Synthesis, characterization and biological performance study of Sr-doped hydroxyapatite/chitosan composite coatings

Abstract

Hydroxyapatite (HA) is widely used in bone repair and regeneration because of its composition and structure similar to human bone. However, the artificially synthesized HA has poor mechanical properties, so it is often necessary to add a second phase to the powder as a supporting phase to enhance its mechanical properties. Strontium (Sr) has the properties of promoting the growth of bone cells, which can increase bone formation in the body and reduce bone self-absorption. Nevertheless, Sr-doped HA composites have been rarely reported in the literature in recent years. In this paper, Sr-doped HA was employed to be complexed with chitosan (CS) for the first time to prepare a composite coating that is dense and uniform, with good adhesion and ductility, in order to expand its clinical applications. Therefore, a series of HA samples doped with different Sr mole fraction (0 mol% (pure HA), 0.5 mol%, 1 mol%, 2 mol%, 4 mol%) were prepared by chemical precipitation method. Then the HA/CS composite coating doped with Sr was prepared on the stainless steel substrate by spin-coating technology. The results showed that Sr2+ ions had replaced part of Ca2+ ions and have been successfully doped into the HA lattice. The synthesized HA particles showed a shortrod-like morphology, and the substitution of Sr ions promoted the growth of Sr-doped HA crystals and increased its grain size. In addition, the synthesized Sr-doped HA/CS composite coating is dense and uniform. In vitro cell culture experiments showed that all composite coatings have good biocompatibility. The HA/CS coating with 4 mol% Sr ion doping is more conducive to cell proliferation, adhesion and osteogenic differentiation.