Self-attaching and cell-attracting in-situ forming dextran-tyramine conjugates hydrogels for arthroscopic cartilage repair

Small cartilage defects are frequently treated with debridement or left untreated, predisposing to early onset osteoarthritis. We propose to fill these defects with a cell-free injectable hydrogel comprising dextran-tyramine conjugates (Dex-TA) that can be applied during arthroscopic procedures. In this study, we report on the adhesion mechanism between cartilage and Dex-TA hydrogels and enhancement of cell ingrowth by incorporation of Heparin-tyramine (Hep-TA) conjugates. The enzyme-catalyzed crosslinking reaction of Dex-TA and Hep-TA hydrogels is based on covalent bonding of hydroxyphenyl residues. We hypothesized that this reaction results in covalent bonding of the hydroxyphenyl residues in Dex-TA and Hep-TA to tyrosine residues in cartilage matrix proteins. The involvement of TA residues was confirmed by modelling the enzymatic reaction occurring during gelation. The mechanical analysis indicated that higher tyramine content led to stronger binding. Interfacial cartilage-hydrogel morphology and Raman spectroscopy demonstrated collagens' reorganization and evidenced the coupling of TA to tyrosine residues in collagen. Moreover, the addition of Hep-TA induced cell recruitment. Collectively, in vitro and ex vivo functional studies evidenced the covalent bonding of TA-containing hydrogels to tyrosine residues in cartilaginous matrix proteins. Moreover, the cell-attracting ability of these hydrogels could be explored to guide tissue repair in focal cartilage defects, preventing or delaying the onset osteoarthritis.