No abstract

In this study, polyacrylamide nanocomposite hydrogels were formulated in combination with sodium montmorillonite (MMT) in the presence of a 2-T magnetic field. This top-down nanomanufacturing approach led to interesting changes in the internal structure of the gel and ultimately to a dramatic improvement in the ability of the composite to separate the two protein probes, ovum serum albumin and carbonic anhydrase. The morphology of the nanocomposite hydrogel was analyzed with cryogenic scanning and transmission electron microscopy, wide-angle X-ray diffraction, and small-angle scattering to determine whether morphological changes would correlate with this improved separation. As the volume fractions of MMT were well under 1% in this study (because of aqueous swelling), scattering data were dominated by the polymer structure. Significant morphological changes were noted at two length scales: (1) the hydrogel cell structure, at hundreds of nanometers, appeared to ex-hibit changes in the anisotropic orientation with magnetization, and (2) the polyamide structure, at tens of nanometers, exhibited decreasing pore size (small-angle Xray scattering). The separation data correlated most closely with a reduction in pore size; however, an additional contribution to separation from local electrostatic effects from the presence of charged MMT in the cell walls could not be discounted. The change in the pore size associated with processing may have been due to the MMT presence altering the diffusion rates of the reactants during polymer formation. The method demonstrated herein could be used ultimately to separate proteins in their native state, with the potential retention of function for downstream applications, such as novel detection techniques or purification.

Nanocomposite polymeric hydrogels have potential to play an important role in clinical diagnostics, therapeutic agents, and electroanalytical devices, among other biotechnological applications. However, the relationship between nanocomposite structure (morphology) and transport specifically of proteins has not been systematically described. In this study, polyacrylamide (PAM) nanocomposites have been synthesized containing various compositions and aspect ratios of gold nanoparticles (GNP). These nanocomposite hydrogels have been characterized for morphology, and examined for their ability to change the effective electrophoretic mobility of a model protein, ovum serum albumin (OSA), under a low applied electric field of 6.7 V/cm. Addition of spherical (low aspect ratio) gold nanoparticles reduces the effective mobility of OSA, a result that cannot be explained by the lower effective cross-link density noted in swelling studies. However, the effective mobility of OSA can be predicted using simple tortuous path models, specifically the Lape-Cussler. An increase in aspect ratio of the nanoparticles produced further reductions in mobility, and this reduction was so significant that tortuous path contribution could not explain it. We expect that percolation of the higher aspect ratio gold nanoparticles (as seen in TEM images) led to preferred conduction through the gold network, and therefore resulted in lower mobility in the buffer. The structure-mobility relationships found here help establish one possible regime for transport of proteins through nanocomposite hydrogels.