3D Printed Electromyography Sensing Systems

Electromyography (EMG) has been widely used in robotics and biomedical applications for sensing and diagnostic purposes. Because of the complex shape of human limbs and the uneven and flexible surface of the human skin, EMG sensing often faces the challenge of stable signal detection. As manufacturing technology advances, additive manufacturing has shown its potential to improve the existing EMG sensing system further. 3D printing technologies offer the advantage of custom fabrication to fit the designated locations of EMG detection. 3D printing also provides flexible and stretchable features, which allow for a comfortable user experience. This paper presents the recent development of novel 3D‐printed EMG sensing systems. The process of EMG signal detection is compared with the standard system. The corresponding applications with 3D‐printed sensing systems in different fields of study are also discussed. Finally, by reviewing the state‐of‐the‐art technology, the future of 3D printing in EMG sensing and the challenges facing the field are discussed.


Introduction
Electromyography (EMG) is a technique that measures the electrical activity generated from the muscle fibers during muscle contraction. [1] Currently, there are two main methods of measuring muscle activity known as intramuscular EMG (iEMG) and surface EMG (sEMG), as shown in Figure 1. [2] The iEMG provides a more precise measurement of muscle signals compared to the sEMG, as it can detect individual motor units within the muscle. This makes the iEMG a suitable choice for investigating specific muscle groups. On the other hand, the sEMG is less invasive and more comfortable for patients as it can collect EMG data on the skin surface. However, the sEMG measures the signals generated by all motor units within the muscle, resulting in a DOI: 10.1002/adsr.202300003 more generalized measurement of muscle activity that may contain more noise signals than the iEMG when studying specific motor units. The iEMG detects the signals by placing the needles or wires into the body. [3] It can acquire EMG signals from muscle fiber sources. [4] However, iEMG could cause potential risks after the operation. [5] On the other hand, sEMG has been commonly used in clinical applications and studies. [6] It collects the EMG signals on the skin surface by the surface electrodes. [7] With the advantage of non-invasive electrodes, the sEMG is suitable for developing wearable devices in muscle activity measurement, such as EMG armbands. [8][9][10] Therefore, sEMG has become preferable to iEMG in the bio-medical field. By utilizing the EMG signals, several human diseases can be detected. Also, injury prevention could be provided by measuring and analyzing sEMG data during physical activities, including sports, occupational and daily activities. For example, the gait is generated by analyzing EMG signals, which are commonly applied to diagnose Parkinson's disease and spondylosis. [11] Also, EMG signals can be used to evaluate muscle dysfunction through neurophysiological evaluation. [12] Nowadays, there are several EMG devices available in the market. The EMG electrodes play an essential role in the sensing system to acquire muscle activity in EMG signals. Commercial EMG devices mainly use solid shapes with rigid dry electrodes, such as gForcePro+ (Oymotion) and Myo armband (Thalmic Labs). [13] In clinical practice, conventional wet electrodes (Ag/AgCl) are used to form a conductive layer on the skin for diagnosis. [14] The inserted electrodes are designed to perform the iEMG data acquisition. These electrodes are fabricated through a micromachining process with a laser on small scales. [15] Compared to wet electrodes, the inserted electrodes can record more distinguishable and more stable biological signals. [16] In recent years, stretchable dry electrodes have been developed to improve the user's comfort and address skin adhesion issues. Due to the outstanding material property of polydimethylsiloxane (PDMS) in providing flexibility and printability, it has become a suitable substrate material choice in stretchable wearable devices. [17] Through the electroplating and standard photolithography fabrication process, the Au and Cu are patterned on the PDMS substrate, and an inexpensive stretchable dry electrode could be fabricated. [18] Moreover, a different approach to nanofiber carbon electrodes was developed through electrospinning. [19] As additive manufacturing (3D printing) technology develops, it enables customizable structures for the EMG electrodes. Compared with conventional manufacturing, 3D printing Raw and filtered EMG signals from sEMG and iEMG were collected during selected muscle movements. The filtered signals are shown as a black line. Reproduced with permission. [2] Copyright 2018, IEEE. allows researchers to create suitable electrodes based on experimental demands. [20] In particular, electrodes with complex internal structures can be fabricated in a shorter time using 3D printing. [21] Moreover, 3D printing expands the use of materials in the manufacturing of electrodes, such as polymer, carbon, and ceramics. [22] This technology has reduced the cost of production to fulfill different applications. [23] Therefore, additive manufacturing has become preferable to traditional manufacturing techniques. [24][25] Many studies on 3D printable electrodes have recently been conducted. [26][27][28] To utilize the EMG signals in a real-world application, it is critical to process the data using a reliable signal acquisition system. [29] By combining the 3D printed electrodes with EMG data acquisition systems, the EMG signals can be used in the advanced field, such as the control of prosthetics. [30] In this paper, we will explore the various EMG sensing systems developed by additive manufacturing techniques and their mechanisms in EMG detection. Furthermore, a comprehensive overview of the EMG sensing system analysis and applications will be discussed.

