Air-permeable hydrogels through viscoelastic phase separation of aerogels.

Hydrogels are widely used in biomedical interfaces, in which effective gas exchange (for example, O2, CO2) within a water-rich environment is essential. However, hydrogels show intrinsically limited air exchange efficiency, owing to the low solubility (C) and diffusivity (D) of non-polar gases in the polar water medium1. This limitation poses a substantial bottleneck in long-term applications, such as wearable health monitors2-7 and tissue engineering8-12. Existing methods13-16 to enhance air permeability suffer from poor robustness and/or an inherent trade-off between permeability and water content (for example, <50 vol%). Here we introduce a viscoelastic phase separation17 (VPS)-enabled strategy to create a non-collapsible, air-rich network in high-water-content hydrogels, achieving a record-high oxygen permeability of 185 barrer with 70 vol% water-a tenfold increase compared with pristine hydrogels. VPS, a ubiquitous phenomenon in soft matter, is used to drive hydrophobic, dry gas particles within a hydrophilic, wet medium into a thin, stable three-dimensional network. This approach allows the facile and scalable fabrication of air-permeable hydrogels across diverse chemistries and form factors. Physiological tests over a 10-day continuous wear condition confirmed their effectiveness in preventing fluid accumulation and maintaining skin health. This strategy paves the way for hydrogels in long-term biomedical applications in which efficient and sustained air exchange becomes critical.