Biological engineering, from a tissue-engineering prospective, can be broadly defined as a design process that seeks to capture critical features of native tissues into a template scaffold that is intended to direct the regeneration and/or reconstruction of a damaged, dysfunctional or missing organ [12]. Given this definition, we have adopted the philosophy that tissue engineering scaffolds should mimic the dimensional characteristics, tertiary structure and specific aspects of the biological activity present in the native extracellular matrix [13]. Conventional fabrication techniques typically produce biomaterials, and diagnostic tools, that are composed of structural elements that are several orders of magnitude larger than the size scale that is observed in biological systems.
The structural network of the native mammalian extracellular matrix is composed of a complex network of fibrillar protein polymers that exist on a nano-scale. Electrospinning has made it possible to fabricate a broad spectrum of materials into individual structural entities that approach this dimensional size. This new class of biomaterials exhibit unique biological [1,11], compositional [3,23] and structural properties [8,9]. The process of electrospinning exhibits a constellation of characteristics that can be exploited to regulate these fundamental variables. For example, for natural polymers like collagen [1,11] and fibrinogen [2], the electrospinning process appears to reconstitute the topological features, and cross-sectional diameters, observed in the native fibrils of these proteins. These features facilitate migration and appear to reduce the antigenic potential of these polymers [11]. The physics and chemistry of electrospinning make it possible to produce hybrid materials composed of native proteins and/or synthetic and natural protein polymers that might not otherwise co-polymerize [3,23,24]. Finally, a variety of process specific [8,9] and post-processing manipulations [25] can be implemented to regulate the biological and mechanical properties of electrospun tissue-engineering scaffolds.
In this study we adopted a biological engineering approach to ask how the specific unique advantages of the electrospinning process might be exploited to produce a new class of research/diagnostic tools. Our experiments demonstrated that electrospinning can be used to (re)engineer the physical properties and performance characteristics of nitrocellulose and charged nylon in Western blot applications. The electrospinning process imparted gross physical features that provided an extensive surface area for protein binding and a highly interconnected pore space that made these materials readily permeable to staining and wash solutions. There may be added, and entirely un-expected, advantages provided by the nano-structure of these electrospun materials. A protein bound to a fibril of electrospun nitrocellulose or electrospun nylon may adopt a very different conformation than a protein that has been immobilized to the surface of the parent starting materials.
Similar to scaffolds designed for tissue engineering, a variety of electrospinning and post-processing techniques might be applied to our system to further modulate and customize membrane performance. For example, membranes composed of polymer fibers of varying diameters and/or varying compositions can be prepared by simultaneously electrospinning from separate source solutions. In this type of construct the small diameter fibers might be used to more effectively capture small molecular weight materials, domains with larger diameter fibers can be used to capture large molecular weight materials. In more exotic applications, for example in the analysis of proteases, it may be possible to incorporate a small concentration of a specific protein, such as collagen, into an electrospun blotting platform. A sample of interest could be separated by SDS gel electrophoresis and then transferred onto the hybrid platform. Theoretically, the bound proteases would attack and degrade the incorporated protein substrate. Upon staining, much like a zymogram, the sites where active proteases were bound would appear as a clear lytic band. As an added advantage, this type of electrospun membrane could be subsequently processed for Western blot to verify enzyme identity and/or to measure enzyme content. In the clinical arena, the flexibility afforded by the electrospinning process could be exploited to produce diagnostic or research grade materials targeted to broad classes of patients, or even to specific individuals.
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