In situ ECM-functionalized hyaluronic acid/dextran composite hydrogels for regenerative soft tissue reconstruction

Conventional injectable soft-tissue fillers act mainly as inert volumizers and often trigger foreign-body reactions. They lack biological cues to support regeneration, and commonly used hyaluronic acid (HA) gels degrade rapidly without stimulating new tissue formation. To address these limitations, we developed a pro-regenerative composite hydrogel designed to deliver sustained biochemical signals while guiding native extracellular matrix (ECM) deposition. The engineered system integrates BDDE-crosslinked HA as an injectable structural matrix, dextran microparticles (DMPs) as AA delivery carriers and mechanical reinforcement elements, and a cell-derived ECM (cdECM) coating to provide biomimetic biochemical cues for improved tissue integration. The fabrication process included the following steps: determining a non-toxic, pro-fibrogenic AA dose (150 μg/mL); synthesizing DMPs (~37 μm) via Williamson etherification; screening eight HA/DMP formulations using rheology, structural characterization, and cell viability; assessing AA incorporation and sustained AA release over 21 days with the majority of bioactive availability during the first 7 days; and evaluating in vivo biocompatibility and degradation in a rat subcutaneous model. AA significantly enhanced fibroblast matrix production, including collagen (17.69% ± 5.53% vs. 1.82% ± 0.90% in controls), fibronectin (30.45% ± 14.13% vs. 2.62% ± 0.91%), and vimentin expression. The optimized formulation (HA50/4D50) demonstrated shear-thinning injectability, the highest elastic modulus (≈576 Pa), and enhanced cell proliferation (147% viability). Hydrogels releasing AA supported markedly greater total protein (0.481 ± 0.013 μg/mL) and collagen deposition than AA-free gels. In vivo, the material degraded steadily over 21 days with complete inflammation resolution, showing no chronic fibrosis. Importantly, AA-loaded hydrogels promoted superior tissue integration, reflected by markedly reduced void areas (9.42% vs. 28.4%). The composite hydrogel shifts soft-tissue fillers from passive materials to active regenerative templates. Sustained AA release combined with cdECM biofunctionalization drives robust fibroblast activity and coordinated tissue ingrowth. The material's degradation matched host ECM deposition, supporting a "sacrificial templating" mechanism. This work establishes proof-of-concept for an injectable, biologically instructive filler that overcomes major limitations of current clinical options and offers a promising strategy for regenerative soft-tissue repair.