A novel Tantalum coating on porous SiC used for bone filling material
Introduction
Implantation of bone autograft or allograft is a known strategy for the treatment of large bone defects. However, limited supply, donor site morbidity and the risk of infection are main shortcomings in their clinical use [1]. Tissue engineering is trying to solve this problem by development of bone substitutes using cells and bio-scaffolds. To date, several bone substitutes have been approved by FDA for clinical applications using a wide range of scaffold materials [2]. Whereas, most of them have relatively poor mechanical strength and cannot meet the requirements for many applications [3]. Hence, there is a need to fabricate new scaffolds with improved mechanical properties and biocompatibility.
In the recent years some investigations which exploit the biomorphic ceramics as new scaffold for bone implants were studied. Among them porous silicon carbide (SiC) have attracted increasing attention due to their excellent physical and chemical properties, such as their strength, resistance to oxidation and corrosion [4]. Wu et al. [5] fabricated biocompatible SiC foam by polymerpyrolysis combined with liquid infiltration-reaction process. SiC foams possessed a continuously connected open cell structure with satisfied mechanical performance. The apparent densities of SiC foams can be controlled between about 0.4 and 1.3 g/cm3, with corresponding compressive strengths ranging from about 13–60 MPa and flexural strengths from about 8–30 MPa [6]. Thus it is proved that the SiC can be used in repairing complex shape and long weight-loading bone defects.
Moreover, to further improve the osseointegration performance of implants, different approaches leading to the formation of a bond across the interface between the implant and the tissue via chemical reactions have been attempted. For this purpose, various kinds of bioactive materials have been developed and successfully applied as coatings to artificial bones, such as hydroxyapatite, glass ceramics and glasses [7].
Due to its good biocompatibility and chemical stability, tantalum (Ta) attracts much attention for biomedical applications [8]. Tantalum has been used in clinical practices since before 1940 and has been found in a wide range of diagnostic and implant applications such as radiographic marker, vascular clips, endovascular stent, cranioplasty plates, and orthopedic and dental implants [9]. However, the high density and cost consuming of tantalum limit its applications in a form of bulk material compared with Titanium implants. Thus, the combination of the excellent mechanical properties and low density of the biomorphic SiC scaffold, used as a base material for implants, with the osteoconducting properties of the bioactive Ta coating opens new possibilities for the development of alternative bone grafts.
In this work, tantalum film was deposited onto SiC substrates using chemical vapor deposition (CVD). CVD is one of the most important methods of film formation. In this process, chemicals in the vapor phase can react at the substrate surface where a solid production forms [10]. The Ta coating was characterized using scanning electron microscopy (SEM), and X-ray diffraction (XRD). The in vitro biocompatibility of Ta-coated porous SiC was evaluated using mesenchymal stem cells (MSCs).
Section snippets
Fabrication of Ta coating
The SiC substrate was supplied by Institute of Metal Research, which was prepared by polymerpyrolysis combined with liquid infiltration-reaction process. Tantalum deposition on porous SiC was fabricated using a low temperature CVD system, as shown in Fig. 1. The substrate was first ultrasonic rinsed with mixed acid solution of HF and HNO3 and dried with nitrogen gas. Powered tantalum pentachloride of 99.95% purity, preheated to 223 °C in a stainless sublimator, is used as the tantalum precursor.
Characterization of the Ta coating on SiC substrate
The surface morphologies of native SiC and Ta-coated substrate were visualized by SEM (as shown in Fig. 2). From Fig. 2(b) it can be clearly seen that a homogeneous coating was covered on the surface of porous SiC scaffold. Native SiC substrate displayed rough surface morphology, whereas after depositing coating displayed relatively flat morphology with dark gray metallic luster of Ta. The coating is well crystallized and the grain size was about 1 µm. As can be seen from the cross section of
Conclusion
The porous SiC scaffolds have been successfully coated with a uniform and adherent bioactive Ta film by CVD method. Ta coating showed excellent cell adhesion on the surface, which indicated its potential for orthopedic application. It is then possible to conclude that porous SiC scaffolds with Ta coating appear as a quite interesting material for bone substitutions, combining the characteristics of both materials into a new product with enhanced mechanical and biochemical properties.
Acknowledgement
This work was financially supported by National Science and Technology Support Program of China (No. 2012BAI17B02).
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These authors contributed equally to this paper.