3D Printing Technologies for the Fabrication of EMG Electrode
An EMG sensing system includes several components which must be fabricated with different materials. These materials vary from polysiloxane (silicone) or thermoplastic elastomer as a substrate to conductive inks such as silver paste to print flexible electrodes. [31] 3D printing technology has been growing significantly for rapid prototyping manufacturing. It is now feasible to perform multi-material printing within several layers. [32,33] In addition, specific 3D printing methods have achieved multimaterial fabrication on a microscale. [34,35] Thus, 3D printing is becoming a promising technology for fabricating EMG sensing systems.

Fused Deposition Modeling (FDM)
Fused deposition modeling (FDM) is a 3D printing technique where the deposition of filaments forms an object through a heated nozzle on a building plate. The nozzle extrudes a thin layer of melted filament to build the structure with stacked layers. [36] This method is widely used among researchers to study and develop. FDM can use various materials, from soft to rigid, such as plastics/polymers, metals, and ceramics. [37] Both iEMG and sEMG electrodes can be fabricated through the FDM technique. Researchers have demonstrated the capability of FDM in manufacturing iEMG sensors. In recent research, a wired microelectrode using polyethylene terephthalate-glycol (PETG) as the filament was printed by Prusa i3 MMU2S (Prusa Research, Czech Republic), shown in Figure 2a. [38] The insulted body was halfprinted first, and the metal wires were then loaded into the body. The remaining half body was printed to complete the electrode structure. However, due to the fabrication complexity of iEMG electrodes, researchers have widely studied the sEMG. Material selection is a crucial step in designing a functional sEMG sensor. sEMG electrodes can be fabricated with various materials with the help of current advances in additive manufacturing techniques. Vaněčková et al. [39] manufactured a 3D printed electrode using polylactic acid (PLA)/carbon black (CB) filaments, shown in Figure 2b. The 3D printed electrode showed nearly ideal electrochemical behavior comparable to the conventional metallic and carbon electrode. In addition to the rigid and brittle materials, soft and flexible are also could be used for the sEMG electrode fabrication. Dijkshoorn et al. [40] designed a conductive sensor by embedding copper tape during the FDM process. The sample showed robustness to the contacts in tensile testing, which has potential for biomedical applications. Wolterink et al. [41] used thermoplastic polyurethanes (TPU) to print a low-cost, flexible sEMG electrode, shown in Figure 2c. The conductive and insulated parts are printed concurrently by the conductive and nonconductive TPUs on FlashForge Creator Pro (FlashForge Corporation, China). By using the electronically conductive composite filaments, the FDM can also 3D print electronics. [42] 3D printing can also fabricate substrates with dielectric and electric properties essential to electronics fabrication. [43] Wu et al. [44] constructed a passive wireless sensor to monitor the quality of liquid food. The structures were built with a multi-nozzle FDM printer. The system allows the electronics to be integrated into a 3D object at a lower cost than traditional manufacturing technology. [45]

Direct Ink Writing (DIW)
Direct ink writing (DIW) is an extrusion-based printing technique in which material is deposited in a controlled pattern. It Adv. Sensor Res. 2023, 2, 2300003 Figure 2. a) Microelectrodes and multi-electrode probes with embedded etched metal and conductive wires can be produced using 3D printing technology. Reproduced with permission. [38] Copyright 2021, Elsevier. b) Cylindrical shape of 3D printed electrodes using PLA-CB filaments by FDM printing. Reproduced with permission. [39] Copyright 2020, Elsevier. c) 3D-Printed electrodes using conductive TPU (black) and non-conductive TPU (orange), which are flexible and elastic. Reproduced with permission. [41] Copyright 2017, IEEE.  [51] Copyright 2020, The authors, published by MDPI. b) FDM 3D printed flexible TPU/MWCUNT (multiwalled carbon nanotube) nanocomposites as an elastic strain sensor. Reproduced with permission. [55] Copyright 2017, Elsevier. c) A wearable patch with 3Dprinted flexible ion sensors and a microfluidic unit. Reproduced with permission. [57] Copyright 2021, Elsevier. d) A flexible strain sensor based on the EHD-printed circuits on TPU substrates for motion monitoring. Reproduced under the terms of the CC-BY license. [59] Copyright 2021, The authors, published by Springer.
