Synthesis and Characterization of Alginate/Poly (4-vinylpyridine) Hybrid System

Polyelectrolyte multilayer (PEC) films of sodium alginate and poly(4-vinylpyridine) were prepared by immersing the sodium alginate (Na-Alg) films into the poly(4vinylpyridine) (P4VP) in 0.1 M hydrochloric acid solution. Then, the multilayer films were formed by the alternating addition of Na-Alg and P4VP respectively. The morphology, topography and chemical structures of the PEC films and its precursors were investigated and characterized by SEM analysis, AFM and FTIR spectroscopy respectively. It was observed that the number of layers and the nature of the outer layer affect the physicochemical characteristics. The thermal properties of the PEC films were examined by thermogravimetric analysis (TGA). The onset of degradation for PEC-2, PEC-3, PEC-4 and PEC-5 is at 180°C, 195°C, 195°C and 200°C respectively. Na-Alg film, on the other hand, decomposes at 215°C while P4VP film gives its first decomposition temperature at 290°C. The crystallinity indexes were calculated by XRD analysis. Complexation reduces the crystallinity comparing with the parent membrane, Na-Alg. Crystallinity index of Na-Alg film is 0.49 whereas the values for PEC-2, PEC-3, PEC-4 and PEC-5 are 0.25, 0.36, 0.42 and 0.39 respectively. The hydrophilicity of the PEC films was examined by using contact angle measurement. When Na-Alg is the outer layer in the PEC, hydrophilicity is higher. Roughness of the film surfaces was characterized by AFM measurements. The solubility of the films was tested in different organic solvents and in aqueous solution of acidic and basic pH values. They are insoluble in water and up to pH=4.2 in acid buffer solution. The swelling properties of the PEC films were studied in acidic aqueous solution of pH value 1.2 and in water. The highest equilibrium % swelling values among the PEC films have been obtained as 215% and 155% for PEC-5, in water and acidic buffer respectively within an hour. The drug loading-release properties for the PEC were studied using ciprofloxacin HCl as a model drug. The three layer film PEC-3, which is composed of Na-Alg outer layer deposited on a P4VP/Na-Alg double layer, is characterized by the lowest roughness (Rq=16.3 nm) and the most hydrophilic surface with a contact angle value of 38.1° among all other films prepared. Its crystallinity index is 0.36, and starts to degrade at 195 °C. It exhibits 130-135% equilibrium swelling capacity in acid buffer and water respectively. PEC-3 is the film with the highest drug loading capacity and drug loading efficiency values of 3.51% and 87% respectively when the initial drug concentration is 12.5 ppm. A cumulative drug release of 65% is obtained from PEC 3 within 24 h in water when the initial concentration of the drug solution is 12.5 ppm. Several kinetic models including zero order, first order, Higuchi and Korsmeyer-Peppas were tested to understand the kinetics and mechanism of the drug release from the PEC films of Na-Alg and P4VP. The best fit was obtained with Higuchi's equation. Release mechanism was found to be Fickian according to the Korsmeyer-Peppas equation. Keywords: sodium alginate, poly(4-vinylpyridine), polyelectrolyte complex, multilayer, ciprofloxacin HCl, LbL