In Situ Nanomechanical Characterization Techniques for Soft Bioelectronic Interfaces and Their Building Blocks

Soft bioelectronic interfaces constitute a paradigm shift for biomedicaldevices. High-resolution monitoring and stimulation of physiologicalprocesses in vivo are becoming possible with minimally invasive devicesoperated without inflicting tissue damage or discomfort over prolongedtimescales. However, the development and commercialization of suchinterfaces still must address significant challenges. Biological tissue issubjected to continuous motion and the related device deformations caneasily trigger fracture or delamination of the device components, puttinglong-term durability of soft implants at risk. In this review, an overview ofexperimental techniques for testing mechanical properties and failuremechanisms of soft bioelectronic devices at the nanoscale while thedeformation takes place (in situ) is provided. Through the tensile test,bending test, nanoindentation, and micropillar compression test, precisemeasurements of the mechanical properties of individual building blocks andthe interfaces themselves can be obtained. Such parameters are crucial todesign, model, and optimize the device’s performance. Then, recent examplesof how this information guides design and optimization of soft bioelectronicinterfaces and devices for healthcare, robotics, and human–machineinterfaces is provided. Last of all, future research that is needed to fullyachieve long-term soft bioelectronic interfaces for integration with the humanbody is discussed.