Photo-iniferter-based thermoresponsive block copolymers composed of poly(ethylene glycol) and poly(N-isopropylacrylamide) and chondrocyte immobilization

A series of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM)-poly(ethylene glycol) (PEG) block copolymers with various PNIPAM contents and copolymer architectures, such as linear, four-armed and eight-armed configurations, were prepared by iniferter-based photopolymerization of dithiocarbamylated PEGs (DC-PEGs) under ultraviolet (UV)-light irradiation. The increase in monomer/DC-PEG feed ratio resulted in an increase in both the molecular weight and PNIPAM content of copolymers. The measurement of the optical transmittances of aqueous solutions of PNIPAM-PEG block copolymers determined the lower critical solution temperatures (LCSTs) of block copolymers, which ranged from 31.3 to 34.0°C. LCST decreased with increasing block length of PNIPAM and with the formation of a branched architecture. Rabbit chondrocytes were immobilized and cultured in a three-dimensional (3D) gel composed of PNIPAM-PEG block copolymer at 37°C. Gels prepared from copolymers with higher PNIPAM contents at higher concentrations appeared to exhibit a minimal decrease in both cell number and cell viability during a 7-day culture. Cell viability dependencies on material and formulation parameters and the potential use of PNIPAM-PEG block copolymers as an in situ formable scaffold for an engineered cartilage tissue were discussed.