**Case Report on: Very Early Afterdepolarizations in HiPSC-Cardiomyocytes—An Artifact by Big Conductance Calcium Activated Potassium Current (Ibk,Ca)**

**András Horváth 1,2,3,**†**,**‡**, Torsten Christ 1,2,\*,**†**, Jussi T. Koivumäki 4,**

**Maksymilian Prondzynski 1,2,§, Antonia T. L. Zech 1,2, Michael Spohn 5, Umber Saleem 1,2, Ingra Mannhardt 1,2, Bärbel Ulmer 1,2, Evaldas Girdauskas 2,6, Christian Meyer 3,7, Arne Hansen 1,2, Thomas Eschenhagen 1,2 and Marc D. Lemoine 1,2,7,\***

Received: 28 October 2019; Accepted: 15 January 2020; Published: 20 January 2020

**Abstract:** Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent an unlimited source of human CMs that could be a standard tool in drug research. However, there is concern whether hiPSC-CMs express all cardiac ion channels at physiological level and whether they might express non-cardiac ion channels. In a control hiPSC line, we found large, "noisy" outward K+ currents, when we measured outward potassium currents in isolated hiPSC-CMs. Currents were sensitive to iberiotoxin, the selective blocker of big conductance Ca2+-activated K+ current (IBK,Ca). Seven of 16 individual differentiation batches showed a strong initial repolarization in the action potentials (AP) recorded from engineered heart tissue (EHT) followed by very early afterdepolarizations, sometimes even with consecutive oscillations. Iberiotoxin stopped oscillations and normalized AP shape, but had no effect in other EHTs without oscillations or in human left ventricular tissue (LV). Expression levels of the alpha-subunit (KCa1.1) of the BKCa correlated with the presence of oscillations in hiPSC-CMs and was not detectable in LV. Taken together, individual batches of hiPSC-CMs can express sarcolemmal ion channels that are otherwise not found in the human heart, resulting in oscillating afterdepolarizations in the AP. HiPSC-CMs should be screened for expression of non-cardiac ion channels before being applied to drug research.

**Keywords:** human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs); iPS cells; stem cells; big conductance calcium activated potassium channel (BK); Maxi-K; slo1; KCa1.1; iberiotoxin; long QT syndrome

#### **1. Introduction**

Human induced pluripotent stem-cell derived cardiomyocytes (hiPSC-CMs) have gained interest as a human model to study heart physiology and pathophysiology [1–4], cardiovascular pharmacology [5] and cardiac repair [6]. In this context, it is important that hiPSC-CMs share properties of human adult CMs. Many reports claimed that characteristics of hiPSC-CMs might differ from adult CMs, a finding frequently interpreted as immaturity. On the one hand, immaturity could be caused by the lack of cardiac ion channels or by differences in expression levels such as the inward rectifier potassium current (IK1) [7–10]. On the other hand, hiPSC-CMs can show ion currents, which are absent in adult human CMs such as the T-type calcium current [11,12]. Based on these findings, there is a need for a detailed electrophysiological characterization of hiPSC-CMs before using them as a model for human CMs. Here we report the coincidently found expression of a non-cardiac ion channel in hiPSC-CMs as a peculiarity of a single control cell line: the big conductance calcium activated potassium current (BKCa; alternatively used names: Maxi-K, slo1, KCa1.1).

BKCa is a voltage- and calcium-gated potassium channel (KCa1.1) generating huge conductivity for potassium. BKCa is widely expressed in the human body, mainly in neural cells, blood vessels, kidney, but not in in cardiomyocytes. Recently, artificial expression of BKCa was shown to be able to shorten action potentials (APs) in murine CMs [13]. Consequently, expression of the non-cardiac BKCa current in human CMs was proposed as a genetic therapy for the long QT syndrome. However, the contribution of individual ion channels to repolarization and resulting AP shape differs from murine to human CMs. Putative impact of BKCa to human cardiac electrophysiology remains unclear.

The goal of this study was to draw attention to the fact that hiPSC-CMs can express non-cardiac ion channels. In addition, we had the chance to elucidate how the expression of BKCa may influence the membrane potential of human CMs. Based on our findings, we propose a regular assessment for expression of non-cardiac ion channels as a part of quality control when using hiPSC-CMs.

