Injectable material could fix broken bones

Back in the '80s, scientists created so-called calcium phosphate cements (CMCs), which have been increasingly recognised for their potential as bone substitutes. That’s because they display an array of desirable properties, such as being injectable and compatible with our bodies.

They’re also intrinsically porous materials, which is ideal in this situation because this allows minerals to flow into, and waste to flow out of, the implant site, facilitating speedy bone regeneration. But the problem scientists have faced is that these holes aren’t big enough to permit bone cells to penetrate deep into the area, or to allow the development of new blood vessels into the healing bone.

An ideal CMC would therefore be littered with a mix of both little and large holes, thus not only encouraging new bone formation but also reinforcing the spongy, or cancellous bone already present. But this hasn’t been easy. Whatever material is used to make the macropores has to be non-toxic for suitability in humans, and also not compromise the material’s mechanical properties. In addition, if the cement ends up overly holey, it could quickly disintegrate upon prolonged exposure to bodily fluids.

But scientists may have come up with a solution that allows all of these boxes to remain ticked: turning the cement into a foam. The chosen material to achieve this feat was a hydrogel called Si-HPMC, a biocompatible polymer that previous work had demonstrated could help the CMC resist cracking. By putting these two materials into separate syringes and then rapidly pushing the plunger to mix them, the researchers were able to introduce just the right amount of air so that a foamy concoction resulted.

Importantly, the procedure did not reduce the CMC's mechanical properties or injectability, and examination revealed the desired presence of both micro and macropores. To test it out, the material was injected into the bones of rabbits that the researchers had introduced defects into under anesthesia. Encouragingly, the researchers report in Acta Biomaterialia, they later observed evidence of new bone formation around the implantation site.

While further investigations are necessary, these preliminary findings suggest we could have a promising material in the pipeline. And the researchers envision that its usefulness may not end with healing broken bones, it could potentially help treat certain bone diseases.

“We think this could be a good biomaterial, perhaps with active molecules, to act against osteoporosis locally,” said lead researcher Pierre Weiss from the University of Nantes. “We need to determine the proof of concept in animal models.”