Abstract
This research aims to investigate nonionic hyperbranched polyesters (HBPs) derived from indole and lignin resources as new nontoxic antimicrobial coatings. Three nonionic HBPs with zero to two methoxy ether substituents on each benzene ring in the polymer backbones were synthesized by melt-polycondensation of three corresponding AB2 monomers. The molecular structures and thermal properties of the obtained HBPs were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry analyses. These HBPs were conveniently spin-coated on a silicon substrate, which exhibited significant antibacterial effect against Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis). The presence of methoxy substituents enhanced the antimicrobial effect, and the resulting polymers showed negligible leakage in water. Finally, the polymers with the methoxy functionality exhibited excellent biocompatibility according to the results of hemolysis and MTT assay, which may facilitate their biomedical applications.
Highlights
Antimicrobial polymers (AMPs) have received growing attention as potentially new coating materials for biomedical devices, due to their enhanced antimicrobial effects, lower toxicity, and nonleaching advantage compared to small molecular antimicrobials.[1−5] Most reported AMPs contain positive charges, whose antimicrobial mechanism largely relies on their ionic interactions with negatively charged bacterial membranes.[6−9] many ionic AMPs suffer from undesirable water solubility, eco-toxicity, poor compatibility with nonionic matrix materials, and fouling potential,[10−15] which could limit their biomedical applications
Due to the lack of ionic interactions with bacterial membranes, nonionic AMPs usually contain certain functionalities that can interact with bacterial membranes by, for example, hydrogen-bonding, hydrophobic, or dipole−dipole interactions.[17−21] A smart strategy to design nonionic AMPs is to utilize naturally existing molecules with antimicrobial properties, such as curcumin, limonene, aspirin, indole, and so forth.[22−26] Grafting such functionalities on linear polymer backbones can yield AMPs with an effective antimicrobial function.[27−32] If such functionalities are densely grafted on highly branched polymers, the interactions with bacterial membranes can be further enhanced, leading to more significant antibacterial effects.[7,8,16,18,31,33]
The aldehyde groups of 3a−c were reacted with indole carboxylate 4 at the three position on indole rings according to an iodine-catalyzed protocol,[63] yielding the corresponding AB2 monomers 5a−c in ∼90% yields and good purity
Summary
Antimicrobial polymers (AMPs) have received growing attention as potentially new coating materials for biomedical devices, due to their enhanced antimicrobial effects, lower toxicity, and nonleaching advantage compared to small molecular antimicrobials.[1−5] Most reported AMPs contain positive charges, whose antimicrobial mechanism largely relies on their ionic interactions with negatively charged bacterial membranes.[6−9] many ionic AMPs suffer from undesirable water solubility, eco-toxicity, poor compatibility with nonionic matrix materials, and fouling potential,[10−15] which could limit their biomedical applications. AMPs usually do not diffuse and release from the matrix and kill the surrounding bacteria (like small antibiotics or metal ions),[40,41] which is due to their relatively large size and slow diffusion rate.[42−44] AMP coatings with an anti-adhesion effect can be achieved by immobilizing antifouling agents such as polyethylene glycol and zwitterions.[45−48] such coatings frequently suffer from harmful biofilm formation, due to the Received: September 10, 2021 Revised: December 7, 2021 Published: December 21, 2021
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