Miroslav Šlouf

Polystyrene Nanofiber Materials Modified with an Externally Bound Porphyrin Photosensitizer

Polystyrene ion-exchange nanofiber materials with large surface areas and adsorption capacities were prepared by electrospinning followed by the sulfonation and adsorption of a cationic 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) photosensitizer on the nanofiber surfaces. The morphology, structure, and photophysical properties of these nanofiber materials were characterized by microscopic methods and steady-state and time-resolved fluorescence and absorption spectroscopies. The externally bound TMPyP can be excited by visible light to form triplet states and singlet oxygen O2((1)Δg) and singlet oxygen-sensitized delayed fluorescence (SODF). The photophysical properties of the nanofibers were strongly dependent on the amount of bound TMPyP molecules and their organization on the nanofiber surfaces. The nanofibers demonstrated photooxidative activity toward inorganic and organic molecules and antibacterial activity against E. coli due to the sensitized formation of O2((1)Δg) that is an effective oxidation/cytotoxic agent. The nanofiber materials also adsorbed heavy metal cations (Pb(2+)) and removed them from the water environment.

Porphyrin-layered double hydroxide/polymer composites as novel ecological photoactive surfaces

Nanocontainer and nanofiller aspects of layered double hydroxides (LDH) were combined to prepare porphyrin-LDH/polymer composites for photoactive coatings. The suggested properties are derived from cytotoxicity of singlet oxygen, O2(1Δg), produced by interaction of molecular oxygen with excited porphyrin molecules located within the interlayer space of ZnRAl and MgRAl LDH. Porphyrins, Pd(II)-5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (PdTPPC) and 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (TPPS) photoproducing O2(1Δg), were successfully intercalated into LDH hosts using the co-precipitation procedure and then used as fillers in two eco-friendly polymers, namely polyurethane (PU) and poly(butylene succinate) (PBS). Porphyrin-LDH/polymer composites were prepared either by the solvent cast/cross-linking technique or melt-compounding with different porphyrin-LDH filler loadings (up to 1.3 wt%). Both X-ray diffraction and transmission electron microscopy measurements indicate a good dispersion of porphyrin-LDH fillers into the polymer matrices and that the porphyrin molecules remain intercalated within LDH layers. The polymers do not block the diffusion of oxygen and the triplet states of the intercalated porphyrins in the composite films have enough long lifetimes to produce O2(1Δg) upon irradiation by visible light. The present composites allow the elaboration of photoactive surfaces with a precise control of the O2(1Δg) concentration depending on porphyrin-LDH filler loadings.

The relationship of polyethylene wear to particle size, distribution, and number: A possible factor explaining the risk of osteolysis after hip arthroplasty

The most critical factor in the development of periprosthetic osteolysis (OL) in total hip arthroplasty (THA) is the biological reaction to wear debris. This reaction is dependent, in part, on the size and concentration of particles, which are determined predominantly by the polyethylene (PE) wear rate. This implies that the risk for developing OL and prosthesis failure can be estimated from wear measurements. We developed a computational algorithm for calculating the total number of PE particles for volumetric wear when particle size and distribution are known. We found that: (i) total number of PE wear particles decreases up to 5 orders of magnitude if the average size of particles increases and the total volumetric wear remains constant; (ii) total amount of PE wear particles decreases up to 4 orders of magnitude if the width of the distribution increases and total volumetric wear remains constant; (iii) for the same volumetric wear, the number of particles significantly decreases/increases with the increase/decrease in their average size and range. These findings suggest that the risk for the development of OL in THA cannot be simply estimated from the volumetric wear alone.

A new route for chitosan immobilization onto polyethylene surface.

