Medical Device Daily National Editor
Mohammad Reza Abidian, a post-doctoral researcher in the Department of Biomedical Engineering at the University of Michigan (UM, Ann Arbor), says that coating technology for microelectrode brain implants has a considerable way to go – from degrading as early as two months after implant, as they often do, to working effectively for at least two years and, hopefully, beyond.
The reasons for current short-term efficacy of these devices are multiple, he told Medical Device Daily, and he worked with other researchers to develop multiple solutions, the results awarded with a recent cover story of the Feb. 24 issue of the journal Advanced Functional Materials; the article: "Multifunctional Nanobiomaterials for Neural Interfaces."
"Current technology doesn't allow [long-term effectiveness] in most cases because of how the tissues of the brain respond to the implants," Abidian said. "The goal is to increase their efficiency and their lifespans."
Abidian and his collaborators believe the new coating will improve brain device treatments for deafness, paralysis, blindness, epilepsy and Parkinson's disease.
He told MDD that the key challenges in this device sector include, on one hand, the extremely delicate work they must do and the brain's natural immune response to foreign materials
The electrical patterns in the brain create considerable "noise" and thereby degrade effectiveness. And what the devices are designed to do is "a really, really small-feature-size recording," he said, and that "a huge impedance increases the noise. As impedance increases, the noise increases."
To counteract this, the researchers developed a special electrically-conductive nanoscale polymer called PEDOT, a material reducing electrical resistance and noise.
Daryl Kipke, PhD, is a professor in the Department of Biomedical Engineering and the director of the Center for Neural Communication Technology, which assisted in testing the electrodes treated with the new coating. He said, "Penetrating microelectrodes provide a means to record from individual neurons, and in doing so, there is the potential to record extremely precise information about a movement or an intended movement. The open question in our field is what is the trade-off: How much invasiveness can be tolerated in exchange for more precision?"
Abidian said that the PEDOT material developed enables the electrodes to operate by reducing or working around the electrical resistance, communicating more clearly with individual neurons.
Recent research has shown that PEDOT coatings enhance electrochemical signals in association with analyte oxidation, compared to no coating support. And Abidian said use of the coating produced a "three order of magnitude" reduction in impedance
Abidian's team then addressed the problem of immune resistance with the two other coating components," a natural, gel-like material called alginate hydrogel, and biodegradable nanofibers loaded with a controlled-release anti-inflammatory drug.
He said that the PEDOT material allowed electrical conduction by passing through it "like a tornado." At the same time the hydrogel served as armor against the immune response when "other cells try to digest the electrodes."
The alginate hydrogel, he said, which is partially derived from algae, serve to make the electrodes mechanical properties look more like actual brain tissue, resulting in the reduction of immune resistance and less tissue damage.
To bolster this protection, the next idea was to reduce another immunization effect, the attempt by the cells in the brain to build encapsulation around foreign materials, thus inhibiting the effect of the electrodes.
"The problem," he said, "is if you use systemic administration of drugs, you get huge side effects. The best-case scenario is a controlled drug release system, delivered as a function of time, but very, very slowly."
So to do this, the researchers added anti-inflammatory medications incorporated into biodegradable nanofibers, the nanofibers working with the alginate hydrogel to release the drugs in a controlled, sustained fashion as the nanofibers themselves break down.
The coatings are seen as potentially helping to promote the two types of activities used in the current and future generation of neural implant microelectrodes: the stimulation of neurons with electrical impulses to override the brain's own signals, or by recording what working neurons are transmitting to non-working parts of the brain and reroute that signal. On-scalp and brain-surface electrodes are giving way to brain-penetrating microelectrodes that can communicate with individual neurons, offering hope for more precise control of signals.
Abidian also noted the development of new applications for these devices, which are likely to require coating materials working over even longer periods of time — implanted microelectrodes that enable paralyzed persons simply to use their thoughts to control a computer mouse or move a wheelchair.
Abidian told MDD that he hopes that the continuing research needed to further develop and refine the new coating – in more animal trials, and then on to human trials — will be pushed faster and further if he is able to obtain a professorship at UM and set up his own lab.
Additionally, David Martin, a professor of Materials Science and Engineering; Biomedical Engineering and Macromolecular Science and Engineering, has founded Biotectix (Ann Arbor), as a UM spin-off. And he is actively working to commercialize the coatings related to those discussed in this paper.
This research is supported by the National Institutes of Health, the Army Research Office Multi-disciplinary University Research Initiative and College of Engineering Translational Research funding.
Michigan Engineering reports being home to 11 academic departments and a National Science Foundation Engineering Research Center. The college plays a leading role in the Michigan Memorial Phoenix Energy Institute and hosts the Lurie Nanofabrication Facility.