Mechanically Reinforcing Polyacrylate/Polyacrylamide Hydrogels through the Addition of Colloidal Particles

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1190-NN03-07

Mechanically Reinforcing Polyacrylate/Polyacrylamide Hydrogels through the Addition of Colloidal Particles Bryan A. Baker1, Rebecca Murff2 and Valeria T. Milam1, 2, 3 School of Materials Science and Engineering1, Wallace H. Coulter Department of Biomedical Engineering2, and Petit Institute for Bioengineering and Bioscience3, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta, Georgia 30332-0245 ABSTRACT Polyacrylamide is a popular material for many bio-related applications ranging from electrophoretic separation to cellular supports. A limitation of polyacrylamidebased hydrogels, however, is their mechanical compliance. The current study examines the effect of colloidal particles as a reinforcing filler phase to enhance the mechanical stiffness of polyacrylamide-polyacrylate hydrogels. Measurements with oscillatory rheology show that for a fixed polymer volume fraction, the presence of colloidal particles with various surface modifications generally results in an increase of the shear storage modulus of the hydrogel-particle composite. Interestingly, this study indicated that no discernable trends can be linked between the values of the shear storage modulus and the particle surface characteristics. INTRODUCTION Hydrogel networks are comprised of cross-linked hydrophilic polymer chains that form three-dimensional networks[1]. While the high water content provides favorable permeability characteristics, these water-swollen networks are mechanically weaker than many physiological tissues. Past approaches to increase the mechanical stiffness of hydrogels have involved increasing the concentration of cross-linker[2], increasing the monomer concentration[3], altering copolymer composition[4], and embedding particles into the hydrogel[5]. Our work seeks to expand upon these efforts by using colloidal particles as interactive filler additions to polyacrylamide-based hydrogels. Oscillatory rheology is used to determine the effects of particle volume fraction as well as various chemical modifications to the particle surface. EXPERIMENT Materials All chemicals were purchased from Sigma (St. Louis, MO) unless otherwise noted. N,N’-methylene-bisacrylamide (BIS), N,N,N′,N′-tetramethylethylenediamine (TEMED), poly(diallyldimethylammonium chloride) (PDDA), and N-ethyl-N’-(3dimethylaminopropyl) carbodiimide hydrochloride (EDAC) were used as-received. DIamond filtered nanopure water (Barnstead International) was used to prepare all initiator and buffer solutions. Phosphate buffered saline (PBS) was diluted from a 10x concentration to a 1x concentration. Sodium acrylate and acrylamide were dissolved in PBS to prepare either 40 or 60 wt% monomer solutions. Ammonium persulfate was

diluted to a 10 wt% solution and used as the initiator. Spermine solution was prepared by adding 500 mg to 1 mL nanopure water. Carboxylated, 0.79 µm diameter, polystyrene particles (Bangs Laboratories, Fishers, IN) served as the colloidal species. Particle Preparation and Zeta Potential For negatively charged particles, carboxylated

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