Dextrose, maltose and starch guide crystallization of strontium-substituted hydroxyapatite: A comparative study for bone tissue engineering application.

A study of the influence of carbohydrates on the crystallization of metal-substituted hydroxyapatite predicts direct relevance to natural bone growth. The present work demonstrates the role of carbohydrates on the crystallization of strontium-substituted hydroxyapatite (SHAP). The order of increasing number of hydroxyl groups, dextrose (monosaccharide) < maltose (disaccharide) < starch (polysaccharide), led to proportionate coordination with Ca/Sr and thus guided SHAP crystallization with crystal size reduced from 35 to 19 nm, lattice volume increased from 518 to 537 Å, and residual carbohydrates increased from 1.8 to 20.2 %. The composites exhibited varying amounts of residual carbohydrates due to their interaction with apatite and/or aqueous insolubility. Compared to pure SHAP, the starch-SHAP with high residual starch increased water uptake from 1.23 ± 0.18 to 4.26 ± 0.21 % and degradation from 0.22 ± 0.06 to 1.53 ± 0.14 %, but decreased microhardness from 0.73 ± 0.12 to 0.38 ± 0.01 GPa and protein affinity from 4.82 ± 0.01 to 0.81 ± 0.01 μg/mg. However, the microhardness value was within the range of bone, and the reduced protein adsorption was masked by its rich osteogenic behaviour. In vitro cellular response demonstrated that the residual carbohydrate and strontium augmented osteocompatibility, proliferation, differentiation and biomineralization. The result concludes that carbohydrates drive SHAP crystallization, and starch-SHAP exhibited desired biophysico-chemical properties to replicate natural bone.