Porous Metal Implants

What is it about?

Porous and functionally graded materials have seen extensive applications in modern biomedical devices – allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although easy to manufacture and lightweight, porous polymers do not inherently exhibit the necessary mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing issues of porous metals has taken place in recent years. Research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility – with the host bone – has been followed up with extensive research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

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Photo by Bogdan condr on Unsplash

Photo by Bogdan condr on Unsplash

Why is it important?

Challenges may still arise with each technique, but porous implants have apparent challenges that need to be resolved. Porous structures display lower mechanical strength, which is disadvantageous for load-bearing applications. The fatigue life of porous structures is significantly reduced due to stress concentration sites at the neck region of each pore. The increased surface area of porous structures tends to increase corrosion rates. Moreover, as mentioned before, surface porosity affects implant anchoring by influencing bone ingrowth. Porous metal structures' corrosion and wear properties depend on the structure's porosity, hardness, and resistance to plastic deformation. It is necessary to understand a porous structure's physical, mechanical, and biological properties based on its porosity, microstructure, and composition, some of which vary drastically depending on the fabrication process. Therefore, in this review article, different fabrication processes for manufacturing porous metal structures have been discussed; microstructural and compositional influences of these processes have been elaborated on. Additionally, an effort has been made to compare porous implant structures' physical, mechanical, and biological properties based on their fabrication procedures.

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