Microstructural PALS study of regulated dimethacrylates: Thiol‐ versus β‐allyl sulfone‐based networks

Radical photocuring of multifunctional (meth)acrylates is lacking control over the irregular chain growth process yielding highly crosslinked, inhomogeneous networks. Chain transfer agents (CTAs, e.g., thiols or β‐allyl sulfones) have been widely used to modify this curing process, thus reducing shrinkage stress and increasing the toughness of the formed photopolymers. Resulting photopolymer networks exhibit higher bulk density, lower crosslinking density, and narrow glass transitions. Consequently, a more homogeneous network structure was postulated for those networks. Whereas macroscopic properties of the modified final materials have already been studied, herein the microstructural arrangement of such modified networks has also been evaluated with the help of positron annihilation lifetime spectroscopy (PALS). A more homogenous network structure with a decreased average free‐volume void size was confirmed for CTA‐based dimethacrylate networks. A sharper distribution of the ortho‐positronium (o‐Ps) lifetime, mainly for the β‐allyl sulfone‐based photopolymers, hints toward a more regulated network structure. Moreover, the combination of PALS, DMTA, density and swelling experiments elucidates relations between void formation, crosslinking density and macroscopic characteristics such as shrinkage stress and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2476–2484     

Mechanical investigation of bilayer vascular grafts electrospun from aliphatic polyesters

Electrospun biodegradable vascular grafts provide a wide range of design components from the selection of materials to the modification of fiber structure. In this study, both single layer and bilayer tubular scaffolds with inner diameter of 6 mm were electrospun from polycaprolactone with different molecular weights and poly(l ‐lactide) caprolactone polymers. Bilayer scaffolds were designed by using different combinations of the polymer types in each layer and obtaining fiber orientation in outer layers. Scaffolds were analyzed morphologically and mechanically. Obtained results of mechanical performance were discussed according to the used polymer‐type composition, fiber orientation, and composite effect of both layer in the final graft. Smooth muscle cells were seeded on the scaffolds to test biocompatibility of presented scaffolds. Results indicate that the use of different biodegradable polymers in different combinations in each layer causes notable differences in fiber morphology and mechanical performance of the scaffolds. Moreover, fiber orientation in outer layer improves tensile strength and burst pressures in radial directions while creating a suitable fibrous layer for smooth muscle cells by mimicking the extracellular matrix of tunica media in native vessels. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal stability of surface-esterified cellulose and its composite with polyolefinic matrix

Thermal stability of hydrophobized cellulose powders was investigated from the perspective of potential use as filler in non-polar polyolefinic matrix. The hydrophobization was done by heterogeneous esterification with three carboxylic acids which differ in chain length (3, 10 and 18 carbons). Data measured by means of thermogravimetry (TG) were recalculated according to model-free isoconversional method to construct time–temperature plots. It was demonstrated that the esterification significantly decreases thermal stability of the material, which reduces feasible processing window. Under non-oxidative atmosphere, the single-step decomposition of materials is prevailing, while the process is more complex in air. In both cases the oleic acid esters showed the lowest stability and the original cellulose was the most stable. Finally, all powders were compounded with polyethylene or polypropylene. Obtained composites were then subjected to color measurement and TG. Even though the materials were partly degraded, which was indicated by the yellowish hue of the composites, virtually no impact of the filler pyrolysis on the polymer matrix decomposition was observed, particularly in case of decanoyl esters.     

Spectrometric and Chromatographic Study of Reactive Oxidants Hypochlorous and Hypobromous Acids and Their Interactions with Taurine

In this study, we focused on the studying of taurine complexes with phenol and sodium hypochlorite, and of taurine with sodium hypobromite by spectrometry, reverse phase chromatography and ion-exchange chromatography. The formed complexes were studied under various conditions such as temperature (10, 20, 30, 40, 50 and 60 °C), and/or time of interaction (0, 5, 10, 15, 20, 25 and 30 min). In addition, we optimized high performance liquid chromatography coupled with UV detector for detection of taurine and its complexes with the acids. Taurine–phenol–hypochlorite complex was effectively separated under isocratic elution, mobile phase water:methanol 30:70 %, v:v, flow rate 1 mL min^?1 and 55 °C. Taurine-bromamine complex was isolated under the following optimized conditions as isocratic elution, mobile phase water:methanol 85:15 % v:v, flow rate 1 mL min^?1 and 55 °C. The limits of detection (3 S/N) were estimated as 1 μM for both types of complexes, i.e. for taurine. Further, we estimated recovery in one sample of urine (male 25 years), commercially achieved energy drink and tea leaves and varied from 79 to 86 %. Further, we aimed our attention at investigating the ability of the above characterized taurine and taurine complexes to scavenge reactive oxygen species. For this purpose, an ion-exchange liquid chromatography with post-column derivatization with ninhydrin and VIS detector was used. It clearly follows from the results obtained that taurine itself reacts with peroxide more intensely than in a bound form, which can be associated with the highest signal decrease. Complexes stabilized structure taurine against peroxide radicals, resulting in slower decreasing of peak heights. The most stable was taurine complexes with phenol and hypobromite.     

Microfluidic tool based on the antibody-modified paramagnetic particles for detection of 8-hydroxy-2'-deoxyguanosine in urine of prostate cancer patients

Guanosine derivatives are important for diagnosis of oxidative DNA damage including 8-hydroxy-2'-deoxyguanosine (8-OHdG) as one of the most abundant products of DNA oxidation. This compound is commonly determined in urine, which makes 8-OHdG a good non-invasive marker of oxidation stress. In this study, we optimized and tested the isolation of 8-OHdG from biological matrix by using paramagnetic particles with an antibody-modified surface. 8-OHdG was determined using 1-naphthol generated by alkaline phosphatase conjugated with the secondary antibody. 1-Naphthol was determined by stopped flow injection analysis (SFIA) with electrochemical detector using a glassy carbon working electrode and by stationary electrochemical detection using linear sweep voltammetry. A special modular electrochemical SFIA system which needs only 10 μL of sample including working buffer for one analysis was completely designed and successfully verified. The recoveries in different matrices and analyte concentration were estimated. Detection limit (3 S/N) was estimated as 5 pg/mL of 8-OHdG. This method promises to be very easily modified to microfluidic systems as "lab on valve". The optimized method had sufficient selectivity and thus could be used for determination of 8-OHDG in human urine and therefore for estimation of oxidative DNA damage as a result of oxidation stress in prostate cancer patients.     

Effect of five different stages of ripening on chemical compounds in medlar (Mespilus germanica L.)

The study of changes of nutritional value of fruit during the ripening process can help estimate the optimal date for fruit harvesting to achieve the best quality for direct consumption and further utilization. The aim of this study was to monitor the changes of chemical composition of medlar fruit (Mespilus germanica L.) measured at five various ripening stages including 134, 144, 154, 164 and 174 days after full bloom (DAFB). Fruits were analyzed and ascorbic acid (AA) and total phenolic compound content with respect to the total antioxidant activity were determined. In addition, selected micronutrients and macronutrients were monitored. The results of our experiments demonstrate that ascorbic acid, total phenolic compound content and total antioxidant activity decreased significantly with increasing time of ripeness. The decreasing tendency in potassium, calcium and magnesium contents during the ripening stages was also determined. During the ripening period, the content of all micronutrients as well as phosphorus and sodium was balanced, with no statistically significant differences between the monitored ripening stages, which can be considered as a positive fact with respect to ideal consumption quality of fruit.