Effects of Composition on Mechanical and Antibacterial Properties of Hydroxyapatite/Gray Titania Coating Fabricated by Suspension Plasma Spraying

TL;DR

This study demonstrates that suspension plasma spraying can produce hydroxyapatite/gray titania coatings with enhanced mechanical and antibacterial properties, suitable for biomedical applications, by transforming titanium oxide phases and improving surface characteristics.

Contribution

It introduces a suspension plasma spray method for creating homogeneous HAp/Titania coatings with improved properties, overcoming limitations of conventional plasma spray techniques.

Findings

SPS successfully deposits homogeneous, less porous HAp/Titania coatings.

Transformation of Ti2O3 into TiO2 with mixed Magneli phases enhances photocatalytic activity.

Coatings exhibit improved interfacial strength, hardness, and antibacterial properties under LED light.

Abstract

This study aims at revealing the effect of composition on mechanical and antibacterial properties of hydroxyapatite/gray Titania coating for biomedical applications. HAp is a bioceramic material used as a plasma-sprayed coating to promote osseointegra-tion of femoral stems. Biomaterial coatings are fabricated mostly using atmospheric plasma spray (APS). However, the conventional plasma spray process requires hydrox-yapatite powder with good flow, and to prepare such free-flowing powder, agglomer-ation, such as spray drying, fusing, and crushing is used. Therefore, it is impossible to spray nano-powder using conventional methods. Here, we designed a suspension-feeding system to feed nanoparticles using a liquid carrier. Suspension plasma spray (SPS) successfully deposited homogeneous HAp/Gray Titania coating with less poros-ity on the surface of titanium substrates. The microstructure of coatings with differ-ent compositions was then characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to identify the crystal structure. All results con-sistently demonstrated that SPS could transform Ti2 O3 into TiO2 with mixed Magneli phases, such as Ti4 O7 and Ti3 O5, which usually show photocatalytic activity. Interfacial strength, hardness, young modulus, and fracture toughness were also improved with a high concentration of TiO2. Antibacterial test for E.Coli under LED light re-vealed that SPSed HAp/Gray Titania coating could significantly enhance antibacterial properties. The possible underlying mechanism of enhanced antibacterial properties can be attributed to increased Magneli phases and better bacterial adhesion caused by hydrophilic properties due to submicron size particles. SPS can fabricate visible light-responsive antibacterial coating, which can be used for medical devices.