A novel Tantalum coating on porous SiC used for bone filling material

doi:10.1016/j.matlet.2016.05.065

Materials Letters

Volume 179, 15 September 2016, Pages 166-169

https://doi.org/10.1016/j.matlet.2016.05.065 Get rights and content

Highlights

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A novel tantalum coated porous SiC scaffolds was designed for bone grafts application.
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An impact and adherent Ta film was obtained by CVD.
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Good adhesion and spreading of MC3T3-E1 on the surface of Ta coating.

Abstract

The bioactive metallic tantalum coating was successfully deposited on the surface of porous SiC by means of chemical vapor deposition (CVD). The morphology and phase composition of tantalum coating were characterized by SEM, EDS and XRD. The cell adhesion test was employed with pre-osteoblast to evaluate the cytocompatibility of Ta coating. The results showed an impact and adherent Ta film was coated on the surface of SiC. The MC3T3-E1 cells showed good adhesion and spreading on the surface of Ta coating, which indicated excellent bioactivity and cytocompatibility. It was proved that the porous SiC with Ta coating could be a potential material for the application as bone substitutes.

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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Subsequently, we observed the differentiation of the pTa composite BMSCs in vitro and explored their mechanism of action to provide a theoretical basis for the clinical application of pTa combined with autologous BMSCs in the treatment of osteonecrosis, bone defects and other clinical applications [23,24]. Both pTi6Al4V and pTa were prepared autonomously by the Laboratory of Orthopedics of the Affiliated Zhongshan Hospital of Dalian University [25]. The dimensions were designed as follows: the solid column beam size was 600 μm, and the aperture was 500 μm.
As an ideal new graft material, porous tantalum (pTa) has excellent mechanical properties and corrosion resistance and has received increased attention in the biomedical field because of its excellent cytocompatibility and ability to induce bone formation. However, the molecular mechanism of its potential to promote osteogenesis remains unclear, and very few reports have been published on this topic.
In this study, we first produced porous Ti6Al4V (pTi6Al4V) and pTa with the same pore size by three-dimensional printing combined with chemical vapour deposition. The number of adhesions between pTa and pTi6Al4V and bone marrow mesenchymal stem cells (BMSCs) after 1 day of culture was detected by the live/dead cell staining method. The proliferation activity of the two groups was determined after culture for 1, 3, 5 and 7 days by the cell counting kit-8 method. In addition, the osteogenic activity, mRNA expression levels of osteogenic genes alkaline phosphatase (ALP), osterix (OSX), collagen-I (Col-I), osteonectin (OSN) and osteocalcin (OCN) and protein expression levels of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signalling pathway marker p-ERK of the two groups cultured for 7, 14 and 21 days were determined by the ALP activity assay, real-time quantitative polymerase chain reaction (Q-PCR) and Western blotting, respectively. Subsequently, the two groups were treated with the MAPK/ERK–specific inhibitor U0126, and then, the mRNA expression levels of osteogenic genes and protein expression levels of p-ERK in the cultures were determined by Q-PCR and Western blotting, respectively.
The live/dead cell staining and cell counting kit-8 assays showed that the adhesion and proliferation activities of BMSCs on pTa were significantly better than those on pTi6Al4V. In addition, the ALP activity assay and Q-PCR showed that pTa harboured osteogenic activity and that the osteogenic genes ALP, OSX, Col-I, OSN and OCN were highly expressed, and by Western blotting, the expression of p-ERK protein in the pTa group was also significantly higher than that in the pTi6Al4V group. Subsequently, using the MAPK/ERK–specific inhibitor U0126, Western blotting showed that the expression of p-ERK protein was significantly inhibited and that there was no difference between the two groups. Furthermore, Q-PCR showed that osteogenic gene expression and ALP expression levels were significantly increased in the pTa group, and there were no differences in the OSX, Col-I, OSN and OCN mRNA expression levels between the two groups.
Overall, our research found that compared with the widely used titanium alloy materials, our pTa can promote the adhesion and proliferation of BMSCs, and the molecular mechanism of pTa may occur via activation of the MAPK/ERK signalling pathway to regulate the high expression of OSX, Col I, OSN and OCN osteogenic genes and promote the osteogenic differentiation of BMSCs in vitro.
The translational potential of this article: Our self-developed pTa material produced by three-dimensional printing combined with the chemical vapour deposition method not only retains excellent biological activity and osteoinductive ability of the original tantalum metal but also saves considerably on material costs to achieve mass production of personalised orthopaedic implants with pTa as a stent and to accelerate the wide application of pTa implants in clinical practice, which have certain profound significance.

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¹: These authors contributed equally to this paper.

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A novel Tantalum coating on porous SiC used for bone filling material

Highlights

Abstract

Introduction

Section snippets

Fabrication of Ta coating

Characterization of the Ta coating on SiC substrate

Conclusion

Acknowledgement

J. Foot Ankle Surg.

Acta Biomater.

Surf. Coat. Technol.

Surf. Coat. Technol.

Mater. Sci. Eng. C

Bone substitutes: an update

Inj. Int. J. Care Inj.