Processing and characterization of protein polymer thin films for surface modification of neural prosthetic devices

The objective of this research has been to develop methods for modifying the surfaces of neural prosthetic devices to enhance biocompatibility. Also central to this work was the characterization of the processes used to modify the surfaces, the resulting macroscopic and microscopic structure, and the relevant physical properties of the new surface. The application required a coating that could attract and adhere cells, mediate the stiffness mismatch between the device and tissue, and facilitate signal transport from the device to tissue. The materials chosen for use as surface modifiers were genetically engineered polypeptides that combine biofunctional sequences with structural segments, creating a processable bioadhesive agent. An electric field mediated deposition process was used to create thin coatings on the devices from these protein polymers. Varying the process parameters was found to exert controllable changes on the morphology, and porous thin films with a range of structures were fabricated. This deposition process was combined with lithographic techniques to generate high-fidelity patterned surfaces. It was anticipated that the surface structure of these films could augment their biochemical composition and facilitate cell adhesion. A Fourier Transform-based method of explicitly quantifying the surface topography was employed to evaluate the effects of process parameters on topography. The mechanical properties of the coatings were examined to determine a suitable morphology for joining the mechanically dissimilar device and tissue. Fibrous coatings composed of randomly oriented filaments exhibited a stiffness gradient while under compression. The films were compliant near the tissue and stiffer near the device. The biological performance of these films was assayed and the films were seen to be potent cellular adhesives. The coatings were also found to be capable of delivering biologically-relevant molecules in vitro.