Elastomer foam templated three dimensional hybrid hydrogels for heterogeneously integrated stretchable electronics

Hydrogels are soft, tissue-like solids with promising potential in biomedical engineering and stretchable electronics. These applications require hydrogels to be shaped into intricate structures and combined with other polymers. This study introduces hybrid hydrogels that use elastomer foams as templates for controlled synthesis. Essentially, TPU foams can be easily structured into diverse 2D or 3D shapes using laser ablation. After hydrophilic modification, these foams absorb hydrogel precursors and crosslink into delicate features of up to 1 mm resolution. The resulting hydrogel/elastomer hybrid exhibits excellent stretchability, capable of withstanding tensile strains exceeding 300 %. Additionally, the hybrid hydrogels can easily bind to conductive CNT nano- composites, creating bilayer electrodes for wearable applications. Tissue adhesive polydopamine-polyacrylamide hydrogels are used to achieve conformal attachment to the skin, achieving lower contact impedance than commercial Ag/AgCl gel electrodes. These electrodes are integrated with stretchable circuits to create multifunctional patches for electrical stimulation and biopotential recording. An integrated epidermal sensing armband captures multichannel biopotential signals from the forearm, recognizing hand gestures through machine learning to act as a human-machine interface. The foam-templated synthesis introduced in this study offers convenient access to structured hydrogels and hydrogel/polymer hybrids for various cutting-edge applications.