In Vitro Calcification Model—Part 1: Apatite Formation on Segmented Polyurethane Containing Silicone Using an Alternate Soaking Process

The effect of silicone on calcification on polyetherpolyurethane (PU) surfaces was studied using an alternate soaking process in vitro. The process is based on a wet process of hydroxyapatite formation that involves alternately soaking in CaCl₂/Tris-HCl (pH 7.4) and Na₂HPO₄ solutions (pH 7.4) at 37°C. We used K-III and Pellethane® 2363 as samples. K-III is a complex of PU containing dimethyldiacetoxysilane and methyltriacetoxysilane. Pellethane® 2363 series contain less Si. Si content was assessed by X-ray photoelectron spectroscopy (XPS). The gravimetric measurements and scanning electron microscopic observations with energy dispersed X-ray analyzer (EDX) were performed after specific reaction cycles. Calcified deposits formed on the surface of K-III were 20 μg/cm² after 10 reaction cycles. EDX results showed remarkable Ca (Kα, Kb), P (Kα), and Si (Kα) peaks by the deposits formed on the surface of K-III. On the other hand, no peaks for Ca of P were observed on the surface of Pellethane® after ten reaction cycles. The reason for calcified deposit formation on PU is not clear. However, it was suggested that Si on the surface of PU is one of the key factors for calcified deposit formation. These results suggest that an alternate soaking process could be a useful evaluation method for an accelerated evaluation of fatigue induced by calcification on polymer substrates.