma may give rise to two types of projections, also referred to as processes. There may be one long axon, also referred to as the nerve fiber, which acts as the main conducting unit of the neural signal (i.e., AP) to other neurons. Other projections, which are generally shorter and branch-like, are dendrites. Dendrites may be thought of as the main neural signal receiving ports in a neuron. Near the end, an axon divides into these branches which communicate with other neurons through the presynaptic terminals. The point of communication between a neuron and other neurons is called a synapse. The cell transmitting the signal is called a presynaptic cell and the one receiving it is called the postsynaptic cell. Presynaptic terminals land on the soma and/or the dendrites of a subsequent cell. Depending on the functions of the cells their morphology may

Wearable Neuromodulators

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Glial cells surround neurons and have various functionalities including acting as the general and structural support for neurons. Schwann cells and oligodendrocytes insulate axons in the PNS and CNS, respectively [3]. Schwann cells form the myelin sheath which essentially acts as insulation around a nerve fiber, referred to as myelination. Fibers may be myelinated or unmyelinated and, consequently, they show different characteristics. In a myelinated fiber, large segments along its length are wrapped by layers of myelin while only small segments between the wrapped segments are left exposed at regular intervals. The exposed segments are referred to as the nodes of Ranvier. There are other types of glial cells that are thought to bring nutrients to cells, provide the blood-brain barrier and help maintain the right ion concentration. They also absorb neurotransmitters and some are only recruited during infection,

In PNS, generally, there are two roots originating from the spinal cord. The dorsal root conveys the sensory information while the ventral root conveys the motor signaling. The dorsal root then enters the dorsal root ganglion, a local accumulation of cell bodies and supporting cells. Peripheral axons may be bundled into what is called nerves. The nerves from the dorsal and ventral roots merge to form the spinal nerve. In CNS, cell bodies may be arranged in two ways. Nuclei are the local accumulations of neurons with similar connections and functionalities, such as the collections found in the cerebrum, brainstem, and spinal cord. The second arrangements are cortices which are sheet-like arrays of cells such as those found in the cerebral hemispheres and cerebellum. The axons in the CNS are gathered into tracts, analogous to nerves in the PNS. Tracts that cross the mid-line of the brain and spinal cord are referred to as commissures. The term gray matter identifies any accumulation of cell bodies and neuropils (synaptically dense regions of dendrites, synaptic terminals, and glial cell processes) in the brain and spinal cord (e.g., nuclei or cortices) while white matter is essentially tracts and

In terms of functionality or the direction of conveying the neural signal, neurons are classified into three major groups: afferents, efferents and interneurons. Afferents carry information from the periphery of the body to the CNS. These neurons are very often interchangeably referred to as sensory neurons although not all afferent communications may lead to a form

vary [1, 2].

injury and seizure [1].

commissures.

**2.3. Afferent and efferent neurons**

After an introduction to human nervous system, fundamentals of neuromodulation are described in this chapter. Key examples of neuromodulation devices are briefly discussed, followed by a note on wearable neuromodulators. This chapter is concluded by a discussion on the design and development of a wearable neuromodulator to treat lower urinary tract (LUT) dysfunctions after spinal cord injury (SCI).

### **2. Human nervous system**

This section is a brief and general introduction to human nervous system, aiming to assist readers in understanding what follows in the chapter.

#### **2.1. Central and peripheral systems**

The human nervous system may be divided into central and peripheral systems. The central nervous system (CNS) comprises the brain and the spinal cord and the peripheral nervous system (PNS) mainly includes the nerves that connect the periphery of the body to the CNS. The brain comprises the cerebral hemispheres, diencephalon, cerebellum, and the brainstem. The spinal cord connects lower parts of the body to the brain and can be divided into four sections, each of which has various segments from top to bottom: cervical (C1–C8), thoracic (T1–T12), lumbar (L1–L5), and sacral (S1–S5) [1].

The PNS comprises the spinal nerves, originating from the spinal cord, and most of the cranial nerves, originating from the brain, above the spinal cord. The peripheral nerves originating from a specific segment of the spinal cord (C-S) generally mediate a specific functionality. The PNS may be subdivided into the autonomic nervous system and somatic nervous system. Generally, the former oversees the involuntary control and the latter provides the voluntary control. The autonomic nervous system may be further divided into sympathetic and parasympathetic nervous systems. The sympathetic nervous system may be perceived to oversee the fight-or-flight response while the parasympathetic nervous system is responsible for the rest-and-digest functions.

#### **2.2. Key elements**

There are two main classes of cells in the nervous system: nerve cells (neurons) and glial cells (glia). Generally, the former are the ones involved in neural signaling and the latter function as support cells. Typically, a neuron may consist of four distinct regions: a soma, dendrites, an axon, and presynaptic terminals [2]. The main function of neurons is to convey the neural signal (i.e., action potential (AP)).