### **2. Methods**


**2. Electrostatic discharge (ESD)**

Electrostatic discharge (ESD) is a common form of component level failure from manufacturing, shipping, and handling. Today, the ESD models and performed for qualification and shipping of semiconductor components are as follows [4]:

Additional models that are still performed, but not used for qualification of components include [4]:

#### **2.1. Human body model (HBM)**

ESD pulse models have been established to quantify the interaction of semiconductor chips and human beings. An important model is the human body model (HBM). Today, HBM is the most widely established standard for the reliability and quality in the semiconductor industry [2–4, 6]. The HBM test is integrated into the qualification and release process of the quality and reliability teams for components in corporations, and foundries [6].

The human body model is regarded as an electrostatic discharge (ESD) event, not an electrical overstress (EOS) event [1–11]. HBM represents the interaction the electrical discharge from a human being and component. The model assumes that the human being is the initial condition.

The human body model (HBM) became of interest in early days in the mining industry in the 1950s. In the Bureau of Mines, investigation reports discussed the issue of electrostatic in the mining industry. A first publication was published by P.G. Guest, V.W. Sikora, and B.L. Lewis as the *Bureau of Mines, Report of Investigation 4833*, U.S. Department of Interior, January 1952 [7]. A second article of interest was published by D. Bulgin, referred as D. Bulgin. Static Electrofication*. British Journal of Applied Physics*, Supplemental 2, 1953 [8].

An early investigator of issues with the human body model standard was T. M. Madzy and L.A. Price II of IBM in 1979 discussed a test system titled "Module Electrostatic Discharge Simulator" [4]. In this article, it was discussed that the ESD simulator was used within IBM since 1974. In 1980, H. Calvin, H. Hyatt, H. Mellberg, and D. Pellinen proposed values for the resistance and capacitance for the human ESD event for the finger tip and field enhanced discharges in "Measurement of Fast Transients and Application to Human ESD," published in the 1980 Proceedings of the EOS/ESD Symposium [4, 10–11]. The proposed resistance for the finger tip was averaged 1920 Ω, and capacitance of 110 pF, whereas the field enhanced discharge was a resistance of 550 Ω, and 120 pF. In 1981, H. Hyatt, H. Calvin, and H. Mellberg investigated the human ESD event, published in the 1981 Proceedings of the EOS/ESD Symposium, titled "A closer look at the human ESD event" [4, 10–11].

**2. Electrostatic discharge (ESD)**

**Figure 1.** ESD, EOS, Latchup, EMI and EMC.

10 System of System Failures

• Human Body Model (HBM).

• Machine Model (MM).

• Transient Latchup.

include [4]:

• Latchup.

• Charged Device Model (CDM).

• Transmission Line Pulse (TLP).

**2.1. Human body model (HBM)**

• Very-Fast Transmission Line Pulse (VF-TLP).

shipping of semiconductor components are as follows [4]:

Electrostatic discharge (ESD) is a common form of component level failure from manufacturing, shipping, and handling. Today, the ESD models and performed for qualification and

Additional models that are still performed, but not used for qualification of components

ESD pulse models have been established to quantify the interaction of semiconductor chips and human beings. An important model is the human body model (HBM). Today, HBM is the most widely established standard for the reliability and quality in the semiconductor industry [2–4, 6]. The HBM test is integrated into the qualification and release process of the quality

and reliability teams for components in corporations, and foundries [6].

HBM failure mechanisms are associated with permanent damage on the peripheral circuitry of a semiconductor chip [3]. Additionally, HBM failures can occur power rails and ESD power clamps between the power rails. HBM failures can occur in both passive and active semiconductor devices. The failure signature is typically isolated to a single device, or a few elements. ESD circuits are designed to be "tuned" to be responsive to specific pulse widths; this is an issue for EOS events since they are not "tuned" for EOS events. For example, the RC-triggered ESD power clamp is tuned to the HBM pulse, not EOS events.

HBM ESD failures are also distinct from EOS events [1, 4]. HBM events will not typically cause failures in the package, printed circuit board (PCB), or single component devices mounted on a printed circuit board.

Human body model (HBM) failures can occur in diode and MOSFET structures. Integrated circuit diode structures fail at the contact interface, silicon surface, or junction region. Human body model failure occurs in a metal oxide semiconductor field effect transistor (MOSFET) structure. Integrated circuit MOSFET structures failure occurs from MOSFET source-to-drain, or at the MOSFET gate. From HBM failures, typically, the failure is MOSFET source-to-drain failures [2, 3].

