Electric Field Mediated Deposition of Bioactive Polypeptides on Neural Prosthetic Devices
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release can be governed by the diameters of the fibers in which the compound is suspended, and also by the porosity of the coating. Properties such as biofunctionality and biodegradability can be changed by processing as well as by materials synthesis. Genetic engineering can produce known combinations of biofunctionality in a given molecule to achieve the desired proportion of each property. Alternately, multilayer coatings of different polypeptides can be produced using electric fields. Three-dimensionally tailored films and coatings of protein polymers serve as scaffolds that stimulate and support cellular growth, with the possibility of programmed degradation once the implant site becomes stable. In the case of biocompatibilizing implanted devices, it can be highly advantageous not just to prevent catastrophic tissue response with a biologically inert coating, but to provide an active framework for biological interaction with the device. An intimate union between the coating and the surrounding tissue could help prevent unintended physical displacement of the device in a chronic implant situation. The emerging field of tissue engineering depends upon the fabrication of threedimensionally tailored structures. Organs are complex assemblies of tissues with specific, spatially-organized functionality. Tissue engineering is predicated on the ability to replicate this organization by providing a scaffolding for cell culture outside the body[ 1]. When the tissue has reached a sufficient level of maturity, it can be implanted in the body as a functional organ, slowly making the transition from a hybrid structure to complete tissue as more cells grow and the scaffold degrades in a controlled way. It is essential to be able to design self-supporting structures onto which target cells will reliably and specifically assemble. Protein Polymers Synthetic protein polymers are generated by recombinantly modified E. Coli. This technology enables the construction of polypeptides with precisely defined amino acid sequences. Sets of sequences make up modular subunits that exhibit technologically useful properties. A silklike amino acid sequence can provide structural stability while and a sequence from naturallyoccurring fibronectin can stimulate cellular adhesion. This combination is found in the primary material used in this study, SLPF (ProNectin® F) [2]. Additionally, functional modular units providing the flexibility of elastin or the cell-specific binding sites of proteins like laminin have been incorporated in this family of silk-like protein polymers. Much of the work in our group has focused on the microstructure of SLPF and SELP (silk and elastin containing polypeptides) [3]. It is evident from this work that the fibronectin binding sites are excluded from the crystalline silk domains, efficiently forming a functionalized surface. The hydrophobic nature of these proteins promotes a strong adhesion to glass and silicon substrates, and the structural stability of the silk backbone allows for processed protein films to be
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