 B.S., 1994, University of South Carolina Phone: 608-262-1086 Email: dlynn@engr.wisc.edu Position: Associate Professor Selected Publications
| Research Description
Research Interests: Research in my laboratory has focused broadly on (i) the design and synthesis of functional organic materials and (ii) the fabrication and physical characterization of macromolecular assemblies and nanoscale materials, with an particular focus on the development of materials and new methods that can be used to deliver biomacromolecules, such as DNA and proteins, to cells. Within this broad context, we seek to understand fundamentally how the structures of organic materials influence their behaviors, and, more specifically, how control over structure provides opportunities to design assemblies and nanostructured materials that permit active, passive, and reversible control over the assembly, disassembly, transport, and release of DNA and other agents in aqueous solution and at interfaces. Our current research is focused in three interrelated areas: Nanostructured Thin Films that Provide Control over the Release of DNA from Surfaces: Methods for the alternating, layer-by-layer adsorption of oppositely charged polymers on surfaces provide nanometer-scale control over the compositions and internal structures of multilayered polymer thin films (or 'polyelectrolyte multilayers'). These methods are entirely aqueous, and can thus be used to incorporate biologically active polyelectrolytes, such as proteins and DNA, often without loss of biological function. Provided that these assemblies can be fabricated in ways that also permit their controlled disruption, these methods present opportunities to design thin films and coatings that provide control over the release of proteins, DNA, and other agents from surfaces. We have designed, synthesized, and incorporated new polymers to explore the range of functionality that can be used to control the disassembly and disruption of polyelectrolyte multilayers in physiologically relevant environments. We have demonstrated that hydrolytically degradable cationic polymers can be used to fabricate nanostructured thin films that erode - and promote the controlled, surface-mediated release of DNA and other agents - by gradual hydrolysis in aqueous media. Small changes in structure influence the functional properties of these materials: systematic changes in polymer hydrophobicity, side chain structure, or charge density can be used to fabricate films that release one or more agents over periods ranging from several hours to several days, weeks, or months using this general approach. Objects coated with these materials promote localized delivery of DNA when placed in contact with cells in vitro and we have demonstrated recently, in collaboration with colleagues at the University of Wisconsin Medical School, that medical devices coated with these materials are capable of promoting localized transgene expression in vivo. Electrochemical Control of Cell Transfection Using Redox-Tunable Cationic Lipids: Cationic lipids have been investigated widely as agents for the delivery of DNA because they interact spontaneously with DNA through electrostatic interactions to form lipid/DNA assemblies (called 'lipoplexes') with sizes, charges, and other properties that promote the internalization and processing of DNA by cells. In collaboration with Professor Nicholas L. Abbott (UW-Madison), we have developed and demonstrated new approaches to active control over the self-assembly of cationic lipids and DNA (and the subsequent delivery of DNA to cells) using redox-active cationic lipids with charge states that can be tuned electrochemically. Our initial work has focused on cationic lipids that can be cycled reversibly between oxidized and reduced states by the chemical or electrochemical oxidation/reduction of ferrocene groups incorporated into the cationic lipid structure. We have demonstrated that changes in the oxidation state of the lipid result in large differences in (i) the physical properties of lipoplexes and also (ii) gene expression when lipoplexes are administered to cells: lipoplexes formed using reduced lipid lead to high levels of gene expression, whereas lipoplexes formed using oxidized lipid yield very low (background) levels of gene expression. These results provide the basis of a new approach that could be used to transform inactive lipoplexes to an active form 'on demand' by the application of externally applied electrochemical potentials. 'Charge-Shifting' Polymers that Promote Self-Assembly and Self-Disassembly with DNA: Cationic polymers also interact spontaneously with DNA to form macromolecular assemblies, and have thus also been investigated widely as non-viral agents for the delivery of DNA. Unfortunately, the same charge-based driving forces that can be used to promote the formation of these assemblies also introduce a fundamental and significant obstacle to their subsequent disassembly (and, thus, the release of DNA). The extent to which charge-based interactions between DNA and cationic materials can (or cannot) be controlled underlies the success (or failure) of many conventional approaches to the delivery of DNA. We have developed a new 'charge-shifting' approach to the design of polymers that can be used to disrupt or change the nature of electrostatic interactions between cationic polymers and DNA. We have designed 'charge-shifting' cationic polymers that undergo changes in charge density (e.g., from cationic to anionic) by the chemical hydrolysis of masked anionic functionality. These new polymers provide tunable control over assembly and disassembly with DNA, both in solution and at surfaces. For example, we have demonstrated that these 'charge-shifting' materials permit control over the self-disassembly of solution-based polymer/DNA nanoparticles, and that these polymers can promote the intracellular release of DNA and improve levels of cell transfection in vitro. These new materials also provide a new mechanism by which to promote the controlled disruption of layer-by-layer thin films. Our work in this area thus also connects closely with the goals and motivations of other aspects of our research described above.
Awards
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