An example of an ESD protection network is known as a dual-diode network [3]. The dualdiode ESD network is a commonly used network for complimentary metal oxide semiconductor (CMOS) technology. A first p-n diode element is formed in an n-well region where the p-anode is the p-diffusion implant of the p-channel MOSFET device and the n-cathode is the n-well region connected to the power supply VDD. This is sometimes referred to as the "up diode." A second p-n diode element is formed in an p-well or p-substrate region where the n-cathode is the n-diffusion implant of the n-channel MOSFET device, or the n+/n-well implant and the p-anode is the p-well region or p-substrate region connected to the power supply VSS. This is sometimes referred to as the "down diode." This circuit provides a "forward bias" ESD protection solution for positive and negative ESD pulse events to the two power rails VDD and VSS. An advantage of the dual-diode ESD network is that it is easily to migrate from technology generation to technology generation. In shallow trench isolation (STI) technology, this structure is scalable. A second advantage is that it has a low turn-on voltage of 0.7 V. A third advantage is that it can be designed with low capacitance, making it suitable for CMOS, advanced CMOS, and RF technologies. A fourth advantage is that it does not contain MOSFET gate dielectric failure mechanisms.

In the calibration and verification procedure, the JEDEC standard requires a 1 GHz oscilloscope, whereas the ESDA standard requires 3 GHz [13]. Both standards today are bandwidth limited signal since the CDM waveform is faster that 1 GHz. These oscilloscopes were chosen based on availability at the time. It is well know that the energy spectrum of the CDM pulse

System and Component Failure from Electrical Overstress and Electrostatic Discharge

http://dx.doi.org/10.5772/intechopen.72677

13

CDM event damage occurs in the semiconductor chip through the substrate. It can also occur through the power supply. Charge is stored on the package, and the substrate.; then the power supply rapidly discharges through the grounded pin. The CDM failure mechanism can be small "pin-hole" in a MOSFET gate structure; this can occur in receiver networks, as

The current path for charged device model (CDM) in components is significantly different from other electrostatic discharge (ESD) events. In the case of the charged device model (CDM), the package and/or chip substrate is charged through a power or ground rail. The component itself is charged slowly to a desired voltage state. As a result, the current flows from the component itself to the grounded pin during ESD testing. This is significantly from other ESD tests that ground a reference, and then apply an ESD event to a signal or power pin. As a result, the current path that a CDM event follows is from inside the component to pin that is grounded during test. To avoid CDM failures of the MOSFET gate structure, an additional charged device model (CDM) ESD network is used [3] The ESD network comprises of a first stage dual-diode network placed adjacent or in proximity of the signal pad. A second set of diodes (e.g. second stage network) are placed adjacent to the receiver circuit. A resistor is placed between the first and second stage. Three paths are possible for the CDM current from a charged ground rail (e.g. p-substrate) to the grounded receiver pin. For a positive charging of the substrate, the current flows from the substrate to any possible path that will reach the grounded signal pad node. A first path is through the n-channel MOSFET receiver circuit gate and to the second stage ESD diode. A second path is through the substrate to the second stage diode network. A

In the case of the first stage ESD protection circuit is far from the signal pad, the substrate resistance can be significant. For the third path, the total resistance from the grounded location to the grounded signal path is the sum of the substrate resistance and the ESD diode series resistance. In the case that the receiver network is adjacent to the second stage ESD network, the current will prefer to follow the second path instead of first path. When the impedance of the n-channel MOSFET receiver (e.g. Path A) is higher than resistance through the second path, the receiver gate structure can avoid rupturing of the MOSFET gate dielectric. To insure that the current flows through the second path through the second stage CDM ESD network, the circuit must be physically close to the receiver, and a low series resistance diode element.

Electrical overstress (EOS) has been an issue in devices, circuit and systems for electronics for many decades, as early as the 1970s, and continues to be an issue today [1]. EOS failures are occurring at the device manufacturer, supplier, assembly and the field. In the electronic

waveform can extend into the 5 GHz frequency.

third path is through the substrate to the first stage ESD network.

**3. Electrical overstress (EOS)**

well as metal interconnects.

