O. Lyutakov

Polymethylmethacrylate doped with porphyrin and silver nanoparticles as light-activated antimicrobial material

Light-activated antimicrobial materials based on polymethylmethacrylate doped with porphyrin and silver nanoparticles were prepared and studied. The inspiration for the material design originates from photodynamic therapy where light is used to destroy pathogen microbes. Antimicrobial response of the materials is controlled by blue light illumination. Porphyrin molecules serve as light absorbers with dual antimicrobial response under illumination they produce reactive oxygen and affect the kinetics of silver release from the polymer. Silver is responsive for the antimicrobial effect, for the protection of porphyrin against photobleaching and for the conservation of energy through suppression of porphyrin luminescence. Triggerable and enhanced antimicrobial response of the material is activated through several possible mechanisms, including local heating of the polymer matrix, transfer of the excited state from porphyrin to silver and the synergetic effect of reactive oxygen and silver. In a passive state the material exhibits weak antimicrobial response against Gram-negative bacteria. In an active state, however, it is fatal for both Gram negative and Gram positive bacteria.

Light-activated polymethylmethacrylate nanofibers with antibacterial activity

The creation of an antibacterial material with triggerable properties enables us to avoid the overuse or misuse of antibacterial substances and, thus, prevent the emergence of resistant bacterial strains. As a potential light-activated antibacterial material, polymethylmethacrylate (PMMA) nanofibers doped with silver nanoparticles (AgNPs) and meso-tetraphenylporphyrin (TPP) were prepared by electrospinning. TPP was chosen as an effectively reactive oxygen species (ROS) producer. Antibacterial tests on Staphylococcus epidermidis (S. epidermidis) and Enterococcus faecalis (E. faecalis) showed the excellent light-triggerable antibacterial activity of the doped materials. Upon light irradiation at the wavelength corresponding to the TPP absorption peak (405nm), antibacterial activity dramatically increased, mostly due to the release of AgNPs from the polymer matrix. Furthermore, under prolonged light irradiation, the AgNPs/TPP/PMMA nanofibers, displayed enhanced longevity and photothermal stability. Thus, our results suggest that the proposed material is a promising option for the photodynamic inactivation of bacteria.

Temperature-responsive PLLA/PNIPAM nanofibers for switchable release

Smart antimicrobial materials with on-demand drug release are highly desired for biomedical applications. Herein, we report about temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) nanospheres doped with crystal violet (CV) and incorporated into the poly-l-lactide (PLLA) nanofibers. The nanofibers were prepared by electrospinning, using different initial polymers ratios. The morphology of the nanofibers and polymers distribution in the nanofibers were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The interaction between PNIPAM and PLLA in the nanofibers was studied by Fourier transform infrared spectroscopy (FTIR) and its effect on the PNIPAM phase transition was also investigated. It was shown that by the changing of the environmental temperature across the lower critical solution temperature (LCST) of PNIPAM, the switchable wettability and controlled CV release can be achieved. The temperature-dependent release kinetics of CV from polymer nanofibers was investigated by ultraviolet-visible spectroscopy (UV-Vis). The temperature-responsive release of antibacterial CV was also tested for triggering of antibacterial activity, which was examined on Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli). Thus, the proposed material is promising value for controllable drug-release.

Antibacterial properties of palladium nanostructures sputtered on polyethylene naphthalate

Resistance of pathogenic bacteria to conventional antibiotics has emerged in recent years as a major problem for public health. In order to overcome this problem, non-conventional antimicrobial agents have recently been under investigation. Pd nanolayers of variable thicknesses ranging from 0.4 to 22.4 nm were prepared by sputtering on polyethylene naphthalate (PEN). Low-temperature annealing was applied to transform these nanolayers into discrete nanoislands homogeneously distributed over the surface of the underlying polymer. The antibacterial properties of these composites were evaluated by drip test using Gram-positive and Gram-negative bacteria as model strains. Inductively coupled plasma, X-ray photoelectron spectroscopy, and atomic force microscopy were used to outline the method of bacterial inhibition by Pd nanostructures. We found that the antibacterial effect of the Pd/PEN composites might be caused by both (i) release of Pd into a physiological solution and (ii) direct contact of bacteria with the Pd/PEN composites. Our results suggest that the samples coated with a 22.4 nm thick Pd layer exhibited significantly enhanced antibacterial properties than the thinner Pd layers.

Thickness and substrate dependences of phase transition, drug release and antibacterial properties of PNIPAm-co-AAc films

Micron and submicron poly(N-isopropylacrylamide)-co-(acrylic acid) (PNIPAm-co-AAc) films were deposited onto silicon and gold substrates by the spin-coating procedure. The influence of polymer–substrate interaction and spatial confinement of macromolecular chains in the ultrathin polymer films on lower critical solution temperature (LCST) was investigated under different pH conditions. Shift and broadening of the LCST temperature range was observed from the critical thickness of polymer film. It was also found that the substrate plays a key role in this shift. The observed phenomenon was applied for the temperature-controllable release of a small molecular dopant (crystal violet, CV) from the ultrathin polymer films. Finally, doped ultrathin polymer films were examined for their antibacterial activity by in-contact and drop methods. It was observed that polymer thickness and support substrate can influence both CV release and antibacterial properties. Despite the fact that the concentration of CV used in PNIPAm-co-AAc was constant and thinner films contained a significantly smaller amount of CV than thicker ones, the antibacterial activity of thin films was found to be greater in several cases.

Plasmooptoelectronic tuning of optical properties and SERS response of ordered silver grating by free carrier generation

Electrical current induced reversible tuning of the optical properties of ordered silver gratings was proposed. Polymer surface was patterned by excimer laser leading to creation of grating. Subsequently, thin silver layer was deposited onto the polymer grating. Prepared structure is capable of supporting surface plasmon polariton excitation and propagation. To introduce an electric current in direction along the features of the grating additional contacts (Au, Ag, Si, Ge, and their combination) were vacuum deposited. Application of the electric voltage leads to the shift of the wavelength position of surface plasmon polariton by several nanometers and to a change of its absolute intensity by up to 30% in regard to its initial value. The observed phenomenon depends strongly on the grating amplitude and contact between the silver grating and the supply electrodes. The strong electric triggering was observed in the case of evaporated silver or gold electrodes. Oppositely, when the semiconductor materials (Ge, Si) were used, no optoelectronic response was observed. The observed optical tuning can be attributed to a change of free electron concentration in the silver grating due to impact ionization of the metal atoms. The observed phenomenon was exploited to modify SERS response of a thin polystyrene layer deposited onto silver grating. Electrically triggered increase and decrease of SERS intensity was found to depend on grating structure and excitation wavelength. The studied phenomenon is dynamic, continuous, reversible and voltage-controlled, and has a broad range of potential applications for example in the field of triggerable plasmon structures.

Polymer nanostructures for bioapplications induced by laser treatment

Modification of polymer substrates can essentially change the properties of material and thereby it allows their usage in attractive fields of material research. Laser treatment can be successfully applied for change in physico-chemical surface properties and/or for selective change of surface morphology with pattern construction. Three major applications of laser induced structures were described, cytocompatibility control, application as anti-bacterial substrate and plasmonic-based detection system. The construction of a second generation antibacterials using the synergic effect of either nanopatterning of polymers by application of a laser or noble metals deposition and consequent modification of nanostructures was presented.