Temperature-sensitive biodegradable mixed star-shaped block copolymers hydrogels for an injection application

3-arm star-shaped poly(d,l-lactic-co-glycolic acid)-b-methoxy poly(ethylene glycol)(3sPLGA-mPEG) and 4sPLGA-mPEG copolymers are synthesized via the arm-first method. A facile method to obtain a temperature-sensitive physical injectable hydrogel is found using simply mixing two 4sPLGA-mPEG block copolymers aqueous solutions individually with thermogelling property (sol-gel-sol transition) or using simply mixing an aqueous sol of a 3sPLGA-mPEG block copolymer with a precipitate of a similar 3sPLGA-mPEG copolymer but with a varying PLGA/mPEG block ratio. A dramatic tuning of the sol–gel transition temperature is conveniently achieved by merely changing mix ratios. The degradation of mixed 3sPLGA-mPEG hydrogel proceeds by hydrolysis of ester bonds followed by the erosion of gel in PBS solution at body temperature for nearly 50 days. The mass loss and reduction of molecular weight are detected with increasing degradation time, and the mix ratios are found to slightly influence the degradation profiles. MTT assay and histological observations are used to examine the mixed copolymer solution. Both in vitro and in vivo results illustrate acceptable biocompatibility of our mixed materials. Collectively, our results show that the mixed star-shaped PLGA-mPEG block copolymer is a promising candidate as a novel injectable gel.