*An example of a signal pin ESD network consisting of a grounded gate n-channel MOSFET device [3]. The grounded gate NMOS (also referred to as GGNMOS) ESD network is a commonly used network for complimentary metal oxide semiconductor (CMOS) technology. Typically, it is a n-channel MOS-FET whose MOSFET drain is connected to the signal pin, and whose MOSFET source and gate are connected to the ground power rail. This circuit remains "off" in normal operation. When the signal pin exceeds the MOSFET snapback voltage, this circuit discharges to the VSS power rail. When the signal pin is below the ground potential, the MOSFET drain forward biases to the p-well or p-substrate region. An advantage of the GGNMOS ESD network is that it is a natural scalable solution. As the technology scales, the MOSFET snapback voltage reduces, leading to an earlier turn-on of the MOSFET.*

#### **2.2. Charged device model (CDM)**

The charged device model is an electrostatic discharge (ESD) test method that is part of the qualification of semiconductor components [4]. The charged device model (CDM) standard is supported by ESD Association as ANSI/ESD ESD-STM5.3.1-1999 [12]. Presently, there are four CDM test standard (ESDA S5.3.1, JEDEC JESD22-C101, AEC-Q100-011 Rev. C, and JEITA ED-4701-300). Each require different test platform, testing, waveform, and calibration requirements [4]. The charged device model (CDM) event is associated with the charging of the semiconductor component substrate and package. The charging of the package occurs through direct contact charging, or field-induced charging process (e.g. the field-induced charge device model (FICDM)).

There is presently an effort to align the CDM standards between the ESD Association and the JEDEC organization, by establishing a joint ESDA/JEDEC standard. The ESDA/JEDEC joint standard (JS-002 2014) will replace existing CDM ESD standards JEDS22-C101 and ANSI/ESD S5.3.1. The new joint standard will preserve test systems in the field, and improve the waveform measurement process.

The charged device model (CDM) pulse is regarded as the fastest event of all the ESD events [4, 12–15]. Note that the CDM pulse waveform is influenced by the test platform and measurement metrology. The test platform is influenced by the field plate, field plate dielectric thickness and material type, and the probe assembly (e.g. test head, and ground plane). The metrology is influenced by the oscilloscope and verification module specifications.

First, the event is oscillatory. The CDM current pulse rise time is on the order of 250 ps, and with peak currents in the range of 10 A. The energy spectrum of the CDM pulse event extends to 5 GHz frequency. The CDM pulse waveform has a fast current pulse. The time scale of the CDM event is significantly lower than the thermal diffusion time; hence CDM events are in the "adiabatic regime" of a Wunsch-Bell power-to-failure curve [4].

In the calibration and verification procedure, the JEDEC standard requires a 1 GHz oscilloscope, whereas the ESDA standard requires 3 GHz [13]. Both standards today are bandwidth limited signal since the CDM waveform is faster that 1 GHz. These oscilloscopes were chosen based on availability at the time. It is well know that the energy spectrum of the CDM pulse waveform can extend into the 5 GHz frequency.

CDM event damage occurs in the semiconductor chip through the substrate. It can also occur through the power supply. Charge is stored on the package, and the substrate.; then the power supply rapidly discharges through the grounded pin. The CDM failure mechanism can be small "pin-hole" in a MOSFET gate structure; this can occur in receiver networks, as well as metal interconnects.

The current path for charged device model (CDM) in components is significantly different from other electrostatic discharge (ESD) events. In the case of the charged device model (CDM), the package and/or chip substrate is charged through a power or ground rail. The component itself is charged slowly to a desired voltage state. As a result, the current flows from the component itself to the grounded pin during ESD testing. This is significantly from other ESD tests that ground a reference, and then apply an ESD event to a signal or power pin. As a result, the current path that a CDM event follows is from inside the component to pin that is grounded during test.

To avoid CDM failures of the MOSFET gate structure, an additional charged device model (CDM) ESD network is used [3] The ESD network comprises of a first stage dual-diode network placed adjacent or in proximity of the signal pad. A second set of diodes (e.g. second stage network) are placed adjacent to the receiver circuit. A resistor is placed between the first and second stage. Three paths are possible for the CDM current from a charged ground rail (e.g. p-substrate) to the grounded receiver pin. For a positive charging of the substrate, the current flows from the substrate to any possible path that will reach the grounded signal pad node. A first path is through the n-channel MOSFET receiver circuit gate and to the second stage ESD diode. A second path is through the substrate to the second stage diode network. A third path is through the substrate to the first stage ESD network.

