Brain Pacemakers for Neurotherapy Flexible Brain Implants for a Better Quality of Life with Parkinson's Disease

Together with European partners, Fraunhofer IZM worked on the development of highly integrated, flexible brain implants. The goal was to create a new, minimally invasive solution for treating neurological conditions such as Parkinson’s disease. Patients benefit from increased comfort and a less invasive surgical procedure.

Neurological diseases such as Parkinson’s have been steadily increasing over the past 25 years. Such a disease places a significant burden on both patients and their families. However, medicine is not powerless to help: therapeutic brain-computer interfaces have established themselves as a promising treatment approach. This involves implanting electrodes in the brain, which are stimulated by a pulse generator located in the upper body.

A brain-computer interface has proven to be an effective treatment for conditions such as obsessive-compulsive disorder and the tremors associated with Parkinson’s disease or multiple sclerosis. However, the implants required for this treatment place a significant burden on patients. Furthermore, current solutions must make do with just two electrodes, which limits the precision of the stimulation.

As an alternative, researchers from across Europe have developed an implant as part of the Minigraph project that combines the entire system into a single package.

Innovative Methods for the Implant

At its core is a custom-designed application-specific integrated circuit (ASIC) that enables bidirectional communication with nerve tissue. The connection is established by microelectrodes made of graphene. With a total of 256 receiving electrodes and 32 modulating electrodes, the resolution—that is, the precision of the stimulation—is significantly improved. In addition, the material allows for higher currents and can thus counteract the development of tolerance.

The implant eliminates the need for the long connection paths—previously required—from the electrodes in the brain to the pulse generator in the upper body, as the entire implant is manufactured on a single 200-mm (7.87-inch) wafer substrate. In developing this design, the Fraunhofer Institute for Reliability and Microintegration IZM was able to demonstrate several innovative technological approaches: To achieve this, the researchers created a two-layer rewiring structure with a line spacing of just 10 micrometers (0.0004 inches). The connections between the layers are even smaller and were created in 10-micrometer-thick biocompatible polyimide via laser ablation. To accommodate the ASIC and the capacitors, the researchers then fabricated contact pads made of nanoporous gold on the two-layer rewiring, which enables a thermal compression process at 100 degrees Celsius instead of the usual 300 degrees Celsius (572°F).

The key feature: The highly sensitive graphene electrodes are deposited only after the nanoporous gold has been produced at the project partner ICN2, using a split-manufacturing process, because an etching step required during the production of the nanoporous gold would otherwise damage the graphene electrodes. The electronics are protected by a barrier layer consisting of biocompatible parylene and an aluminum oxide structure.

The result is impressive: After thinning, the ASIC and the 17 capacitors are 70 micrometers (0.0028 inches)  thick, and the entire implant is only 100 micrometers (0.0039 inches) thick. This allows the entire implant to remain flexible and adapt to the shape of the brain.

In addition, researchers at Fraunhofer IZM, in collaboration with researchers at ICN2, were able to demonstrate for the first time that they can deposit and structure graphene on micrometer-thin gold. To insert the implant, the project partners also developed a minimally invasive, robot-assisted implantation procedure that is faster and less complicated than the two-stage surgery previously used.