A new type of brain implant may have implications for both brain research and future treatments of neurological diseases such as epilepsy.
Researchers from DTU, the University of Copenhagen, University College London, and other institutions have developed a long, needle-thin brain electrode with channels—a so-called microfluidic Axialtrode (mAxialtrode), named for its ability to distribute functional interfaces along the length of the implant, enabling both neural signal recording and precisely targeted medication delivery across different brain regions.
The research results have been published in the renowned journal Advanced Science.
The technology has primarily been developed for basic research into the brain. It can help researchers better understand how signals move across brain layers, for example in epilepsy, memory, or decision-making. In the longer term, the researchers point out that the mAxialtrode may be important for treatment—for example, in targeted drug delivery combined with electrical or light-based stimulation of specific areas of the brain.
Postdoc Kunyang Sui, who led the development of the mAxialtrode concept together with Associate Professor Christos Markos, emphasizes that it has made it possible to combine several functions in a single implant which makes brain research less invasive and more precise.
"Most current brain implants are based on hard materials such as silicon, which can irritate the brain and trigger inflammatory reactions in the tissue. The new implant differs in that it is made of soft, plastic-like optical fibers and has a specially angled tip that makes it smaller and reduces the damage caused when it is placed in the brain," says Kunyang Sui.
He emphasizes that extensive testing, further development, and approvals are still needed before the technology can be used in clinical practice.
Today, brain researchers often use conventional flat-end optical fibers. These are thin glass or plastic fibers that can conduct light deep into the brain, for example for so-called optogenetics, where nerve cells are activated with light. The disadvantage is that this type of fiber only affects the brain in one place: at the very tip.
The outermost end is called the distal tip—in other words, the "nose" of the fiber. All light emission and all contact with the brain tissue takes place here. This means that researchers can only stimulate or measure activity in one layer of the brain at a time, even though many important brain functions involve interaction between several layers and deeper areas.
How the technology is built
The needle-thin mAxialtrode is manufactured using a process in which a large polymer rod is heated and drawn out into a very thin fiber—the process can be compared to making sugar thread, only much more precisely. In the middle runs a core that conducts light. Around it are eight microscopic channels that can carry fluid and also accommodate very thin metal wires for electrical measurements.
The fiber is less than half a millimeter thick and is so flexible that it moves with the brain instead of cutting through the tissue. The difference in stiffness is important because hard implants often trigger inflammatory reactions in the brain over time.
Proven technology
The researchers have not only tested the technology in the laboratory, but also "in vivo"—that is, in mice. Here, the brain electrode was implanted in the brain and connected to light sources, measuring equipment, and small pumps for fluid supply.
The experiments showed that the researchers could stimulate nerve cells with blue and red light, measure electrical activity simultaneously from both superficial and deeper brain layers, such as the cerebral cortex and hippocampus, and inject different substances at different depths, up to almost three millimeters apart. All examinations and stimulations could be performed with a single, lightweight fiber that the animals could carry without any obvious signs of discomfort.
The in vivo experiments and neurophysiological validation were carried out in close collaboration with Associate Professor Rune W. Berg from the University of Copenhagen and Associate Professor Rob C. Wykes from University College London, who contributed expertise in neural circuit analysis and epilepsy-relevant models.
The researchers behind the brain electrode are in the process of patenting the underlying technology and clarifying the possibilities for testing the electrode on patients in a clinical department.