In the case of the first stage ESD protection circuit is far from the signal pad, the substrate resistance can be significant. For the third path, the total resistance from the grounded location to the grounded signal path is the sum of the substrate resistance and the ESD diode series resistance. In the case that the receiver network is adjacent to the second stage ESD network, the current will prefer to follow the second path instead of first path. When the impedance of the n-channel MOSFET receiver (e.g. Path A) is higher than resistance through the second path, the receiver gate structure can avoid rupturing of the MOSFET gate dielectric. To insure that the current flows through the second path through the second stage CDM ESD network, the circuit must be physically close to the receiver, and a low series resistance diode element.


**2. Classification of head injury**

 Hearing loss is a well known entity following head injury. The degree of hearing loss may vary depending on the severity of the head injury. The severity of Head injury is measured clinically using the Glasgow coma scale scoring system (G.C.S). The Glasgow Coma Scale was first published by Teasdale and Jennett in 1974. Several years later it was modified by Jennett and Teasdale and by Rimel et al (Rimel RW et al 1981, 1982) .This scoring system provides the best measure of severity of head injury. The score is the sum of the scale's three measures of eye opening, best motor and verbal responses. This ranges from a score of 3 for a patient with no motor, verbal response or eye opening to painful stimuli, to 15 for a patient who is oriented, follows commands, and has spontaneous eye opening. Patients, who do not follow commands, speak or open their eyes, with a score of 8 or less, are by definition in coma. Head injury is defined as mild when the GCS score is either 13 or 14–15, moderate by a score of 9–12 or 13, and severe by a score of 3–8. The GCS score on admission, and its prognostic usefulness, are easily confounded by other factors particularly substance misuse, but sequential monitoring after admission plays a crucial role in detecting early deterioration and in its management.

Culotta (Culotta VP et al, 1996) following a retrospective study found that patients with a GCS score of 13–15, represent a heterogeneous group with statistically significant different head tomography abnormalities. On the basis of findings they suggested separating patients with GCS score 13–14 into a different category from patients with a GCS score of 15, thus effectively redefining minor head injury. These findings were confirmed by a similar study by Gomez (Gomez PA,et al1996). Hsiang , on the basis of a cohort study of 1360 patients with GCS score of 13–15 suggested that this group of patients could also be divided into two subgroups, mild head injury and high risk mild head injury(Hsiang JNK et al,1997). Mild head injury is defined as GCS 15 without radiographic abnormalities, high risk mild head injury being defined as GCS 13–14, or a GCS 15 with acute radiographic abnormalities. More recently Swann and Teasdale recognizing the limitation of the GCS with regard to minor head injury have suggested another sub classification. Mild head injury is defined as GCS 13–14. Minor head injury is defined as GCS score of 15. The authors recognized in their monograph that this is a somewhat arbitrary definition. However in Clinical practice GCS is used in evaluation of Head injury (Swan IJ,Teasdale Gm 1999)

Glasgow coma scale and score (Table-1). Glasgow coma score: (E+M+V) = 3–15.

Table 1. Glasgow coma score

In India, in the year 2000, official statistics revealed that 80,118 persons died and 3, 42,200 were injured in road traffic accidents . However this is an underestimate, as not all accidents are reported to the police. A study done in Haryana (India) recorded all traffic-related

 Hearing loss is a well known entity following head injury. The degree of hearing loss may vary depending on the severity of the head injury. The severity of Head injury is measured clinically using the Glasgow coma scale scoring system (G.C.S). The Glasgow Coma Scale was first published by Teasdale and Jennett in 1974. Several years later it was modified by Jennett and Teasdale and by Rimel et al (Rimel RW et al 1981, 1982) .This scoring system provides the best measure of severity of head injury. The score is the sum of the scale's three measures of eye opening, best motor and verbal responses. This ranges from a score of 3 for a patient with no motor, verbal response or eye opening to painful stimuli, to 15 for a patient who is oriented, follows commands, and has spontaneous eye opening. Patients, who do not follow commands, speak or open their eyes, with a score of 8 or less, are by definition in coma. Head injury is defined as mild when the GCS score is either 13 or 14–15, moderate by a score of 9–12 or 13, and severe by a score of 3–8. The GCS score on admission, and its prognostic usefulness, are easily confounded by other factors particularly substance misuse, but sequential monitoring after admission plays a crucial role in detecting early

