Ion Beam Techniques for Thin Calcium Phosphate Coating Production

Abstract

Calcium phosphate (CaP) coatings produced by the plasma-spraying method show frequent fractures and dissolution in their coatings as well as at the titanium interface after implantation, leading to peeling off of the coating due to the thick, porous, nonuniform, poorly adherent CaP layer. These peeled fragments of a certain size may induce phagocytosis by macrophages, leading to inflammation. Therefore, it is necessary to develop coatings that are defect-free and strongly adherent to titanium substrates. Such coatings must allow rapid osteogenesis and thereafter complete resorption in the host tissues so they may be eventually entirely replaced by bone tissue. CaP coatings should not be thicker than absolutely necessary to facilitate osteogenesis (remodeling of bones) at sites of resorption of old bone. The thin CaP coatings produced by ion beam techniques have inherent properties, such as fewer defects in the coatings themselves and superior adhesion between the coatings and underlying metals, that offer several advantages: They prevent fractures in CaP ceramics; they do not change the surface topography, which has a marked effect on cell behavior; and they enable immobilization of functional proteins and drugs. This chapter describes the ion beam technique, mechanical properties of the coatings, change in bond strength and solubility by heat treatment, mechanism for debonding of CaP coatings, and biological responses.