Surface properties of silver doped titanium oxide films

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Abstract

Silver doped titanium oxide coatings for biomedical application were prepared by ion beam assisted deposition in an oxygen atmosphere. X-Ray photoelectron spectroscopy (XPS) was used to examine the chemical states and composition. Critical surface tension, dispersive and polar components of the surface energy were investigated by contact angle analysis. The influence of experimental conditions on the chemical states, composition and surface energy were investigated. The chemical state of silver was not affected by the process parameters and silver existed always in metallic state. XPS analysis confirmed the presence of TiO, Ti2O3 and TiO2, and the concentrations of the different oxidation states were influenced by the deposition rate of Ti and Ag. The oxygen flow rate had only a minor influence. On the other hand, dispersive and polar components of the surface energy were significantly affected by the oxygen atmosphere. The results also showed that samples with a higher concentration of silver exhibited a somewhat larger critical surface tension.

Introduction

Titanium and its alloys have been used for many years in the dental, orthopedic and cardiovascular area because of their combination of mechanical stability and good biocompatibility [1]. It is believed that the good biocompatibility is associated with the oxide layer formed on the surface of titanium and its alloys [2]. This suggests a potential for improving the biocompatibility by preparing titanium oxide coatings. In vitro and in vivo experiments demonstrated that titanium oxide coatings exhibit good blood compatibility [3], [4]. In vivo investigation showed that the amount of thrombus formation at a titanium oxide surface was much less than that of LTI-Carbon (low temperature pyrolytic carbon), which is widely used to fabricate artificial heart valves. There was almost no platelet aggregation found on the titanium oxide films, no damage to red blood cells, and no fibrin adhesion at the surface of the titanium oxide films [4].

Infections are another serious problem when biomaterials are implanted into the human body. They are usually caused by adherence and colonization of bacteria on biomaterials, and make patients develop serious complications, sometimes with lethal consequences. An effective treatment to reduce bacterial infection is the synthesis of a thin silver coating on biomaterial by ion beam assisted deposition [5], [6], [7], [8]. To achieve bactericidal properties and blood compatibility at the same time, silver doped titanium oxide coatings were developed. Our results showed that silver doped titanium oxide coatings exhibited good bactericidal properties [9].

The blood compatibility is conditioned by the interface formed between biomaterial and tissue. The composition and stabilization of the interface are mainly determined by the surface properties of the implant device such as elemental composition and surface energy [10], [11]. It is well known that a protein layer is adsorbed on the surface of the implant device as soon as it comes in contact with blood. If the protein layer contains a large amount of fibrinogen, the implant shows bad blood compatibility [12], [13]. Since the formation of the protein layer on the surface of the implant largely depends on the surface energy [9], [14], [15], the surface energy is a very important parameter for the function of biomedical materials. The chemical composition also influences the blood compatibility of the implant device. For example, it has been shown that the existence of the Ti2+ and Ti3+ oxidation states could improve the blood compatibility of titanium oxide films [3].

The aim of this paper is to investigate the surface properties of silver doped titanium oxide films prepared by ion beam assisted deposition. The chemical state and composition of the films were examined by X-ray photoelectron spectroscopy (XPS). The surface energy was measured by the contact angle method. The influence of film processing and composition on the results are discussed.

Section snippets

Experimental details

Titanium cuts were used as substrates. All substrates were wet-polished with 180–4000 grit SiC paper. Then they were polished down to 1-μm diamond paste followed by a 0.1-μm alumna suspension. Afterwards, the substrates were cleaned ultrasonically with isopropanol.

Silver doped titanium oxide coatings were prepared in an ion beam assisted deposition (IBAD) facility equipped with a 2- and 6-kW electron beam evaporator, in which silver and titanium evaporated, respectively, and bombarded

Results and discussion

XPS scans from the samples confirmed the content of silver, titanium, oxygen and carbon. No other contaminations were detected, except the above mentioned elements. Fig. 1 shows the typical carbon 1s high-resolution spectrum obtained from the as-deposited surface of silver doped titanium oxide films. It includes two components, one component at 284.6 eV was attributed to the presence of hydrocarbons (C–C and C–H), and the other component of C1s at approximately 286.3 eV was attributed to C–O

Conclusions

Silver doped titanium oxide coatings were synthesized on polished titanium substrates by argon ion beam assisted deposition, in which titanium and silver were deposited simultaneously by electron beam evaporation in an oxygen atmosphere. The surface composition and properties of the coatings were investigated by X-ray photoelectron spectroscopy and contact angle analysis. The silver existed always in the metallic state and the titanium analysis confirmed the presence of TiO, Ti2O3 and TiO2.

Acknowledgements

One of the authors (Dr F. Zhang) is financially supported by the Alexander von Humblodt Foundation. This work is also supported partially by the National Key Fundamental Research Program of China (973). The authors are grateful to Ms K. Heister and Dr Y.J. Yang for their help with the XPS measurements.

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