Sequential SDF-1/CGRP-releasing smart composite hydrogel promotes osteoporotic fracture healing by targeting sensory nerve-regulated bone remodeling

Osteoporotic fractures typically exhibit delayed healing due to impaired cell recruitment, chronic inflammation, and disrupted neurovascular signaling. Sensory nerve signaling plays a crucial role in fracture repair, and its deficiency is a significant factor leading to delayed healing. Addressing these deficiencies is crucial to overcoming the challenges associated with delayed bone repair in osteoporosis. In this study, a smart composite hydrogel (denoted as OCS-MPC) was synthesized by embedding CGRP-functionalized polydopamine-coated MXene nanosheets (MXene/PDA/CGRP) into boronic acid-modified oxidized hyaluronic acid-crosslinked carboxymethyl chitosan (OHA-PBA/CMCS) hydrogel loaded with SDF-1. OCS-MPC hydrogel enables the controlled release of SDF-1 and CGRP, aiming to promote early callus formation and late-stage callus remodeling in osteoporotic fractures. Due to dynamic crosslinking via imine and borate ester bonds, OCS-MPC exhibits rapid gelation, injectability, and self-healing properties. In vitro experiments demonstrated excellent osteogenic, angiogenic, and neurogenic properties of OCS-MPC hydrogel. In vivo studies using an osteoporotic femoral fracture model showed that OCS-MPC hydrogel enhanced MSCs recruitment via the SDF-1/CXCR4 signaling axis, significantly improving callus formation in the early stages of fracture repair. Additionally, OCS-MPC hydrogel significantly promoted callus mineralization and remodeling in the later stages of osteoporotic fracture healing through enhancing CGRP signaling. Immunofluorescence analysis further confirmed increased expression of TUBB3, CGRP, and CD31, indicating successful regeneration of the neurovascular network. These findings highlight the potential of OCS-MPC hydrogel in addressing both early and late-stage challenges of osteoporotic fracture healing, providing a promising therapeutic strategy for enhancing bone regeneration in osteoporotic patients.