Soma houses cell genes and proteins are synthesized in it. A soma may give rise to two types of projections, also referred to as processes. There may be one long axon, also referred to as the nerve fiber, which acts as the main conducting unit of the neural signal (i.e., AP) to other neurons. Other projections, which are generally shorter and branch-like, are dendrites. Dendrites may be thought of as the main neural signal receiving ports in a neuron. Near the end, an axon divides into these branches which communicate with other neurons through the presynaptic terminals. The point of communication between a neuron and other neurons is called a synapse. The cell transmitting the signal is called a presynaptic cell and the one receiving it is called the postsynaptic cell. Presynaptic terminals land on the soma and/or the dendrites of a subsequent cell. Depending on the functions of the cells their morphology may vary [1, 2].

Glial cells surround neurons and have various functionalities including acting as the general and structural support for neurons. Schwann cells and oligodendrocytes insulate axons in the PNS and CNS, respectively [3]. Schwann cells form the myelin sheath which essentially acts as insulation around a nerve fiber, referred to as myelination. Fibers may be myelinated or unmyelinated and, consequently, they show different characteristics. In a myelinated fiber, large segments along its length are wrapped by layers of myelin while only small segments between the wrapped segments are left exposed at regular intervals. The exposed segments are referred to as the nodes of Ranvier. There are other types of glial cells that are thought to bring nutrients to cells, provide the blood-brain barrier and help maintain the right ion concentration. They also absorb neurotransmitters and some are only recruited during infection, injury and seizure [1].

In PNS, generally, there are two roots originating from the spinal cord. The dorsal root conveys the sensory information while the ventral root conveys the motor signaling. The dorsal root then enters the dorsal root ganglion, a local accumulation of cell bodies and supporting cells. Peripheral axons may be bundled into what is called nerves. The nerves from the dorsal and ventral roots merge to form the spinal nerve. In CNS, cell bodies may be arranged in two ways. Nuclei are the local accumulations of neurons with similar connections and functionalities, such as the collections found in the cerebrum, brainstem, and spinal cord. The second arrangements are cortices which are sheet-like arrays of cells such as those found in the cerebral hemispheres and cerebellum. The axons in the CNS are gathered into tracts, analogous to nerves in the PNS. Tracts that cross the mid-line of the brain and spinal cord are referred to as commissures. The term gray matter identifies any accumulation of cell bodies and neuropils (synaptically dense regions of dendrites, synaptic terminals, and glial cell processes) in the brain and spinal cord (e.g., nuclei or cortices) while white matter is essentially tracts and commissures.

#### **2.3. Afferent and efferent neurons**

or be completely autonomous and this depends on the application. Most of them are portable and may be on the person while they go about their daily life. Invasive neuromodulators may not be removed when desired. However, if they are composed of external and implanted units, the external part may be detached from the patient if needed. While connectivity can be readily incorporated in such devices, this is not at this stage a fundamental part of such solutions. After an introduction to human nervous system, fundamentals of neuromodulation are described in this chapter. Key examples of neuromodulation devices are briefly discussed, followed by a note on wearable neuromodulators. This chapter is concluded by a discussion on the design and development of a wearable neuromodulator to treat lower urinary tract

This section is a brief and general introduction to human nervous system, aiming to assist

The human nervous system may be divided into central and peripheral systems. The central nervous system (CNS) comprises the brain and the spinal cord and the peripheral nervous system (PNS) mainly includes the nerves that connect the periphery of the body to the CNS. The brain comprises the cerebral hemispheres, diencephalon, cerebellum, and the brainstem. The spinal cord connects lower parts of the body to the brain and can be divided into four sections, each of which has various segments from top to bottom: cervical (C1–C8), tho-

The PNS comprises the spinal nerves, originating from the spinal cord, and most of the cranial nerves, originating from the brain, above the spinal cord. The peripheral nerves originating from a specific segment of the spinal cord (C-S) generally mediate a specific functionality. The PNS may be subdivided into the autonomic nervous system and somatic nervous system. Generally, the former oversees the involuntary control and the latter provides the voluntary control. The autonomic nervous system may be further divided into sympathetic and parasympathetic nervous systems. The sympathetic nervous system may be perceived to oversee the fight-or-flight response while the parasympathetic nervous system is responsible for the

There are two main classes of cells in the nervous system: nerve cells (neurons) and glial cells (glia). Generally, the former are the ones involved in neural signaling and the latter function as support cells. Typically, a neuron may consist of four distinct regions: a soma, dendrites, an axon, and presynaptic terminals [2]. The main function of neurons is to convey the neural

(LUT) dysfunctions after spinal cord injury (SCI).

readers in understanding what follows in the chapter.

racic (T1–T12), lumbar (L1–L5), and sacral (S1–S5) [1].

**2. Human nervous system**

72 Wearable Technologies

**2.1. Central and peripheral systems**

rest-and-digest functions.

signal (i.e., action potential (AP)).

