Covalently Injectable Chitosan/Chondroitin Sulfate Hydrogel Integrated Gelatin/Heparin Microspheres For Soft Tissue Engineering

Microspheres and injectable hydrogels derived from natural biopolymers have been extensively investigated as drug carriers and cell scaffolds. In this study, we report a preparation of composite scaffolds basing microspheres and hydrogel via the Schiff's base reaction. Hybrid gelatin/heparin microspheres loading insulin-like growth factor-1 (IGF-1) with a diameter of 5-10 mu m were fabricated using an emulsion cross-linking method. Synchronously, water-soluble carboxymethyl chitosan (CMC) and oxidized chondroitin sulfate (OCS) were prepared for cross-linking of hydrogels, which were embedded with microspheres to produce a composite microspheres/gel scaffold. The mechanism of scaffold cross-linking is attributed to the Schiff's base reaction between amino and aldehyde groups of biopolymers. Currently, gelation rate, morphology, mechanical properties, swelling ratio, weight loss, and IGF-1 release of the composite scaffolds were examined in vitro. The results show that mechanical and bioactive properties of CMC-OCS hydrogel can be significantly improved by embedding gelatin/heparin microspheres containing IGF-1. Compressive modulus of composite gel scaffolds containing 3 wt% of microspheres was 16 kPa, which was higher than the control hydrogel without microspheres. Cumulative release of IGF-1 during 7 days from microspheres embedded hydrogel was 70%, which was significantly lower than those of microspheres and hydrogels. Moreover, the composite microspheres/gel scaffolds exhibited higher swelling ratio and slower degradation rate than the control. Potential of the composite scaffolds was demonstrated by encapsulation of human adipose-derived stem cells (ASCs) in vitro. Cell culture showed that this composite hydrogel could support survival and proliferation of ASCs. These results demonstrate the potential of gelatin/heparin microspheres embedded CMC-OCS hydrogels as an injectable scaffold in soft tissue engineering.