Silk nanoengineering for in situ forming injectable ECM-inspired hydrogels

The microenvironment within hydrogels is essential for tissue regeneration and cell colonization, yet it presents a significant obstacle to the development of injectable hydrogel biomaterials. Hyaluronic acid (HA) has garnered substantial interest in injectable therapeutic applications. However, it is confronted with the obstacles of lacking an ECM-mimicking structure and a compromise between mechanical properties and injectability. In this study, we develop an in situ forming injectable ECM-mimicking hydrogel that concurrently replicates structural proteins and glycosaminoglycans by combining with nanofibrillated silks (nanosilks) containing RGD tripeptide with Tyramine-modified HA (HA-Tyr). The precursor solution exhibits favorable injectability (extrusion force < 2 N) and undergoes rapid in situ gelation, ensuring that it conforms precisely to the tissue defect. Through covalent interfacial crosslinking, the nanosilk network simultaneously enhances mechanical strength, elastic recovery, and enzymatic resistance, thereby resolving the challenging trade-off among these properties. Moreover, the incorporated nanosilks provide critical cues for improving the proliferation and long-term survival of encapsulated stem cells in vitro. Following subcutaneous implantation, the HA-Tyr/nanosilks hydrogels exhibit good biocompatibility, structural retention, and the ability to support cell survival and host tissue integration. This study presents a bioactive and cell-instructive injectable material, thereby expanding the potential of stem cell-based minimally invasive therapies. STATEMENT OF SIGNIFICANCE: Injectable hydrogels encounter two significant obstacles. One of the challenges is the inability to create appropriate microenvironments that support pertinent biological and structural functions. The second issue is the challenge of reconciling the conflict between injectability and mechanical properties. This work develops a silk nanoengineering strategy to construct an in situ forming injectable hydrogel that mimics the native ECM. By integrating nanosilks containing RGD with tyramine-modified hyaluronic acid, this composite concurrently replicates both structural proteins and glycosaminoglycans. This design eliminates the conventional trade-offs between enzymatic stability, elastic recovery, mechanical strength, and injectability. This injectable hydrogel offers an effective strategy for minimally invasive therapies in soft tissue repair.