Modular and reconfigurable wireless e-tattoo platform for mobile physiological sensing
Moving from traditional healthcare methods of monitoring biometrics to an individualized wearable modality promises to reduce healthcare expenses and to present better values to the end-user. Over the past few years, ultrathin and ultrasoft epidermal electronics (a.k.a. e-tattoos) have emerged as the next generation wearables. Considering health monitoring’s unlimited potential applications in telemedicine, performance tracking, human-machine interface (HMI), and personalized mobile health, it is paramount to develop more affordable, dependable, and unobstructive biometric monitoring methods compared to current expensive and confining systems. However, it is impossible to build an all-purpose e-tattoo that can accommodate such a wide range of applications, and e-tattoos are only practically useful when they can operate wirelessly. Thus, I report the design, fabrication, and validation of modular and reconfigurable wireless e-tattoos for personalized physiological sensing. Such modular e-tattoos are comprised of a multilayer stack of stretchable layers featuring distinct functionalities: a) a near field communication (NFC) layer capable of wireless power harvesting and data transmission, or battery charging, b) Bluetooth (BT) long-distance data transmission, c) functional circuit layers, d) a passive electrode/sensor layer. These layers can be disassembled and swapped out multiple times to form custom e-tattoos with user-specified sensing capabilities. To implement such flexible e-tattoos, I invent a “cut-solder-paste” microfabrication method which is rapid-prototyped via a dry, digital and cost-effective freeform manufacture process. The mechanical strain and strain-dependent characteristics of the stretchable antenna have been analyzed by finite element method (FEM). I also demonstrate reconfigurability of such modular e-tattoos so that they can be disassembled and reassembled multiple times. Multimodal e-tattoos are stretchable by up to 20% and capable of wirelessly measuring skin hydration, skin temperature, oxygen saturation level (SpO₂), heart rate, electrocardiogram (ECG), seismocardiogram (SCG) and body motion, also estimating continuous real-time blood pressure (BP). Moreover, I report a novel magnetic field repeater (feeding coil) on clothes by leveraging embroidery method and wireless capability. Utilizing this engineering framework, it enables not only more dependable and long-term but also continuous and real-time ambulatory monitoring of a variety of biometrics. I believe that this platform opens the door for accessible, and affordable personalized healthcare monitoring in the near future.