The application of titanium (Ti) based biomedical materials which are widely used at present, such as commercially pure titanium (CP-Ti) and Ti-6Al-4V, are limited by the mismatch of Young's modulus between the implant and the bones, the high costs of products, and the difficulty of producing complex shapes of materials by conventional methods. Niobium (Nb) is a non-toxic element with strong β stabilizing effect in Ti alloys, which makes Ti-Nb based alloys attractive for implant application. Metal injection molding (MIM) is a cost-efficient near-net shape process. Thus, it attracts growing interest for the processing of Ti and Ti alloys as biomaterial. In this investigation, metal injection molding was applied to the fabrication of a series of Ti-Nb binary alloys with niobium content ranging from 10wt% to 22wt%, and CP-Ti for comparison. Specimens were characterized by melt extraction, optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Titanium carbide formation was observed in all the as-sintered Ti-Nb binary alloys but not in the as-sintered CP-Ti. Selected area electron diffraction (SAED) patterns revealed that the carbides are Ti2C. It was found that with increasing niobium content from 0% to 22%, the porosity increased from about 1.6% to 5.8%, and the carbide area fraction increased from 0% to about 1.8% in the as-sintered samples. The effects of niobium content, porosity and titanium carbides on mechanical properties have been discussed. The as-sintered Ti-Nb specimens exhibited an excellent combination of high tensile strength and low Young's modulus, but relatively low ductility.

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Homing of cells to their target organs for tissue defect repair poses a significant challenge to biomaterials scientists and tissue engineers, due to the low efficiency of homing of effective cells to defect sites as well as the difficulties in coordinating cell migration, adhesion, spreading and differentiations. Recent advances in biomaterials have successfully improved the efficiency of homing of mesenchymal stem cells (MSCs) and cell homing-based tissue regeneration. In this review, the process of cell-homing based tissue regeneration was discussed from three different perspectives, including cell surface engineering, scaffold optimization and signaling molecules interactions. Cell surface modification by using polymeric materials offers a simple way to administrate cell migration. Besides, the ordered or anisotropic structures are proved to be more efficient for cell adhesion, spreading and infiltration than relatively random or isotropy structures. Moreover, the coordinated release of different growth factors (GFs), e.g. achieved via core-shell microspheres, can orchestrate the biological processes, including cell growth and differentiations, and significantly enhance the osteogenic differentiation of low population density of MSCs. These developments in biomaterials are not only important for fundamental understanding of materials-cell interactions, but also help understand cell homing-based tissue regeneration from the perspective of materials, which is crucial for the design and fabrication of a new generation of highly functional biomaterials for tissue regeneration.

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Metal injection moulding was applied to fabricate Ti–22Nb alloy as a low modulus material for biomedical applications. Tensile test specimens were injection moulded, followed by debinding and sintering. Sintering was at 1500°C for 4 h under vacuum (10–3 Pa). Selected as-sintered Ti–22Nb samples were hot isostatically pressed at 915°C/100 MPa for 2 h. The nature of the titanium carbide precipitates in the as-sintered Ti–22Nb alloy was investigated. Selected area electron diffraction patterns revealed that the carbides are Ti2C with a fcc structure. The calculation of the phase diagram showed a significant decrease of carbon solubility in Ti–22Nb compared with that in Ti from 500 to 1500 °C, contributing to the carbide precipitation in Ti–22Nb. Due to the carbide precipitation, the as-hipped Ti–22Nb alloy exhibited higher tensile strength but lower elongation than conventionally processed Ti–22Nb.

Owing to their relatively low Young's modulus, high strength, good resistance to corrosion and excellent biocompatibility, β-titanium (Ti) alloys have shown great potential for biomedical applications. In β-Ti alloys, carbon can exist in the form of titanium carbide (TiC x) as well as interstitial atoms. The TiC binary phase diagram predicts a minimum carbon solubility value of 0.08 wt.% in β-Ti, which has been used as the carbon limit for a variety of β-Ti alloys. However, noticeable grain boundary TiC x particles have been observed in β-Ti alloys at impurity levels of carbon well 2 below the predicted 0.08 wt.%. This review focuses its attention on the trace carbon (≤ 0.08 wt.%) in biomedical β-Ti alloys containing niobium (Nb) and molybdenum (Mo), and discusses the nature and precipitation mechanism of the TiC x particles in these alloys.

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