For centuries, inflammatory/foreign body reactions have plagued the attempts of clinicians to use metals for tissue and bone reconstructions. Since corrosion contributes to the rejection of metal by the body, an extremely bioinert metal—tantalum— has been successfully used in medicine. The outstanding biocompatibility and flexibility of tantalum established the basis for a growing cadre of clinical applications. One important application which benefited from the introduction of powder (particle) metallurgy is use of tantalum as bone implants. Porous materials have re-shaped the landscape of bone implants, as they allow for bone ingrowth and biological fixation, and eliminate implant loosening and related treatment failures. The unique bone-mimicking properties of porous tantalum enabled the use of tantalum as a material for bulk implants, and not only for coatings, as is the case with other porous metals. Moreover, porous tantalum also facilitates the ingrowth of soft tissue, including the formation of blood vessels that were found to assemble on the surface and within the structure of the porous tantalum. Also, since tantalum is strongly radiopaque due its high atomic number, this property is widely employed for marking in orthopedics and in endovascular medical devices. Another important development was the production of nanoparticles based on tantalum. These particles have been shown to be superior to iodinated contrast agents for blood pool imaging applications due to their longer circulation time. Their properties are similar to gold nanoparticles, but are far more cost-effective, and thus, well-positioned to replace gold in regenerative medicine for labeling and tracking of cell grafts through x-ray-based imaging. However, the amount of tantalum nanoparticles that can be taken up by stem cells is not enough to make individual cells visible in x-ray images. Thus, alternative strategies are needed, such as hydrogel or nanofiber scaffolds, which can be loaded with higher concentrations of nanoparticles, to increase the precision of cell deposition and allow tracking under x-ray guidance.
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