Towards injured joint rehabilitation: structural color hydrogels for accelerated wound healing and rehabilitation exercise monitoring†

Joint injuries caused by severe acute trauma seriously affect patients’ mobility and quality of life. Traumatic or postoperative wound healing and rehabilitation training are both essential for restoring joint functions, calling for effective wound healing materials that are also capable of monitoring rehabilitation training for joint condition evaluation and physical therapy guiding. Herein, a structural color hydrogel for wound care and naked-eye rehabilitation exercise monitoring of injured joints is designed by constructing a hybrid double-network, which contains a covalently crosslinked network and a Zn²⁺ coordination based dynamic network. The crosslinking formed by Zn²⁺ coordination endows the structural color hydrogel with enhanced mechanical properties for joint wounds with motion requirements, as well as antibacterial, anti-inflammatory, and pro-angiogenic properties that promote wound healing. Meanwhile, the Poisson's ratio of the structural color hydrogel can be easily tuned by varying the covalently-crosslink density to achieve sensibility ranging from 3.6 nm to 6.2 nm photonic-bandgap shift per 1% strain, achieving a remarkable color change responding to joint range-of-motion from minimal (0–2°) to wide-range (0–90°) bending during rehabilitation exercises. This structural color hydrogel provides an approach to the multi-stage management of joint injuries and real-time clinical insights into rehabilitation progress.