Vertebral compression fractures account for approximately 700,000 out of the 1.5 million total osteoporotic fractures that occur annually in the USA. There is growing interest in substituting currently utilized clinical treatments for vertebral compression fractures with an injectable, degradable, and bioactive system. In this research we studied the osteoinductive effect of calcium phosphate incorporation into cellulose nanocrystal/chitosan hydrogels with varying ratios of carbonate as an ionic crosslinker and genipin as a covalent crosslinker. As calcium and phosphate ions have been shown to be osteoinductive in time and concentration dependent manners, dibasic calcium phosphate was chosen as a bioactive additive due to its desirable controlled ion delivery potential. Gelation time, swelling ratio, erosion, compressive strength, and ion release behavior of different dibasic calcium phosphate incorporated hydrogels were evaluated. Mesenchymal stem cells were then exposed to mechanically competent hydrogels found capable of maintaining calcium and phosphate concentrations within the established bioactive range in order to assess their cytotoxicity and osteoinductivity. Our results demonstrate that hydrogels with higher covalent crosslinking possessed better mechanical properties and stabilities as well as more controlled calcium and phosphate ion release. Interestingly, dibasic calcium phosphate incorporation not only improved hydrogel bioactivity but also resulted in greater compressive strength.
Keywords: calcium phosphate; cellulose nanocrystals; chitosan; hydrogel; vertebral compression fractures.