**3. Material and Methods**

The purpose of the research was to identify the factors deemed to have a significant impact on the utility and function of a DWPT system. In order to collect user and stakeholder data, a morning workshop followed by focus groups in the afternoon was organised. An approach was adopted that used the PEST framework in combination with semi-structured discussions was supported by a review of the appropriate literature in the area of DWPT and ERS. These concepts are explained below:

By combining the PEST framework, semi-structured discussion and a rapid review of the literature, the purpose was to develop a comprehensive understanding and mapping of the macro-environment into which DWPT is to be deployed. Through this, the significant factors that would determine the success of a DWPT system could be extracted and a taxonomy or classification of the significant factors generated. The process followed a number of discrete steps that are outlined below:


*2.3. P*µ*SL Method*

Projection micro-stereolithography (PµSL) is a sophisticated 3D printing method because of its low cost, precision, velocity, and also the variety of the materials such as ceramics, biomaterials, curable

1.3 1.5 3.8 150 1.51

*2.3. PμSL Method*

photopolymer, polymer, and nanoparticle composites [54]. This method has demonstrated potential in different implementations for example micro-resonators, micro-grippers, micro-optics, biomedical micro devices, micro-fluidics, and so on [57–59]. Studies on PµSL are ongoing in terms of the quality and accuracy of the construction process, which affects the production of complex 3D microstructures and makes it attractive enough to be considered for commercial applications [60]. This technology begins by creating a 3D construction via a computer-assisted design program and then transforms the construction into a set of digital mask images. The working basis of PµSL is shown in Figure 3 [61]. potential in different implementations for example micro-resonators, micro-grippers, micro-optics, biomedical micro devices, micro-fluidics, and so on [57–59]. Studies on PμSL are ongoing in terms of the quality and accuracy of the construction process, which affects the production of complex 3D microstructures and makes it attractive enough to be considered for commercial applications [60]. This technology begins by creating a 3D construction via a computer-assisted design program and then transforms the construction into a set of digital mask images. The working basis of PμSL is shown in Figure 3 [61]. Using a digital micro mirror device as the dynamic mask eliminates the cost of manufacturing a

curable photopolymer, polymer, and nanoparticle composites [54]. This method has demonstrated

*Micromachines* **2020**, *11*, x 6 of 13

Projection micro-stereolithography (PμSL) is a sophisticated 3D printing method because of its

Using a digital micro mirror device as the dynamic mask eliminates the cost of manufacturing a mask for each layer. Besides, the PµSL method reduces production time since each layer is produced in one exposure, and the time for mask alignment is eliminated. Moreover, this method has the least mechanical moving parts and requires only one accurate *z*-axis motorized linear stage. Consequently, PµSL decreases the cost of construction and protection [62]. mask for each layer. Besides, the PμSL method reduces production time since each layer is produced in one exposure, and the time for mask alignment is eliminated. Moreover, this method has the least mechanical moving parts and requires only one accurate *z*-axis motorized linear stage. Consequently, PμSL decreases the cost of construction and protection [62]. All images symbolize a thin layer of the 3D structure. Along a production period, a single image

All images symbolize a thin layer of the 3D structure. Along a production period, a single image is demonstrated on the reflective LCD panel. The image from the LCD is then mirrored on the liquid surface. All layers (ranging between 5–40 µm thick) are polymerized. When the layer has been solidified, it is dipped in the resin to allow a new thin layer of liquid to form. Repeating the loop forms a 3D microstructure from a layer stack. For the PµSL method, IP-S resin, which is a photopolymer, was used as the material. The properties of the photopolymer resin, which were specially developed for this 3D printer and utilized in the fabrication of the micro beam, are shown in Table 2 [54]. is demonstrated on the reflective LCD panel. The image from the LCD is then mirrored on the liquid surface. All layers (ranging between 5–40 μm thick) are polymerized. When the layer has been solidified, it is dipped in the resin to allow a new thin layer of liquid to form. Repeating the loop forms a 3D microstructure from a layer stack. For the PμSL method, IP-S resin, which is a photopolymer, was used as the material. The properties of the photopolymer resin, which were specially developed for this 3D printer and utilized in the fabrication of the micro beam, are shown in Table 2 [54].

**Figure 3. Figure 3.** Schematic of the projection micro-stereolithography (P Schematic of the projection micro-stereolithography (Pµ μ SL) method [ SL) method [62]. 62].