can also perform multi-material printing to create complex 3D shapes. [46] Studies have shown that wood, metals, and ceramics can be deposited through this method. [47][48][49] Several DIW printing mechanisms can be used for material extrusion. The pneumatic extrusion uses air pressure through a flexible tube to control the extrusion rate. [50] Chen et al. [51] utilized the pneumatic extrusion with multi-nozzle to fabricate a sensing pad, shown in Figure 3a. It has a soft and rigid structure that can be applied to the flexible finger for robotic study. Screw extrusion is another mechanism that translates a rotary screw to a pumping action to extrude materials. [52] Instead of filaments, pellets are commonly used in screw extrusion. The rotating screw feeds the pellets into the nozzle after melting from the melting zone. [53] The plunger extrusion is the most common mechanism used in DIW printing, which uses a plunger to push the feedstock into the nozzle. [54] It was also referred to as piston extrusion or ram extrusion. Christ et al. [55] designed a highly elastic sensor printed by multi-material plunger extrusion, shown in Figure 3b. The thermoplastic polyurethane/multiwalled carbon nanotube (TPU/MWCNT) was a flexible material with excellent piezoresistive behavior.

Other 3D Printing Technologies
Aside from the two standard 3D printing techniques, some other printing techniques were applied to fabricate an EMG sensing system, such as inkjet printing, electrohydrodynamic (EHD) jet printing, and digital light processing (DLP) printing. Inkjet printing ejects ink droplets onto a substrate and solidifies them with a curing process, such as UV curing. [56] Kalkal et al. [57] reported that wearable sensors with polymer substrate had been developed using inkjet printing, shown in Figure 3c. The sensors, including EMG sensing, can be directly applied to the biomedical field. EHD jet printing creates a fluid flow using an electric field to deposit inks onto a substrate. [58] Khan et al. [59] fabricated a soft wearable sensing system utilizing EHD jet printing, shown in Figure 3d. The system was designed to monitor the muscle motion of humans, such as finger bending. DLP printing uses liquid resin to create plastic objects layer by layer, cured by UV light from a digital light projector. [60] While conductive 3D printing using DLP is challenging, Lopez-Larrea et al. [61] were able to develop 3D-printed hydrogels with conductive inks using poly (3,4-ethylenedioxythiophene) (PEDOT). The printed hydrogels demonstrated high conductivity and long-term reproducible detection of EMG recording. . 3D-printed sensing system for mimicking sensory receptors, neurons, and synapses integrated with 3D-printed components. Reproduced with permission. [67] Copyright 2021, Elsevier.

EMG Detection with the 3D Printed Sensing Systems
The 3D-printed EMG sensing system collects the raw EMG signals from the muscle contractions. 3D printing techniques make the devices flexible to fully cover the human skin compared with conventional rigid devices. [62] However, the raw EMG signals must be preprocessed to acquire interpretable data for further applications. Filtering [63] and amplifying [64] are two essential steps after obtaining raw EMG data. First, the raw signals are filtered to remove the noise signals within a range of the assigned high and low pass frequencies. Then, the filtered signals are increased in amplitudes through the amplifier to be recorded. Traditionally, signal preprocessing was performed following encoded electronic circuits. [65] The 3D-printed electronic circuit boards advanced a suitable and customizable platform for EMG sensing applications. The printed sensing system has been widely used in wearable applications. [66] Due to the adaptive customization ability of 3D printing, the sensing system can be developed individually for compatibility. Bao et al. [67] presented a 3D-printed sensing system with signal conversion and transmission functionality, shown in Figure 4. Using 3D printing technology, they fabricated all the components, including inductors, capacitors, and resistors.

