Injectable thermosensitive alginate/β‐tricalcium phosphate/aspirin hydrogels for bone augmentation

In this study, an injectable and thermo‐sensitive alginate/β‐tricalcium phosphate hydrogel (TSAH/β‐TCP) was prepared for aspirin release to a bone defect. Aspirin was dissolved into a mixture of poly(N‐isopropylacrylamide) (PNIPAAm), an aminated alginate‐g‐PNIPAAm co‐polymer, and β‐TCP powders. Scanning electron microscopy showed that TSAH/β‐TCP had an interconnected porous microstructure with a porosity of 86.78%. The cross‐linked hydrogel released approximately 40% of the aspirin in the first 3 days and then slowly released the remainder. At a low concentration (≤100 μg/mL), aspirin did not promote cell proliferation, but enhanced the alkaline phosphatase activity, and osteocalcin (OCN) and collagen I expression of human bone marrow‐derived mesenchymal stem cells. The TSAH/β‐TCP/aspirin hydrogel was injected into the periosteum of the rat cranial bone, and its in vivo bone‐forming ability was evaluated at 12 weeks. A bone morphogenetic protein 2 (BMP‐2)‐loaded TSAH/β‐TCP hydrogel was injected as a control. Micro‐computed tomography showed that the percentage of mineralized tissue in the TSAH/β‐TCP/BMP‐2 and TSAH/β‐TCP/aspirin groups were similar and significantly higher than that in the TSAH/β‐TCP group. Immunohistochemical staining showed considerable expression of OCN, especially in the TSAH/β‐TCP/BMP‐2 and TSAH/β‐TCP/aspirin groups. These results suggest that the injectable TSAH/β‐TCP/aspirin hydrogel has great potential for bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1739–1751, 2018.