In vitro hydroxyapatite deposition onto a film surface-grated with organophosphate polymer.

To produce a bone-bonding polymer surface that is capable of inducing deposition of a hydroxyapatite (HA) layer in the body fluid, an organophosphate polymer was covalently immobilized onto a high-density polyethylene film by surface graft polymerization of a phosphate-containing monomer. The grafted film was immersed in simulated physiologic solution (SPS). The chemical composition and structure of the formed apatite layer as well as its bonding strength to the polymer surface were investigated. To distinguish the effect of phosphate groups on the deposition of apatite layer from the simple calcium absorption by the anion, a comparative study was done using a polyethylene film with surface immobilized carboxylic groups. Calcium phosphate deposition was observed on all the materials investigated, but the kinetics, composition, deposit amount, and bonding strength of the new phase were found to be significantly different among the modified materials, depending on the density and chemical nature of the surface immobilized ionic groups. It was found that the polymeric materials modified by surface graft polymerization of a phosphate-containing monomer produce a carbonated HA layer firmly bonded with the material upon immersion in SPS. Carboxyl groups in the grafted layer was not enough to activate bonding with the HA layer.