September 2021

Self-Powered Implantable Device Stimulates Fast Bone Healing

Wang holds the FED he and his lab designed. When placed over a fracture, the device generates electricity from movement, accelerating bone healing. Photograph by Jason Daley.

The latest invention by Xudong Wang, PhD, a professor of materials science and engineering at the University of Wisconsin–Madison, makes electrostimulation a more convenient option than it currently is to speed up healing of broken bones. His thin, flexible device is self-powered, implantable, and bioresorbable, so once the bone is knitted back together, the device’s components dissolve within the body.

Bone is known to produce a tiny bit of electricity when under strain. This electricity stimulates factors that promote bone growth and healing, which is why electrostimulation is an effective therapy. While there are external stimulators that create an electric field to accelerate healing indirectly, the ideal solution is stimulating the bone directly. Putting the device inside the body has unique requirements—not the least of which is powering it, according to Wang.

The researchers’ initial tests on the new fracture electrostimulation device (FED) confirmed that small movements of the device created an electrical stimulation of about 4 volts, which it could sustain for over 6 weeks. When tested on rats, the animals implanted with the device completely recovered from a tibia fracture in about 6 weeks, much more quickly than the control group. The mineral density and flexural strength of the healed bones also reached the same level as healthy bones in the animals that received the electrostimulation. After treatment, the devices degraded and absorbed into the rats’ bodies with no complications and no need for surgical removal.

Wang said that it’s possible to fine-tune how long the stimulator will last within the body by tweaking the properties of the bioresorbable material coating the device. Eventually, he would like to scale up the FED so it will work in humans. However, when someone has a broken bone, they need to restrict their movement, so someone wearing a cast might not produce enough mechanical energy to power the triboelectric nanogenerator, he said. “We may need the device to respond to other types of internal mechanical sources, like blood pressure changes,” said Wang, who’s already looking to the FED’s future.

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