Culotta (Culotta VP et al, 1996) following a retrospective study found that patients with a GCS score of 13–15, represent a heterogeneous group with statistically significant different head tomography abnormalities. On the basis of findings they suggested separating patients with GCS score 13–14 into a different category from patients with a GCS score of 15, thus effectively redefining minor head injury. These findings were confirmed by a similar study by Gomez (Gomez PA,et al1996). Hsiang , on the basis of a cohort study of 1360 patients with GCS score of 13–15 suggested that this group of patients could also be divided into two subgroups, mild head injury and high risk mild head injury(Hsiang JNK et al,1997). Mild head injury is defined as GCS 15 without radiographic abnormalities, high risk mild head injury being defined as GCS 13–14, or a GCS 15 with acute radiographic abnormalities. More recently Swann and Teasdale recognizing the limitation of the GCS with regard to minor head injury have suggested another sub classification. Mild head injury is defined as GCS 13–14. Minor head injury is defined as GCS score of 15. The authors recognized in their monograph that this is a somewhat arbitrary definition. However in Clinical practice GCS is

**2. Classification of head injury**

deterioration and in its management.

Table 1. Glasgow coma score

used in evaluation of Head injury (Swan IJ,Teasdale Gm 1999)

Glasgow coma scale and score (Table-1). Glasgow coma score: (E+M+V) = 3–15.

Spontaneous - 4 Obeys commands - 6 Oriented - 5

No motor response - 1

EYE OPENING BEST MOTOR RESPONSE VERBAL RESPONSE

In India, in the year 2000, official statistics revealed that 80,118 persons died and 3, 42,200 were injured in road traffic accidents . However this is an underestimate, as not all accidents are reported to the police. A study done in Haryana (India) recorded all traffic-related

Abnormalextension - 2 No verbal response -1

To speech - 3 Localizes to pain - 5 Confused, Disoriented-4 To pain - 2 Withdraws (Flexion) - 4 Inappropriate words - 3 None - 1 Abnormal flexion -3 Incomprehensible sounds -2 injuries and deaths through bi-weekly home visits to all households in 9 villages for a year. This study showed that the ratio between critical, serious and minor injuries was 1:29:69. (Varghese .M .Mohan.D 2003).


**2. Structure of diamond**

In ultra-precision and nanometric cutting operations, the most preferred tool material is single-crystal diamond due to its extraordinary properties, including highest hardness, very strong resistance to wear, perfect chemical stability and satisfactory service life, as well as the least sharpness, when finished. Due to its extreme strength and hardness, recently diamond has become an attractive choice in engineering processes and in a variety of other technological applications. Considering the morphology and structure of diamond, its mechanical and physical properties vary not only with the different crystallographic planes but also with different crystallographic directions on a plane.

### **Figure 4.** *Crystal structure of single crystal diamond.*

Diamond is a crystal allotropic form of Carbon and has diamond cubic crystal structure with a lattice parameter of 0.3567 nm (see **Figure 4**). Each C atom has four neighboring C atoms in a tetrahedron structure with bond angle between the atoms of 109°28′. The C atoms are covalently bonded together with sharing of one of its outer four electrons with each of four other C atoms resulting in sp3 hybridization. This sharing of electrons results in a strong binding among each pair of C atoms in all three dimensions.

Diamond has some outstanding properties which makes it an obvious choice for the cutting tool material.

iii.It has highest atom-number density.

iv.At room temperature, it has highest thermal conductivity of any solid.

**Table 1** shows the mechanical properties of diamond. Diamond is categorized into four categories:

Diamond naturally occurs produced in nature at high pressure and temperature in volcanic shafts. With high pressure synthesis, it is able to produce diamond possessing the strength similar to natural diamond. Generally, the natural and synthetic diamond are used for cutting purposes. Diamonds usually exist with other allotropes

#### **Figure 5.**

*Hardness of various tooling materials.*

#### **Table 1.**

*Mechanical properties of diamond.*

of carbon and they can be characterized by knowing the structure, atomic vibration and electronic states. The diamond characteristics are usually determined using X-ray diffraction, electron microscopy and Raman spectroscopy. For diamond to be qualified, it must have the following characteristics:

i.A crystalline morphology revealed by electron microscopy

ii.Crystalline structure with a single phase identified by X-ray diffraction

iii.A sharp peak at 1332 cm−1 detected by Raman spectrum

Diamond occurs predominantly in three different forms in cubic (100), octahedron (111) and dodecahedron (110) and their combinations. These three forms are based on the three planes ((100), (110) and (111)) from a simple cubic crystal structure. **Figure 6** shows the schematic of the (100) cubic, the (110) dodecahedral and the (111) octahedral. The octahedral form of diamond crystal is the most common form.

