ABSTRACT
Electrophoretic transport, or, more generally, electric-field-induced molecular motion, in uncharged hydrophilic materials with nanometer-scale pore structure is important in a number of processes, including biochemical separation and purification methods, electric-fieldenhanced drug delivery for biomedical engineering applications, and some biological phenomena. For example, electrophoresis in polymer hydrogels has been extensively used and developed for the separation and purification of biological macromolecules. A wide range of materials, from fibrous membranes to chemically and physically cross-linked gels and polymer solutions, has been utilized for electrophoretic separations. Recent interest has also focused on electrophoresis and chromatography in silicon and other inorganic surfaces (with and without polymeric supports) with etched channels of nanometer-to-micrometer dimension. Many electrophoretic processes have been developed that use these media under various electric field conditions, from constant applied voltages or currents to single or multidimensional pulsed electric fields. In addition, separation methods such as capillary electrophoresis, electrochromatography, and field flow fractionation may utilize hydrophilic polymeric media to increase the resolution of macromolecular separations in situations where the applied electric field is coupled to bulk solution-phase hydrodynamic flow via electro-osmotic flow or pressure-driven flow. Electric fields have also been used to enhance the ultrafiltration of proteins by altering the structure of the protein gel layer formed on the ultrafiltration membrane surface. Other examples where applied electric fields affect macromolecular transport in media consisting of polymeric materials include transport through biological tissue (e.g., biopolymers of proteins or polysaccharides) under the influence of constant or pulsed electric fields. This is of much current interest for applications in the development of transdermal drug delivery processes via iontophoresis and electroporation, for cancer treatment, for wound healing, and for understanding the general effects of electric fields on biological cells, membranes, and tissues.
