Biodegradable Ceramics Consisting of Hydroxyapatite for Orthopaedic Implants

Thomas Monsees,Alina Vladescu,Iulian Pana,Robin Booysen,Cosmin Cotrut,Mariana Braic,Adrian Kiss,Radwan Abdulgader,Funda Ak Azem,Isil Birlik

doi:10.3390/coatings7110184

Abstract

This study aims to analyze hydroxyapatite (HAP) coatings enriched with Mg and Ti prepared by a magnetron sputtering technique on Ti6Al4V substrate. For preparation of the coatings, three magnetron targets (HAP, MgO and TiO2) were simultaneously co-worked. The concentration of Mg added was varied by modifying the power applied to the MgO target. In all coatings, the Ti concentration was maintained constant by keeping the same cathode power fed during the whole deposition. The influence of different Mg dopant contents on the formation of phase, microstructure and morphology of the obtained Ti-doped HAP coatings were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Moreover, the effects of Mg addition upon corrosion, mechanical and biological properties were also investigated. Mg- and Ti-doped HAP coating obtained at low radio-frequency (RF) power fed to the MgO target provided material with high corrosion resistance compared to other coatings and bare alloy. A slight decrease in hardness of the coatings was found after the Mg addition, from 8.8 to 5.7 GPa. Also, the values of elastic modulus were decreased from 87 to 53 GPa, this being an advantage for biomedical applications. The coatings with low Mg concentration proved to have good deformation to yielding and higher plastic properties. Biological test results showed that the novel surfaces exhibited excellent properties for the adhesion and growth of bone cells. Moreover, early adherent vital cell numbers were significantly higher on both coatings compared to Ti6Al4V, suggesting that Mg ions may accelerate initial osteoblast adhesion and proliferation.

Highlights

Calcium phosphate (CaP) coatings promote bone growth on the interface between a bone and an implant [1]
This study aims to analyze the influence of Mg incorporation in a Ti-doped HAP coating system in terms of structural, mechanical, corrosion and biological properties
Surface roughness of the coatings increases with Mg incorporation into a Ti-doped HAP structure

Summary

Introduction

Calcium phosphate (CaP) coatings promote bone growth on the interface between a bone and an implant [1]. The use of substituted HAP that incorporates different ions has been studied in order to control osteoblastic behavior of HAP coatings such as silicon (SiO4 4− ), magnesium (Mg2+ ), carbonate (CO3 2− ), zinc (Zn2+ ), fluoride, (F− ), potassium (K− ), cerium (Ce4+ /Ce3+ ) or strontium (Sr2+ ). These ions are substituted into the HAP lattice to mimic the complex chemistry of human bone [6]. The reduced amount of Mg in bone unfavorably disturbs the stages of skeleton metabolism, promoting bone growth, by decreasing the activity of osteoblasts and weakening bone strength [10]

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Conclusion