Physicochemical and antimicrobial properties of boron-complexed polyglycerol-chitosan dendrimers

A polyglycerol with dendritic structure (PGLD) was synthesized by ring-opening polymerization of deprotonated glycidol using a polyglycerol as core functionality in a step-growth process. Then, PGLD reacted with O-carboxymethylated chitosan to obtain PGLD-chitosan dendrimer (PGLD-Ch). After the reaction of PGLD-Ch with boric acid, there was a marked increase in the bulk viscosity evidencing physically that boron can initiate a charge transfer complex formation, (PGLD-Ch)B. Gel permeation chromatography analysis was used to characterize the molecular weight and the polydispersivity of the synthesized PGLD-Ch. A dendritic structure with a molecular mass of 16.7 kDa and a narrow polydispersity (Mw/Mn = 1.05) was obtained. 1H-NMR and 13C-NMR measurements were employed to assess the degree of branching in PGLD. The obtained value of 0.85 indicates the tendency toward a dentritic structure for PGLD. The glass transition temperature values of (PGLD-Ch)B membranes containing 10% and 30% PGLD were -19 degrees C and -26 degrees C, respectively, which favor its potential use as surface coating of several polymers. The in vitro cytotoxicity was evaluated using the minimum essential medium elution test assay. Extracts of boron-complexed PGLD exhibited lower cytotoxicity than the controls, suggesting that the material has an improved biocompatibility. Antibacterial studies of (PGLD-Ch)B against Staphylococcus aureus and Pseudomonas aeruginosa showed a significant activity. Our study confirms and supports the effectiveness of (PGLD-Ch)B as an antimicrobial coating due to its capacity in suppressing the bacterial proliferation. The best in vivo response was found for (PGLD-Ch)B-30 membranes, which exhibited higher synthesis of collagen fibers than PGLD-ChB-10.