Mechanical Characterization of Stimuli-Responsive Biohybrid Material Composed of Hinge-Motion Binding Protein within Acrylamide Hydrogel

Stimuli-responsive hydrogels are useful for controlled drug delivery applications. In this regard, the material and the drug are combined in such a way that drug is released from the material in a predesigned manner, the material can be used repeatedly for a number of cycles, and it allows for an easy fabrication of an implantable device. In order to achieve these goals, it is extremely important that such a device be mechanically robust. Here we have studied mechanical properties of a new biohybrid material that is composed of genetically engineered hinge-motion binding protein, calmodulin (CaM) within the bulk of an acrylamide hydrogel. Mechanical action in such a hydrogel is generated by the conformational change of the CaM molecules upon interaction with the ligand. Different amounts of the CaM monomer and CaM dimer were utilized to fabricate these hydrogels. The tensile, compressive, and dynamic mechanical behavior along with the various viscoelastic parameters, e.g. storage and loss moduli, damping parameter (tan delta) of these hydrogels was analyzed. These parameters were also correlated with the protein concentration, the chain lengths, and the cross-linking density of the hydrogels. Increase in the tensile modulus, i.e. stiffness, (~56.9%) and decrease in the elongation at break (~33.6%) was observed for the CaM-based hydrogels as compared to that of the CaM-free hydrogels. This biohybrid material exhibited improved mechanical properties and stability over a range of temperatures (34 - 40 oC) and frequencies (0.01 - 2 Hz). This makes them interesting for applications under physiological conditions. Such an understanding of the these stimuli-responsive biohybrid materials will be useful for the development of novel biomedical systems and MEMS/NEMS devices.