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A micromachined silicon substrate sieve electrode was implanted within transected toadfish ( Opsanus tau) otolith nerves. High fidelity, single unit neural activity was recorded from seven alert and unrestrained fish 30 to 60 days after implantation. Fibrous coatings of genetically engineered bioactive protein polymers and nerve guide tubes increased the number of axons regenerating through the electrode pores when compared with controls. Sieve electrodes have potential as permanent interfaces to the nervous system and to bridge missing connections between severed or damaged nerves and muscles. Recorded impulses might also be amplified and used to control prosthetic devices.

A silklike protein with fibronectin functionality (SLPF) (ProNectin F, Protein Polymer Technologies, Inc.) is a genetically engineered protein polymer containing structural and biofunctional segments. The mechanical properties and deformation mechanisms of electrostatically deposited SLPF thin films were examined by scratch testing, tensile testing, and nanoindentation. Scanning electron microscopy and scanned probe microscopy revealed that the macroscopic properties were a sensitive function of microstructure. The SLPF films were relatively brittle in tension, with typical elongation-to-break values of 3%. Nanoindentation data were fit to a power law relationship.

We have developed processing schemes for depositing three-dimensionally tailored layers of protein polymers on a variety of solid substrates. One of our goals is to create stable, biocompatible coatings on silicon devices for implantation in the central nervous system. Our research has identified several candidate coatings whose morphologies lie in the biologically significant 0.1 to 100 micrometer length scale. Using electric field mediated deposition, we are able to process polypeptides into biologically-responsive films and coatings. Quantitative analysis of the structural evolution of the coating enables us to fine-tune its morphology by varying the field strength and geometry or solution concentration. The interaction of the coated substrates with neurons and glial cells are examined in vivo and in vitro. Data collected from light optical microscopy, atomic force microscopy, transmission electron microscopy, and scanning electron microscopy provide insight about the relationship between the microstructure of these coatings and their macroscopic properties.