Integrating microfabricated stretchable electronics with biomimetic soft substrates for building novel bioelectronics

Abstract

Recent developments in soft functional materials have created opportunities for building bioelectronic devices with tissue-like mechanical properties. Their integration with the human body could enable advanced sensing and stimulation for medical diagnosis and therapies. However, the currently reported flexible bioelectronics primarily have electronic functions, with substrates that provide limited functionality beyond mechanical support. Many existing functional materials, such as porous polymers, textiles, aerogels, biomimetic hydrogels, and synthetic foams, naturally possess breathability, thermal conductivity, stimuli-responsive properties, and unconventional mechanical properties, which facilitate good compatibility with human tissues. Integrating these soft functional materials with high-performance electronics may create new opportunities for the development of novel bioelectronics, including on-skin electronics, implantable electronics, and electronic scaffolds. To breathable and skin-conformal electronics, we develop a fabrication strategy that a hybrid integration of high-performance microfabricated sensors and nanofibrous soft substrates is made possible with stamp-based transferring techniques combined with electrospinning. The resulting membrane devices exhibit tissue-like mechanical properties with high permeability for vapor transport. In addition, kirigami structures can be introduced into these membranes, providing high stretchability and 3D conformability for large-area integration on the skin. The multifunctional sensors array allows for spatiotemporal measurement of bioelectrical signals, temperature, skin hydration, and potentially many other physiological parameters. To robust kirigami electronics, we report a versatile materials platform based on a composite nanofiber framework (CNFF) is exploited for the engineering of wearable kirigami electronics. The self-assembled fibrillar network involving aramid nanofibers and poly(vinyl alcohol) combines high toughness, permeability, and manufacturability. Multiscale simulations are conducted to explain the high fracture resistance of the CNFF-based kirigami structures and provide essential guidance for the design, which can be further generalized to other kirigami devices. Various microelectronic sensors are integrated onto a CNFF-based materials platform to achieve electrophysiological sensing. To programmable magnetic hydrogel robots, we design an assembly strategy for magnetic hydrogel robots (MHRs) with programmable magnetization profiles and geometries, constructed from discrete integration of magnetized hydrogels and a designed elastomer membrane. The resulting robots exhibit sophisticated deformations under varying magnetic fields, enabling effective carrying and delivery of solid drugs. Moreover, the proposed fabrication method preserves the highly porous and hydrophilic microstructures of the hydrogels, facilitating the loading and transport of liquid drugs in combination with magnetic properties. Besides, integrating ultrathin and multifunctional microfabricated electronics into the MHRs is also achieved for physiological sensing and simulation, which has negligible effects on their intrinsic mechanics and deformability. To tendon-mimetic hydrogels, we propose multifunctional tendon-mimetic hydrogels constructed from anisotropic assembly of aramid nanofiber composites. The stiff nanofibers and soft polyvinyl alcohol in these anisotropic composite hydrogels (ACHs) mimic the structural interplay between aligned collagen fibers and proteoglycans in tendons. The ACHs exhibit outstanding mechanical properties and many additional characteristics matching those of natural tendons. Soft bioelectronic components can be integrated on ACHs, enabling in situ sensing of various physiological parameters. The reported fabrication methods and material development in this thesis shed new insights for the construction of novel bioelectronics, providing a range of opportunities for scientific research and technological innovation.