**2.2. Key elements**

In terms of functionality or the direction of conveying the neural signal, neurons are classified into three major groups: afferents, efferents and interneurons. Afferents carry information from the periphery of the body to the CNS. These neurons are very often interchangeably referred to as sensory neurons although not all afferent communications may lead to a form of sensation [1]. Efferents or the motor neurons carry the neural signal and commands from the CNS to muscles and glands. Interneurons, which are neither sensory nor motor, constitute the largest group of neurons [1]. Interneurons convey APs over long or short distances from a neuron to the other.

soma and travel down the axon at velocities ranging from about 1-120 m/s depending on the fiber type [4]. Different activities are mediated via this signal throughout the nervous system by the neural circuits mentioned before. The actual command or information is not perceived by the variation of the signal (i.e., AP) but different effects are mediated through the paths

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Generally, there are three main temporal phases in an AP. The resting potential, the transmembrane voltage from inside to outside in the absence of any stimuli, is a negative value. Upon an increase in the transmembrane potential beyond a threshold, it rapidly increases to a specific positive value. This phase is called the depolarization period. The AP generation is an all-or-none process, meaning that any rise smaller than the said threshold does not yield such a response. The depolarization phase is followed by the subsequent reduction in the transmembrane potential which is called the repolarization phase. The transmembrane potential reduces even below its initial resting potential for a period which is referred to as the hyperpolarization phase. There exists the absolute refractory period in which no action potential may be triggered in the segment of the membrane under question. This is followed by the relative refractory period during which period a stronger than normal stimulus may

The generation and propagation of APs are mediated by voltage-gated ion channels in the membrane and the subsequent influx and outflow of ions. These channels are ion specific, meaning that when they are open they are only permeable to a specific ion. Also, the state that these channels are at depends on the transmembrane potential. Supposing that two media are separated by an ion specific channel and the density of that ion is different in the two media, ion flows against the concentration gradient. It is noted that ions do not exist in isolation, meaning that a positive ion is paired with a negative one. Thus, as ions that the barrier is permeable to diffuse, assuming a positive ion is diffusing, an electric field is built up in the direction of the concentration gradient. The opposing forces of the concentration-dependent diffusion and electric field reach an equilibrium, at which stage there is no net ion flow. By equating these opposing forces, the transmembrane electric potential at which the equilibrium is reached can be calculated. This is referred to as Nernst voltage. Nernst voltage is measured from intracellular to the extracellular space. Thus, a higher concentration of a positive ion outside the cell results in a positive Nernst voltage for that ion. Where several ion species are present, the transmembrane potential can then be calculated using the Goldman-Hodgkin-Katz formulation. Building on the Nernst equation, if the membrane becomes more permeable to a specific species, the equilibrium potential tends to the Nernst potential of that

species. The resting potential is not a case of equilibrium but that of the steady state.

The permeability of channels is governed by the voltage-gated channels mentioned before. The pioneering work of Hodgkin and Huxley (HH) [6] laid the foundation for the existing systematic understanding of the channel mechanisms. By setting the transmembrane voltage to a predetermined value and measure the transmembrane current for the said voltage in the giant axon of loligo, HH formed a set of curves of the conductivity of the membrane to potassium and sodium versus time for various depolarization voltages. Apart from the overall time trace, they noticed that as the clamp voltage increases, the rate at which the conductance

APs travel and their firing pattern.

produce a new AP [5].

#### **2.4. Neural circuits, receptors and transmitters**

Neurons are organized to form neural circuits and reflexes which may, for instance, process the sensory information and elicit motor responses. A typical circuit on the afferent end may be terminated by sensory receptors. These are nerve endings which transduce specific stimulus energies into the corresponding receptor potentials. Receptors are specialized in terms of the energy they transduce which may be electromagnetic, mechanical, thermal or chemical [4]. A complex sensation such as pain may recruit different receptors. The receptor potential then travels along the attached afferent fiber with a specific AP firing pattern. The attached afferents may covey a specific mode of sensation as well. The cell bodies of these afferents may be in the corresponding ganglia. The central axon of the mentioned cell might enter through the dorsal horn of the gray matter of the spinal cord and synapse with central neurons. Namely, it may synapse with interneurons or motoneurons in the spinal cord.

The basic forms of the synaptic transmission between neurons are electrical and chemical while most of the transmissions are chemical [4]. While at an electrical synapse a low resistance electrical path exists between the two associated cells, at chemical synapses neurons are separated completely by a small space called the synaptic cleft. The entities that essentially pass the neural signal from a presynaptic cell to a postsynaptic cell are called neurotransmitters. The arrival of an AP at the presynaptic side of a synapse leads to the release of chemical neurotransmitters which then diffuse across the cleft and interact with the receptors of the postsynaptic side. This interaction leads to either excitation or inhibition. The former leads to the suppression of the AP generation while the latter leads to the generation of APs. The type of the resulting action, primarily, depends on the type of the transmitter and receptor involved. Also, the synaptic input may add up from various presynaptic cells.

