Responsive polymers for dynamic modulation of bio-macromolecular transport properties (original) (raw)

Responsive self-assembling polymers are used in wide range of applications in the food, pharmaceutical, agricultural, electronic and environmental industries, as well as in the biomedical field. The proper design of such polymers is critical for the particular applications being considered. In this thesis, different matrices that can be modulated dynamically by the application of appropriate stimuli were designed and used for two applications: electrophoretic separation and gene transfection. Light represents an attractive trigger to change the properties of a polymer solution because it enables structural transitions to be induced under isothermal conditions without the addition of other chemical species to the solution, and is externally reversible and hence amenable to device design and automation. Amphiphilic copolymers with azobenzene moieties are of interest because the azobenzene can undergo reversible trans-cis photoisomerization leading to conformational isomers with significantly dissimilar dipole moments and hydrophobicities and thus different propensities to aggregate into nanoscale structures in aqueous media. Copolymers of 4methacryloyloxyazobenzene (MOAB) and N,N-dimethylacrylamide aggregate strongly in aqueous solutions with concentration-dependent aggregate size distributions and welldefined boundaries between the dilute and semi-dilute regimes. The copolymers are strongly surface active, an uncommon observation for random copolymers, and exhibit pronounced photoviscosity effects at higher concentrations. Trans-to-cis isomerization under UV light leads to partial dissociation of the azobenzene aggregates that form physical crosslinks, thereby significantly affecting the polymer solution rheology, with a consequent tenfold loss of viscoelasticity upon irradiation, especially in concentrated polymer solutions. Photo-responsive poly(N,N-dimethylacrylamide-co-methacryloyloxyazobenzene) (MOAB-DMA) and temperature-responsive Pluronic F127 (PF127) copolymers were blended to obtain mixed micellar systems that were responsive to both stimuli. The azobenzene groups of DMA-MOAB in the trans conformation self-associate and the interactions with PF127 are less pronounced when compared to those with cis conformation of the azobenzene groups. The cis-isomer of the MOAB-DMA copolymer self-associates less strongly than does the trans conformation, and thus the copolymer micelles dissociate upon UV irradiation. These polymeric unimers can form mixed micelles with the PF127 present. This causes the sol-gel transition temperature of the MOAB-DMA/PF127 blend to be 2-6 degrees lower upon UV irradiation than under dark conditions depending on the molar ratio of the two polymers. It has been found that I would like to express my gratitude to all those who have helped me to get to this stage. I am grateful to my advisors T. Alan Hatton and Kenneth A. Smith for giving me the opportunity to work in their group. Alan has helped me become a better researcher by letting me explore my ideas. I would also like to thank my thesis committee members, Prof. William Deen, Prof. Patrick Doyle and Prof. Daniel Wang for all of their contributions during my committee meetings. I am highly indebted to Dr. Lev Bromberg for his help with my research and for lending his time and effort for discussing my research problems even amidst his long lists of other commitments. I would also like to thank Hatton group members past and present for their help. In particular, I would like to thank Lino Gonzalez for imparting me some of his knowledge of optics and Comsol, and Sanjoy Sircar and Huan Zhang for timely discussions. I am also grateful to Harpreet, Saurabh and Abhinav for all their help and chats, which were a good break from research and how could I not mention: allowing me to gorge on their home-made food. I want to extend my thanks to my collaborators Prof.