Abstract
The work herein describes the preparation of thermoresponsive microgels with potential antimicrobial properties. Most of the work performed so far regarding microgels with antimicrobial activity, deals with the ability of microgels to carry and release antibiotics or antimicrobial agents (antimicrobial peptides). The originality of this work lies in the possibility of developing intrinsic antimicrobial microgels by copolymerization of the well-known thermoresponsive monomer, N-isopropylacrylamide (NIPAM) with dimethylaminoethyl methacrylate (DMAEMA), a water-soluble monomer, to form microgels via precipitation polymerization (radical polymerization). Due to the presence of a tertiary amine in the DMAEMA comonomer, microgels can be modified by N-alkylation reaction with methyl and butyl iodide. This quaternization confers positive charges to the microgel surfaces and thus the potential antimicrobial activity. The effect of DMAEMA content and its quaternization with both, methyl and butyl iodide is evaluated in terms of thermal and surface charge properties, as well as in the microgel size and viscoelastic behavior. Finally, a preliminary study of the antimicrobial activity against different microorganisms is also performed in terms of minimum inhibitory concentration (MIC). From this study we determined that in contrast with butylated microgels, methylated ones show potential antimicrobial activity and good physical properties besides of maintaining microgel thermo-responsiveness.
Highlights
Microgels, intramolecularly cross-linked submicron size polymer particles are an interesting subset of polymer gels that can be designed to respond to environmental external stimuli like temperature, magnetic field, pH, ionic strength or electric field [1,2]
We report the effect of dimethylaminoethyl methacrylate (DMAEMA) content and its quaternization, on the hydrodynamic diameter, surface charge, thermal properties of the obtained microgels as well as the influence in the viscoelastic properties of microgel dispersion
Since the main objective of the work was the development of polycationic microgels that might present antimicrobial activity, the step of the work consisted in the quaternization of the tertiary amine of DMAEMA by the N-alkylation reaction with methyl iodide and butyl iodide following the procedure described in the experimental section
Summary
Intramolecularly cross-linked submicron size polymer particles are an interesting subset of polymer gels that can be designed to respond to environmental external stimuli like temperature, magnetic field, pH, ionic strength or electric field [1,2]. Polymers 2019, 11, 606 scale [9,10,11,12], and as active sites incorporated within functional polymer matrices so that the design of tailored multifunctional materials can be obtained [13,14]. Following this idea, in a recent work we used thermoresponsive poly(N-isopropylacrylamide), (PNIPAM) based microgels as active sites encapsulated into polymeric nanofiber as a first approach toward the design of new active wound dressings [15,16]. The development and use of antimicrobial materials have become necessary to overcome the increasing problem of infectious diseases and multi-resistant microorganisms, the latter being one of the greatest threats for health and health care systems as stated by the World Health Organization [17]
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