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) surfa ces was studied using an alternate soaking process in vitro. The process is based on a wet process of hydroxyapatite formation that involves alternate ly soaking in CaCl2/Tris-HCl (pH 7.4) and Na2HPO4 solutions (pH 7.4) at 37 degrees C. We used K-III and Pellethane(R) 2363 as samples. K-III is a comp lex of PU containing dimethyldiacetoxysilane and methyltriacetoxysilane. Pe llethane(R) 2363 series contain less Si. Si content was assessed by X-ray p hotoelectron 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 mu g/cm(2) after 10 reaction cycles. EDX re sults showed remarkable Ca (K alpha, Kb), P (K alpha), and Si (K alpha) pea ks by the deposits formed on the surface of K-III. On the other hand, no pe aks for Ca of P were observed on the surface of Pellethane(R) after ten rea ction 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 alte rnate soaking process could be a useful evaluation method for an accelerate d evaluation of fatigue induced by calcification on polymer substrates.