Chitosan-EDTA conjugate: A novel polymer for topical gels

A recently developed chitosan-EDTA conjugate, neutralized with sodium hydro xide (NaChito-EDTA), has been tested for possible topical use. The technica l properties and microbial stability of NaChito-EDTA have been compared wit h those of carmellose sodium (NaCMC), hydroxypropylmethylcellulose (HPMC), sodium polycarbophil (NaPCP) and sodium carbopol 980 (NaC980), well establi shed gelatinizing agents. NaChito-EDTA forms stable, colourless, completely transparent hydrogels at a polymer concentration of 0.5%. Of the polymers tested the novel polymer h ad the lowest incompatibility with multivalent cations and with ethanol, an d much the best swelling properties. After 28 days of incubation at room te mperature the rates of growth of the complete bacterial spectrum occurring in demineralized water and of Escherichia coli, serving as model strain rep resentative of Gram-negative bacteria, were at least 2 log and 5.7 log, res pectively, lower in NaChito-EDTA gels than in the other hydrogels. This ant imicrobial activity of NaChito-EDTA can be explained by its highest binding affinity towards magnesium, which stabilizes the outer membrane of Gram-ne gative bacteria. However, this antimicrobial effect is insufficient to guar antee microbial stability. Further results showed that the antimicrobially acting polypeptide nisin can be recommended as an alternative novel preserv ative for NaChito-EDTA gels, because its antimicrobial spectrum could also be increased towards Gram-negative bacteria in combination with chelating e xcipients. NaChito-EDTA seems, therefore, to be a promising novel polymer for topicall y-used gels, with advantages over well established gelatinizing agents.