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SYNTHESIS OF BIMETALLIC–CHITOSAN COMPLEXES AS ANTIBACTERIAL MATERIALS

Chitosan-based hydrogels have found many applications in biomedicine due to their biocompatibility, biodegradability and bioactivity. Chitosan (CHT) is a non–toxic, polycationic biopolymer with antibacterial properties which can be improved through complexation with transition metals such as copper, zinc and silver. Cu2+, Zn2+ and Ag+ ions are used in biomedicine due to beneficial properties in the repair and regeneration of different tissues. Furthermore, the addition of these metal ions into CHT matrix enhances antibacterial properties against Gram-positive and Gram-negative bacteria. The strong affinity of these ions towards –NH2 and –OH groups of chitosan is responsible for the complexation process that can be used to prepare stable hydrogels with defined structure and improved antibacterial properties. To date, there is no study conducted on the synthesis of chitosan- based materials through simultaneous complexation with two metal ions. Therefore, the aim of this work was to investigate the structural properties and stability of chitosan-based hydrogels when two different metal ions are added into CHT solution. In this work, the complex solutions (CHT/Cu, CHT/Cu–M0.5 and CHT/Cu–M5) were in situ prepared by mixing the appropriate volume of 1.2 wt.% CHT solution (medium molecular weight, degree of deacetylation = 85 %) and solutions of metal ions according to their volume ratio: VCHT/(VCu2++VM)=7.33, where M is the solution of Zn2+ or Ag+ ions with two different concentrations. The molar ratio of amino groups and Zn2+ or Ag+ ions was adjusted to n(– NH2):n(M)=1:0.009 and 1:0.09. In the case of Cu2+ ions, ratio was constant in all complexes with value of n(–NH2):n(Cu2+) =1:0.09. Due to poor solubility of Ag acetate, CHT/Cu–Ag5 complex solution was prepared with minor changes. The prepared solutions of complexes were neutralized with 5 wt.% NaOH solution during 24 h and obtained hydrogels were extensively washed with distilled water until pH neutral. The prepared hydrogels were then frozen and lyophilized to obtain dry materials which were characterized by ATR-FTIR spectroscopy and their morphology was investigated by SEM. The preliminary results show the stable and porous microstructure of all prepared hydrogels. The addition of a second metal ion increases stability of hydrogels, in comparison with CHT/Cu hydrogels. Furthermore, shifts in absorption bands in FTIR spectra of all samples indicate successful complexation of CHT with metal ions. The results imply strong interactions of metal ions with –NH2 and –OH groups of chitosan and that complexation process can be used as a potential method for obtaining stable bimetallic– chitosan hydrogels as antibacterial materials.

chitosan ; copper ; zinc ; silver ; complex ; antibacterial properties

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