Injectable Biodegradable Thermosensitive Hydrogel Composite for Orthopedic Tissue Engineering. 1. Preparation and Characterization of Nanohydroxyapatite/Poly(ethylene glycol)−Poly(ε-caprolactone)−Poly(ethylene glycol) Hydrogel Nanocomposites

In this study, we synthesized a biodegradable triblock copolymer poly(ethylene glycol)−poly(ε-caprolactone)−poly(ethylene glycol) (PEG−PCL−PEG, PECE) by ring-opening copolymerization, and nanohydroxyapatite (n-HA) powder was prepared by a hydrothermal precipitation method. The obtained n-HA was incorporated into the PECE matrix to prepare injectable thermosensitive hydrogel nanocomposites. 1H NMR, FT-IR, XRD, DSC, and TEM were used to investigate the properties of PECE copolymer and n-HA/PECE nanocomposites. The rheological measurements for n-HA/PECE nanocomposites revealed that the gelation temperature was approximately 36 °C. The sol−gel−sol transition behavior and phase transition diagrams were recorded through a test tube inverting method. The results showed that n-HA/PECE nanocomposites still had thermoresponsivity like that of PECE thermosensitive hydrogel. The morphology of the nanocomposites was observed by SEM; the results showed that the nanocomposites had a 3D network structure. In addition, the effects of n-HA contents on the properties of n-HA/PECE nanocomposites are also discussed in the paper. From the results, n-HA/PECE hydrogel is believed to be promising for injectable orthopedic tissue engineering due to its good thermosensitivity and injectability.