Materials design of flexible bioelectronics for reliable electrochemical signal transduction and electrical signal transmission

Both sophisticated electronic systems and human biological systems rely on signal transduction and transmission to achieve all operations and complex tasks. However, there are many fundamental differences between these two systems. For example, the human biological system contains deformable and soft organs/tissues under solution environments, mainly based on chemical reactions to transduce/transmit bio-signals. In comparison, electronics contain non-deformable rigid components under ambient environment mainly, based on electrons to transduce/transmit electrical signals. Even though it is difficult to merge gaps between these two systems, translation of existing electronics to be compliant with our biological tissues will render a wide panel of applications such as wearable health and wellness monitoring platforms, implantable/ingestible devices, artificial prosthesis, surgery robots, etc. As a researcher in materials science and engineering, I am applying reductionism to approach this complicated question by firstly decomposing electronic materials’ properties into chemical, electrical, and mechanical domains, then engineering material properties in each domain to be compatible with biological systems as needed. However, the most difficult part is that materials’ chemical, electrical and mechanical properties are always coupled and interacted with one another, thus rarely allowing us to independently tune each of them. For example, highly conductive materials (e.g. Au) are normally mechanically fragile (low crack onset strain), which will lead to distorted electrical signal transmission under strain imposed by organ/tissue movement. To improve mechanical compliance of these materials, it normally needs to compensate for their electrical properties (e.g. lower conductivity). As another example of materials for electrochemical bio-signal transduction, it requires to apply voltage to transduce target bio-signals into electrical signals, while also inevitably oxidizing non-target electroactive species to generate noise. In this case, applying lower voltage will simultaneously lower both the target bio-signal and unwanted noise. In this thesis, as the building block towards envisioned applications, Chapter 1 firstly introduces the background and design rationales for two fundamental units: bio-signal transduction module (e.g. electrochemical biosensing interface) and signal-transmission module (stretchable interconnects). Chapter 2 is focused on describing a material design methodology (based on Pt nanoparticles and p-Phenylenediamine-based permselective membrane), serving as an example of a reliable bio-signal transduction interface to simultaneously improve the sensitivity and selectivity of enzymatic-based electrochemical sensing. In Chapter 3, we devise a wearable freestanding electrochemical system that enables high-fidelity biomarker data acquisition under body movement in daily activities. As the core, it utilizes the anisotropic conductive film as the substrate for the developed sensing interface (in Chapter 2), coupled with microfluidic housing to achieve strain-isolated biomarker information delivery pathway. Subsequently, in Chapter 4, we integrate this technique with miniaturized iontophoresis interfaces and wearable hybrid control/readout electronics to achieve autonomous sweat extracting and glucose tracking in a day. In the end, in Chapter 5, I presented my preliminary research results for two future directions to use anisotropic conductive film to 1): decouple strain-effect on thin-film conductive materials’ conductivity (in bending mode) to achieve compliant electronics and 2) composite with silver-nanowire-based elastomer to achieve strain-resilient stretchable electrochemical sensing materials