Soft strain-insensitive bioelectronics featuring brittle materials

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. Description Staying soft and conductive under strain Most electrically conductive materials tend to be stiff and brittle, whereas human tissue is soft and compliant. It is thus a challenge to make conductive biomaterials that are sufficiently compliant but do not show a loss or distortion in performance. Zhao et al. used a three-layer design to couple strain-induced cracked films with a strain-isolated conductive pathway (see the Perspective by Rafeedi and Lipomi). Upon an initial prestrain to 100%, the brittle solid film on top cracks to dissipate the strain energy. However, this cracking permits a type of parallel, interconnected charge transport in which the charge carriers move between the layers to circumvent the cracks. —MSL A library of soft, stretchable, strain-insensitive bioelectronics was made using brittle interfacial materials.