Generation and characterisation of gallium titanate surfaces through hydrothermal ion-exchange processes

Matthew D Wadge,Bryan W Stuart,Kathryn G Thomas,David M Grant

doi:10.1016/j.matdes.2018.05.060

Matthew D Wadge, Bryan W Stuart + Show 2 more

Open Access

https://doi.org/10.1016/j.matdes.2018.05.060

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Journal: Materials & Design	Publication Date: May 28, 2018
Citations: 20	License type: cc-by

Affiliation: University of Nottingham

Abstract

Infection negation and biofilm prevention are necessary developments needed for implant materials. Furthermore, an increase in publications regarding gallium (Ga) as an antimicrobial ion has resulted in bacterial-inhibitory surfaces incorporating gallium as opposed to silver (Ag). The authors present the production of novel gallium titanate surfaces through hydrothermal ion-exchange reactions. Commercially-pure Ti (S0: Cp-Ti) was initially suspended in NaOH solutions to obtain sodium titanate (S1: Na2TiO3) layers ca. 0.5–1 μm in depth (2.4 at.% Na). Subsequent suspension in Ga(NO3)3 (S2: Ga2(TiO3)3), and post-heat-treatment at 700 °C (S3: Ga2(TiO3)3-HT), generated gallium titanate layers (9.4 and 4.1 at.% Ga, respectively). For the first time, RHEED analysis of gallium titanate layers was conducted and demonstrated titanate formation. Degradation studies in DMEM showed S2: Ga2(TiO3)3 released more Ga compared to S3: Ga2(TiO3)3-HT (2.76 vs. 0.68 ppm) over 168 h. Furthermore, deposition of Ca/P in a Ca:P ratio of 1.71 and 1.34, on S2: Ga2(TiO3)3 and S3: Ga2(TiO3)3-HT, respectively, over 168 h was seen. However, the study failed to replicate the antimicrobial effect presented by Yamaguchi who utilised A. baumannii, compared to S. aureus used presently. The authors feel a full antimicrobial study is required to assess gallium titanate as a candidate antimicrobial surface.

Highlights

Study by Dulda et al demonstrated micrographs of GaO(OH) precipitates formed through alkali precipitation, which morphologically are similar to the flake-like precipitates on S3: Ga2(TiO3)3-HT [56] and correlates with the GaO(OH) peak noted in Fourier transform infrared spectroscopy (FTIR) (Fig. 3B), suggesting these are GaO(OH) flakes
Energy dispersive X-ray spectroscopy (EDX) analysis demonstrated no sodium was detectable on either gallium-treated samples, matching the lack of a Na 1s peak in X-ray photoelectron spectroscopy (XPS), indicating gallium ions readily ion-exchange with sodium in the titanate structure, supporting the postulated ionexchangeability
Significant morphological changes were demonstrated at high-resolution on titanium surfaces upon hydrothermal treatment in NaOH, ion-exchange in Ga(NO3)3, and subsequent heat-treatment

Summary

Introduction

The only FDA approved process for improving implant surfaces utilises high-temperature (droplet temperatures N1500 K [5]) plasma spray methods to deposit coatings of osteoconductive hydroxyapatite (HA) [6]; mimicking the main mineral component, and chemical and crystal structure, of cortical bone. These coatings, are ideal for improving metallic implant biocompatibility and enhancing osseointegration [7]. Plasma-sprayed HA layers have been shown to spall due to their brittle nature [13], and weak mechanical adhesion (55–62 MPa; just higher than the FDA's minimum requirement of 50.8 MPa) [14,15]. Further methods for providing a stable HA layer have been proposed, such as sputtering, but often have issues related to the crystal orientation, amorphous structure requiring subsequent treatments, or the relatively high manufacturing costs [20]

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