Material scientists at Friedrich Schiller University Jena and the University of Würzburg in Germany have developed a bone replacement based on calcium phosphate cement and reinforced with carbon fibers that increase damage tolerance and ensure that cracks in the material repair themselves.
Calcium phosphate cement already is widely used as a bone substitute in medicine. It stimulates bone formation and increases the ingrowth of blood vessels. Also, it can be introduced into the body in a minimally invasive procedure, where its malleability allows it to bind closely to the bone structure.
“Due to its high degree of brittleness, however, cracks form in the material when it is subjected to excessive load. These cracks can quickly widen, destabilize the implant, and ultimately destroy it, similar to concrete on buildings,” said professor Frank A. Müller of the University of Jena.
“For this reason, calcium phosphate cement has so far mainly been used on bones that do not play a load-bearing role in the skeleton‚ for example, in the mouth and jaw area,” said Müller.
Cracks in the new calcium phosphate cement, though, do not develop into catastrophic damage. Instead, the material itself seals them thanks to the carbon fibers that have been added to the material.
“Firstly, these fibers significantly increase the damage tolerance of the cement because they bridge cracks as they form and thus prevent them from opening further,” said Müller.
“Secondly, we have chemically activated the surface of the fibers. This means that as soon as the exposed fibers encounter bodily fluid, which collects in the openings created by the cracks, a mineralization process is initiated. The resulting apatite, a fundamental building block of bone tissue, then closes the crack again,” said Müller.
The researchers simulated this process by deliberately damaging the calcium phosphate cement and healing it in simulated bodily fluid. The intrinsic self-healing ability and the greater load-bearing capacity associated with fiber reinforcement could considerably expand the areas in which bone implants made of the cement could be used, possibly including load-bearing areas of the skeleton in the future.
The study, “Self-Healing Capacity of Fiber-Reinforced Calcium Phosphate Cements,” was published by Scientific Reports.
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