Mechanical durability of screen-printed flexible silver traces for wearable devices

There is increased usage of flexible electronics recently in various applications such as wearable devices, flexible displays and sensors. Studies on the durability of conductive metal traces under cyclic mechanical loading is crucial since these conductors will be subjected to repeated bending. In this work, the mechanical and electrical behavior of silver printed conductors was tested using cyclic three-point bend test. The samples were flexible polymer thick film (PTF) silver (Ag) ink printed on a flexible polyethylene terephthalate (PET) substrate. The durability of this PTF Ag ink, which has a hyper-elastic binder and Ag flakes, was studied by performing cyclic bending tests. Four-point resistivity measurements and imaging of the sample both before and after bending were performed. A custom tester machine was used to apply strain to the circuit and measure the resistivity of the silver trace. The results of the bending test show that the silver trace does not undergo significant deformation and the change in resistance is less than 0.6% under both tensile and compressive tests. Fatigue tests were also performed by cyclic bending tests for three trials in which batches of 10,000 cycles were completed. The printed silver wire withstood 30,000 cycles of bend tests and produced only 2.64% change in resistance. This indicates that the printed wires are very durable even after 30,000 cycles of outer bending. Imaging was also conducted on these samples to study the effect of repeated bending on the morphology of the silver conductive trace. Although there was an increase in surface roughness before and after cyclic bending, there was no obvious deformation or delamination observed in the samples

Portable data acquisition and fluidic system for electrochemical Sensors

The recent outbreak of infectious diseases has highlighted the necessity of point-of-care detection compared to central lab analysis for more effective epidemic control. Recent developments in the field of biosensors have allowed sensitive, accurate disease diagnosis using low-cost devices. In this work, we describe the development of a portable data acquisition and fluidic system for miniature electrochemical biosensors. The data acquisition system was designed as a single printed circuit board and can perform cyclic voltammetry. The fluidic chamber was designed to work with three miniature sensors which are placed on a single platform. Leakage tests were performed to ensure that each chamber allows sensor isolation and avoids any cross- contamination. Measurements using the fabricated potentiostat board were taken and compared with a commercial potentiostat. It was found that the designed potentiostat was able to measure the same resolution and peak separation in cyclic voltammetry measurements

Simulation of geometrical parameters of Screen Printed Electrode (SPE) for electrochemical-based sensor

— Screen printing is a known method to produce disposable and low-cost sensors. Depending on the application such as food analysis, environmental health monitoring, disease detection and toxin detection, screen-printed electrodes can be fabricated in a variety of sizes and shapes. Modification of the electrode’s material and geometrical dimension may be done to produce effective screen-printed three-electrodes system. Thus, the effects of varying the working electrode (WE) area in radius of 0.9 mm to 2 mm, gap spacing between electrodes ranging from 0.5 mm to 1.6 mm, and the width of the counter electrode in range of 0.7 to 1.3 mm on sensor’s performance was investigated in this study through COMSOL simulation. It was found that the modification of the working electrode radius and the gap between the electrodes has the most significant effect on sensor’s performance, while modifying the width of the counter electrode (CE) shows no significant effect. Sensors with 0.9 mm radius or 2.54 mm² WE area and 0.5 mm gap spacing has shown the optimum performance with 0.026 A/m² current density which is contributed by 0.044 pF capacitance value. As a conclusion, regardless of the width of counter electrodes, a smaller gap between electrodes and a smaller working area would lead to optimal performance of a screen-printed three-electrode sensor system

Screen-printed nickel–zinc batteries: a review of additive manufacturing and evaluation methods

