Professor Michael Cima and his colleagues are now designing brain implants that can not only deliver electrical stimulation but also record brain activity or deliver drugs to very targeted locations. (Credit: Christine Daniloff/MIT)

Many diseases, including Parkinson’s disease, can be treated with electrical stimulation from an electrode implanted in the brain. Researchers have now demonstrated that making these electrodes much smaller can essentially eliminate scarring, potentially allowing the devices to remain in the brain for much longer.

The researchers measured the effects of both reducing the size of the implants and coating them with a soft polyethylene glycol (PEG) hydrogel. The coating was designed to have an elasticity similar to that of the brain. They were able to control the thickness of the coating, and they devised a way to apply the hydrogel and then dry it, so that it becomes a hard, thin film. After the electrode is inserted, the film soaks up water and becomes soft again.

The researchers tested both coated and uncoated glass fibers with varying diameters and found that there is a tradeoff between size and softness. Tests in mice suggested that a 30-µm, uncoated fiber is the optimal design for implantable devices in the brain. The question now is whether fibers that are only 30 µm in diameter can be adapted for electrical stimulation, drug delivery, and recording electrical activity in the brain.

They had some initial success developing such devices, which could be used for treating Parkinson’s disease or other neurological disorders. The devices could also be used to remove fluid from the brain or to measure brain activity that might indicate when an epileptic seizure is about to occur.