EMG Analysis and Applications
As one of the critical components in the EMG sensing system, different patterns and textures of printed EMG electrodes have been developed to improve signal detection for EMG analysis. Pani et al. [68] designed a circular textile electrode where the conductive ink is printed on a piece of cotton fabric, shown in Figure 5a. After printing, the electrode is cured in an oven at 70°C for 15 min as post-treatment. The printed electrode was compared to the conventional gelled electrode in signal acquisition. The noise and raw signals detected by both electrodes were similar, which suggested that the printed electrode can be used as an alternative in EMG detection. Spanu [69] also reported a stretchable textile electrode for EMG detection on the leg mus-cles. The movement of leg muscles requires significant stretching, which is challenging for maintaining consistent surface conductivity. The stretchable textile electrode remained stable after 500 stretch cycles while providing accurate signal readings compared with AG/AgCl electrodes. The number of ink layers was also optimized to increase the conductivity of the printed electrodes. As a result, the three layers of printed electrode showed the best conductivity. In addition, the size of the printed electrode was reduced due to closer contact with the skin. Scalisi et al. [70] used inkjet printing to fabricate a flexible electrode matrix based on conductive silver ink. The sample created a lower skin-electrode impedance, further improving the detection of EMG signals in sEMG. In particular, the electrode matrix performed well in the low-pressure, high-frequency recording scenario. The novel printing method allows the electrode matrix to be customized to devices with minimum modifications. Toral et al. [71] introduced laser-induced graphene (LIG) electrodes as a low-cost material with a simple fabrication process, shown in Figure 5b. The stretchable LIG electrode collected a higher root mean square (RMS) value than the traditional AgCl electrode, which demonstrated that the LIG electrode removed more noise signals overall. Also, the structure of the printed electrode gave a more comfortable fit for the user compared to the commercial ones. With the 3D printed electrodes having similar or better performance than commercial electrodes, they have been implanted for the analysis of gesture recognition. Abass et al. [72] employed 3D-printed conductive PLA electrodes to replace the snap-on flat electrodes with flexibility in customization. In the study, the EMG data from printed electrodes could distinguish five different gestures through a support vector machine (SVM) classifier. Five PLA electrodes were fabricated to detect the EMG signals on the user's forearm. The PLA electrodes performed the gesture classification with an average of 85% accuracy. In another study, Rosati et al. [73] approached gesture recognition with the printed electrode matrix structure. The electrode consists of eight channels and is positioned on the forearm for EMG detection. Through a series of tests with multiple volunteers, the accuracy of gesture classification was 93-95% consistently across the volunteers. These studies have shown the stability of the 3D printed electrodes as reliable sensing devices in EMG detection and analysis.
Other than injury prevention and diagnostic applications, EMG data can detect the amputee's desired gesture in prosthetic devices. Currently, the demand for prosthetic hands has continuously increased to support hand amputees worldwide. [74] However, prosthetic hands are not affordable for most patients. [75] With the advancement of 3D printing technology, 3D-printed prosthetic hands can be cost-efficient and customizable. [76] Therefore, a reliable system for the users to control the prosthetic hands is needed. 3D printed sEMG sensing techniques show promising performance for detecting grasping gestures in the prosthetic hand [30] as it has several advantages over conventional methods. [77] A precise and user-customized sEMG sensor could reduce the post-processes after the signal measurement. Recently, AI-based data processing methods, including machine learning algorithms, have been widely used to detect the amputee's grasping gesture from EMG data. Nevertheless, these methods require lots of computational costs and time. 3D-printed electronics could provide a flexible and patient-specific solution so that fewer post-processing steps would be needed for gesture Figure 5. a) Printed circular textile electrodes on cotton fabric (black) compared with Ag/AgCl electrodes (silver) at 24 and 10 mm in diameter. Reproduced under the terms of the CC-BY license. [68] Copyright 2019, The authors, published by IEEE. b) A developed stretchable LIG electrode with a multi-layer structure, including electrode (black), wire, isolation layer (orange), and flexible adhesive (white). Reproduced under the terms of the CC-BY license. [71] Copyright 2020, The authors, published by IEEE. c) Prosthetic hand connection with EMG electrodes, the detected signals from forearm muscle controls prosthesis movement. Reproduced under the terms of the CC-BY-NC 4.0 license. [78] Copyright 2019, The authors, published by Thieme. d) Electrodes and tracks printed on the orthosis at the position of the gastrocnemius muscle for EMG signal detection. Reproduced with permission. [80] Copyright 2021, IEEE. e) Flexible micro-needle array electrode pad reinforces the contact with skin to ensure its compatibility and conductivity. Reproduced with permission. [83] Copyright 2017, Elsevier.