The advent of personalized wearable devices has boosted the demand for portable, compact power sources. Compared with lithographic techniques, printed devices have lower fabrication costs, while still maintaining high throughput and precision. These factors make thick film printing or additive manufacturing ideal for the fabrication of low-cost batteries suitable for personalized devices. This article provides comprehensive guidelines for thick-film battery fabrication and characterization, with the focus on printed nickel–zinc (Ni-Zn) batteries. Ni-Zn batteries are a more environmental-friendly option compared with lithium-ion batteries (LIBs) as they are fully recyclable. In this work, important battery fundamentals have been described, especially terms of electrochemistry, basic design approaches, and the printing technology. Different design approaches, such as lateral, concentric, and stacked, are also discussed. Printed batteries can be configured as series or parallel constructions, depending on the power requirements of the application. The fabrication flow of printed battery electrodes for the laboratory-scale prototyping process starts from chemical preparation, mixing, printing, drying, pressing, stacking to finally sealing and testing. Of particular importance is the process of electrolyte injection and pouch sealing for the printed batteries to reduce leakage. This entire process flow is also compared with industrial fabrication flow for LIBs. Criteria for material and equipment selection are also addressed in this article to ensure appropriate electrode consistency and good performance. Two main testing methods cyclic voltammetry for the electrodes and charge–discharge for the battery are also explained in detail to serve as systematic guide for users to validate the functionality of their electrodes. This review article concludes with commercial applications of printed electrodes in the field of health and personalized wearable devices. This work indicates that printed Ni-Zn and other zinc alkaline batteries have a promising future. The success of these devices also opens up different areas of research, such as ink rheology, composition, and formulation of ink using sustainable sources

Biosynthesis of thin film derived from microbial chitosan for piezoelectric application

The aim of this paper was to synthesize and characterize microbial chitosan thin films for potential piezoelectric application. Microbial chitosan was derived from the Aspergillus oryzae fungus via extraction and deacetylation. Chitosan thin film was characterized for its surface morphology, chemical properties, tensile strength, and surface topography. For the potential application of chitosan as a piezoelectric material, its piezoelectric char-acteristics were presented in terms of its electromechanical coupling coefficient and piezoelectric coefficient. The fabrication of the chitosan thin films was optimized via the one-factor-at-a-time (OFAT) method, where the parameters were type of acid solvent, acid concentration and mixing time. The chitosan film prepared using formic acid at a concentration of 0.25 M for 3 h of mixing time had the highest tensile strength (129.29 MPa), electromechanical coupling factor (0.0045), and piezoelectric coefficient d31 (10 pC/N). The results obtained, from the optimized fabrication of the chitosan thin film, were validated against fungal chitosan, and it was shown that the properties of the thin film were comparable to those of commercial PVDF thin films. Therefore, the prospect of using microbial chitosan thin film as wearable piezoelectric energy harvester or nano-generator is promising

Mechanical durability of screen-printed flexible silver traces for wearable devices

There is increased usage of flexible electronics recently in various applications such as wearable devices, flexible displays and sensors. Studies on the durability of conductive metal traces under cyclic mechanical loading is crucial since these conductors will be subjected to repeated bending. In this work, the mechanical and electrical behavior of silver printed conductors was tested using cyclic three-point bend test. The samples were flexible polymer thick film (PTF) silver (Ag) ink printed on a flexible polyethylene terephthalate (PET) substrate. The durability of this PTF Ag ink, which has a hyper-elastic binder and Ag flakes, was studied by performing cyclic bending tests. Four-point resistivity measurements and imaging of the sample both before and after bending were performed. A custom tester machine was used to apply strain to the circuit and measure the resistivity of the silver trace. The results of the bending test show that the silver trace does not undergo significant deformation and the change in resistance is less than 0.6% under both tensile and compressive tests. Fatigue tests were also performed by cyclic bending tests for three trials in which batches of 10,000 cycles were completed. The printed silver wire withstood 30,000 cycles of bend tests and produced only 2.64% change in resistance. This indicates that the printed wires are very durable even after 30,000 cycles of outer bending. Imaging was also conducted on these samples to study the effect of repeated bending on the morphology of the silver conductive trace. Although there was an increase in surface roughness before and after cyclic bending, there was no obvious deformation or delamination observed in the samples.Funding Agencies|Asian Office of Aerospace Research and Development [FA2386-21-1-4026]</p