### **3. Fabrication**

### *3.1. Fabrication with the DLP Method*

The micro beam shown in Figure 4 was fabricated by a DLP technology-based MiiCraft 3D printing device. 3D printing technology entails an input CAD model of the parts that may be designed in software or obtained from reverse engineering such as 3D scanners. When the CAD model of the micro beam is completed, it is transformed into standard STL format, which is most commonly used to *3.1. Fabrication with the DLP Method*

**3. Fabrication**

represent 3D CAD models in 3D printing. In an STL file, the CAD model is symbolized using triangular facets, which are described by the x-, y-, and z-coordinates of the three vertices. The step-by-step schema of the 3D printing operation is displayed in Figure 5. The slicer first divides the object into a stack of flat layers, followed by describing these layers as linear movements of the 3D printer extruder, fixation laser, or equivalent. All these movements, together with some specific printer commands like the ones to control the extruder temperature or bed temperature, are finally written in the g-code file, that can be transferred after to the printer. symbolized using triangular facets, which are described by the x-, y-, and z-coordinates of the three vertices. The step-by-step schema of the 3D printing operation is displayed in Figure 5. The slicer first divides the object into a stack of flat layers, followed by describing these layers as linear movements of the 3D printer extruder, fixation laser, or equivalent. All these movements, together with some specific printer commands like the ones to control the extruder temperature or bed temperature, are finally written in the g-code file, that can be transferred after to the printer. During fabrication of the micro beam, the printing parameters for example the layer thickness

model of the micro beam is completed, it is transformed into standard STL format, which is most commonly used to represent 3D CAD models in 3D printing. In an STL file, the CAD model is

*Micromachines* **2020**, *11*, x 7 of 13

The micro beam shown in Figure 4 was fabricated by a DLP technology-based MiiCraft 3D printing device. 3D printing technology entails an input CAD model of the parts that may be

During fabrication of the micro beam, the printing parameters for example the layer thickness (LT), the light intensity (LI), and the curing time (CT) of all layer significantly affect the print quality. In this study, each parameter is selected for the printing material and TL = 30 µm, and CT = 3 s are set. When the first layer is printed, LI is set to 50% of the brightness to provide a layer bond to the platform. (LT), the light intensity (LI), and the curing time (CT) of all layer significantly affect the print quality. In this study, each parameter is selected for the printing material and TL = 30 μm, and CT = 3 s are set. When the first layer is printed, LI is set to 50% of the brightness to provide a layer bond to the platform.

There are supports to the arms of this design. The number of supports to the arm is 20, the diameter is 3 µm, and the height is 5 µm. Some unsuccessful experiments were done before this design. Breakages were experienced during the manufacturing when the number of supports to the arm was low. Concerning the experiments, the average distance between the supports should be 10 µm to avoid breakages. When the supports are not printed correctly, they cause a collapse and break off the micro beam. An image of the micro beam manufactured with the DLP is shown in Figure 6. This image was taken with the microscope of the 3D printer device. There are supports to the arms of this design. The number of supports to the arm is 20, the diameter is 3 μm, and the height is 5 μm. Some unsuccessful experiments were done before this design. Breakages were experienced during the manufacturing when the number of supports to the arm was low. Concerning the experiments, the average distance between the supports should be 10 μm to avoid breakages. When the supports are not printed correctly, they cause a collapse and break off the micro beam. An image of the micro beam manufactured with the DLP is shown in Figure 6. This image was taken with the microscope of the 3D printer device.

**Figure 4.** CAD design of the micro beam. The structures at the top of the design were designed as support. **Figure 4.** CAD design of the micro beam. The structures at the top of the design were designed as support.

### *3.2. Fabrication with the PμSL Method 3.2. Fabrication with the P*µ*SL Method*

The micro beam shown in Figure 7 was manufactured by a projection micro-stereolithography (PμSL) method based MiiCraft 3D printing device. The manufacturing of the supported design with The micro beam shown in Figure 7 was manufactured by a projection micro-stereolithography (PµSL) method based MiiCraft 3D printing device. The manufacturing of the supported design with the PµSL method was not possible for two reasons. First, the supported structures represent the system as a 3D design. However, it is not possible to fabricate 3D structures with devices of MiiCraft 3D printing, based on PµSL technology. Second, these devices have a resolution of 65 µm and can fabricate a minimum thickness of up to 30 µm.

