Factors controlling crystallization of calcium phosphates on solid surfaces

摘要

The heterogeneous nucleation of the calcium phosphates, octacalcium phosphate (OCP), hydroxyapatite (HAP) and fluorapatite (FAP), has been studied on polymer surfaces, poly(methyl methacrylate (PMMA) and poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), silicone rubber, titanium oxides. The influence of radiofreqency glow discharge treatment (RFGD) has also been investigated. Surface properties were characterized by contact angle measurements. Although the Lifshitz-van der Waals surface tension components ( gamma ~(LW)) are approximately the same for all these material, the Lewis acid-base surface tension components ( gamma ~(AB)) vary greatly. In supersaturated solutions, effective nucleation of calcium phosphates was observed only on those surfaces with relatively high values of Lewis acid-base surface tension component ( gamma ~(AB)>5.0x10~(-3) J/m~2) or, more specifically, Lewis base parameters ( gamma >20x10~(-3) J/m~2). At the same relative supersaturation ( sigma ), the induction period ( tau ) for calcium phosphate nucleation on hydrophilic surfaces is less than that on more hydrophobic surfaces. Thus, at sigma _(OCP) = 1.67, the experimental values of tau were 63 and 85 minutes on anatase ( gamma = 48x10~(-3) J/m~2) and rutile surfaces ( gamma =16x10~(-3) J/m~2), respectively.