Phase stability and biological property evaluation of plasma sprayed hydroxyapatite coatings for orthopedic and dental applications

Abstract

In this work we have investigated the effects of strontium (Sr) dopant on in vitro protein release kinetics and in vivo osteogenic properties of plasma sprayed hydroxyapatite (HA) coatings, along with their dissolution behavior. Plasma sprayed HA coatings are widely used in load-bearing implants. Apart from osseointegration, the new generation of HA coating is expected to deliver biomolecules and/or drugs that can induce osteoinduction. This paper reports the preparation of crystalline and amorphous HA coatings on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray, and their stability at different solution pH. Coatings prepared at 110 mm working distance from the nozzle showed average Ca ion release of 18 and 90 ppm in neutral and acidic environments, respectively. Decreasing the working distance to 90 mm resulted in the formation of a coating with less crystalline HA and phases with higher solubility products, and consequently higher dissolution over 32 days. A 92% release of a model protein bovine serum albumin (BSA) in phosphate buffer with pH of 7.4 was measured for Sr doped-HA coating, while only a 72% release could be measured for pure HA coating. Distortion of BSA during adsorption on coatings revealed strong interaction between the protein and the coating, with an increase in α-helix content. Osteoid formation was found on Sr-HA implants as early as 7 weeks post implantation compared to HA coated and uncoated Ti implants. After 12 weeks post implantation, osteoid new bone was formed on HA implants; whereas, bone mineralization started on Sr-HA samples. While no osteoid was formed on bare Ti surfaces, bone was completely mineralized on HA and Sr-HA coatings after 16 weeks post implantation. Our results show that both phase stability and chemistry can have significant influence towards in vitro and in vivo response of HA coatings on Ti implants.

The Influence of Process Parameters on the Structure, Phase Composition, and Texture of Micro-Plasma Sprayed Hydroxyapatite Coatings

“…However, with the rapid development of surface technology, HA coatings deposited by using surface technology on a metal substrate provide excellent biocompatibility and good mechanical properties. The plasma spraying technique is a common method for depositing HA coating on metal implants [4][5][6]. However, the overheating of HA particles in the plasma jet can cause the decomposition of the HA powders.…”

Role of implants surface modification in osseointegration: A systematic review

“…Hydroxyapatite (HA) is commonly applied in PS processes. Vahabzadeh et al reported that both stability and chemistry can be influenced significantly in vivo and in vitro by the plasma-sprayed HA coatings on Ti implants (Vahabzadeh, Roy, Bandyopadhyay, & Bose, 2015). But the loss of crystallinity of HA during spraying cannot be ignored and invokes further research studies (Zyman, Cao, & Zhang, 1993).…”

Synthesis of the hydroxyapatite coatings on the Ti substrates by mechanical alloying

“…Some works [7,[41][42][43] observed the deposition of different kinds of HA coating (with or without reinforcements) on Ti and Ti based alloys using other methods, such as hydrothermal synthesis, electrodeposition, radio frequency sputtering, and plasma spray. These methods made it possible to obtain rather high quality coatings on Ti and Ti based substrates.…”