Physical Crosslinked Poly(N-isopropylacrylamide)/Nano-Hydroxyapatite Thermosensitive Composite Hydrogels

Injectable and thermosensitive poly( N -isopropylacrylamide) (PNIPA)/nano-hydroxyapatite (nano-HA) composite hydrogels were synthesized by physical crosslinking of N -isopropylacrylamide with nano-HA as cross-linker to improve the mechanical property of hydrogels and avoid the use of chemical cross-linker. Internal morphology, thermosensitive, rheological, swelling, and hemocompatibility properties of the prepared hydrogels were investigated. The PNIPA/HA composite hydrogels had a phase transition from sol to gel, and the lowest critical solution temperature was about 32.5 °C. The PNIPA/HA composite hydrogels had regular pore structures and the nano-HA dispersed well throughout the network. Differential scanning calorimetry and thermogravimetric analysis showed that the addition of nano-HA had no significant effect on the LCST and thermal stability of the PNIPA/HA hydrogels. When the temperature was above 32.5 °C, the storage modulus ( G′ ) and complex viscosity increased with the increasing nano-HA content. All PNIPA/HA composite hydrogels possessed the thinning behavior. The PNIPA/HA hydrogels exhibited a good water absorption capacity and the swelling ratio decreased with the increasing nano-HA content. As revealed by biocompatibility results, PNIPA/HA composite hydrogels were considered to be a non-hemolytic biomaterial. Therefore, PNIPA/HA hydrogels can be used as injectable materials for the potential applications of science and technology, such as tissue engineering scaffolds.