Promising initial results seen with bone graft substitute using carbon nanotubes

Trials with a new porous biodegradable compound showed it satisfactorily regenerated bone during in vitro and in vivo experiments, according to a researcher at the Health Unit of Tecnalia at the University of Basque Country in Spain.

As part of her PhD thesis, Beatriz Olalde developed a porous foam material made of polylactic acid (PLA) and hydroxyapatite. Her goal was to produce a material that would act as a bone graft substitute that temporarily substituted for bone while inducing bone regeneration, according to an Elhuyar Fundazioa press release.

The biodegradable porous foam support that Olalde created and defended in her thesis represents a completely new approach to solving the problem of replacing damaged bone. Furthermore, her creation is capable of chemically and electrically interacting with bone cells or adjoining bone tissue to accelerate bone recovery, according to the press release.

Because PLA is biodegradable, Olalde added hydroxyapatite to the composite material to provide calcium that would facilitate its integration into the surrounding bone.

She then enhanced the compound’s resistance to stress by using carbon nanotubes, which also provided the electrical properties of the matrix. This permitted an electric field to be applied, which could direct the bone cells toward the porous support and accelerate the regeneration process.

In her trials, Olalde found the foam demonstrated optimum mechanical properties to sufficiently support bone, yet did not break up following implantation. She observed bone growth in the in vivo experiments at as early as 3 weeks post-implantation. By 16 weeks, the new bone showed mechanical, histomorphometric and densitometric properties similar to those of intact or healthy bone, according to the press release.

This new material seems to be a somewhat random combination of biomaterials that may work well together, but have little science behind them. PLA comes in many different forms and combinations of D and L isomers that can have dramatic effects on resorption and mechanical properties. Throwing in a form of calcium (hydroxyapatite)and a few nanotubes, while interesting, requires a lot more than a couple in vitro and in vivo studies with “satisfactory” results.

As for having mechanical, histomorphometric and densitometric properties similar to those of intact or healthy bone tissue, the term “similar” can be interpreted very broadly. How similar are they? Wasn’t the material’s mechanical properties similar to bone to begin with? How much did it change in vivo? Was it resorbed or completely intact? We know that allograft, as well as many different calcium phosphate products would give very “similar” results. This researcher has barely scratched the surface of proving equivalence, let alone, superiority of this new product to allograft bone or other currently available materials.

– Vikas V. Patel, MD
Department of Orthopedics, Colorado University
AOP Spine Center, Aurora, Colo.

Follow OrthoSuperSite.com on Twitter