New research from the University of Freiburg (Germany) has demonstrated that adding a coating of the polymer PEDOT onto a polyimide neural implant can delay side effects that stem from the body’s reaction to the device and allows for more effective drug delivery, according to a report on the school’s website.
Microscope image of a polyimide neural probe with 4 PEDOT/Dex coated electrode sites shown in blue (a). Probe insertion is performed according to the process shown in 'b' with an optical fibre as guiding tool. The final placement of the electrodes can be seen in 'c'. The connection of the active probe to the recording/stimulation equipment is achieved via a connector placed on the head of the animal (d). (Uniuversity of Freiburg)
Over time, the body rejects bi-directional electrodes, which measure and stimulate simultaneously, and forces the implant’s functionality to be limited to only a few weeks of use. Building off previous work that demonstrated the advantages of using polyimides (rather than silicon), the researchers added a coating of PEDOT that could absorb the anti-inflammatory compound dexamethasone and, when a negative voltage was applied, release it.
This breakthrough could allow for lower dosages and to limit the effects of the drug to specific areas, which in turn limits negative side effects.
The article explained, “Even after 12 weeks it is still able to deliver strong signals. Now that such implants are no longer required to be replaced as often, they are able to open the doors for better diagnoses while making life easier for the chronically ill – such as Parkinson's patients that need to be treated with brain stimulation methods.”
The researchers argued that they were on the brink of a tipping point in new neural interfaces and microprobes.
The research was recently published in Biomaterials. The abstract read:
“Stable interconnection to neurons in vivo over long time-periods is critical for the success of future advanced neuroelectronic applications. The inevitable foreign body reaction towards implanted materials challenges the stability and an active intervention strategy would be desirable to treat inflammation locally.
“Here, we investigate whether controlled release of the anti-inflammatory drug Dexamethasone from flexible neural microelectrodes in the rat hippocampus has an impact on probe-tissue integration over 12 weeks of implantation. The drug was stored in a conducting polymer coating (PEDOT/Dex), selectively deposited on the electrode sites of neural probes, and released on weekly basis by applying a cyclic voltammetry signal in three electrode configuration in fully awake animals.
“Dex-functionalized probes provided stable recordings and impedance characteristics over the entire chronic study. Histological evaluation after 12 weeks of implantation revealed an overall low degree of inflammation around all flexible probes whereas electrodes exposed to active drug release protocols did have neurons closer to the electrode sites compared to controls.
“The combination of flexible probe technology with anti-inflammatory coatings accordingly offers a promising approach for enabling long-term stable neural interfaces.”