An Injectable Bioorthogonal Dextran Hydrogel for Enhanced Chondrogenesis of Primary Stem Cells

The purpose of this study is to corroborate the feasibility of an injectable dextran hydrogel, in situ formed through a catalyst-free bioorthogonal reaction, for cartilage regeneration with adult chondrocytes or adipose-derived stem cells (ADSCs). To this end, an injectable dextran (dextran-AN) hydrogel encapsulating the rabbit adult chondrocytes or rabbit ADSCs (rADSCs) or human ADSCs (hADSCs) was successfully prepared by simply incubating the cells with dibenzocyclooctyne-dextran conjugate and azide-dextran conjugate under physiological conditions through a copper-free bioorthogonal reaction without using additional reagents. The possibility of dextran-AN hydrogel/adult rabbit chondrocyte constructs for in vivo chondrogenesis was first assessed in a rabbit osteochondral defect model. Data indicated that the hydrogel was biocompatible against surrounding tissue and could promote adult chondrocyte survival and in vivo chondrogenesis within 8 weeks. Next, in vitro and in vivo chondrogenetic differentiation of rADSCs encapsulating in dextran-AN hydrogel was studied systemically. Compared to the agarose hydrogel as a positive control, the dextran-AN hydrogel elicited comparable ability to support in vitro chondrogenesis of rADSCs within 3 weeks but caused better cartilage regeneration within 6 weeks in a rabbit osteochondral defect model. Furthermore, miR29A downregulating of hADSCs was applied for in vivo chondrogenesis by subcutaneous in situ formation of dextran-AN hydrogel containing the hADSCs in a balb/c nude mouse model. Within 4-week regeneration, the hydrogel group illustrated upregulated mRNA expression level of chondrogenesis-related biomarkers. In addition, improved production of neocartilage extracellular matrices (type-II collagen and glycosaminoglycan) was found for miR29A-downregulatd hADSC group in comparison with miR29A-upregulated hADSC and untreated hADSC control groups. The results of this study show that bioorthogonal dextran-based hydrogel is capable of supporting in vitro and in vivo chondrogenesis of chondrocytes and human stem cells, thus highlighting high feasibility of bioorthogonal hydrogels for clinical translation in stem cell-based cartilage regeneration.