Low-density polyethylene (LDPE) belongs to commodity polymer materials applied in biomedical applications due to its favorable mechanical and chemical properties. The main disadvantage of LDPE in biomedical applications is low resistance to bacterial infections. An antibacterial modification of LDPE appears to be a solution to this problem. In this paper, the chitosan and chitosan/pectin multilayer was immobilized via polyacrylic acid (PAA) brushes grafted on the LDPE surface. The grafting was initiated by a low-temperature plasma treatment of the LDPE surface. Surface and adhesive properties of the samples prepared were investigated by surface analysis techniques. An antibacterial effect was confirmed by inhibition zone measurements of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The chitosan treatment of LDPE led to the highest and most clear inhibition zones (35 mm(2) for E. coli and 275 mm(2) for S. aureus).

Polyelectrolyte-surfactant complexes formed by poly[3,5-bis(trimethylammoniummethyl)4-hydroxystyrene iodide]-block-poly(ethylene oxide) and sodium dodecyl sulfate in aqueous solutions.

Formation of polyelectrolyte-surfactant (PE-S) complexes of poly[3,5-bis(trimethylammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) and sodium dodecyl sulfate (SDS) in aqueous solution was studied by dynamic and electrophoretic light scattering, small-angle X-ray scattering (SAXS), atomic force microscopy, and fluorometry, using pyrene as a fluorescent probe. SAXS data from the QNPHOS-PEO/SDS solutions were fitted assuming contributions from free copolymer, PE-S aggregates described by a mass fractal model, and densely packed surfactant micelles inside the aggregates. It was found that, unlike other systems of a double hydrophilic block polyelectrolyte and an oppositely charged surfactant, PE-S aggregates of the QNPHOS-PEO/SDS system do not form core-shell particles and the PE-S complex precipitates before reaching the charge equivalence between dodecyl sulfate anions and QNPHOS polycationic blocks, most likely because of conformational rigidity of the QNPHOS blocks, which prevents the system from the corresponding rearrangement.

Synergistic effects in mechanical properties of PLA/PCL blends with optimized composition, processing, and morphology

Poly(lactic acid) (PLA) is a promising material for biomedical applications due to its biodegradability and high stiffness, but suffers from low toughness. We report that blending of PLA with another biodegradable polymer, poly(e-caprolactone) (PCL), can increase the impact strength above the values of the individual components, while the other important macro- and micromechanical properties remain at well-acceptable level (above the theoretical predictions based on equivalent box model). Although some previous studies indicated incompatibility of PLA and PCL polymers, we demonstrate that the melt-mixing of the polymers with optimized viscosities (PLA/PCL viscosity ratio ∼ 1), the optimized composition (PLA/PCL = 80/20 by weight), and the optimal processing (compression molding with fast cooling) leads to optimal morphology (∼0.6 μm particles of PCL in PLA matrix) and synergistic effect in the mechanical performance of the systems. In an additional set of experiments, we show that the addition of TiO2 nanoparticles slightly improves stiffness, but significantly reduces the toughness of the resulting nanocomposites. The investigated systems were characterized by electron microscopy (SEM and TEM), notched impact strength, dynamic mechanical analysis, and microindentation hardness testing.

The multifunctional role of ionic liquids in the formation of epoxy-silica nanocomposites

This work addresses the use of ionic liquids (ILs) as additives for formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. The application of different methylimidazolium based ILs allows controlling the silica structure and modifying interphase interaction, thus producing hybrids with diverse morphologies and improved mechanical properties. Both the anionic and cationic components of the ILs affected the hybrid formation and the final properties. The application of 1-decyl-3-methylimidazolium tetrafluoroborate ionic liquid together with HCl as an acid catalyst promotes both hydrolysis and condensation in the sol–gel process as well as the self-assembly ordering of the IL. This system produces a very fine hybrid morphology with well dispersed silica nanodomains and a significantly increased rubbery modulus due to physical crosslinking by the ordered domains of decyl-substituents.

