A range of neurological diseases are now being researched or treated using fully implantable electronic systems to either record or modulate brain activity in humans. These implants are currently being protected using polymer coatings that envelop the implant and help keep body fluids away from the sensitive electronics. Brain implants with complex three-dimensional geometries, like the Utah Electrode Array (UEA) provide a challenge for current encapsulation techniques. Parylene has been the gold standard for encapsulation of neural and biomedical implants in general due to its well-suited combination of biocompatibility, electrical properties and chemical inertness. However recording capabilities of long-term neural implants (>6 months) encapsulated with Parylene show signs of degradation. To address this problem, we propose to develop and evaluate performance and biocompatibility/safety of a new Silicon Carbide (SiC) based encapsulation designed to extend the long term stability and implantable lifetime for a high density Utah Slant Electrode Array (HD-USEA) in line with lifetime expectations for conventional cochlea implant electrodes. The HD-USEA is used as penetrating auditory nerve electrode in a new type of intracranial auditory prosthesis that targets the auditory nerve en route to the brainstem in order to substantially improve hearing performance over the current standard of care, the cochlear implant (CI) (NIH 1UG3NS107688-01). SiC has been studied in the past as encapsulation and electrode material due to its outstanding inherent material properties. This encapsulation layer, novel to biomedical field, will retain all the advantages of Parylene while utilizing vastly superior dielectric properties of silicon carbide layer to create a much longer lasting and more electrically stable biomedical implants. This layer encapsulation scheme may be seamlessly incorporated into our existing fabrication process flow for our flagship product, the UEA. This encapsulation will work on different surfaces (metal, semiconductor, polymer, ceramic) and on devices with integrated wireless components making it ideal for coating any complex medical device intended for long term implant. Our preliminary results with silicon carbide coated UEA are very promising in support of the proposed work. We have shown that silicon carbide yields more stable leakage current, and stable impedance (with <5% change). This superior performance of suggests its potential usefulness for chronic implants with complex surface geometries.
Neuroprosthetic systems require chronic implantation of neural interfaces which are able to perform for years or decades to reduce surgical risks from follow-up surgeries and generate levels of efficacy that justifies the risks associated with the implants. The device has to be protected from the harsh body environment to allows it to perform its intended use. Therefore, encapsulation of implantable device is critical to its functionality, stability, and longevity. This project addresses one of the key failure modes of current biomedical devices. We are developing a novel encapsulation scheme specifically for neural interfaces that can be extended to cover other biomedical implants. Our encapsulation scheme will be transformed to manufacturing scale and applied to commercially available neural interfaces from Blackrock Microsystems. This technology has great potential to outperform the existing Parylene encapsulation methods.
