Functionalization of the Parylene C Surface Enhances the Nucleation of Calcium Phosphate: Combined Experimental and...

Interactions at the solid-body fluid interfaces play a vital role in bone tissue formation at the implant surface. In this study, fully atomistic molecular dynamics (MD) simulations were performed to investigate interactions between the physiological components of body fluids (Ca²⁺, HPO₄^2-, H₂PO₄^-, Na⁺, Cl^-, and H₂O) and functionalized parylene C surface. In comparison to the native parylene C (-Cl surface groups), the introduction of -OH, -CHO, and -COOH surface groups significantly enhances the interactions between body fluid ions and the polymeric surface. The experimentally observed formation of calcium phosphate nanocrystals is discussed in terms of MD simulations of the calcium phosphate clustering. Surface functional groups promote the clustering of calcium and phosphate ions in the following order: -OH > -CHO > -Cl (parent parylene C) ≈ -COO^-. This promoting role of surface functional groups is explained as stimulating the number of Ca²⁺ and HPO₄^2- surface contacts as well as ion chemisorption. The molecular mechanism of calcium phosphate cluster formation at the functionalized parylene C surface is proposed.