The sensory information may be conveyed through the white matter of the spinal cord to different regions in the brain for further processing. In which case, the response of the brain may be conveyed back to the target cells through different regions of the white matter of the spinal cord. A spinal reflex on its own may result in a motor activity without any modulatory input from the brain [1]. Through the ventral horn of the gray matter, efferent fibers leave and land on target muscles or organs. At a neuromuscular junction, neurotransmitters are released and the corresponding contraction or relaxation effects are mediated.

#### **2.5. Action potential**

Having presented an overview of different elements and aspects of the human nervous system, we now discuss the AP as the most fundamental phenomenon in the nervous system further. An AP is a rapid (~1 ms) variation (~100 mV) of the transmembrane potential [1, 3]. APs are naturally triggered in the initial segment of the attachment of an axon to its corresponding soma and travel down the axon at velocities ranging from about 1-120 m/s depending on the fiber type [4]. Different activities are mediated via this signal throughout the nervous system by the neural circuits mentioned before. The actual command or information is not perceived by the variation of the signal (i.e., AP) but different effects are mediated through the paths APs travel and their firing pattern.

of sensation [1]. Efferents or the motor neurons carry the neural signal and commands from the CNS to muscles and glands. Interneurons, which are neither sensory nor motor, constitute the largest group of neurons [1]. Interneurons convey APs over long or short distances from

Neurons are organized to form neural circuits and reflexes which may, for instance, process the sensory information and elicit motor responses. A typical circuit on the afferent end may be terminated by sensory receptors. These are nerve endings which transduce specific stimulus energies into the corresponding receptor potentials. Receptors are specialized in terms of the energy they transduce which may be electromagnetic, mechanical, thermal or chemical [4]. A complex sensation such as pain may recruit different receptors. The receptor potential then travels along the attached afferent fiber with a specific AP firing pattern. The attached afferents may covey a specific mode of sensation as well. The cell bodies of these afferents may be in the corresponding ganglia. The central axon of the mentioned cell might enter through the dorsal horn of the gray matter of the spinal cord and synapse with central neu-

rons. Namely, it may synapse with interneurons or motoneurons in the spinal cord.

involved. Also, the synaptic input may add up from various presynaptic cells.

the corresponding contraction or relaxation effects are mediated.

The basic forms of the synaptic transmission between neurons are electrical and chemical while most of the transmissions are chemical [4]. While at an electrical synapse a low resistance electrical path exists between the two associated cells, at chemical synapses neurons are separated completely by a small space called the synaptic cleft. The entities that essentially pass the neural signal from a presynaptic cell to a postsynaptic cell are called neurotransmitters. The arrival of an AP at the presynaptic side of a synapse leads to the release of chemical neurotransmitters which then diffuse across the cleft and interact with the receptors of the postsynaptic side. This interaction leads to either excitation or inhibition. The former leads to the suppression of the AP generation while the latter leads to the generation of APs. The type of the resulting action, primarily, depends on the type of the transmitter and receptor

The sensory information may be conveyed through the white matter of the spinal cord to different regions in the brain for further processing. In which case, the response of the brain may be conveyed back to the target cells through different regions of the white matter of the spinal cord. A spinal reflex on its own may result in a motor activity without any modulatory input from the brain [1]. Through the ventral horn of the gray matter, efferent fibers leave and land on target muscles or organs. At a neuromuscular junction, neurotransmitters are released and

Having presented an overview of different elements and aspects of the human nervous system, we now discuss the AP as the most fundamental phenomenon in the nervous system further. An AP is a rapid (~1 ms) variation (~100 mV) of the transmembrane potential [1, 3]. APs are naturally triggered in the initial segment of the attachment of an axon to its corresponding

a neuron to the other.

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**2.5. Action potential**

**2.4. Neural circuits, receptors and transmitters**

Generally, there are three main temporal phases in an AP. The resting potential, the transmembrane voltage from inside to outside in the absence of any stimuli, is a negative value. Upon an increase in the transmembrane potential beyond a threshold, it rapidly increases to a specific positive value. This phase is called the depolarization period. The AP generation is an all-or-none process, meaning that any rise smaller than the said threshold does not yield such a response. The depolarization phase is followed by the subsequent reduction in the transmembrane potential which is called the repolarization phase. The transmembrane potential reduces even below its initial resting potential for a period which is referred to as the hyperpolarization phase. There exists the absolute refractory period in which no action potential may be triggered in the segment of the membrane under question. This is followed by the relative refractory period during which period a stronger than normal stimulus may produce a new AP [5].