When the support structures are removed, as shown in Figure 7, it is possible to perform the fabrication as the micro beam design can be introduced to the device (a PµSL technology-MiiCraft 3D

printer) in two dimensions. An image of the micro beam manufactured with the PµSL is shown in Figure 8. This image was taken with the microscope of the 3D printer device. 3D printer) in two dimensions. An image of the micro beam manufactured with the PμSL is shown in Figure 8. This image was taken with the microscope of the 3D printer device.

fabrication as the micro beam design can be introduced to the device (a PμSL technology-MiiCraft

*Micromachines* **2020**, *11*, x 8 of 13

the PμSL method was not possible for two reasons. First, the supported structures represent the system as a 3D design. However, it is not possible to fabricate 3D structures with devices of MiiCraft 3D printing, based on PμSL technology. Second, these devices have a resolution of 65 μm and can

**Figure 5.** The step-by-step diagram of the 3D printing operation. **Figure 5.** The step-by-step diagram of the 3D printing operation.

*Micromachines* **2020**, *11*, x 9 of 13

*Micromachines* **2020**, *11*, x 9 of 13

**Figure 6.** Image of the micro beam fabricated with the DLP method. **Figure 6.** Image of the micro beam fabricated with the DLP method. **Figure 6.** Image of the micro beam fabricated with the DLP method.

**Figure 7.** CAD design of the micro beam. The support structures under the micro beam are removed. **Figure 7.** CAD design of the micro beam. The support structures under the micro beam are removed. **Figure 7.** CAD design of the micro beam. The support structures under the micro beam are removed.

*Micromachines* **2020**, *11*, x 10 of 13

**Figure 8.** Image of the micro beam fabricated with the PμSL method. **Figure 8.** Image of the micro beam fabricated with the PµSL method.

### **4. Conclusions 4. Conclusions**

In this study, a micro beam fabricated with conventional MEMS methods, was manufactured for the first time using the DLP and PμSL methods, which are 3D printing procedures. First, the printable scale of the DLP 3D printing method was evaluated, and it demonstrated that the printer could produce structures with a size of 86.7 μm. In this study, a micro beam fabricated with conventional MEMS methods, was manufactured for the first time using the DLP and PµSL methods, which are 3D printing procedures. First, the printable scale of the DLP 3D printing method was evaluated, and it demonstrated that the printer could produce structures with a size of 86.7 µm.

The experimental studies showed that 3 μm diameter supports were fabricated with the DLP method. However, they could not be fabricated with the PμSL method even when the diameters of the supports were 3 μm. After these support structures were removed, the micro beam was fabricated with PμSL. It was determined that PμSL was not suitable for complex structures. The results show the success of the 3D printer and the suitability of manufacturing a micro beam using the DLP printing method with fast and high sensitivity. The experimental studies showed that 3 µm diameter supports were fabricated with the DLP method. However, they could not be fabricated with the PµSL method even when the diameters of the supports were 3 µm. After these support structures were removed, the micro beam was fabricated with PµSL. It was determined that PµSL was not suitable for complex structures. The results show the success of the 3D printer and the suitability of manufacturing a micro beam using the DLP printing method with fast and high sensitivity.

As a result of this study, it was found that DLP is more appropriate because it allows the manufacturing of complex 3D structures with smaller dimensions, while PμSL is only suitable for simple 2D microstructures. It is expected that this paper will contribute to the literature in terms of fabrication of a micro device through the use and comparison of different techniques. As a result of this study, it was found that DLP is more appropriate because it allows the manufacturing of complex 3D structures with smaller dimensions, while PµSL is only suitable for simple 2D microstructures. It is expected that this paper will contribute to the literature in terms of fabrication of a micro device through the use and comparison of different techniques.

**Funding:** This research received no external funding. **Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest. **Conflicts of Interest:** The authors declare no conflict of interest.

#### **References References**

U-Beam MEMS Vibration Ring Gyroscope. *Micromachines* **2019**, *10*, 186.

© 2020 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).


**8. Adenoviral latency**

The term "adenoviruses" has an ecological coloration, reflecting the tendency to persistence in the lymphoid tissue, so that adenoviruses can be isolated from the tonsils, adenoids, appendix, and lymph nodes of practically healthy people.

