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. Materials that can be produced include: fluoropolymers, which have excellent resistively and inertness to long-term implantation, and silicones, which have excellent flexibility, adhesion, and biocompatibility. The goal of this work is to combine these characteristics into a composite material that satisfies all of the requirements of chronic implantation in a neurological environment. In Phase I, the feasibility of combining silicones and fluoropolymers was demonstrated using two approaches: (1) a bi-layer comprising silicone as a base layer and fluoropolymer as a surface layer, and (2) a fluorinated silicone copolymer. Coatings were produced, tested for mechanical durability, stability, and resistively, and compared against Parylene-C, a commercially available vapor-deposited coating. Although both approaches performed comparably to Parylene-C in insulating resistance, the bi-layer showed better adhesion to a wide range of substrates and superior soak stability. Based on these results, and the excellent long-term stability exhibited by other iCVD silicone coatings (2+ years under soak without any loss in resistively), the bi-layer structure was selected for further development in Phase II. In Phase II, the range of compositions used in the bi-layer structure will be expanded. The process for producing silicone coatings will be scaled up to allow a multitude of complex, three-dimensional devices to be coated. More rigorous, long-term testing will be performed using real-world device components as substrates, and the performance of GVD's coatings will be compared against state-of-the-art commercial coatings. In addition to mechanical and electrical performance testing, compatibility to nerve cells and tissue will be systematically examined and animal implantation studies performed. Phase II investigations will also address how these new coating materials can be biologically modified to mitigate the brain tissue foreign-body response. 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 coating under this Phase II will enable that goal to be achieved. The success of this Phase II will allow GVD to offer to researchers & manufacturers a proven, effective tool for the insulation and encapsulation of neuroprosthetic devices. The 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. ? ? ?
| Achyuta, Anil Kumar H; Stephens, Kyle D; Lewis, Hilton G Pryce et al. (2010) Mitigation of reactive human cell adhesion on poly(dimethylsiloxane) by immobilized trypsin. Langmuir 26:4160-7 |
| Achyuta, Anil Kumar H; Polikov, Vadim S; White, Aleksandr J et al. (2010) Biocompatibility assessment of insulating silicone polymer coatings using an in vitro glial scar assay. Macromol Biosci 10:872-80 |
| Leach, Jennie B; Achyuta, Anil Kumar H; Murthy, Shashi K (2010) Bridging the Divide between Neuroprosthetic Design, Tissue Engineering and Neurobiology. Front Neuroeng 2:18 |
| Achyuta, Anil Kumar H; White, Aleksandr J; Pryce Lewis, Hilton G et al. (2009) Incorporation of Linear Spacer Molecules in Vapor Deposited Silicone Polymer Thin Films. Macromolecules 42:1970-1978 |