The generation and propagation of APs are mediated by voltage-gated ion channels in the membrane and the subsequent influx and outflow of ions. These channels are ion specific, meaning that when they are open they are only permeable to a specific ion. Also, the state that these channels are at depends on the transmembrane potential. Supposing that two media are separated by an ion specific channel and the density of that ion is different in the two media, ion flows against the concentration gradient. It is noted that ions do not exist in isolation, meaning that a positive ion is paired with a negative one. Thus, as ions that the barrier is permeable to diffuse, assuming a positive ion is diffusing, an electric field is built up in the direction of the concentration gradient. The opposing forces of the concentration-dependent diffusion and electric field reach an equilibrium, at which stage there is no net ion flow. By equating these opposing forces, the transmembrane electric potential at which the equilibrium is reached can be calculated. This is referred to as Nernst voltage. Nernst voltage is measured from intracellular to the extracellular space. Thus, a higher concentration of a positive ion outside the cell results in a positive Nernst voltage for that ion. Where several ion species are present, the transmembrane potential can then be calculated using the Goldman-Hodgkin-Katz formulation. Building on the Nernst equation, if the membrane becomes more permeable to a specific species, the equilibrium potential tends to the Nernst potential of that species. The resting potential is not a case of equilibrium but that of the steady state.

The permeability of channels is governed by the voltage-gated channels mentioned before. The pioneering work of Hodgkin and Huxley (HH) [6] laid the foundation for the existing systematic understanding of the channel mechanisms. By setting the transmembrane voltage to a predetermined value and measure the transmembrane current for the said voltage in the giant axon of loligo, HH formed a set of curves of the conductivity of the membrane to potassium and sodium versus time for various depolarization voltages. Apart from the overall time trace, they noticed that as the clamp voltage increases, the rate at which the conductance varies increases too. They decided to use first order kinetics (multiple processes if necessary) to fit the experimental data and consider activation and inactivation variables to explain the cessation of conductivity following its initial rise. Although HH developed a merely empirical formulation for the observations but the overall macroscopic system of equations they defined is compatible with the microscopic understanding which exists today [1]. The channels have gates that depending on the voltage across them the rate at which they open or close varies. For a channel to conduct, all its gates should be open. The concentration of the sodium ions in the extracellular space is much more than those in the intracellular space while that of potassium ions is the other way around. Therefore, the opening of the sodium channels results in a rise of the transmembrane potential while the opening of the potassium channels results in its reduction.

the extracellular potential. Assuming a cathode–anode pair is placed along a fiber at a distance away from it, the extracellular space near the cathode may become more negative and this forces transmembrane voltage there more positive. This may lead to the generation of a propagating AP in that position. This yields a very simplistic view of electrical stimulation. The actual process is far more complex and requires an understanding of HH type models of the fiber.

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In an electrical conductor, charge carriers are primarily electrons while in the tissue they are ions. Thus, electrodes may be thought of as the interface between these two media. It is, therefore, understandable that the processes involved are electrochemical and reduction and oxidation processes may happen at the electrodes which are not infinitely fast and unimpeded. Furthermore, due to the adsorption of charges and redux processes, the interface impedes the flow of current. The contact impedance due to these plays an important role in electrode material selection and design. Enough charge should be pumped into the medium to sufficiently perturb the extracellular potential. When applied as a pulse, the strength and duration of the pulse dictate how much charge is delivered. This leads to the formation of the strengthduration curves that identify a balance between the amplitude and the duration of stimulus pulses. The electrode design, its relative position with respect to the nerve and characteristics of the surrounding tissue, among other features, play a significant role in defining the stimulus pulse design. Moreover, there are safety considerations when charge is injected into the tissue. To understand the dynamics and safety considerations when injection stimulus cur-

As an electrode is put into contact with an electrolyte (tissue) a potential develops which is primarily governed by the Nernst formulation and is referred to as the equilibrium potential of the electrode. As the current is injected through the electrode, the potential of the electrode rises above the equilibrium, at which time the potential dependent reversible and irreversible Faradaic processes may occur. Such reactions are dependent on the fastness of the kinetics of the said reactions and the speed of the mass transport [7]. A kinetically fast process with respect to the mass transport requires a small over-potential, defined as the variation of the electrode potential from its equilibrium potential, to lead to a significant amount of current flowing. As the reactants, consequently, do not move away from the surface, applying current in the reversed direction may force the reactions to be reversed (i.e., biphasic charge balanced stimulation). Kinetically slower reactions are limited by the mass transport. Thus, the reactants move away from the surface as the reactions occur at higher over-potentials [7]. These reactions are referred to as the irreversible Faradaic processes while those involving kinetically fast processes are reversible. One of these irreversible processes is the electrolysis of water. This may happen above and below a certain positive and negative potential, respectively, for a given electrode material. The range of the potential below these limits (i.e., safe limits) is referred to as the water window. The electrolysis of water results in pH changes and gas formation which may lead to tissue and electrode damage. It is noted that electrode material forms a very important feature of the design. The safe limits of the charge injection and the general electrical properties of the electrode should be considered. Under most neural stimulation conditions, the Faradaic processes dominate [8], noting the existence of non-Faradaic currents at the electrode interface as well. Thus, it is important to ensure a given material can safely deliver the required charge. Electrodes may be implanted or surface electrodes may be used. The former

rent through electrodes the following description should be considered.

