Dual-Crosslinked Hydrogels With Enhanced Mechanical and Thermal Properties

Creating artificial skin requires materials that can mimic the mechanical properties and structural integrity of natural skin. This study develops a dual-crosslinking approach combining tannic acid-a naturally occurring, biocompatible polyphenol-with dynamic, covalent imine bonds. Hydrogels singly crosslinked with hydrogen-bonded tannic acid achieved gel fractions of up to 90% but fragmented during handling, rendering them impractical for wound dressing applications. In this work, we performed sequential dual-crosslinking, where ethylenediamine and aldehydes first form a covalent imine network, followed by the addition of tannic acid for hydrogen-bonding reinforcement. This produced robust, handleable hydrogels with superior properties. The optimal formulation (0.25 ethylenediamine:0.5 tannic acid) achieved a maximum tensile strength of 2.17 MPa, elongation with a break at 1425%, and a toughness of 1.71 MJ/m3-exceeding human skin toughness twofold and representing two to three times improvements over systems crosslinked with tannic acid alone. Critically, dual-crosslinked materials maintained structural integrity with 69% gel fraction, controlled swelling (1129%), and 92% water content suitable for wound healing. Comprehensive characterization by FTIR, thermogravimetric analysis, dynamic mechanical analysis at physiological temperatures, tensile testing, and swelling studies validated this bio-inspired platform for mechanically robust, dimensionally stable artificial skin applications.