Conformal assessment of bioelectronics on tissue

Bioelectronics bridges the gap between electronic devices and biological systems through interfaces. The conformability of interfaces is significant in improving the quality of acquired physiological signals. However, practical methods for conformal assessment of arbitrary interfaces are still lacking. Mechanical predictions are imprecise for soft tissue that has curved shapes and is under dynamic deformation. Thus, current conformal assessment relies on visual inspections of contact status or feedback derived from acquired signals. Here, a quantitative and non-contact method is proposed to assess the conformability of bioelectronics on tissue. Biocompatible speckles enhance feature points on the target surface, and its deformed shape is reconstructed based on binocular stereo vision. A normalized metric, mean gap height, is proposed for conformal assessment, which intuitively quantifies conformability as a percentage and reflects the gap caused by partial contact. The method is applied to assess the conformability of a stretchable film covering a static hemisphere, and the results highlight the effects of various conformal strategies and offer guidelines to prevent overdesign. Furthermore, the method illustrates the interface evolution of surface electromyography devices during a muscle contraction cycle, demonstrating potential applications in optimizing electrophysiological monitoring interfaces for daily healthcare.