Biocompatibility assessment of wearable C/TPU/Tegaderm strain sensors

The rapid advancement of wearable technology has sparked significant interest in developing innovative sensors that can seamlessly integrate with the human body. Strain sensors have been widely used in wearable devices for human motion detection. The choice of materials for the substrate and electrodes of the strain sensors plays a crucial role in determining their biocompatibility. Existing wearable strain sensors commonly utilize polymeric films and planar structures, leading to restricted airflow in the area of attachment. Consequently, this limited ventilation can potentially elevate the risk of skin irritation, and bacterial infections, and cause discomfort for the users. In this paper, a biocompatible strain sensor for wearable technology is presented. The strain sensor design is discussed and fabricated using the printing technique. The biocompatibility of the sensor is assessed by conducting cell morphology and cell viability analysis. The finding shows that the C/TPU/Tegaderm strain sensor is noncytotoxic and highly biocompatible after being exposed to HFF-1 cells. These biocompatible sensors are promising for safe use on human skin

Performance Analysis of Optimized Screen-Printed Electrodes for Electrochemical Sensing

The screen-printed electrode (SPE) sensor is widely employed in food analysis, environmental health monitoring, disease detection, toxin detection and other applications. As it is crucial for the SPE sensor to have an outstanding performance, this study examined the effects of manipulating the working electrode (WE) area, gap spacing between electrodes, and counter electrode (CE) width on the performance of an SPE sensor. Finite element simulation on various geometrical dimensions was done prior to screen-printed electrode SPE sensors fabrication at Jabil Circuits Sdn Bhd. The electrodes performance is measured through cyclic voltammetry (CV) using a potentiostat at an optimum scan rate of 0.01 V/s and a voltammetry potential window range of -0.2 to 0.8 V in 0.01 M Phosphate Buffered Saline (PBS) solution. It is discovered that adjusting the WE area and the gap separation between the electrodes had the most impact on sensor performance compared to varying the CE width. In both simulation and CV measurement, a WE with a radius of 0.9 mm, an area of 2.54 mm2, and a gap spacing of 0.7 mm has shown the highest current density which is translated as the highest sensitivity. Further CV measurement in nicotine sensing application has proven that the SPE sensor can effectively detect the nicotine oxidation indicating its promising potential as a biosensor. Combination of optimum SPE dimension together with suitable electrode modification process serves as the basis for an effective and sensitive SPE sensor for various biosensing applications

Performance Analysis of Optimized Screen-Printed Electrodes for Electrochemical Sensing

The screen-printed electrode (SPE) sensor is widely employed in food analysis, environmental health monitoring, disease detection, toxin detection and other applications. As it is crucial for the SPE sensor to have an outstanding performance, this study examined the effects of manipulating the working electrode (WE) area, gap spacing between electrodes, and counter electrode (CE) width on the performance of an SPE sensor. Finite element simulation on various geometrical dimensions was done prior to screen-printed electrode SPE sensors fabrication at Jabil Circuits Sdn Bhd. The electrodes performance is measured through cyclic voltammetry (CV) using a potentiostat at an optimum scan rate of 0.01 V/s and a voltammetry potential window range of -0.2 to 0.8 V in 0.01 M Phosphate Buffered Saline (PBS) solution. It is discovered that adjusting the WE area and the gap separation between the electrodes had the most impact on sensor performance compared to varying the CE width. In both simulation and CV measurement, a WE with a radius of 0.9 mm, an area of 2.54 mm2, and a gap spacing of 0.7 mm has shown the highest current density which is translated as the highest sensitivity. Further CV measurement in nicotine sensing application has proven that the SPE sensor can effectively detect the nicotine oxidation indicating its promising potential as a biosensor. Combination of optimum SPE dimension together with suitable electrode modification process serves as the basis for an effective and sensitive SPE sensor for various biosensing applications