Effect of water glass coating of tricalcium phosphate on in vitro cellular proliferation and osteogenic differentiation

Background In this study, the properties of the water glass (WG, sodium-silicate glass) were utilized to control the biodegradability of the beta tricalcium phosphate materials by the WG coating on the tricalcium phosphate disc surface with various coating thickness, chemistry, and heat-treatment. Methods Four types of disc specimens were prepared. A sample group A consisted of pure hydroxyapatite (HA) as a negative resorption control; a sample group B consisted of pure beta tricalcium phosphate as a positive resorption control; a sample group C consisted of beta tricalcium phosphate coated with WG as an early resorption model; and a sample group D consisted beta tricalcium phosphate coated with WG and heat-treated at 500°C as a delayed resorption model. Using human bone marrow-derived mesenchymal stem cells, for the analysis of cellular attachment and proliferative activity, 4-6-Diamidino-2-Phenylindole fluorescence technique was used. For the analysis of osteteogenic differentiation, alkaline phospastase (ALP) activity was measured. Results The mean z-scores of four groups (A, B, C, and D) in cellular attachment at 4 h after seeding were -1.21, -0.15, 0.42, and 0.94, respectively, and statistically significantly different in all groups respectively. Seven days after seeding, the mean z-scores of cellular proliferation were 1.97, 0.71, 1.48, and 1.83 in the four groups, respectively. The mean z-scores of the ALP activity per the mean z-scores of cell numbers of respective groups on the seventh day were 0.40, -1.51, 0.12, and 0.06, respectively, in four groups. Conclusion Initial cellular attachment is better on beta tricalcium phosphate than on HA and is enhanced by WG coating, especially with sintering at the high temperature. Cellular proliferation is considered to be increased by maintaining its attachment site through reduced dissolution of beta tricalcium phosphate by WG coating. Osteogenic differentiation in in-vitro study on the WG-coated beta tricalcium phosphate is thought to be as the result of increased silicon ion release from the WG.