Hydrogels are three-dimensional polymer networks. They have attracted considerable attention due to their ability to react to changes of their environment. This stimulus responsiveness is mostly associated with a swelling or deswelling of the material and can be elicited by changes in temperature, pH or photon flux. Stimuli induced phase transitions e.g. have been exploited for controlled drug release from nanosized (S. Nayak, L. A. Lyon, Angew. Chem. Int. Ed. 2005, 44, 7686.) and macroscopic networks.(N. A. Peppas, J. Z. Hilt, A. Khademhosseini, R. Langer, Adv. Mat. 2006, 18, 1345.) A more specific trigger to induce changes in the physicochemical properties of hydrogels is the recognition of biomolecules. Polymer networks containing a covalently incorporated antibody Fab fragment showed reversible volume changes upon incubation with the antigen fluorescein.(Z. R. Lu, P. Kopeckova, J. Kopecek, Macromolecular Bioscience 2003, 3, 296.) Another antibody containing hydrogel when applied as a membrane exhibited pulsatile permeation of a macromolecular model drug in response to stepwise changes in the antigen concentration.(T. Miyata, N. Asami, T. Uragami, Nature 1999, 399, 766.)
In
the context of this proposal we will employ DNA hydrogels that exhibit an even
higher informational content than protein containing networks. We will realize
DNA polymer networks from different building blocks, namely DNA side chain
polymers, DNA star polymers and amphiphilic DNA diblock copolymers.
Cross-linking of these entities will be achieved by hydrogen bonding and
hydrophobic interactions. Due to the reversibility of these interactions there
is the possibility of dissagregation of the networks. On the other hand one can
induce volume changes of the DNA hydrogels. Important to mention is that these
events can be triggered sequence specifically allowing programmable control of
gelation and mesh sizes and associated therewith controlled release of
entrapped molecules.
