Fig. 2. Mechanical, electrical, and biological characterization of a bioresorbable, stretchable substrate, and encapsulation material.

a Schematic illustration of the key requirements for the materials: dissolvability (i.e., bioresorbability), mechanical stretchability, impermeability against biofluids, and biocompatibility. Adhesion properties. b Schematic illustration of the adhesion mechanism associated with the stretchable bioresorbable dynamic covalent polyurethane (b-DCPU) and its self-bonding behavior induced by thermally activated dynamic bond exchange reactions (left); chemically anchored b-DCPU on an inorganic bioresorbable component by covalent bonding (right). c Adhesion energy between bonded pieces of b-DCPU with different crosslinking ratios (70, 80, 90, and 100). n = 3 independent samples. The inset schematic illustrates contributions from the (i) interfacial energy and (ii) cohesion energy. d Adhesion energy between b-DCPU 80 and other inorganic bioresorbable materials, including Si, SiO₂, Mg and Mo, after the bonding process. n = 3 independent samples. Biofluid Impermeability. e Changes in resistance of a Mo electrode without encapsulation (black circle), with b-DCPU 80 (red square), and poly(lactic-co-glycolic acid) (PLGA) 65:25 encapsulation (orange triangle) as a function of the immersion time in PBS (pH 7.4) at 37 °C. Mechanical stretchability. f Stress–strain curves for b-DCPU materials with different crosslinking ratios (olive, b-DCPU 100; orange, b-DCPU 90; red, b-DCPU 80; black, b-DCPU 70). g Changes in resistance of serpentine Mo electrodes encapsulated in b-DCPU 80 during uniaxial stretching (up to the maximum strain of ~50%). The inset shows a photograph and FEA results of b-DCPU-encapsulated Mo serpentine electrodes under uniaxial tensile strains of 50%. The rainbow color scale bar indicates the simulated strain values, from 0% (blue) to 0.6% (red). In vitro dissolution kinetics. h Measured changes in weight as a function of the immersion time of b-DCPU 80 (black circle) and PEG containing b-DCPUs (polycaprolactone (PCL): polyethyleneglycol (PEG) = 42:38, red triangle; PCL:PEG = 22:58, orange square) in PBS (pH 7.4) at physiological temperature (37 °C). In vitro biocompatibility. i Biocompatibility of various b-DCPU samples in live/dead staining assays of healthy mouse fibroblasts (L929) after 3 days of culture: tissue culture polystyrene (TCPS); normal b-DCPU 80 (Pristine); Degraded b-DCPU 80 (Degraded or Deg.) corresponds to gel-textured b-DCPU; fully dissolved b-DCPU 80 in PBS (Solution or Sol.). n = 5 repeated independently with similar results. j Normalized in vitro viability assay data. n = 5 independent samples. In c, d, and j the results are shown as means ± s.e.m. Data available in source data file.