(520a) Tuning Protein Transport in Nanostructured Block Copolymer Hydrogel Systems

Water soluble PEO-PPO-PEO triblock copolymers are capable of forming thermoreversible gels that consist of packed micellar aggregates with nanoscale periodicity. These micellar crystals have interstitial spacings on the order of several nanometers, which can be used to template comparably sized nanoparticles or globular proteins with hydrodynamic diameters (D_h) ranging from 4-7 nm.  The resulting structure of such a nanoparticle-hydrogel composite system is that of spatially ordered nanoparticle arrays which are embedded within a nanostructured block copolymer matrix. This work characterizes the transport behavior of nanoparticles (proteins) in these micellar crystals using fluorescence recovery after photobleaching (FRAP). Relevant parameters for controlling particle transport in these systems such as nanoparticle loading, particle size, and block copolymer phase are identified and quantified. The diffusivity of three fluorescently tagged proteins (Lactalbumin, D_h=3.8  nm; BSA, D_h=7 nm, Gamma globulin, D_h=9.4nm) is measured in a series of different block copolymer hydrogels with different unit cell dimensions. Protein diffusivity is measured in a wide range of block copolymer concentrations, which covers block copolymer phases spanning from disorded micellar fluids to packed micellar structures.The measured protein diffusivities in the gels are reduced by several orders of magnitude when compared to diffusion in free solution, and demonstrate the versatility of these self-assembled systems for controlling nanoparticle transport.