Fig. 3. Methods for establishing sensor–tissue interfaces with mucosa.

a | Illustration of the structural (left) and materials (right) engineering approaches for establishing robust sensor–tissue interfaces. b | Schematics of various structural engineering approaches that convert plastic materials into stretchable conductors, showing the conductors before and after stretching. The axis shows a range of reported maximum stretchability for each approach. c | Schematic showing the enhancement of the sensor–tissue interface by minimizing the mechanical mismatch with the tissue using a soft hydrogel (right) compared with a sensor–tissue interface with a conventional electrode (left). The insets show the corresponding equivalent circuit diagrams, comprising capacitors (C) and resistors (R). d | Schematic showing the formation of covalent bonds between a conductive hydrogel and tissue to simultaneously realize strong adhesion and low electrical impedance at the sensor–tissue interface. e | Schematics showing the initial hydrogel (left), the fragile swollen state of the hydrogel following fluid uptake (middle) and the swelling-triggered toughening mechanism that involves the diffusion of encapsulated crosslinker molecules in the first polymer network (polymer 1) and then crosslinking of a second polymer network (polymer 2) to enhance the toughness of the hydrogel after fluid uptake (right).