Assuming only sodium and potassium ions are involved, a full cycle of the AP generation is described as follows. The inputs in an axon hillock raise the transmembrane potential beyond a threshold at which point the permeability of the membrane to sodium and potassium ions increases. The conductivity of sodium channels increases faster than those of potassium ions. Thus, the influx of sodium ions brings the transmembrane potential closer to the equilibrium potential of sodium ions. At the higher transmembrane potentials, the conductivity of the membrane to potassium ions increases while sodium channels start to inactivate, reducing the membrane permeability to sodium ions. This results in repolarization of the membrane. The inactivation of sodium channels and the prolonged permeability of the membrane to potassium ions result in the lowering of the membrane potential below the resting potential and closer to the equilibrium potential of potassium ions. Several more channel types may be involved in different species but the overall process is generally similar.

When an AP is generated, it automatically induces the generation of other APs in its vicinity [1, 4]. Considering unmyelinated fibers, the extracellular and intracellular current flows along the fiber induce an increase in the transmembrane potential near the depolarized segment. When the AP is induced in a segment of the fiber, the preceding segment is in the hyperpolarization phase, thus, the AP travels in a specific direction. In the case of a myelinated fiber, as the current loops are relatively weak where the myelin insulation is present, the loops are at their highest intensity from a node to the other, resulting in the AP essentially hoping from a node to the other, rendering the transmission much faster. Apart from myelination, fiber diameter also affects the conduction velocity. Larger fiber diameters generally have higher conduction velocities. Depending on the size and conduction velocity of fibers, Erlanger's (A, A, Aδ, B and C) and Lloyd's (I, II, III and IV) systems have been proposed for a classification of fibers [1, 4].

### **3. Fundamentals of neuromodulation**

Neuromodulation has two components. The first component involves the delivery of the stimulus current to produce APs in a target neural tissue and the second one is the way this leads to a response. If a nerve is pierced via an electrode and the transmembrane voltage is forced more positive, then APs may be generated. Often, fibers are stimulated by merely perturbing the extracellular potential. Assuming a cathode–anode pair is placed along a fiber at a distance away from it, the extracellular space near the cathode may become more negative and this forces transmembrane voltage there more positive. This may lead to the generation of a propagating AP in that position. This yields a very simplistic view of electrical stimulation. The actual process is far more complex and requires an understanding of HH type models of the fiber.

varies increases too. They decided to use first order kinetics (multiple processes if necessary) to fit the experimental data and consider activation and inactivation variables to explain the cessation of conductivity following its initial rise. Although HH developed a merely empirical formulation for the observations but the overall macroscopic system of equations they defined is compatible with the microscopic understanding which exists today [1]. The channels have gates that depending on the voltage across them the rate at which they open or close varies. For a channel to conduct, all its gates should be open. The concentration of the sodium ions in the extracellular space is much more than those in the intracellular space while that of potassium ions is the other way around. Therefore, the opening of the sodium channels results in a rise of the transmembrane potential while the opening of the potassium channels

Assuming only sodium and potassium ions are involved, a full cycle of the AP generation is described as follows. The inputs in an axon hillock raise the transmembrane potential beyond a threshold at which point the permeability of the membrane to sodium and potassium ions increases. The conductivity of sodium channels increases faster than those of potassium ions. Thus, the influx of sodium ions brings the transmembrane potential closer to the equilibrium potential of sodium ions. At the higher transmembrane potentials, the conductivity of the membrane to potassium ions increases while sodium channels start to inactivate, reducing the membrane permeability to sodium ions. This results in repolarization of the membrane. The inactivation of sodium channels and the prolonged permeability of the membrane to potassium ions result in the lowering of the membrane potential below the resting potential and closer to the equilibrium potential of potassium ions. Several more channel types may be

When an AP is generated, it automatically induces the generation of other APs in its vicinity [1, 4]. Considering unmyelinated fibers, the extracellular and intracellular current flows along the fiber induce an increase in the transmembrane potential near the depolarized segment. When the AP is induced in a segment of the fiber, the preceding segment is in the hyperpolarization phase, thus, the AP travels in a specific direction. In the case of a myelinated fiber, as the current loops are relatively weak where the myelin insulation is present, the loops are at their highest intensity from a node to the other, resulting in the AP essentially hoping from a node to the other, rendering the transmission much faster. Apart from myelination, fiber diameter also affects the conduction velocity. Larger fiber diameters generally have higher conduction velocities. Depending on the size and conduction velocity of fibers, Erlanger's (A, A, Aδ, B and C) and Lloyd's (I, II, III and IV) systems have been proposed for a clas-

Neuromodulation has two components. The first component involves the delivery of the stimulus current to produce APs in a target neural tissue and the second one is the way this leads to a response. If a nerve is pierced via an electrode and the transmembrane voltage is forced more positive, then APs may be generated. Often, fibers are stimulated by merely perturbing

involved in different species but the overall process is generally similar.

results in its reduction.

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sification of fibers [1, 4].