Diamond breaks along {111} crystal planes also known as cleavage planes. Bonding is less strong perpendicular to these planes as compared to the other directions due to lower total number of bonds and hence the diamond fractures favorably along

*Diamond as a Precision Cutting Tool DOI: http://dx.doi.org/10.5772/intechopen.108557*

#### **Figure 6.**

*Schematic diagrams showing the location of {111}, {100} and {110} planes on an octahedron diamond.*

#### **Table 2.**

*Diamond classification based on impurity level [10].*

these planes. Diamonds are also categorized into four types based on the presence of nitrogen as an impurity in their crystals. These are: Ia, Ib, IIa, IIb. Majority of natural diamonds (~99%) come in type Ia. Type Ia consists of nitrogen in the form of aggregates in the crystal. All synthetic diamonds are of type Ib with an even distribution of nitrogen atoms in the crystal. Types IIa and IIb are very rare in nature but can be synthesized for industrial purposes. In all natural diamonds, there exist many impurity elements such as nitrogen, hydrogen, boron and oxygen. **Table 2** shows different classifications of diamond.


2.1.1. Substrate Pretreatment

PCrNi1MoA steels (10 × 10 × 1 mm3 in size) were used as substrates. The substrates were mechanically ground using sandpaper from P240 up to P2000 and then polished by diamond suspension from 3 μm to 1 μm. The polished substrates were ultrasonically cleaned in acetone for 15 min and then dried with cold air. The chemical compositions of the alloy steel are shown in Table 1.

**Table 1.** Chemical composition of the alloy steel.

#### 2.1.2. Deposition Device

This experiment adopts DC magnetron sputtering (DCMS) technology and the equipment is single-target magnetron sputtering instrument (JCZK350A, Juzhi Vacuum Equipment Company, China), which mainly includes a deposition chamber, vacuum system, cooling system, gas supply system, heating system, control system, etc. Figure 1 shows a schematic diagram of the magnetron sputtering.

## 2.1.3. Deposition Conditions

The cleaned substrates were installed on a substrate holder and loaded into the chamber. A Ta target (purity: 99.95%) was used with dimensions of Φ50 mm × H4 mm. The substrate-to-target distance was 70 mm. A chamber pressure of below 6.0 × 10−4 Pa was reached before coating depositions. In deposition processes, Ar pressure and the deposition time were fixed at 0.5 Pa and 1 h, respectively. The substrate temperature (Tsub) was from 200 ◦C to 400 ◦C and the sputtering power (Pspu) was from 100 W to 175 W. The deposition parameters are listed in Table 2.

**Figure 1.** Schematic diagram of magnetron sputtering.

**Table 2.** Deposition parameters for Ta coatings.

#### *2.2. Characterization*

The crystalline phase of coatings was identified by X-ray diffraction (XRD, Empyrean, PANalytical, the Netherlands) with Cu-Kα radiation (λ = 0.154 nm) over a 2θ range of 20◦–90◦. The surface and cross-section morphology were characterized using a field emission scanning electron microscope (FESEM, Quanta-250, FEI Company, Hillsboro, OR, USA) at an accelerating voltage of 20 kV. The three-dimensional profiler (ST400, Nanovea company, Irvine, CA, USA) equipped with confocal optical microprobe was used to collect the microscopic morphology, roughness, and flatness in a specific area of the sample surface. The collection range was 1 mm × 1 mm and the collection accuracy was 0.02 μm.

The hardness and elastic modulus of Ta coatings were measured by a nano-indentation tester (TI-980, Bruker, Billerica, MA, USA) at a loading force of 5 mN. Five measures were recorded for each sample to ensure reliable results and all indentation depths were less than 10% of the coating thickness to avoid the effect of the steel substrate.

The qualitative and quantitative adhesive properties of the samples were analyzed in 2 ways. Firstly, using Rockwell hardness tester (HRD-150, Bangyi Precision meter company, China), the loading force of the Rockwell hardness meter was set to 150 kgf, an indentation was pressed on the sample surface, and we observed the indentation under the optical microscope to evaluate qualitatively the adhesion. Secondly, we quantified the adhesion by the scratch tester (MST, Anton Paar, Austria) with a Rockwell C diamond indenter (200 μm of radius). The scratch length, loading rate, and maximum loading force were 5 mm, 25 N/min, and 30 N, respectively. The larger the measured critical load, the better the coating adhesive performance of the sample.


