Nanosphere and Nanorod Transport through Sticky, Nearly Homogeneous, and Degrading Hydrogels

This presentation will explore single nanoparticle dynamics in hydrogels. In silica-polyacrylamide hydrogel nanocomposites, the attraction between poly(ethylene glycol) (PEG) grafted nanoparticles and immobile silica particles dominates dynamics. We demonstrate that attractive interactions can be tuned by changing the pH, providing a handle to control nanoprobe mobility. Compared to the heterogeneous network formed by polyacrylamide, tetra-PEG hydrogels form a nearly homogeneous mesh, which acts as a model matrix for transport studies. During gelation of tetra-PEG hydrogels, nanorods exhibit enhanced dynamics compared nanospheres suggesting that nanorods can invoke transport mechanisms unavailable to nanospheres. This behavior is supported by direct observation of single particle tracking of nanorods. Network defects also have a pronounced effect on probe dynamics. The extent of this effect depends on the size of the nanoparticle compared to the length scale of the defects in tetra-PEG hydrogels. In summary, by identifying factors that impact nanoparticle dynamics in networks at the nanoscale, including probe-particle interactions, probe shape and size, and network defects, the design of hydrogels as filtration membranes and drug delivery systems can be advanced.