Blooming gelatin: an individual additive for enhancing nanoapatite precipitation, physical properties, and osteoblastic responses of nanostructured macroporous calcium phosphate bone cements

In recent years, there has been a great interest in using natural polymers in the composition of calcium phosphate bone cements to enhance their physical, mechanical, and biological performance. Gelatin is a partially hydrolyzed form of collagen, a natural component of bone matrix. In this study, the effect of blooming gelatin on the nanohydroxyapatite precipitation, physical and mechanical properties, and cellular responses of a calcium phosphate bone cement (CPC) was investigated. Various concentrations of blooming gelatin (2, 5, and 8 wt.%) were used as the cement liquid and an equimolar mixture of tetracalcium phosphate and dicalcium phosphate was used as solid phase. The CPC without any gelatin additive was also evaluated as a control group. The results showed that gelatin accelerated hydraulic reactions of the cement paste, in which the reactants were immediately converted into nanostructured apatite precipitates after hardening. Gelatin molecules induced 4%-10% macropores (10-300 μm) into the cement structure, decreased initial setting time by ~190%, and improved mechanical strength of the as-set cement. Variation in the above-mentioned properties was influenced by the gelatin concentration and progressed with increasing the gelatin content. The numbers of the G-292 osteoblastic cells on gelatin-containing CPCs were higher than the control group at entire culture times (1-14 days), meanwhile better alkaline phosphatase (ALP) activity was determined using blooming gelatin additive. The observation of cell morphologies on the cement surfaces revealed an appropriate cell attachment with extended cell membranes on the cements. Overall, adding gelatin to the composition of CPC improved the handling characteristics such as setting time and mechanical properties, enhanced nanoapatite precipitation, and augmented the early cell proliferation rate and ALP activity.