Synthesis and characterization of hyaluronic acid–poly(ethylene glycol) hydrogels via Michael addition: An injectable biomaterial for cartilage repair

Injectable hydrogels based on hyaluronic acid (HA) and poly(ethylene glycol) (PEG) were designed as biodegradable matrices for cartilage tissue engineering. Solutions of HA conjugates containing thiol functional groups (HA-SH) and PEG vinylsulfone (PEG-VS) macromers were cross-linked via Michael addition to form a three-dimensional network under physiological conditions. Gelation times varied from 14 min to less than 1 min, depending on the molecular weights of HA-SH and PEG-VS, degree of substitution (DS) of HA-SH and total polymer concentration. When the polymer concentration was increased from 2% to 6% (w/v) in the presence of 100 U ml−1 hyaluronidase the degradation time increased from 3 to 15 days. Hydrogels with a homogeneous distribution of cells were obtained when chondrocytes were mixed with the precursor solutions. Culturing cell–hydrogel constructs prepared from HA185k-SH with a DS of 28 and cross-linked with PEG5k-4VS for 3 weeks in vitro revealed that the cells were viable and that cell division took place. Gel–cell matrices degraded in approximately 3 weeks, as shown by a significant decrease in dry gel mass. At day 21 glycosaminoglycans and collagen type II were found to have accumulated in hydrogels. These results indicate that these injectable hydrogels have a high potential for cartilage tissue engineering.