Protein Adsorption Property of a Biomimetic Apatite Coating

Abstract

Hydroxyapatite (HA) coating applied on metallic orthopedic joint implants can improve bone apposition, presumably through selective protein adsorption from blood plasma. However, the detailed interaction mechanism of HA coating with serum proteins remains to be largely elucidated. Protein adsorption behavior of a biomimetic apatite (BAp) coating in bovine calf serum and alpha calf fraction was investigated in this study. Plasma sprayed HA (PSHA) coating was tested in alpha calf fraction. The microstructure and composition of the coatings before and after serum incubation were characterized and the proteins adsorbed during the incubation were extracted from the coatings and analyzed. Microstructural transformation of the BAp coating accompanied by selective serum protein adsorption was observed after incubation in both media. The total protein amount adsorbed by the BAp coating in alpha calf faction was about three times that of the PSHA coating. To test the potential use of BAp coating as a carrier of therapeutic agents, interaction between the BAp coating and transforming growth factor (TGF)-β1 was studied. The growth factor was successfully loaded onto the coating in a sodium acetate buffer. Because of its high affinity to the coating, TGF-β1 could not be easily eluted in a bovine serum albumin containing solution but could be recovered after coating dissolution in acid. The strong protein adsorption property of the BAp coating was found to be due mainly to its unique nanoporous structure. The BAp coating can serve as an ideal carrier of therapeutic agents for aiding in the healing of bone and soft tissues.