Alginate-polypyrrole ionomers for biomaterials engineering
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Alginic acid and its salts (alginates) are carbohydrate polymers that are easily cross-linked by Ca2+ ions to form hydrogels of controllable viscoelasticity. They are under active investigation as scaffolds for tissue engineering applications. Pyrrole can be polymerized by persulfate salts in the presence of sodium alginate to form a water-dispersible material that possesses electronic, as well as ionic, conductivity. However, the polymerization reaction releases protons, which in turn catalyzes the decomposition of the persulfate to generate other, more kinetically agressive oxidizing agents. These species cleave the biopolymer backbone, diminishing its solution viscosity and ability to crosslink. By maintaining a neutral pH, the depolymerization is prevented without negatively impacting the polypyrrole formation. The material is easy to process and can be extruded with a 3D printer to produce complex shapes. Cast thin films of the composites are strong and flexible, show good electrical conductivity and can support the growth of cells.