A freeze-proof hydrogel

Abstract

Hydrogels are invaluable for making medical devices, tissue-engineering scaffolds, and sensors. Being mostly water, though, they freeze and become useless at subzero temperatures. A new hydrogel averts this pitfall at subzero temperatures while also boasting high strength, moldability, adhesiveness, and self-healing powers (ACS Appl. Mater. Interfaces 2019, DOI: 10.1021/acsami.9b05652). The material stays stretchy down to –80 °C and is stronger than most other synthetic and natural polymer-based gels, says Junjie Li, a chemical engineer at Tianjin University. Li, Fanglian Yao of Tianjin University, and colleagues soaked a gelatin hydrogel precursor for 3 h in a water-glycerol solution containing sodium citrate. Glycerol prevents the freezing of water below 0 °C, Yao says. The gel’s strength comes from hydrogen bonds between the gelatin chains and glycerol and from ionic interactions between gelatin and the citrate ions. The gelatin chains also easily intertwine and untwine, making the gel moldable and hea...