Development and Characterization of a Biological-like Apatite Based on a Suspension Sprayed Using Induction Plasma Technology

Calcium phosphates coatings are well-known for their use as bones subsitutes considering their excellent biocompatibility. Synthetic hydroxypatite (HAp) can be represented by the chemical formula Ca₁₀(PO₄)₆(OH)_2. Altough the crystallographic structure of the HAp is similar to natural bone, biological apatite are always non-stoechiometric and presents some incorporated elements on trace level in its lattice. Several studies have shown that these elements, even in trace levels, play an important role on the biological process as well during implantation as during the life-time of the bone.

The purpose of this study is to develop a biological-like hydroxyapatite co-subsituted (Mg, K, Na, Cl, F) using Suspension Plasma Spraying (SPS) with an inductively coupled plasma and characterized its dissolution behavior using a simulated body fluid (SBF)A suspension based on nitrates and ammonium was prepared in order to obtain the precursor suspension material. Once SPS has been completed some coatings were subjected to heat treatments.  The obtained coatings were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and neutron activation (NA). Results showed a microstructure with an open microporosity near 10 μm while β-TCP and HAP phasis were observed by XRD. The NA results show an elemental composition very close (less than 0,05%wt) to natural bone with a Ca/P ratio identical to biological apatite. The SBF study shows a reactivity of the coating for the as-sprayed coating as well as for the heat-treated one. A phenomenon of dissolution-precipitation resulting in a plate-like growing on the surface was observed on the as-sprayed coating after several weeks while a simple precipitation occurred on the heat treated sample, due to the highest stability induced by the heat treatment.