Crystalline Character and Microhardness of Gamma‐Irradiated and Thermally Treated UHMWPE

Relationships between Vickers microhardness, x‐ray and differential scanning calorimetry (DSC) crystallinity, x‐ray long period, and melting points were determined for ultrahigh molecular‐weight polyethylene (UHMWPE) of various histories (as‐produced, irradiated, annealed, and remelted). It was shown that the microhardness responds very sensitively to both the irradiation conditions (total radiation dose, radiation dose rate) and the thermal treatment (annealing below the melting temperature, remelting). As microhardness reflects the yield point parameters, the results show that not only the total dose, but also the irradiation dose rate has a considerable influence on mechanical properties of UHMWPE. It was demonstrated that neither x‐ray nor DSC results are so sensitive to treatment as the microhardness results. The most important differences in properties were found between remelted samples and those thermally untreated or annealed.

Superparamagnetic Fe3O4 Nanoparticles: Synthesis by Thermal Decomposition of Iron(III) Glucuronate and Application in Magnetic Resonance Imaging.

Monodisperse superparamagnetic Fe3O4 nanoparticles coated with oleic acid were prepared by thermal decomposition of Fe(III) glucuronate. The shape, size, and particle size distribution were controlled by varying the reaction parameters, such as the reaction temperature, concentration of the stabilizer, and type of high-boiling-point solvents. Magnetite particles were characterized by transmission electron microscopy (TEM), as well as electron diffraction (SAED), X-ray diffraction (XRD), dynamic light scattering (DLS), and magnetometer measurements. The particle coating was analyzed by atomic absorption spectroscopy (AAS) and attenuated total reflection (ATR) Fourier transform infrared spectroscopy (FTIR) spectroscopy. To make the Fe3O4 nanoparticles dispersible in water, the particle surface was modified with α-carboxyl-ω-bis(ethane-2,1-diyl)phosphonic acid-terminated poly(3-O-methacryloyl-α-D-glucopyranose) (PMG-P). For future practical biomedical applications, nontoxicity plays a key role, and the PMG-P&Fe3O4 nanoparticles were tested on rat mesenchymal stem cells to determine the particle toxicity and their ability to label the cells. MR relaxometry confirmed that the PMG-P&Fe3O4 nanoparticles had high relaxivity but rather low cellular uptake. Nevertheless, the labeled cells still provided visible contrast enhancement in the magnetic resonance image. In addition, the cell viability was not compromised by the nanoparticles. Therefore, the PMG-P&Fe3O4 nanoparticles have the potential to be used in biomedical applications, especially as contrast agents for magnetic resonance imaging.

Kinetics and mechanism of the biodegradation of PLA/clay nanocomposites during thermophilic phase of composting process

The degradation mechanism and kinetics of polylactic acid (PLA) nanocomposite films, containing various commercially available native or organo-modified montmorillonites (MMT) prepared by melt blending, were studied under composting conditions in thermophilic phase of process and during abiotic hydrolysis and compared to the pure polymer. Described first order kinetic models were applied on the data from individual experiments by using non-linear regression procedures to calculate parameters characterizing aerobic composting and abiotic hydrolysis, such as carbon mineralization, hydrolysis rate constants and the length of lag phase. The study showed that the addition of nanoclay enhanced the biodegradation of PLA nanocomposites under composting conditions, when compared with pure PLA, particularly by shortening the lag phase at the beginning of the process. Whereas the lag phase of pure PLA was observed within 27days, the onset of CO2 evolution for PLA with native MMT was detected after just 20days, and from 13 to 16days for PLA with organo-modified MMT. Similarly, the hydrolysis rate constants determined tended to be higher for PLA with organo-modified MMT, particularly for the sample PLA-10A with fastest degradation, in comparison with pure PLA. The acceleration of chain scission in PLA with nanoclays was confirmed by determining the resultant rate constants for the hydrolytical chain scission. The critical molecular weight for the hydrolysis of PLA was observed to be higher than the critical molecular weight for onset of PLA mineralization, suggesting that PLA chains must be further shortened so as to be assimilated by microorganisms. In conclusion, MMT fillers do not represent an obstacle to acceptance of the investigated materials in composting facilities.