text: Cross-linked copolymers of acrylic acid (sodium acrylate) and acrylamide were synthesized by free radical polymerization. The copolymer hydrogel was studied for capture of copper ion from aqueous solution. Effects of macromolecular structure (i.e., content of the acrylic acid, the quantity of the carboxyl groups neutralized with sodium hydroxide, and the degree of cross-linking) on water-sorption and copper ion uptake were investigated. With an increase in the content of acrylic acid (sodium acrylate), the copper sulfate uptake increases, and water sorption decreases quickly and then slowly increases when the acrylic acid content is high enough. The copper ion uptake is accompanied with a release of sodium ions from the copolymer. Increasing the percentage of the carboxyl groups neutralized by sodium hydroxide will increase the uptake of copper sulfate and water. With an increase in the content of the cross-linking agent, both copper sulfate uptake and water sorption decrease. Even though valence of copper ion is two times that of sodium ion, the copper ions sorption and sodium ions release do not follow a simple ion exchange relation because of insertion of acrylamide co-monomers in macromolecular chain. When copper ions interact with carboxyl groups in the copolymer to form chelating complexes, the water sorption decreases substantially. An analysis of adsorption isotherm indicates that at relatively low concentrations of CuSO4 in water, the copper ion sorption into the copolymer follows the Langmuir model. The wide angle X-ray diffraction (WAXD) data reveal that the copper sulfate sorbed in the hydrogel is not in crystalline state.
  Metal-polymer nanocomposites consisting of gold nanorods and temperature-responsive hydrogel nanoparticulates were investigated for use in externally-controlled drug delivery systems. Several different thermo-responsive hydrogels including poly(N-isopropyl acrylamide) (PNIPAAm) and poly(N-isopropryl acrylamide-co-acrylic acid) (P(NIPAAm-co-AA)) nanoparticles were synthesized for these nanocomposites using an aqueous dispersion polymerization method. In addition, nanoparticles of interpenetrating polymer networks (IPN) composed of poly(acrylamide) (PAAm) and poly(acrylic acid) (PAA) were synthesized using a water-in-oil emulsion polymerization. Temperature-responsive equilibrium swelling behavior of nanoparticles with varying crosslinking densities was characterized using dynamic light scattering. IPN systems exhibited a positive swelling response upon heating while PNIPAAm and copolymer systems collapsed upon increase in temperature above the transition point. Nanoparticles were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which demonstrated shape and morphology of polymer particles. Gold-polymer nanocomposites were formed by grafting gold nanorods to the surface of the polymer nanoparticles. Amine-functionalized gold nanorods were coupled to polymers using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (Sulfo-NHS) to activate carboxyl groups on the surface of the polymer nanoparticles. TEM confirmed successful formation of the metal-polymer nanocomposites. Loading and release of a model therapeutic were done to assess the potential use of the polymer component of the nanocomposite for drug delivery. Fluorescein, a model for chemotherapeutics, was loaded into P(NIPAAm-co-AA) polymer nanoparticulates. Loading of the compound was shown to be a function of crosslinking density in the polymer network. Maximum loading was achieved using nanoparticles synthesized with a 10 mol% crosslinker feed ratio with entrapment efficiencies of 80.0 % and loading capacities of 12.0 %. Cytotoxicity studies were performed using a NIH/3T3 mouse fibroblast cell model. Cell viabilities in presence of P(NIPAAm-co-AA) nanoparticles were comparable to (not statistically different than) controls at concentrations up to 4 mg/ml. Similarly, gold-polymer composite concentrations up to 0.5 mg/ml caused limited cell death. / text
  
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