SUMMARY

In recent years hydrogels have become an interesting material of choice for in vivo biomedical applications. Their high porosity and hydrophilic nature makes them structurally similar to natural tissue. Meanwhile, the large volume changes observed throughout the volume-phase transition, gives these gels the unique ability to induce transport, and force solvent in and out of the polymer network. These shape changes can be leveraged to achieve a variety of tasks on the microscale, like particle capture and drug delivery. However, the mechanics of these microgels is not well understood in part due to inhomogeneities within the network. Full-scale atomistic modeling of micrometer-sized gel networks is currently not possible due to the large length and time scales involved. In our work we develop a mesoscale model based on dissipative particle dynamics to examine the mechanics and kinetics of microgels in solvent. By varying the osmotic pressure of the gels, we probe the changes in bulk modulus for different values of the Flory-Huggins parameter and compare these results to experimental models (Flory-Rehner theory). We then examine the kinetics of spherical microgel particles during swelling/deswelling and we find good agreement with Tanaka’s theory. An interesting finding in our work is that during deswelling the network becomes highly inhomogeneous, as the polymer chains begin to bundle with nearby neighbors, which serves to speedup the collapse of the network. Using our mesoscale polymer model we also construct various hydrogel-based microdevices, like a self-actuating microswimmer and an artificial phagocyte. At the moment we are studying how the bulk and shear moduli of large microgel suspensions change under different solvent conditions and packing fractions.