Rigid, porous titanium foam   (Source: Fraunhofer IFAM)
Titanium foam is just as flexible and rigid as real human bone

Researchers at the Fraunhofer Institute for Manufacturing and Advanced Materials IFAM in Dresden have developed a new implant that has a structural configuration just like the inside of a human bone, but is made out of titanium foam

Dr.-Ing Peter Quadbeck of the Fraunhofer Institute for Manufacturing and Advanced Materials is lead developer of the "TiFoam" project and has created a titanium foam implant that is rigid and flexible like a real human bone. Most importantly, it allows ingrowth into surrounding bones. 

Other massive bone implants have not worked in the past because they contained characteristics that are different from the human skeleton, such as stiffness. Massive bone implants that are not flexible like a real human bone causes more stress to be put on the implant instead of the adjacent bone, which, as a result, could lead to the deterioration of that bone.

Bones that are exposed to lesser strains normally have lesser bone density. Stress on the bone "stimulates the growth of the matrix." Also, the rigidity of real bones allows blood vessels and bone cells to grow in the pores and channels this shape offers. So while these stiff implants can be good for defects in load-bearing bones, they do not promote ingrowth to surrounding bones because they are neither flexible nor shaped rigidly like real bones.

The secret behind the new titanium foam implants is a foam-like structure that resembles spongiosa inside human bones, and a powder metallurgy-based molding process that consists of open-cell polyurethane (PU) foams being saturated with a solution that contains a binding medium and a fine titanium powder. The powder adheres to the foams cellular structures, and the binding agents and the PU are vaporized. The end result is a "semblance of the foam structures, which is ultimately sintered."

"The mechanical properties of titanium foams made this way closely approach those of the human bone," said Quadbeck. "This applies foremost to the balance between extreme durability and minimal rigidity."

This careful balance allows the forces of weight and motion to sustain, the forces of stress to be transmitted, the formation of new bone cells and healing of the implant. Doctors may be able to use this new material to bond implants to patient's bones more efficiently and on a more stable basis.

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