A Novel In Vitro Model to Study the Calcification of Biomaterials

A novel in vitro model based on a solution mainly composed of sodium, calcium, chloride and phosphate ions, was developed to study the calcification of biomaterials at near physiological conditions. This model, due to its ability to quickly calcify the tested materials, is called Accelerated Calcification Solution (ACS). PolyactiveTM 30170, PolyactiveTM 70/30 and its composites with nano-apatite were used as testing materials because of their known calcification behaviour. The results showed that PolyactiveTM 70/30 and its composites could calcify in ACS in a relatively short period, while the polymer without filler failed to induce calcium phosphate precipitation in more conventional Simulated Body Fluid (1.5 SBF) in 9 days in this study. PolyactiveTM 30170 did not calcify in ACS and 1.5 SBF. As these results agreed well with the known in vitro and in vivo calcification behaviour of PolyactiveTM, we conclude that the ACS solution is a suitable model to study the calcification behaviour of biomaterials. The Ca-P mineral layer induced from ACS on PolyactiveTM 70/30 and its composites was composed of octacalcium phosphate (OCP) and calcium hydroxyapatite. It is likely that the OCP first nucleated and grew on PolyactiveTM 70/30 and its composites, then gradually transformed to calcium hydroxyapatite via hydrolysis. Also, the results showed that nano-apatite has the ability to promote calcification because nano-apatite/PolyactiveTM 70/30 composites could quickly calcify in ACS as well as in 1.5 SBF.