At Rutgers University, in collaboration with Lucent Technology, we have embarked on the design of a new class of biomaterials from DMA crosslinked hydrogels that promises to have a wide rage of applications from drug delivery to prosthetics. Hybridization chemistry and strand displacement mechanisms based on branch migration allow these materials to be reversibly assembled and disassembled. Choice of base sequence allows for the design of gels that are degraded by particular restriction endonucleases or by particular messenger RNA strands. Altering the composition of the polymer, the length of the DNA strands, or the density of the crosslinks allows these materials to exhibit a wide range of mechanical properties. These gels are synthetic materials that exhibit tensegrity (prestress) and, thus, represent a novel class of biomimatic materials that may shed light on the mechanical basis of cell shape stability. Based on the success in our initial 3 years of research, here we propose to measure some of the more basic mechanical properties of polyacrylamide DNA-crosslinked gels. We will determine the elastic moduli and yield strengths, as a function of composition. In addition, we will map out the degree to which the compliance of such gels can be made modulated through the application of DNA strands. We will also map out the degree of prestress that can be built into such gels and determine how closely such gels can be made to mimic the mechanical properties of the cytoskeleton. DNA-crosslinked polyacrylamide gels provide an ideal framework for studying cell interactions with substrates of varying stiffness because the acrylamide chemistry enables easy attachment of the gel to glass. The stiffness is easily controlled by the amount of crosslinking DNA present, and stiffness gradients within the gel are possible by regulating the delivery of the crosslinking solution. Furthermore, thermo- and DNA-actuated reversibility of the gel provides attractive features for tissue engineering studies, since substrate rigidity has been found to regulate the transition of cells from mitogenic to functionally mature and may, in some cases, direct cell differentiation. We will investigate the use of these materials to alter the response of stem cells to the mechanical properties of their environment. In particular, the ability to change the mechanical properties of DNA-crosslinked gels, spatially and temporally, without changing temperature and/or the chemical composition of the buffer, should make DNA-crosslinked gels ideal for the investigation of embryonic stem migration and differentiation in response to gradients and temporal changes in the elastic moduli. We will carry out such studies using a murine embryonic cell line. These studies will also allow us to address issues of biocompatibility and the effect that embryonic stem cells might have on DNA crosslinks. Magnetic microneedles will be used to monitor the compliance properties of the gel during the course of the experiment. Our long-term goal is to create tissue engineered reversible dynamic three-dimensional scaffolds, which will comprise an acryl-based hydrogel that can be reversibly crosslinked with DNA strands to dynamically modulate its stiffness and apply force. Moreover, the biomaterial will also be functionalized with bioactive matrix molecules to support cell attachment, growth, and migration.
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