New research into the electricity that bones generate has the potential to improve the prosthetics industry. Scientists from the Catalan Institute of Nanoscience and Nanotechnology (ICN2), a research centre located at the Autonomous University of Barcelona, have discovered that bone is flexoelectric. They used this to calculate the precise magnitude of a repairing bone’s electric field. Flexoelectricity is the mechanoelectrical production of electricity by bending a material. With this information, new materials that reproduce or amplify this flexoelectric effect could be used to guide tissue regeneration, leading to more successful assimilations of implants.
Bones in all animals, including humans, generate electricity under pressure to stimulate self-repair and remodelling. This was first discovered in the late 1950s, was initially attributed to piezoelectricity, the electrical charge that accumulates in certain solid materials, such as bone, DNA and various proteins. However, the researchers at ICN2, led by Professor Gustau Catalan, found that bone also had the same flexoelectric properties as ceramic materials. They then began to question whether the bone flexoelectricity fulfilled any physiological role.
One of the lead researchers on the project, PhD student Fabián Vásquez-Sancho, explained: “We found in other scientific reports a relation between the bone remodelling and micro-cracks that was not yet fully understood. Specifically, it was already known that the repair of bones is triggered by the chemicals released by cells that die in the neighbourhood of a crack, but it was not known what causes the apoptosis (programmed death) of those neighbouring cells. In parallel, we learnt, also from existing studies, the size of the electric fields required to cause cell apoptosis.”
“The next step was thus to calculate whether the flexoelectric fields generated by cracks are comparable to those that are known to be able to induce apoptosis, and the answer was yes. When multiplying our experimentally measured flexoelectric coefficients by the strain gradients generated near a crack, the resulting flexoelectric field exceeds the critical value of 5kV/m in a radius of about 50 microns around the crack tip. Our final conclusion is thus that flexoelectricity could be the trigger that ‘electro-stimulates’ the cells to initiate the process of bone remodelling.”
This new knowledge of bone remodelling has potentially life-changing implications for the prosthetics industry and the development of biomimetic self-healing materials. For example, not every patient who requires a prosthetic implant can receive one due to the intensity of surgery and physiotherapy it entails, while the loss of a limb can also have a negative impact on a patient’s mental health. Harnessing the flexoelectricity of bone for medical purposes could make the process of receiving prosthetics easier and thus help to alleviate these issues.
The team have already started a ‘proof of concept’ project to demonstrate the feasibility of flexoelectric prosthetic implants. By exploiting flexoelectricity to improve the mineralisation of implants, they can be more firmly embedded into the bone, reducing the risk of loosening or the need for replacement, as tends to happen with current metallic implants.
The researchers are still several years away from creating a prosthetic device with materials already medically approved for use in prosthetics. However, once the concept is proved in a laboratory setting, the scientists hope to pass the baton of their findings to medical professionals who could begin trialling in vivo experiments with patients.