Silicone Coatings for Biostable Chronic Neural Prostheses

DESCRIPTION (provided by applicant): The miniaturization of neuroprosthetic technology has led to an urgent need for insulating coatings that retain their biocompatibility and stability over long periods. Initiated Chemical Vapor Deposition (iCVD) is an attractive alternative to applying polymers using solvent-based techniques such as dip/spray and curing. iCVD has the benefits of thinness, conformality (conforms very well to complex shapes) and high purity. Recent preliminary experiments at MIT (where GVD's technology was invented) have demonstrated that a pure silicone coating possessing many of the material properties required for insulation of neuroprosthetics can be deposited from the vapor phase using the iCVD process. Silicones offer many advantages over other coating materials, including exceptional resistance to a variety of chemical environments, inert under soak, and both an extremely high resistivity and a low dielectric constant. Silicones also offer the additional advantage of excellent adhesion to a variety of substrates - a critical requirement for neuroprosthetic components which consist of multiple materials and interfaces. The goal of this work is to optimize the processing conditions for this new silicone coating and develop a material that satisfies all of the requirements of chronic implantation in a neurological environment. In the Phase I work, GVD plans to address several challenges of the current coating process, including improving yield of coatings free of defects, decreasing processing temperatures that can damage sensitive neural devices, and increasing the rate of coating deposition for commercial feasibility. These goals will be achieved by optimizing the process chemistry to enable reproducible coating at more benign process conditions. In addition to these tasks, in vitro biocompatibility testing will be performed including USP Class VI testing and targeted cytotoxicity testing using PC12 neuronal cells. In Phase I, coatings will be produced and tested on flat substrates approximating neural devices and interdigitated electrodes (IDEs) to measure insulation properties. In Phase II, the work would be expanded to optimizing the coating for neural devices for testing by researchers in the field and in vivo biocompatibility testing. The ultimate goal of this work is to achieve single step encapsulation of three-dimensional neural probe arrays and of neural prosthetic assemblies. The development of a stable, durable, biocompatible insulating silicone coating under this Phase I will enable that goal to be achieved. The success of this Phase I will allow GVD to offer to researchers & manufacturers of neural prostheses a new option for a safe and robust biopassivation coating for the insulation and encapsulation of neuroprosthetic devices. The silicone coating developed under this work will provide greater flexibility in the design of devices, the choice of materials used, and the minimum dimensions which can be achieved in neuroprosthetic devices. Therapeutically, the coating will perform better when implanted and provide safe and effective protection of devices in chronic applications. The long-term impact will be to de-bottleneck the development of devices and accelerate their proliferation as treatments for neurological disorders.