detection. Ku et al. [78] reported a prosthetic hand utilizing the myoelectric interface for motion control, shown in Figure 5c. The EMG electrodes were directly connected to the prosthetic hand. By detecting the voltage changes of the EMG signals through the sensing system, the prosthetic hand was controlled to the related motion based on the user's muscle contraction on the forearm. Cognolato et al. [79] evaluated a 3D-printed dexterous prosthetic hand for sophisticated gesture recognition in EMG control. The performance was tested by the Myo armband. After the calibration, the prosthetic hand was tested on real-time control, which minimized the movement time gap after the muscle contraction. As a result, the prosthetic hand could perform several gestures in various response times, such as fisting, grasping, and pinching. Depending on the complexity of the gesture, the motion performance time was varied with an average of 2 s. These studies have proven the feasibility of 3D printing in prosthesis applications. Therefore, the printed electrodes and prosthesis can create a fully customizable EMG sensing device, reducing the manufacturing time and being affordable to more users with increased demands. Cantù et al. [80] proposed a prosthesis integrated with a printed EMG multi-electrodes matrix for rehabilitation purposes, shown in Figure 5d. The aerosol jet printing technique fabricated the electrode matrix with conductive silver ink. The 3D printing allowed the direct integration of the EMG sensing system as it was printed on the prosthesis. The electrode matrix layout refers to the EMG detection locations of the commercial electrodes. The customized sensing system provided favorable feedback on the EMG signal acquisition during muscle contractions. Compared with the standard electrode, the printed electrode matrix showed similar results with only a slightly low amplitude of the time features. The advancement of 3D printing creates the capability of reducing the difficulty in fabricating the EMG-based prosthesis.
The sensing system can be implanted into the prosthesis as a single manufacturing process. [81] The customizable sensing system allows the designers to develop suitable devices of different shapes to fit the prosthesis based on its application. Although 3D-printed prosthesis has great potential, there are still disadvantages, such as the relatively slow printing speed, limited printing dimension, and low fabrication resolution.
3D printing has further enabled printed EMG sensing in the biomedical/clinical field. [82] The customized and flexible structures are suitable for tracing the irregular shape of the human body parts, providing the maximum amount of electrode-skin contact area to increase the sensor's precision. Dabbagh et al. [83] developed a 3D-printed flexible microneedle electrode for multiple biomedical applications, such as drug delivery, EMG signal acquisition, and medical diagnosis, as shown in Figure 5e. The microneedle electrode was fabricated using stereolithography (SLA) and digital light processing (DLP) 3D printing. It was printed on relatively small scales, ranging from 25 to 100 micrometers, then compared with conventional electrodes during the EMG test on the biceps brachii and elbow. The custom electrodes with 36 needles recorded the highest amplitude of the EMG signals from the muscle contractions. In addition, the number of needles can be increased to reduce the electrode skin's impedance, further improving the signal quality. [28] This iEMG sensing system can be applied for muscular dystrophy diagnosis in the clinical field. [81] Wearable health monitoring devices have recently been widely applied to discover potential diseases/disorders for clinical purposes. [84] Due to the complex process of bio-signal monitoring in clinical practice, conventional wet/dry electrodes can provide poor signal recording in daily life. [85] Therefore, the printed flexible and stretchable electrodes can resolve the listed Figure 6. a) Sensing robot hand measuring EMG signals on the forearm muscle with electrodes printed on the index, middle, and ring fingers of the hand. Reproduced with permission. [90] Copyright 2021, John Wiley and Sons. b) Printed eyeglass temple prototypes with printed conductive lines and electrodes for the EMG measurement on the head. Reproduced under the terms of the CC-BY license. [91] Copyright 2018, The authors, published by ACM.
