Hydrogel interfaces for merging humans and machines

The last few decades have witnessed unprecedented convergence between humans and machines that closely operate around the human body. Despite these advances, traditional machines made of hard, dry and abiotic materials are substantially dissimilar to soft, wet and living biological tissues. This dissimilarity results in severe limitations for long-term, reliable and highly efficient interfacing between humans and machines. To bridge this gap, hydrogels have emerged as an ideal material candidate for interfacing between humans and machines owing to their mechanical and chemical similarities to biological tissues and the versatility and flexibility in designing their properties. In this Review, we provide a comprehensive summary of functional modes, design principles, and current and future applications for hydrogel interfaces towards merging humans and machines.