Short communicationA novel electrochemical strategy for improving blood compatibility of titanium-based biomaterials
Introduction
For blood-contacting medical implants, such as heart valves, vascular stents and circulatory support devices, it is important to minimize the adsorption of platelets on the surface, which could lead to blood coagulation and thrombosis. Titanium (Ti) and Ti-based materials are known for their biocompatibility and have been widely used in blood-contacting medical devices. Blood coagulation and thrombosis are largely determined by physical and chemical characteristics of the foreign material surface [1]. Various surface modifications have been developed for improving the hemocompatibility of Ti and Ti-based materials. Inorganic coatings like carbon based coatings [2], [3], silicon carbide [4], titanium oxides [5] and titanium nitrides [6] have been widely investigated for blood compatibility. Drug-eluted coatings such as heparin, paclitaxel, and rapamycin also have been demonstrated to be able to decrease the risk of thrombosis [7], [8], [9], [10]. Some drug-eluted coatings have already been applied in clinical settings, but they are usually not durable, and do not fully satisfy clinical requirements.
The interactions between blood and artificial materials are very complicated. The wettability of the material surface is an important factor in the adhesion and activation of platelets. Superhydrophobic surfaces with a water contact angle (CA) of greater than 150° have attracted considerable interest due to their practical application in different domains [11]. Some methods have been developed to fabricate superhydrophobic surface on various metallic materials [12], [13], [14], [15]. This non-wettable characteristic has been used in biomedical applications such as blood vessel replacement and wound management [16]. Sun et al. proved that the blood compatibility could be largely improved by simply introducing special nanostructure to make the poly(carbonate urethane)s (PCUs) films superhydrophobic [17]. Khorasani and Mirzadeh indicated that the polydimethylsiloxane (PDMS) surface endowed with superhydrophilic or superhydrophobic property exhibited better blood compatibility compared with pure PDMS [18]. Both superhydrophobic and superhydrophilic materials are anticipated to possess good blood compatibility for biomedical applications. However, it is difficult to obtain superhydrophobic and superhydrophilic surface for titanium implants merely through altering the surface chemical composition.
In this letter, we applied a combination of electrochemical anodization and surface self-assembly technique to construct two kinds of biocompatible TiO2 nanotube layers with extreme wettability contrast (superhydrophilic/superhydrophobic). The blood compatibilities of the two extreme cases were examined and the mechanism of the different blood compatibilities was briefly discussed. It was demonstrated that the superhydrophobic TiO2 nanotube layers exhibited better performance in resisting the adhesion of platelets and the spreading of the platelets pseudopodium compared with that of the plain Ti substrates and the superhydrophilic TiO2 nanotube layers as well. These findings would be valuable for further understanding of hemocompatibility and development of blood compatible Ti-based biomaterials.
Section snippets
Sample preparation and electrochemical anodization
The substrate was Ti metal (2 mm thick, 99.5% purity). Prior to electrochemical anodization, the Ti sheets (10 mm × 10 mm) were mechanically ground by a series SiC papers from P200 to P1500. Then they were degreased in an ultrasonic bath in acetone, anhydrous ethanol and deionized (DI) water successively, followed by rinsing with DI water and drying in air.
The TiO2 nanotube film was prepared on the Ti sheet by the electrochemical anodization in 0.5 wt% HF electrolyte at 20 V for 20 min, using a
Results and discussion
Fig. 1a gives a typical SEM image of the mechanically polished Ti substrate before electrochemical anodization. The surface was relatively smooth, with features of polished ridges, grooves and pits at the micron scale. Fig. 1b shows the SEM micrograph of vertically orientated TiO2 nanotubes with inner diameter of approximately 80 nm grown on Ti substrate after anodization. The side view image (inset of Fig. 1b) indicates that the self-organized TiO2 nanotubes are opened at the top and closed at
Conclusions
A facile electrochemical surface construction and a self-assembly technique have been developed to fabricate superhydrophobic TiO2 nanotube layers with an extremely low adhesion for improving its blood compatibility and anti-coagulation property. It was found from the in vitro assays that the superhydrophobic TiO2 nanostructured surface possessed excellent blood compatibility, which is able to remarkably resist the adhesion and activation of platelets. Thus, it could be a promising alternative
Acknowledgments
This study is supported by the National Natural Science Foundation of China (20773100, 20620130427), the National Basic Research Program of China (2007CB935603) and the International Scientific and Technological Cooperation Projects of MOST (2007DFC40440).
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