Quaternized poly(2-(dimethylamino)ethyl
methacrylate) (PDMAEMA)
brushes bearing quaternary ammonium groups of different alkyl chain
lengths (ACLs) were prepared and assessed as biocidal coatings. For
the synthesis of the antimicrobial brushes, first well-defined PDMAEMA
chains were grown by surface-initiated atom transfer radical polymerization
on glass and silicon substrates. Next, the tertiary amine groups of
the polymer brushes were modified via a quaternization reaction, using
alkyl halides, to obtain the cationic polymers. The polymer films
were characterized by Fourier-transform infrared spectroscopy, ellipsometry,
atomic force microscopy, and water contact angle measurements. The
effect of the ACL of the quaternary ammonium groups on the physicochemical
properties of the films as well as the contact killing efficiency
of the surfaces against representative Gram-positive and Gram-negative
bacteria was investigated. A hydrophilic to hydrophobic transition
of the surfaces and a significant decrease of the degree of quaternization
of the DMAEMA moieties was found upon increasing the ACL of the quaternization
agent above six carbon atoms, allowing the wettability, the thickness,
and the pH-response of the brushes to be tuned via a facile postpolymerization,
quaternization reaction. At the same time, antimicrobial tests revealed
that the hydrophilic polymer brushes exhibited enhanced bactericidal
activity against Escherichia coli and Bacillus
cereus, whereas the hydrophobic surfaces showed a significant
deterioration of the in vitro bactericidal performance. Our results
elucidate the antimicrobial action of quaternized polymer brushes,
dictating the appropriate choice of the ACL of the quaternization
agent for the development of coatings that effectively inhibit biofilm
formation on surfaces.
Well-defined poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) has been modified at low degrees of quaternization of the tertiary amine groups using alkyl halides with long alkyl chains as the quaternization agents. The resulting PDMAEMA-co-PQDMAEMA copolymers were studied in aqueous solution using potentiometric titrations, turbidimetry, surface tensiometry, dynamic light scattering and zeta potential measurements. An increase of the hydrophilicity of the precursor polymer, leading to an increase or even elimination of the lower critical solution temperature (LCST) for the quaternized copolymers was found; this extended the temperature range of the stable polymer solution. At the same time, it was shown that the hydrophobic character of the polymer increases upon quaternization, leading to higher surface activity compared to the precursor PDMAEMA homopolymer, and, thus, to more effective polymeric surfactants. This contradiction in the copolymer behavior was attributed to the interplay between the polymer self-assembly in the aqueous medium and the polymer adsorption at the air/water interface, which dominate the cloud point and the surface properties, respectively.
Thymyl-methacrylate functionalized, hybrid 3D scaffolds, fabricated by multi-photon lithography, exhibit excellent biocompatibility and antimicrobial action for bone and dental tissue engineering.
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