*4.3. Additional Applications*

There is a great diversity of potential bioelectronics applications, and this review will focus on those that have gained attention for high throughput fabrication. However, many other applications, such as implantable cerebrovascular and arterial stents, brain–machine interfaces, and fully printed wearable devices, are of tremendous interest [10,150]. Other systems have been successfully fabricated with high throughput methods, as summarized in Table 4 [37,129,162–166]. One area of critical interest is wearable electrophysiology monitoring. Traditional electrocardiogram (ECG), electromyogram (EMG), electrooculogram (EOG), and electroencephalogram (EEG) electrodes are based on a hydrogel that can cause irritations in long term use, especially in neonates and those with sensitive skin, and they are highly prone to motion artifacts [8,17]. In contrast, printed dry electrodes can conform to the patient's skin and interface without any damaging gels, making them excellently suited to continuous monitoring, even during patient motion [9,10]. In two reported works, Tan et al. and Chalihawi et al. used carbon black and AgNP and MWCNTs, respectively, to fabricate dry electrodes. Tan et al. used doctor blade coating on a TPU substrate to produce high-performing electrodes for textile integration that can endure over 50 washing cycles [165]. In addition, Chalihawi et al. screen printed AgNP interconnections and an electrode pad, then used doctor blade coating to deposit a functional MWCNT sensor, which was shown to achieve similar ECG signals when compared to a gel-based Ag/AgCl sensor [166]. Images of the fabricated electrodes with (i) Ag layer and (ii) MWCNT layer are provided in Figure 10d, and the ECG performance is shown in (iii) [166]. Although it was not assessed, it would be of great interest to determine these electrode's performance during patient motion. Another interesting area of research is the development of capacitive touch sensors, which have been widely reported in the literature using traditional MEMS fabrication. Lee et al. created such a touch sensor with an air gap instead of PDMS dielectric, and noted that the increased dielectric constant of air allowed for highly improved sensitivity (∆C/C<sup>0</sup> (%) of 0.118%) and high linear sensing range from 0–20 KPa [37]. One area of high interest is in printing on TPU substrates, and this was the focus of a recent investigation by Jansson et al. using screen-printed AgNP inks. In this experiment, various dimensions were cut in a roll-to-roll laser process and filled with AgNP inks, and ink was filled from both the cutting side and the opposite side [162]. It was determined that the via diameter had a minor impact on conductivity and reliability, but the match between via diameter and screen opening, optimization of printing thickness and side from which the via is printing were of high importance [162]. In addition, Alsuradi et al. demonstrated a very high control of capacitive and inductive behavior in screen-printed traces based on geometries adapted from integrated microwave circuits, then optimized for thicker depositions common in screen printing [129]. As a result, inductances and capacitances could be reliably controlled to within 5% error, which

is considered acceptable for many commercial passive components [129]. Finally, polymer materials like poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are outside the scope of this review, but it is worth noting that polymer inks can be printed with high throughput methods, such as screen printing, to manufacture bioelectronics systems. For instance, Khan et al. demonstrated a fully printed PEDOT:PSS photoplethysmography array based on screen printing for use in patients recovering from skin graft surgery. The device is shown along with sensitivities to oxygenated and deoxygenated hemoglobin in Figure 10e [163]. In summary, many additional bioelectronics applications could be scaled with high throughput fabrication methods. It is an open challenge to the reader to apply these techniques to their area of expertise.

**Figure 10.** Bioelectronics applications (**a**) Image of screen-printed conductive traces. (reprinted with permission from *Ind. Eng. Chem. Res*. (2019), 58, 43, 19909–19916, Copyright 2020, ACS). (**b**) Illustration of roll-to-roll slot-die coated electrochemical sensors. (reprinted with permission from *Biosens. Bioelectron.* (2020), 165, 112428. Copyright 2020 Elsevier). (**c**) Schematic of a graphene-based enzymatic biosensor. (reprinted with permission from *Biosens. Bioelectron.* (2017), 87, 7–17. Copyright 2017 Elsevier). (**d**) Screen-printed ECG electrodes with (**i**) Ag and (**ii**) MWCNT layers. (**iii**) Example ECG signals are shown compared to commercial Ag/AgCl gel electrodes. (reprinted with permission under Creative Commons license CC BY-NC-ND 4.0 from *Sens Biosensing Res* (2018), 20, 9–15.) (**e**) Overview and operation of a screen-printed reflectance oximeter array (ROA). (**Top left**) placement of the ROA after skin graft surgery. (**Top right**) illustration of ROA pixel array. (**Bottom left**) Image of the printed ROA. (**Bottom right**) Molar extinction coefficients for oxygenated and deoxygenated hemoglobin as a function of wavelength. (reprinted with permission from *PNAS*, (2018) 115 (47) E11015–E11024, Copyright 2018, PNAS).


**Table 3.**High-throughput nanomaterial-based biosensor fabrication.

**Table 4.** Additional bioelectronics applications fabricated with high throughput methods.

