Mechanisms and Performances of Physically and Chemically Crosslinked Gelatin-Based Hydrogels as Advanced Sustainable and Reusable "Jelly Ice Cube" Coolants.

A novel reusable, plastic-free, and stable cooling medium, Jelly Ice Cubes (JIC), is developed based on crosslinked gelatin hydrogels for sustainable temperature control. A novel process involving a rapid-freezing-slow-thawing treatment and a subsequent photo-crosslinking reaction induced by menadione sodium bisulfite, a newly discovered photosensitizer, is able to effectively consolidate a three-dimensional (3-D) hydrogel network to survive repeated application freeze-thaw cycles (AFTCs). This study reveals the mechanisms and evidence of the synergistic effects of the physical and chemical crosslinking reactions. The results experimentally prove that the rapid-freezing-slow-thawing treatment induces the generation of gelatin microcrystalline domains, refines the protein polymeric network, and reduces the intervening distance for subsequent photo-crosslinking sites. The refined hydrogel 3-D network is consolidated by the photo-crosslinking reaction occurring at the intersectional areas of the gelatin microcrystalline domains. The proposed crosslinking approach yields JICs with superior mechanical properties, robustness, and consistent water content, even after repeated AFTCs, all the while retaining cooling efficiency and biodegradability. The proposed crosslinked hydrogel structure is potentially applicable to engineering other hydrogel materials, offering sustainble and biodegradable solutions with enhanced resilience against phase changes.