Study of two hydroxyapatite/poly(alkoxysilane) implant coatings

Bioactive hydroxyapatite coatings onto bioinert metallic implants have recently received considerable attention. This work presents a new low-temperature bi-layer hydroxyapatite (HA) coating. First, a thin pre-coating was made with polyalkoxysilanes to promote the adhesion of hydroxyapatite/polyalkoxysilanes composite second layer. In order to optimize the coating cohesion, various parameters were studied such as the metallic support roughness, the nature of alkoxysilanes and the drying temperature of coatings. Two polysiloxanes mixtures were studied: glycidoxypropyltrimethoxysilane (GPS) mixed either with 3-aminopropyltrimethoxysilane (APTS) or with [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAPTS). The results showed that the structural cohesion of the bi-layer coating was achieved by 3D oligomerisation of silanols. Better results were obtained with the GPS/AEAPTS mixture and structural investigations showed no HA structure modification. The advantage of our process is to allow a perfect control of the apatitic phase and to open perspectives such as including biological molecules of pharmaceutical interest during the surface treatment.