Soft strain-insensitive bioelectronics featuring brittle materials

Abstract

Advancing electronics to interact with tissue necessitates meeting material constraints in electrochemical, electrical, and mechanical domains simultaneously. Clinical bioelectrodes with established electrochemical functionalities are rigid and mechanically mismatched with tissue. Whereas conductive materials with tissue-like softness and stretchability are demonstrated, when applied to electrochemically probe tissue, their performance is distorted by strain and corrosion. We devise a layered architectural composite design that couples strain-induced cracked films with a strain-isolated out-of-plane conductive pathway and in-plane nanowire networks to eliminate strain effects on device electrochemical performance. Accordingly, we developed a library of stretchable, highly conductive, and strain-insensitive bioelectrodes featuring clinically established brittle interfacial materials (iridium-oxide, gold, platinum, and carbon). We paired these bioelectrodes with different electrochemical probing methods (amperometry, voltammetry, and potentiometry) and demonstrated strain-insensitive sensing of multiple biomarkers and in vivo neuromodulation.

Technology Roadmap for Flexible Sensors

“…Another strategy is to use built-in circuits to compensate for strain-induced variation. , Since these strategies are poised to increase system design complexity, the realization of strain-insensitive sensor arrays with high density will rely on innovations in integration strategies and high-resolution high-yield fabrication. A recently proposed strategy with potential to overcome these limitations is to bridge brittle functional thin films and stretchable conductors through ACFs, which, despite the cracking of functional thin films under tensile strain, offer alternative electronic conduction pathways that are unaffected by strain. The laminates demonstrated nearly strain-insensitive electrochemical sensing and stimulation using a library of brittle functional materials.…”

Highly conductive and stretchable hydrogel using a percolated network of whiskered gold nanosheets

“…Metal nanomaterials such as silver nanowires and gold nanosheets have high intrinsic electrical conductivity, which makes them popular conductive ller materials for elastomer-based stretchable conductors in comparison to other llers such as carbon or polymeric materials such as carbon nanotubes and PEDOT:PSS 16,[26][27][28] . However, these metal nanomaterials have rarely been used as conductive components of CSHs 23 .…”

“…Consequently, CSHs have been considered as a promising conductive material for soft bioelectronics [19][20][21][22] . However, their electrical conductivity is far inferior to that of elastomer-based stretchable conductors 9,[23][24][25] .Therefore, increasing the conductivity of CSHs has been an overarching goal for their applications to soft bioelectronics.Metal nanomaterials such as silver nanowires and gold nanosheets have high intrinsic electrical conductivity, which makes them popular conductive ller materials for elastomer-based stretchable conductors in comparison to other llers such as carbon or polymeric materials such as carbon nanotubes and PEDOT:PSS 16,[26][27][28] . However, these metal nanomaterials have rarely been used as conductive components of CSHs 23 .…”

In Situ Formation of Conductive Epidermal Electrodes Using a Fully Integrated Flexible System and Injectable Photocurable Ink

“…Quick response to emergency and public health crises through the rapid deployment of large numbers of health monitoring devices enables timely collection of health data from a large population, thereby facilitating the precise identification of potential risks and the timely adjustment of disease prevention policies. For example, countries such as Singapore and Korea distributed wearable devices like TraceTogether Tokens, wristbands, and citywide tracking and alert systems to monitor the health of residents during pandemics. , Although wearable devices have been explored in conductive elastic materials, , stretchable structures, , and wireless bioelectronic technologies, , rapid manufacturing and deployment of a large number of electronic devices present significant challenges in terms of cost and complexity. The fixed styles and wearing locations of prefabricated wearable devices also make it challenging to implement a single type of wearable device for various monitoring requirements, necessitating repeated investments in different wearable devices.…”