problems. The close skin contact with soft materials provides a comfortable user experience for wearable EMG monitoring. [86] Huang et al. [87] fabricated a flexible carbon electrode for EMG monitoring, demonstrating high conductivity and flexibility for long-term sensing applications. It was integrated into a smart wearable device in the study. The sensing system measured the EMG signals from both leg and arm muscles and distinguished the motion difference and strength level. The study proposed the stability of a printed wearable EMG system for health monitoring. In addition to daily monitoring, the wearable EMG can also be utilized in different situations. For example, vehicle drivers with unforeseen medical issues during driving can cause severe disasters and danger to them and others. [88] Therefore, Said et al. [89] reported a 3D-printed wearable bracelet to detect potential health risks. The bracelet consists of three electrodes located at the wrist and elbow. By extraction of features, the EMG signals can be divided into two groups, safe and dangerous signals. The system would consistently monitor the driver's EMG signals. When a hazardous signal was triggered, the bracelet would warn the driver to confirm their health condition. If the driver did not respond to the system, an emergency protocol would be activated to avoid a vehicle collision.
Aside from the prosthesis and clinical applications, the 3D printed sensing system has also been applied in robotics and motion sensing. Kim et al. [90] developed a sensing robot with specific 3D-printed origami-structured EMG electrodes placed on the robotic hand's fingertips, as shown in Figure 6a. The robot was designed to provide medical assistance by touching the users to acquire EMG data. The soft robot hand structure provided a relatively safe interaction than most commercial rigid robot hands. Zhang et al. [91] proposed a 3D-printed eyeglass temple with implanted EMG sensing system to measure the signals generated from temporalis contraction, shown in Figure 6b. The temple would trace the shape of the face to give close skin contact. This prototype can potentially be applied for facial motion sensing and control in the smart glasses area.

Conclusion
This paper demonstrates an overview of the 3D-printed EMG sensing systems and their applications. The 3D printing tech-nology showed its reliability in the fabrication of the EMG devices. Various printing techniques were described, which can be applied to create EMG electrodes. Comprehensive feasible selections of materials for 3D printing EMG sensors were reported. The multi-material manufacturing further strengthened the printing efficiency in complex structures. [92] Studies show that soft and flexible EMG electrodes provide a more comfortable experience for users in EMG detection. The flexibility of the electrodes can conform the electrodes to the uneven skin surface to maximize skin contact and improve skin adhesion. Compared with the commercial EMG system, the 3D printed EMG sensors demonstrated similar performance with a lower fabrication cost. 3D printing also created the possibility of customization of the EMG system. The system can be modified to improve the suitability of different designs in EMG acquisition. The 3D printing EMG sensors were adapted to various fields in practical applications. EMG sensing was widely used in the field of prosthetics and health monitoring. 3D printing offers the ability to integrate sensing systems for long-term use fully. The whole sensing system could also be fabricated with one process through 3D printing. Therefore, the dimension of the devices can be further reduced compared with the traditional assembly process. Additionally, 3D-printed EMG sensing can be applied to wearable devices to utilize EMG signals in different human body locations.

Future Perspectives
The 3D printed EMG sensing system opens the development of EMG control and monitoring devices from different perspectives. The related studies based on the 3D printing technology have a high potential for future EMG devices as a customizable and affordable manufacturing approach. Several advantages of the 3Dprinted EMG sensing system can be summarized as follows: • Rapid prototyping: The system can be printed after it was designed; • Cost efficiency: Additive manufacturing process reduces the use of materials compared to the traditional fabrication process; • Customization: The system can be personalized based on the user's demands, size differences, and locations of detection; www.advancedsciencenews.com www.advsensorres.com • Low risk of failure: 3D printing is a low-cost fabrication technology. It provides an affordable fabrication to generate an initial design; • Future improvement: As the system continues to be upgraded from experiments, the prototype can be easily modified without massive adjustments in fabrication steps.
Despite the benefits of 3D printing for EMG listed above, this technology still faces some challenges and improvements, as follows: • Unlike traditional manufacturing processes, 3D printing has limited material usage. Thus, 3D printing optimization shows a limitation in indicating the required and removable elements. [93] • Different 3D printing methods can only use certain materials in fabrication. Therefore, the users must consider the compatibility of their designs with suitable 3D printing methods. [94] • Using 3D printing to fabricate the whole EMG sensing system can also create quality control and maintenance issues. • The lifetime of the 3D-printed electrodes can be over ten thousand bending cycles. [95] However, enhancement of the electrode durability is needed to fulfill the daily detection of EMG.
As a revolutionary fabrication method, several researchers have devoted themselves to optimizing 3D printing technologies to be sustainable and reliable to compete with the traditional process. Therefore, the 3D printed EMG sensing technology has a bright future.