Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol–gel method: Bonding to titanium and scanning electron microscopy

Abstract

Objectives

Hydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) production has been characterised and optimised by the sol–gel method and the dissolution and biological properties of these materials were investigated. It was the objective of this study to investigate the potential bond strength and interaction of these materials with titanium.

Methods

HA, FHA and FA were synthesised by a sol–gel method. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol–water based solution. Different amounts of ammonium fluoride (NH 4 F) were incorporated for the preparation of the FHA and FA sol–gels. Using a spin coating technique the sol–gels were coated onto commercially pure titanium disks and crystallised at various temperatures. Using scanning electron microscopy (SEM) and elemental analysis, the surface characteristics, coating thickness and interaction of the Ti substrate and coating were investigated. The bond strengths of the coating to the Ti were investigated using an Instron Universal Load Testing Machine. Statistical analysis was performed with a two-way analysis of variance and post hoc testing with a Bonferroni correction.

Results

(1) Coating speed inversely influenced the coating thickness. (2) Increasing fluoride ion substitution and heating temperature significantly increased bond strength and (3) increasing fluoride ion substitution increased the coating thickness.

Significance

FHA and FA synthesised using the sol–gel technique may offer a superior alternative to coating titanium implants with HA and plasma spraying. HA, FHA and FA materials synthesised by the sol–gel method may also have a use as bone grafting materials.

Introduction

Titanium (Ti) has gained much interest and success as a hard tissue implant due to its biocompatibility. The osseointegration of bone and Ti implant can be improved by surface treatment, such as sand blasting, acid etching, oxidation, and hydroxyapatite (HA) coatings . Among those, the HA coatings are widely used to enhance bone ingrowth due to their osteoconductivity and bioactivity, where bioactivity may be viewed as the enhanced and direct bonding of bone to the coating surface, i.e. osteoinduction. Due to the altered properties to the HA structure that can be achieved by fluoride substitution with the hydroxyl ions to produce fluor-hydroxyapatite (FHA) and fluorapatite (FA) these have been suggested as an alternative to HA coatings , for applications such as hip stems and external fixator pins . Currently, most HA coatings have been produced by a plasma-spraying method. However, the plasma-sprayed coating can result in phase and structural inhomogeneity, which can lead to differences in coating resorption from area to area and a reduction in coating-substrate interfacial strength . In this work, the sol–gel coating method was utilised. The sol–gel method has the benefits of phase and structural homogeneity due to low temperature processing. Moreover, it is simple, cost efficient, and beneficial for complex shaped material .

Previous studies have characterised and optimised the production of HA, FHA and FA by the sol–gels method . Having optimised the synthesis of phase pure apatites, it was the purpose of this study, to determine whether the apatites could be successfully coated onto titanium, assess the chemical interaction that these materials have with titanium, including assessing the bond strength that may be achievable with a view to development as coating for dental implants with improved osteconductivity, homogeneity and longevity.

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Nov 25, 2017 | Posted by in Dental Materials | Comments Off on Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol–gel method: Bonding to titanium and scanning electron microscopy
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