**3. Fundamentals of neuromodulation**

In an electrical conductor, charge carriers are primarily electrons while in the tissue they are ions. Thus, electrodes may be thought of as the interface between these two media. It is, therefore, understandable that the processes involved are electrochemical and reduction and oxidation processes may happen at the electrodes which are not infinitely fast and unimpeded. Furthermore, due to the adsorption of charges and redux processes, the interface impedes the flow of current. The contact impedance due to these plays an important role in electrode material selection and design. Enough charge should be pumped into the medium to sufficiently perturb the extracellular potential. When applied as a pulse, the strength and duration of the pulse dictate how much charge is delivered. This leads to the formation of the strengthduration curves that identify a balance between the amplitude and the duration of stimulus pulses. The electrode design, its relative position with respect to the nerve and characteristics of the surrounding tissue, among other features, play a significant role in defining the stimulus pulse design. Moreover, there are safety considerations when charge is injected into the tissue. To understand the dynamics and safety considerations when injection stimulus current through electrodes the following description should be considered.

As an electrode is put into contact with an electrolyte (tissue) a potential develops which is primarily governed by the Nernst formulation and is referred to as the equilibrium potential of the electrode. As the current is injected through the electrode, the potential of the electrode rises above the equilibrium, at which time the potential dependent reversible and irreversible Faradaic processes may occur. Such reactions are dependent on the fastness of the kinetics of the said reactions and the speed of the mass transport [7]. A kinetically fast process with respect to the mass transport requires a small over-potential, defined as the variation of the electrode potential from its equilibrium potential, to lead to a significant amount of current flowing. As the reactants, consequently, do not move away from the surface, applying current in the reversed direction may force the reactions to be reversed (i.e., biphasic charge balanced stimulation). Kinetically slower reactions are limited by the mass transport. Thus, the reactants move away from the surface as the reactions occur at higher over-potentials [7]. These reactions are referred to as the irreversible Faradaic processes while those involving kinetically fast processes are reversible. One of these irreversible processes is the electrolysis of water. This may happen above and below a certain positive and negative potential, respectively, for a given electrode material. The range of the potential below these limits (i.e., safe limits) is referred to as the water window. The electrolysis of water results in pH changes and gas formation which may lead to tissue and electrode damage. It is noted that electrode material forms a very important feature of the design. The safe limits of the charge injection and the general electrical properties of the electrode should be considered. Under most neural stimulation conditions, the Faradaic processes dominate [8], noting the existence of non-Faradaic currents at the electrode interface as well. Thus, it is important to ensure a given material can safely deliver the required charge. Electrodes may be implanted or surface electrodes may be used. The former is invasive but the delivery of charge is direct while the latter may be non-invasive but the current have a large spread. Unfortunately, it has been shown that risk versus expected benefit has a linear relationship, the higher the risk the more substantial reported benefits, for different methods of stimulation [9]. This may be attributed to efficacy and selectivity. While non-invasive electrodes are simply conductive patches attached to the surface of the body, minimally invasive electrodes may be designed as needles piercing the skin to deliver the stimulus current. General classes of invasive electrodes for PNS in increasing order of invasiveness include extraneural, interfascicular, intrafascicular and those relying on the regeneration of the neural tissue in them. Examples of these electrodes are cuff electrodes, flat interface nerve electrodes (FINESs), longitudinal intrafascicular electrodes (LIFEs), transverse intrafascicular electrodes (TIMEs) and various multi-channel electrodes [10]. For the CNS, the general classification of electrodes is superficial/distal and those for deeper structures.

Deep brain stimulation (DBS) is one of the key applications of neuromodulation that has found applications in treating Parkinson's disease [16], essential tremor [17], dystonia [18], Tourette syndrome [19], chronic pain [20], epilepsy [21], Huntington's disease [22] and even mental disorders [23] with different sites of stimulation. A linear electrode array is implanted deep in the brain. In many of the above cases the exact mechanisms that lead to desirable outcomes using DBS are not known due to the complexity of neural circuits in the brain.

Wearable Neuromodulators

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A very successful example of neuromodulators is the cochlear implant [24] in which the auditory nerve is stimulated via electrodes placed on a flexible platform that is placed in a layer of the cochlea (basilar membrane). Sound is recorded externally and upon processing the stimulation paradigm is inductively transmitted to the electrodes. Sound as a mechanical wave hits the tympanic membrane (i.e., eardrum). Ossicles, three bones connected to the tympanic membrane, convey this motion to the cochlea which is filled by fluid. At a layer of the cochlea there exists the basilar membrane which is stiff and narrow near the ossicles and wide and flexible on the other end. Due to this structure, the thinner segments *resonate* with higher frequencies. The hair cells on the basilar membrane then translate this to a neural signal which is conveyed through the auditory nerve. The basilar membrane may be appropriately stimu-

