Development, characterization and antibacterial activity of polyether-co-amide matrix films incorporating choline-calixarene nanoassembly

Introduction Calix[n]arenes are a family of phenolic-based macrocycles of great interest for their synthetic versatility and ability to self-assembly in nanostructured systems. In the search for novel antibacterial agents, we previously demonstrated that the micellar calix[4]arene amphiphile (Chol-Calix), bearing hydrophilic choline moieties and long hydrophobic aliphatic chains, is a nanocarrier for antibiotics (ofloxacin, tetracycline and chloramphenicol) and possesses intrinsic antibacterial properties also against antibiotic-resistant bacteria. To extend the research, here we develop a novel material by incorporating the Chol-Calix into a polyether-co-amide matrix (Pebax®2533) and study its physico-chemical and antibacterial properties. Materials and Methods Flexible films based on Pebax®2533 loaded with Chol-Calix were prepared by solution casting method. The films were characterized for morphology, phase miscibility, thermal stability, gas transport, spectral properties, and Chol-Calix release. The antibacterial activity of the films, neat Pebax® and Pebax® blends loaded with Chol-Calix (0.5, 1, 5 wt%), was evaluated against Escherichia coli ATCC 10536 and Staphylococcus aureus ATCC 6538 at different time intervals (2, 4, 6, 8, 10, 24 h) by cell number evaluation and time kill plots construction. The effect on biofilm formation was estimated by biomass measurements. MTT assay was employed to investigate the interference on vitality of mouse embryonic fibroblast cells (NIH-3T3). Results The thermal stability of the copolymer was not affected by the Chol-Calix incorporation, nevertheless it was detected an increase of crystallinity, gas permeability and wettability of the blend films according to the additive concentration. Leaching of Chol-Calix was tracked by release tests. Neat Pebax® and Pebax®-0.5 wt% Chol-Calix showed no significant antibacterial activity against both E. coli and S. aureus. Pebax®-1 wt% Chol-Calix displayed good antibacterial activity against S. aureus, with a reduction of 1.8 and 2.1 log CFU/mL observed at 10 and 24 h, respectively. A clear effect was observed with Pebax®-5 wt % Chol-Calix that reduced the number of viable E. coli cells of 2.57 and 2.66 log CFU/mL at 10 and 24 h, respectively. A similar trend was observed for S. aureus with a reduction of 2 log CFU/mL at 10 h that increased to 2.49 log CFU/mL at 24 h. Pebax®-5 wt % Chol-Calix showed biofilm biomass reduced (~30%) as compared to the neat polymer. The films were non-cytotoxic as revealed by MTT assay. Discussion and Conclusions The results indicate the Pebax®/Chol-Calix combination as a promising approach for the development of novel biocompatible flexible antibacterial thin-films upgradable by loading antibacterial drugs in the Chol-Calix nanocarrier.