Aqueous interfacial casting of hydrogel thin films with programmable shapes and ultralow adhesion

Hydrogel thin films are critical components in advanced technologies, from biomedical devices, flexible electronics, to tissue engineering. These films are conventionally fabricated by coating polymeric solutions onto solid substrates by spinning or blading methods. However, these methods offer poor control over film uniformity and geometry, especially for films made from low-viscous liquid. In addition, the strong film-substrate adhesion often leads to defects and rupture during film exfoliation. To address these limitations, we present an aqueous interfacial casting method to fabricate large-area, ultrathin (~3-20 µm) hydrogel films. These films exhibit scalable dimensions (up to ~100 mm in diameter) and programmable shapes. In particular, they have negligible adhesion to the aqueous substrate, enabling facile film exfoliation and transfer. Compared to films fabricated on various solid substrates, aqueous-cast films are two orders of magnitude thinner and exhibit enhanced mechanical properties (~3-fold increases in critical strength and fracture energy). These large-area films can further be rendered electrically conductive, enabling continuous monitoring of human physiological signals. Overall, aqueous interfacial casting provides a simple and versatile method for fabricating thin hydrogel films with significant potential for diverse biomedical applications.