Visual prosthesis is another example of using neuromodulation to restore function. One of the most common forms of blindness in the developed world is neural blindness. This is generally due to the loss of photoreceptors. In many cases part of the neural circuits between the receptors and the brain survive and this may be harvested to restore vision. Light passes through the cornea, pupil and lens and is shone on the retina. Retina is covered by photoreceptors (rod cells, more populous and specialized for dim light and cone cells, for bright light and colors) that transduce light to a neural signal which goes through the visual pathway to be perceived in the visual cortex of the brain. Electrical stimulation may be delivered in various places [25]. The stimulation may be delivered via epiretinal [26], subretinal [27] or suprachoroidal [28] electrode arrays. Stimulation may be delivered by deriving the appropriate pattern via an external sensor like camera and transmitted via an inductive link to the array or the photo sensors may be integrated with the electrodes. Stimulus current may also be delivered to optic

Electrical stimulation may be applied to restore or rehabilitate motor function. In this case it is referred to as functional electrical stimulation (FES). While not in all cases of FES a neural reflex may be modulated, due to its significance we briefly discuss it here. FES may be delivered via implanted electrodes [32], percutaneously [33] or transcutaneous [34] in various places. FES have been used in a variety of applications such as improving activity after stroke [35], chronic heart failure [36] or control and rehabilitation of extremities following spinal

Neuromodulation may be used to treat various lower urinary tract dysfunctions that arise upon spinal cord injury. A more elaborate description of such interventions is presented as a

nerve [29], lateral geniculate nucleus [30] or even the visual cortex itself [31].

case study in designing a wearable neuromodulator later in this chapter.

cord injury [37] or other forms of neural disease.

However, its efficacy has promoted its use and further research.

lated to induce hearing perception.

The second component of neuromodulation is the way the stimulus current leads to a desired response from the associated neural circuits. This may be a simple motor response by stimulating the very same motor fibers or may involve much more complex circuits involving PNS and CNS. Thus, in designing the stimulus signal one should also consider the appropriate features that lead to the desired response. This may include, but is not limited to, stimulus waveform and frequency.

### **4. Example applications of neuromodulation**

A very well-known example of neuromodulators is the cardiac pacemaker. Electrodes are inserted transvenously and placed at the targeted chamber of the heart. The pulse generator is placed in a subcutaneous or submuscular position. Electrical stimulus may be applied in a unipolar or bipolar fashion and the process can be synchronized with hearts pace [11].

One of the applications of neuromodulation is for chronic pain management. Transcutaneous electrical neural stimulation (TENS) owing to its simple delivery method has been investigated for many years. Various waveforms and frequencies have been used. The placement of electrodes may be directly over the painful area, its peripheral neural supply, the dermatome of the associated spinal roots and known trigger points. It is thought that the resulting analgesia is due to the activation of central inhibitory mechanisms. For instance, stimulation of Aβ afferent fibers are thought to lead to inhibition of nociceptive C and Aδ afferent fibers in some cases. Examples of devices developed based on TENS concepts include NEMOS (Cerbomed GmbH, Erlanger, Germany), a portable device that targets the auricular branch of the vagus nerve via electrodes placed on the concha of the outer ear, Cefaly (CEFALY-Technology, Seraing, Belgium), a wearable device for supraorbital stimulation by a bipolar electrode patch on the forehead and gammaCore (electroCore LLC, NJ, USA), a handheld noninvasive vagal nerve stimulator, all for the treatment and management of migraine. Spinal cord stimulation using implanted electrodes [12], occipital nerve stimulation using implantable electrodes [13], transcranial magnetic stimulation [14] and transcranial direct current stimulation [15] have also been used to treat various neuropathic pain patients.

Deep brain stimulation (DBS) is one of the key applications of neuromodulation that has found applications in treating Parkinson's disease [16], essential tremor [17], dystonia [18], Tourette syndrome [19], chronic pain [20], epilepsy [21], Huntington's disease [22] and even mental disorders [23] with different sites of stimulation. A linear electrode array is implanted deep in the brain. In many of the above cases the exact mechanisms that lead to desirable outcomes using DBS are not known due to the complexity of neural circuits in the brain. However, its efficacy has promoted its use and further research.

is invasive but the delivery of charge is direct while the latter may be non-invasive but the current have a large spread. Unfortunately, it has been shown that risk versus expected benefit has a linear relationship, the higher the risk the more substantial reported benefits, for different methods of stimulation [9]. This may be attributed to efficacy and selectivity. While non-invasive electrodes are simply conductive patches attached to the surface of the body, minimally invasive electrodes may be designed as needles piercing the skin to deliver the stimulus current. General classes of invasive electrodes for PNS in increasing order of invasiveness include extraneural, interfascicular, intrafascicular and those relying on the regeneration of the neural tissue in them. Examples of these electrodes are cuff electrodes, flat interface nerve electrodes (FINESs), longitudinal intrafascicular electrodes (LIFEs), transverse intrafascicular electrodes (TIMEs) and various multi-channel electrodes [10]. For the CNS, the general classification of