Plasma-Induced Crystallization of TiO₂ Nanotubes.

Metka Benčina,Matjaz Valant,Rok Zaplotnik,Miran Mozetič,Aleš Iglič,Ita Junkar

doi:10.3390/ma12040626

Abstract

Facile crystallization of titanium oxide (TiO2) nanotubes (NTs), synthesized by electrochemical anodization, with low pressure non-thermal oxygen plasma is reported. The influence of plasma processing conditions on TiO2 NTs crystal structure and morphology was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the first time we report the transition of amorphous TiO2 NTs to anatase and rutile crystal structures upon treatment with highly reactive oxygen plasma. This crystallization process has a strong advantage over the conventional heat treatments as it enables rapid crystallization of the surface. Thus the crystalline structure of NTs is obtained in a few seconds of treatment and it does not disrupt the NTs’ morphology. Such a crystallization approach is especially suitable for medical applications in which stable crystallized nanotubular morphology is desired. The last part of the study thus deals with in vitro biological response of whole blood to the TiO2 NTs. The results indicate that application of such surfaces for blood connecting devices is prospective, as practically no platelet adhesion or activation on crystallized TiO2 NTs surfaces was observed.

Highlights

IntroductionImproved biological response to the TiO2 NTs is, among others, the result of increased surface roughness and larger surface area
Self-aligned TiO2 nanotubes synthesized by electrochemical anodization of Ti foil are highly promising materials for biomedical applications due to their advanced biocompatibility in comparison to commonly used plain metal surfaces, and as such can be employed as orthopaedic and dental implants, vascular stents, antibacterial devices or surfaces and smart drug-delivery platforms [1,2,3,4,5,6,7,8].Improved biological response to the TiO2 NTs is, among others, the result of increased surface roughness and larger surface area
The TiO2 NTs were subjected either to annealing or highly reactive oxygen plasma treatment at different input powers and at different treatment times and the influence of such treatments was further studied in terms of altered surface morphology and crystallization. It has been shown in our previous work [25] and recently in Ref. [28] that TiO2 NTs were deformed after exposure to elevated temperatures and that NTs’ stability depended on diameter

Summary

Introduction

Improved biological response to the TiO2 NTs is, among others, the result of increased surface roughness and larger surface area. The tunable morphology of NTs that can be controlled by altering the anodization parameters such as voltage and time, allows for selective response of biological material. Proteins, platelets and cell adhesion, cell morphology, proliferation and differentiation are highly affected by the TiO2 NTs diameter [9]. This is especially important in applications, in which the adhesion of certain cell types is preferred, as in the case of vascular stents. As-anodized amorphous TiO2 NTs are, often subjected to crystallization process in order to enhance their bio-performance. It has been shown that annealed TiO2 NTs layers with anatase crystal structure have a much better corrosion resistance and bioactivity than amorphous NTs; they tend to induce more, and faster, hydroxyapatite deposition, which is crucial for successful bone bonding

Methods

Results

Conclusion