Characterization of alginate-polypyrrole composites for tissue engineering scaffolds

Abstract

Event Abstract Back to Event Characterization of alginate-polypyrrole composites for tissue engineering scaffolds Cassandra J. Wright1, Binbin Zhang2, Melissa Kuester3, Paul J. Molino2 and Timothy W. Hanks3 1 University of Washington Bothell, Engineering and Mathematics, United States 2 University of Wollongong, Intelligent Polymer Research Institute, Australia 3 Furman University, Chemistry, United States Statement of Purpose: Alginic acid and its salts (alginates) are block copolymers of β-D-mannuronate (M) and α-L-guluronate (G)[1]. Ca2+, and other multivalent ions, act as efficient cross-linkers, which results in gels with variable viscoelasticity. The rigidity of the material is largely a function of the ion density and distribution in the host polymer. We are interested in alginate-based composites of containing polycationic intrinsically conducting polymers, particularly polypyrrole (PPy) that do not need additional dopants such as polystyrene sulfonate. These composites can be developed as 3D printable conducting polymer scaffolds for tissue engineering. Methods: Sodium alginate (ALG, 2% w/v), pyrrole, and sodium persulfate were dissolved in deionized water and stirred for 6h in an ice bath to allow the polymerization of PPy in the presence of ALG. This was followed by 48h of dialysis for purification. Concentration of pyrrole was investigated to enhance conductivity. Initial molar ratios of 1:1, 1:1.5, 1:2, and 1:3 molar equivalents ratios of alginate to polypyrrole were used (further referred to as 1:1, etc.). The resultant materials were analyzed using FTIR for composition, rheometer for viscosity, 4-point probe for conductivity, and SEM for structure. Crosslinking was performed on the materials for 4-point probe and SEM experiments using calcium carbonate and glucono-delta-lactone. Preliminary cell studies were performed using rat PC12 cells cultured on tissue culture polystyrene, alginate, and 1:2 ALG-PPy. Proliferation and differentiation conditions (t=24, 48, & 72h) were assessed using live-dead stain & immunofluorescence staining (β-tubulin and DAPI) for cell count and morphology, respectively. Results: Polymerization of the pyrrole in the presence of alginate did result in a significant decrease in the viscosity of all ALG-PPy solutions compared to ALG only solutions (Fig 1). Conductivity was found to increase from 1:1 and 1:1.5eq to 1:2. No statistical difference was found between the 1:2 and 1:3 (Fig 2). 1:5 formed fractured films and thus was not suitable for some measurements. SEM images suggest that the PPy is polymerizing directly onto the framework of the alginate as higher pyrrole content corresponded to increased wall thickness (Fig 3). Preliminary cell studies indicated decreased cell clustering on the ALG-PPy compared to ALG. Figure 1: Viscosity measurements of ALG and ALG-PPy hydrogels. Figure 2: Conductivity of crosslinked ALG-PPy films using 4-point probe Figure 3: SEM (1000X Mag) SEM (1000x Magnification) showing the pore structure of each of the crosslinked substrates (a) Alginate, (b) 1:1 ALG:PPy, (c) 1:1.5 ALG:PPy, (d) 1:2 ALG:PPy Conclusions: This work serves to show that alginate can serve as a direct framework on which PPy can polymerize without the need for additional dopants. Alginate has been shown to serve as an ionomeric dopant for polypyrrole, resulting in a conducting composite possessing electronic conductivity. Acceptable physical properties are obtained up to relatively high polypyrrole loading, offering a promising approach to a unique cellular scaffold. This work was supported through a GEAR:RE award from South Carolina EPSCoR/IDeA.; CJW was supported by SC-INBRE PACD fellowship (P20GM12345 from the National Institute of General Medical Sciences).; CJW was also supported by an Endeavour Research Fellowship (Australian Government Department of Education and Training).