Abstract
BackgroundSeveral cationic polymers exhibit a useful antimicrobial property, however the structure–activity relationship still requires a more complete investigation. The main objective of this work is the comparison between the antimicrobial activity and toxicity of free and immobilized poly (diallyldimethylammonium) chloride (PDDA) in biocompatible poly (methylmethacrylate) (PMMA) nanoparticles (NPs).ResultsNPs synthesis by emulsion polymerization is performed over a range of [PDDA] at two methylmethacrylate (MMA) concentrations. The PMMA/PDDA dispersions are characterized by dynamic light-scattering for sizing, polydispersity and zeta-potential analysis, scanning electron microscopy (SEM), plating plus colony forming unities (CFU) counting for determination of the minimal microbicidal concentrations (MMC) against Escherichia coli, Staphylococcus aureus and Candida albicans and hemolysis evaluation against mammalian erythrocytes. There is a high colloidal stability for the cationic PMMA/PDDA NPs over a range of [PDDA]. NPs diverse antimicrobial activity against the microorganisms reduces cell viability by eight-logs (E. coli), seven-logs (S. aureus) or two-logs (C. albicans). The NPs completely kill E. coli over a range of [PDDA] that are innocuous to the erythrocytes. Free PDDA antimicrobial activity is higher than the one observed for PDDA in the NPs. There is no PDDA induced-hemolysis at the MMC in contrast to the hemolytic effect of immobilized PDDA in the NPs. Hemolysis is higher than 15 % for immobilized PDDA at the MMC for S. aureus and C. albicans.ConclusionsThe mobility of the cationic antimicrobial polymer PDDA determines its access to the inner layers of the cell wall and the cell membrane, the major sites of PDDA antimicrobial action. PDDA freedom does matter for determining the antimicrobial activity at low PDDA concentrations and absence of hemolysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0123-3) contains supplementary material, which is available to authorized users.
Highlights
Several cationic polymers exhibit a useful antimicrobial property, the structure–activity relationship still requires a more complete investigation
Preparation and characterization of PMMA/poly (diallyldimethylammonium) chloride (PDDA) NPs Emulsion polymerization of MMA in the presence of PDDA with azobisisobutyronitrile (AIBN) as the radical initiator is done under N2 flow in order to prevent the precocious termination of the free radicals required for the MMA addition reaction and the synthesis of the PMMA particles
A formulation A3 means that particle synthesis was carried out with 0.56 M MMA and 3 mg/mL PDDA whereas a formulation B4 means that 1.32 M MMA and 4 mg/mL PDDA were used for particle’s synthesis
Summary
Several cationic polymers exhibit a useful antimicrobial property, the structure–activity relationship still requires a more complete investigation. The main objective of this work is the comparison between the antimicrobial activity and toxicity of free and immobilized poly (diallyldimethylammonium) chloride (PDDA) in biocompatible poly (methylmethacrylate) (PMMA) nanoparticles (NPs). QACs such as dioctadecyldimethylammonium bromide (DODAB) are miscible with some biocompatible polymers such as poly (methylmethacrylate) (PMMA) in spin-coated films, do not leak from the polymeric matrix and kill bacteria upon contact [11]. PMMA NPs containing CTAB or DODAB synthesized by emulsion polymerization display high bactericidal activity [13]. The available sites for polymerization are the monomer droplets of the methylmetacrylate (MMA) in water dispersed as a microemulsion [19]. We synthesize PMMA/PDDA NPs by surfactant-free emulsion polymerization of MMA in the presence of PDDA in order to determine the effect of PDDA immobilization on its activity against microorganisms or red blood cells
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