**6. Discussion**

Dr Ivan Ribar settlement in New Belgrade and its "smelly buildings" is one of many examples of the so called "least cost" mentality, which has led to construction decisions that prioritized cost savings, but whereby multiple prices of the entire investment were ultimately paid due to omissions. In this case, it was a legal obligation to purchase certain material from a domestic manufacturer whose production was not adequately controlled. This led to the appearance of a certain amount of material that did not correspond to the quality for which there was a certificate but possessed substances that later turned out to be toxic and could endanger the health of the inhabitants.

Considering the linear model of the construction process, the problem occurred within the contract phase, during the purchase of the specific type of product. The case of smelly buildings indicates that stricter control of products used in the construction of facilities and interior equipment, and especially the so-called byproducts, is needed. The significance of the case of the smelly building is in the fact that it drew the attention of the scientific and professional public to the importance of IAQ control, but also to the importance of outdoor air quality control because these two are inextricably linked.

These experiences indicate the need to further work on improving the existing legislation governing the field of air quality control, especially in light of the emergence of a new generation of pollutants, as well as the adoption of legislation and development of guidelines for IAQ. Special attention should be paid to the critical group of materials used in and during construction, in order to investigate the various effects, they may have on IAQ, and thus on endangering the health of residents.

Having in mind the complexity of the construction process and the domain of IAQ, FM with its scopes and activities have the potential to accompany all phases, including the preparation of short-term and long-term FM maintenance plans. Facility managers and those with facility-related responsibilities must make the risk analysis, which also addresses indoor environmental risks. This includes audit reports that trigger new maintenance needs, but, more importantly, to change the protocols and start immediate actions to prevent IAQ related incidents from occurring in the first place. Auditing health and safety issues should create measures to fulfil the regulatory requirements and control regular measures.

The research indicates the importance of the engagement of facility managers during the entire construction process and the building life cycle as an independent actor. This is especially important in contract and construction phases. In the contract phase, FM could control purchasing, contracting and negotiation processes to achieve adopted building and quality performance targets. On the other side, independent construction management could include control in the application of building codes and standards, as well as checking the quality of materials and equipment.

This is especially important for public investments such as social and affordable housing complexes like in Belgrade's case of the Dr Ivan Ribar settlement, which is not an isolated case of public construction facing this problem. In the period from 2012 to 2015, cases of reconstruction of the theatre and maternity hospital in Vranje, a residential complex in Novi Sad and a stem cell bank in Belgrade were recorded. On the one hand, the situation can be seen from the aspect of irresponsible disposal and spending of public funds, and on the other hand, it is necessary to allocate additional funds to solve the problem. The example of the Dr Ivan Ribar residential complex pointed out the following groups of additional costs and material losses:

	- costs of the rentals
	- relocation costs
	- deposit for renting an apartment
	- and agency commission costs
	- all overhead costs in the purchased apartment

In addition to the above costs, one should keep in mind the creation of a bad reputation for the entire settlement, which caused a reduction in the market price of real estate, but also stress and suffering for tenants and their families over a period of several years (endangered health, relocation, postponement of the final solution, negotiations, etc.).

On the other side, FM practice is likely to be case-specific by nature, dealing with the diversities of facility, organization, business sector, surrounding environment and context, and circumstance [26]. From that perspective, Urban FM is very important to improve citizens' health and well-being, especially from the perspectives of healthy buildings, accessibility and services to the vulnerable population. Using the community-based approach of FM is important to recognize the risks, enable the enhancement and contribute to a healthier society. Similarly, understanding the needs of neighborhoods requires engaging with citizens, leading to their empowerment to understand, recognize and report the sickness parameters, and consequently, to better support a healthy environment.

**Author Contributions:** Conceptualization, M.V., A.T.S. and A.S.; methodology M.V., A.T.S. and A.S.; validation, M.V., A.T.S. and A.S.; investigation M.V. and A.T.S.; resources, M.V., A.T.S. and A.S.; writing—original draft preparation, M.V.; writing—review and editing, M.V., A.T.S. and A.S.; visualization, M.V.; supervision, A.T.S. and A.S. All authors have read and agreed to the published version of the manuscript.

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

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Used data belong to the domain of publicly available information, and in this paper their systematization and critical interpretation is performed.

**Acknowledgments:** We take this opportunity to express our gratitude to Roberto Alonso González Lezcano, Guest Editor for inviting us to publish our research within Sustainability Special Issue entitled: "Sustainable Building and Indoor Air Quality".

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