Materials and Processing for Wearable Healthcare Electronics Systems: Flexible Circuit Boards and Stretchable e-Textile Patches for Surface Electromyography

Abstract: Skin-adhesive electrodes – more preferably, integrated electronic systems with embedded signal processing and transmittance – that can be worn comfortably on a patient have irreplaceable importance in healthcare. For example, surface electromyography (sEMG) is a non-invasive electrodiagnostic medical technique to detect, record, and interpret electric activity of groups of muscles from skin surface right above them. If skin-adhesive sEMG electrodes can be integrated with wireless data processing and transmittance system in a compact and wearable format, these devices can provide unprecedented opportunities for applications such as posture monitoring for rehab medicine, swallowing self-coaching, and muscle fatigue detector. However, there are stringent demands for form factors that are specific for the target locations in body, such as required level of flexibility, foldability and stretchability. The conversion of electronics into such advanced form factors has been arising the current challenges in the skin-adhesive electronic systems, such as poor reusability, complicated fabrication methods, and poor connection between soft and hard components in the electronics system. In this thesis, we have explored the potential solutions to solve these problems.Overall, this thesis is divided into two themes. In the first theme, we developed a versatile technology with capability of rapid, simple, customizable fabrication of flexible printed circuit boards (Flex-PCBs) and sensors. A simple and cost-effective wax-printing technique to pattern flexible interconnects allowed the system-level integration of sensing, processing, power, and wireless communication units. The flexible circuitry with reusable adhesive can follow the contour of curvilinear skin topology, thus allow enhanced wearability for skin-adhesive electronic systems. In the second theme, we developed textile-based electronics, also known as 'e-textiles', which offer stretchability and comfort for patients. A stretchable conductive silver ink was developed for ink-jet printing to pattern stretchable circuits on nano-textiles. The deep permeation of ink into nano-textiles resulted in stable adhesion, mechanically and electrically strengthen. With our custom-developed electronic circuits, we demonstrated a sEMG system with wireless data emission.