Functionalization of Hydroxyapatite Ceramics: Raman Mapping Investigation of Silanization

Abstract

Surface modification of bioceramic materials by covalent immobilization of biomolecules is a promising way to improve their bioactivity. This approach implies the use of organic anchors to introduce functional groups on the inorganic surface on which the biomolecules will be immobilized. In this process, the density and surface distribution of biomolecules, and in turn the final biological properties, are strongly influenced by those of the anchors. We propose a new approach based on Raman 2D mapping to evidence the surface distribution of organosilanes, frequently used as anchors on biomaterial surfaces on hydroxyapatite and silicated hydroxyapatite ceramics. Unmodified and silanized ceramic surfaces were characterized by means of contact angle measurements, atomic force microscopy (AFM) and Raman mapping. Contact angle measurements and AFM topographies confirmed the surface modification. Raman mapping highlighted the influence of both the ceramic’s composition and silane functionality (i.e., the number of hydrolysable groups) on the silane surface distribution. The presence of hillocks was shown, evidencing a polymerization and/or an aggregation of the molecules whatever the silane and the substrates were. The substitution of phosphate groups by silicate groups affects the covering, and the spots are more intense on SiHA than on HA.