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) shown in the figure, 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 combat this problem Blackrock Microsystems proposes a novel bi-layer encapsulation scheme that combines Plasma Assisted Atomic Layer Deposited (PA-ALD) alumina layer underneath the Parylene layer. This encapsulation scheme, novel to biomedical field, will retain all the advantages of Parylene while utilizing vastly superior dielecric properties of underlying ALD alumina layer to create a much longer lasting and more electrically stable biomedical implants. This bi-layer encapsulation scheme may be seamlessly incorporated into our existing fabrication process flow for our flagship product, the UEA. The bi-layer The UEA with integrated electronics encapsulation method 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. The project has 4 specific aims:
Specific Aim 1 : Optimize an ALD alumina/Parylene bi-layer encapsulation scheme and compare performance with Parylene-only encapsulation on test devices.
Specific Aim 2 : Develop etch methods to selectively expose active electrode sites on UEAs coated with optimized ALD alumina/Parylene bi-layer.
Specific Aim 3 : Evaluate charge injection/impedance characteristics of ALD alumina/Parylene bi-layer coated UEAs.
Specific Aim 4 : Comparison of in vivo performance of ALD alumina/Parylene bi-layer coated UEAs to Parylene-only coated UEAs. Our preliminary results with Parylene and alumina coated planar interdigitated electrode (IDE) test structures are very promising in support of the proposed work. We have shown that the bi-layer encapsulation yields more stable leakage current, and stable impedance (with <5% change) at 67 ?C for about 5 months (approximately equivalent to 40 months at 37 ?C). This superior performance of bi-layer encapsulation suggests its potential usefulness for chronic implants with complex surface geometries. At the end of the Phase I 'Lab to Marketplace' SBIR project, Blackrock expects to have developed protocols and standards to transform this research from its current early-stage lab setting into a commercial-grade manufacture process.
Neuroprosthetics systems require chronic implantation of neural interfaces 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. Th device has to be protected from the harsh body environment, which 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 with integrated wireless architecture but 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.
| Caldwell, Ryan; Mandal, Himadri; Sharma, Rohit et al. (2017) Analysis of Al2O3-parylene C bilayer coatings and impact of microelectrode topography on long term stability of implantable neural arrays. J Neural Eng 14:046011 |
