Abstract
The objective of this study was to evaluate thermosensitive mPEG-polyester hydrogels prepared from diblock copolymers methoxy poly(ethylene glycol)-(polylactide-co-glycolide) (mPEG-PLGA) and methoxy poly(ethylene glycol)-(valerolactone-co-lactide) (mPEG-PVLA) for chondrocyte encapsulation in cartilage tissue engineering applications. Different block lengths of mPEG-polyester copolymers were prepared by ring-opening polymerization and preliminary results showed that hydrogels prepared from mPEG-PLGA sized (550-1405) and mPEG-PVLA sized (550-1405) and (750-1916) were capable of gelation under physiological temperature. The swelling ratio of mPEG-PVLA (750-1916) hydrogel was significantly higher than those compared by at least 2-folds. Copolymer solutions prepared in phosphate buffer saline (PBS) resulted in acidic pH environments of 4.1~4.9 within the hydrogel which is hostile to encapsulated cells. Substituting PBS with Dulbecco’s modified eagle medium (DMEM) resulted in neutral hydrogels with pH ~7. Degradation study showed that hydrogels underwent incomplete degradation within a 30 day period with mPEG-PVLA exhibiting slower degradation compared to mPEG-PLGA due to greater hydrophobicity. Viability of chondrocytes encapsulated was confirmed by thiazolyl blue tetrazolium bromide (MTT) and LIVE/DEAD staining which demonstrated homogenous encapsulation as well as over 50% viability immediately post-encapsulation. Taken together with DNA quantification results, we concluded that the hydrogels were capable of supporting proliferation of chondrocytes within 7 days of culturing in vitro. In addition to proliferation, extracellular matrix (ECM) proteins namely glycosaminoglycans (GAGs) increased most significantly in mPEG-PVLA (750-1916) hydrogel with a 11.8-fold increase from day 1 to day 21. On day 14, the collagen content mPEG-PVLA (750-1916) was higher than all other groups (p<0.05). The addition of 5% collagen type I did not significantly affect proliferation and GAG or collagen secretion as was expected. Results of this study indicate that mPEG-polyester hydrogels are capable of supporting chondrogenesis in vitro and that their application as injectable cartilage tissue engineering systems is promising.