After acute infections, many serotypes are not eliminated from the body for a long time. Most of the latent viruses belong to subgroups B2 and C. They can persist for years in the lymphoid tissue of the pharyngeal ring and, apparently, other localizations (e.g., in the mesenteric lymph nodes). Once in the intestine, adenoviruses asymptomatically replicate in the epithelial cells and/or Peyer's patches, periodically evolving from feces.

released into the environment through excreta. Therefore, a vaccine containing live strains of adenovirus is not recommended for use in children or the general population. Despite the longterm stability of the adenovirus genome, which is confirmed by the efficacy of ongoing vaccination among the US military, random mutations or homologous recombination events, which can lead to changes in the antigenicity of adenovirus, are not excluded. In addition, over time, the epidemic types of adenovirus have changed, and in recent years, highly pathogenic serotypes 14 and 55 have been distributed throughout the world. Finally, the circulation of the types of adenoviruses can vary geographically; for example, in China, the most common types associated with acute respiratory infections (ARI) are types 3, 7, and 55 [28]. Therefore, attention should be paid to developing new adenoviral vaccines based on currently circulating adenovirus strains.

Introductory Chapter: Human Adenoviruses http://dx.doi.org/10.5772/intechopen.82554 7

Representatives of the genus *Mastadenovirus* served as objects of research in the field of molecular biology. The intrigue around the pathogenetic function of adenoviruses aggravated after their tumorigenic properties, the ability to induce malignant tumors in animals (newborn hamsters), was recorded. In 1962, Trentin et al. described the first case of the induction of a malignant tumor in animals by the human pathogenic virus—adenovirus-12, which caused tumors in rodents [29]. The oncogenic potential of adenoviruses has served as a stimulus for their careful study, which has proved useful for studying the mechanisms of viral infection and molecular processes in eukaryotic cells. On the model of adenovirus infection, splicing, adenylation, and capturing of matrix RNA, sequence and expression regulation of viral genes, their integration with cellular chromosomes, etc. were first studied with human tumors. In a series of works [30, 31], it was shown that high-oncogenic type 12 adenoviruses and type 18 adenoviruses induce chromosomal aberrations in nonpermissive cells for them. The mutagenic effect at the chromosomal level has been demonstrated for human type 2 adenoviruses and type 5 in rat cells [32], as well as for bovine adenovirus type 3 in Chinese hamster cells [33]. In humans, despite intensive research, the association of malignant tumors with adenoviruses has not been identified.

The promise of using adenoviruses as vectors is due to the fact that a relatively large fragment can be inserted into their linear DNA. With the advent of second-generation vectors, it became possible to embed foreign DNA sequences up to 35 kb in the adenovirus genome, while maintaining only inverted repeats and packaging site. In addition, adenovirus receptors (e.g., termination of the fibers) can be genetically modified in such a way as to increase the tropism of the virus in relation to the tumor tissue. As a product of the transgene, which allows to destroy a tumor, you can use the herpes virus thymidine kinase (family *Herpesviridae*) or the chicken anemia virus apoptin (family *Circoviridae*). In the first case, the patient is prescribed of acyclovir; in the second case, the tumor is destroyed as a result of vector-induced apoptosis. Unfortunately, genetically engineered constructions based on adenoviral vectors have not yet found clinical

**12. The use of adenoviruses as vectors for gene therapy**

**11. The mutagenic effect**

Latency creates the possibility of endogenous recurrences of acute infection and chronic hyperplasia (in fact, chronic inflammation) of infected lymphoid tissue. The possibility of activating a viral infection in the tonsils (chronic tonsillitis), mesenteric lymph nodes, and appendix is not excluded. Adenoviruses can be activated on the background of immunosuppressive therapy in AIDS patients. A number of new serotypes (serotypes 43–47 of subgroup D) were first isolated from AIDS patients (from feces), allowing to believe that a persistent infection creates favorable conditions for the evolution of adenoviruses [25].

The mechanism of persistence of adenoviruses in the lymphoid tissue still remains unclear. Most likely, this is due to the low content of sensitive (permissive) cells and very slow replication of the virus in lymphocytes, that is, with severely limited productive infection. It is significant that in the experiments of W. Rowe et al., who discovered adenoviruses in 1953, it took several weeks for the degeneration of a culture of adenoid tissue associated with the reproduction of latent adenoviruses. The possibility of integrative virogeny with partial expression of the viral genome is not excluded. In approximately 50% of the tonsils in adults, it was possible to detect adenoviral antigens in the absence of an infectious virus.