Date Published: July 8, 2016
Publisher: Public Library of Science
Author(s): Hong Wang, Bingjing Zhao, Changkui Liu, Chao Wang, Xinying Tan, Min Hu, Jie Zheng.
Electron beam melting (EBM) and selective laser melting (SLM) are two advanced rapid prototyping manufacturing technologies capable of fabricating complex structures and geometric shapes from metallic materials using computer tomography (CT) and Computer-aided Design (CAD) data. Compared to traditional technologies used for metallic products, EBM and SLM alter the mechanical, physical and chemical properties, which are closely related to the biocompatibility of metallic products. In this study, we evaluate and compare the biocompatibility, including cytocompatibility, haemocompatibility, skin irritation and skin sensitivity of Ti6Al4V fabricated by EBM and SLM. The results were analysed using one-way ANOVA and Tukey’s multiple comparison test. Both the EBM and SLM Ti6Al4V exhibited good cytobiocompatibility. The haemolytic ratios of the SLM and EBM were 2.24% and 2.46%, respectively, which demonstrated good haemocompatibility. The EBM and SLM Ti6Al4V samples showed no dermal irritation when exposed to rabbits. In a delayed hypersensitivity test, no skin allergic reaction from the EBM or the SLM Ti6Al4V was observed in guinea pigs. Based on these results, Ti6Al4V fabricated by EBM and SLM were good cytobiocompatible, haemocompatible, non-irritant and non-sensitizing materials. Although the data for cell adhesion, proliferation, ALP activity and the haemolytic ratio was higher for the SLM group, there were no significant differences between the different manufacturing methods.
Rapid prototyping (RP) is a series of advanced manufacturing technologies and is being implemented in industrial and biomedical areas [1–5]. Electron beam melting (EBM) and selective laser melting (SLM) are two advanced types of RP and direct metal melting layer manufacturing technologies [6–9]. EBM and SLM enable the direct fabrication of complex structures and geometric shapes using computer-aid-design (CAD) without any tooling, which saves time and is highly effective. The fabrication processes for EBM and SLM are to selectively melt raw powder materials with either an electron beam or a focused laser based on the data in the part’s associated CAD file. Due to the different fabrication processes, the microstructure, mechanical and chemical properties of EBM and SLM metal products are different from those fabricated from wrought, cast or powder metallurgy materials [10–15]. Furthermore, different fabrication parameters, including power size, scan speed and building speed between the EBM and SLM systems result in different microstructures as well. Thijs et al and Sallica-Leva et al demonstrated that a SLM Ti6Al4V sample exhibited a very fine aciclar martensite grain structure [10–11]. Murr et al demonstrated that an EBM Ti6Al4V sample had a uniform, acicular α-phase microstructure (with β-phase), which was similar to a wrought product . Koike et al described EBM Ti6Al4V that consisted of prominent acicular α-plates and SLM Ti6Al4V that consisted of a mixture of α-phase and α’ martensite . In addition, the microstructure is related to the mechanical and chemical properties of metal. Rafi et al showed that the tensile strength and fatigue properties in SLM Ti6Al4V samples is higher than for EBM Ti6Al4V samples . They attributed the difference in mechanical properties to the differences in the microstructures. Koike et al discussed how SLM Ti6Al4V exhibited better corrosion resistance than EBM Ti6Al4V. This result was from the acicular α-plates in the α-phase dominating in the EBM specimen to a greater extent than the α’ martensite in the SLM specimen . Due to the high efficiency, lack of tooling required, complex geometric structures capable of being fabricated from CT or CAD data, EBM and SLM are two superior metal manufacturing methods for medical applications. Good biocompatibility is the basic requirement for any clinical application of a medical material. Metallic medical implants remain in long-term contact with bodily fluids and tissues, which may lead corrosion and the release of alloying elements into the body. The release of alloying elements causing adverse effects has been investigated in [16–18]. Accordingly, the biocompatibility of SLM and EBM Ti6Al4V must be investigated prior to clinical applications. Warnke et al and Kawase et al summarized that SLM Ti6Al4V products had good biocompatibility and were suitable for medical applications [19–20]. Studies from Peppo et al and Harbe et al demonstrated that an EBM titanium alloy supports cell attachment, growth and differentiation [21–22]. Nevertheless, there have been few investigations on the comparison of the biocompatibility between EBM and SLM products. In this study, we assessed and compared the in vitro and in vivo biocompatibility of Ti6Al4V fabricated by EBM and SLM. Commercial medical Ti6Al4V was employed as a control.
Metallic materials, especially titanium and its alloys, are extensively used in bone substitution, dentistry, orthotics, cranio-maxillofacial surgery and replacement arthroplasty due to their light weight, excellent mechanic properties, corrosion resistance and good biocompatibility [26–31]. Compared to traditional fabrication methods of metallic materials, EBM and SLM are two advanced direct metal fabrication techniques, which are optimal choices for complex structured implants. In addition, porous metallic scaffolds fabricated by EBM and SLM have completely interconnected and possessed the modified pore size, pore shape and proper mechanical strength suitable for bone tissue engineering [32–33].
In summary, the results of the cytocompatibility, blood biocompatibility, skin irritation and skin sensitivity tests indicated that the Ti6Al4V samples fabricated by EBM and SLM have good biocompatibility both in vitro and in vivo. Although the data associated with cell viability, osteogenic ability and the haemolytic ratio was higher for the SLM group, there was no significant difference between the results for the two groups. The variance may be related to different microstructure, physical and chemical properties of the Ti6Al4V fabricated by EBM and SLM. Relevant examinations of these factors are addressed in further study. Additionally, more in vivo and long-term studies are needed to evaluate and compare the biocompatibility of Ti6Al4V implants fabricated using EBM and SLM. The superior fabrication method for metallic materials should be determined to provide an actual requirement for biomedical applications.