Abstract
The objective of this study was to discuss the thermoresponsive properties of a novel poly(ester-amide) polymer, i.e. methoxy poly(ethylene glycol)-poly(pyrrolidone-co-lactide)(mPDLA) diblock copolymers and evaluate its capability of chondrocyte encapsulation for cartilage tissue engineering. A series of amphiphilic diblock copolymers were synthesized by ring-opening polymerization of mPEG550, D,L-lactide and 2-pyrrolidone. The initial ratio of monomers in mPDLA was [PD]/[LA]=30/70 and the target molecular weight of hydrophobic segment were 1105, 1405, 1705 respectively. The copolymers were characterized via1H-NMR,FT-IR spectroscopy, and GPC. The results indicated that the diblock copolymers formed nano-micelles at low concentrations in aqueous phase. The micelle properties were also measured. The critical micelle concentration(CMC) was ranged from 0.1 to 0.3 mg/ml.As the temperature increased, micelles aggregation was observed by DLS. The diblock copolymer P3L7-1405 solution underwent a sol-to-gel phase transition, which was confirmed by test tube inverting method. Rheology results showed that viscoelastic properties of the copolymer solution varied with temperature, indicative of the formation of a gel. The mPDLA diblock copolymer solutions exhibited sol-gel transition behavior as a function of temperature. In vitro degradation test showed that the acidity of degradation was effectively reduced by introducing the monomer PD into polyester hydrogel. mPDLA alsoexhibited higher water content from swelling ratio. It would provide an environment that is preferred by cells; therefore, mPDLA diblock copolymer exhibited better biocompatibility in vitro. As an injectable scaffold, the viability, cell proliferation and chondrogenesis of chondrocytes encapsulated in mPDLA hydrogel were investigated. MTT and DNA quantification showed proliferation of cells within 2 weeks. By Live/Dead stain we can confirm that the morphology of cells in hydrogel was typical sphere which mature chondrocytes supposed to be. Also, ECM content was significant increased within 2 weeks compared with initial amount. In vivo test showed the repair of cartilage defect treated with 15% mPDLA hydrogel. From above results, we deduced that this thermosensitive hydrogel was sutible as an injectable scaffold for cartilage tissue engineering.