Effect of Polyvinylidene Fluoride Membrane Production Conditions on Its Structure and Performance Characteristics.

Poly (vinylidene fluoride) membranes were prepared by freeze-casting. The effects of PVDF concentration, and freezing temperature on the morphology, crystallization, and performance of prepared membranes were examined. Polymer concentration was varied from 10 to 25 wt%. The freezing temperature was varied from -5 to -25 °C. Dimethyl sulfoxide (DMSO) and distilled water were used as solvents and non-solvents, respectively. The first step of this study was devoted to estimating the optimal concentration of PVDF solution in DMSO. Membranes prepared at different ratios were characterized using physical and mechanical characteristics and porosity. The second step was to optimize the time required for the production of the membranes. In the third step, it was shown that the freezing temperature had a remarkable effect on the morphology of the membranes: as the temperature decreases, there is a transition from spherulite structures to interconnected pores. It was shown that the diversity in the pore pattern for PVDF affects remarkably the water permeability through the polymer membrane. During the monitoring of the spread of crystallized areas during the formation of the membrane, it was found that the crystallization of the solvent begins at localized points of the microscale, further crystallized areas spread radially or unevenly along the surface of the solution, forming contact borders, which can lead to changes in the properties of the membrane in its area.

Force spectroscopy of interactions between Yersinia pseudotuberculosis and Yersinia pestis cells and monoclonal antibodies using optical tweezers.

The interactions of a microbial cell with host cells and humoral factors play an important role in the development of infectious diseases. The study of these mechanisms contributes to the development of effective methods for the treatment of bacterial infections. One of the possible approaches to studying bacterial adhesion to host cells is based on the use of the optical trap method. The aim of this work was to assess the significance of lipopolysaccharide O-antigen on the adhesiveness of Yersinia pseudotuberculosis using a model system including a bacterial cell captured by a laser beam and monoclonal antibodies (mAbs) bound covalently to a glass substrate. Registered interaction forces between Y. pseudotuberculosis cells and complementary antibodies to the O-antigen of lipopolysaccharide (LPS) or the B antigen outer membrane protein were 5.9 ± 3.3 and 2.0 ± 1.8 pN, respectively. Interaction forces between O-antigen deficient Y. pestis cells and the mentioned mAbs were 4.2 ± 2.9 and 9.6 ± 4.9 pN. The results are qualitatively consistent with earlier data obtained by using a model system based on polymer beads sensitized with LPS from Y. pseudotuberculosis and Y. pestis and surfaces coated by the aforementioned antibodies. This indicates that the immunochemical activity of Y. pseudotuberculosis cells is mediated mainly by the lipopolysaccharide. The model described can be used in similar studies of physicochemical and immunochemical mechanisms of bacterial adhesiveness.

Evaluation of intermolecular forces between lipopolysaccharides and monoclonal antibodies using atomic force microscopy.

Understanding of interactions between a bacterium and an immune or non-immune host organism at the cellular and subcellular level is important in order to improve new and existing immunobiological tools for the treatment of bacterial infections (including pseudotuberculosis). The aim of this work was to quantify the interaction force between Yersinia pseudotuberculosis and monoclonal antibodies (mAbs) in the model system "lipopolysaccharide (LPS) - mAbs" by atomic force microscopy (AFM). Our research findings provided the methodical approaches to force measurements between an AFM probe, which was functionalized with Y. pseudotuberculosis LPS, and mica coated by different mAbs. Based on the criteria for force estimation there was shown a greater binding force in the system "LPS - complementary mAbs" than in the system "LPS - heterologous mAbs". In both cases binding force increase followed by increase a contact time between the functionalized AFM probe and mica from 1 to 5 s. It has been shown that single bonds between LPS and complementary mAbs molecules also included a clearly defined non-specific component along with immunochemically specific one. The evidence suggests a significant proportion of applied force exerted to unfolding of high-molecular aggregates whose length may attain many hundreds of nanometers.

Force interactions between Yersiniae lipopolysaccharides and monoclonal antibodies: An optical tweezers study.

This article reports the force spectroscopy investigation of interactions between lipopolysaccharides (LPSs) of two species from Yersinia genus and complementary (or heterologous) monoclonal antibodies (mAbs). We have obtained the experimental data by optical trapping on the "sensitized polystyrene microsphere - sensitized glass substrate" model system at its approach - retraction in vertical plane. We detected non-specific interactions in low-amplitude areas on histograms mainly due to physicochemical properties of abiotic surface and specific interactions in complementary pairs "antigen - antibodies" in high-amplitude areas (100-120 pN) on histograms. The developed measurement procedure can be used for detection of rupture forces in other molecular pairs.

Assessment of Primary Cell Wall Nanomechanical Properties in Internal Cells of Non-Fixed Maize Roots.

The mechanical properties of cell walls play a vital role in plant development. Atomic-force microscopy (AFM) is widely used for characterization of these properties. However, only surface or isolated plant cells have been used for such investigations, at least as non-embedded samples. Theories that claim a restrictive role of a particular tissue in plant growth cannot be confirmed without direct measurement of the mechanical properties of internal tissue cell walls. Here we report an approach of assessing the nanomechanical properties of primary cell walls in the inner tissues of growing plant organs. The procedure does not include fixation, resin-embedding or drying of plant material. Vibratome-derived longitudinal and transverse sections of maize root were investigated by AFM in a liquid cell to track the changes of cell wall stiffness and elasticity accompanying elongation growth. Apparent Young's modulus values and stiffness of stele periclinal cell walls in the elongation zone of maize root were lower than in the meristem, i.e., cell walls became more elastic and less resistant to an applied force during their elongation. The trend was confirmed using either a sharp or spherical probe. The availability of such a method may promote our understanding of individual tissue roles in the plant growth processes.

AFM analysis reveals polymorphism of purified flax rhamnogalacturonans I of distinct functional types.

Functionally distinct polymers organized on the basis of rhamnogalacturonan I (RG-I) backbone with more than a half of rhamnose residues substituted by the side chains containing mostly galactose were purified from flaxseed mucilage, the primary cell wall of young hypocotyls and tertiary cell walls of bast fibers and characterized by atomic force microscopy. Seed mucilage RG-I with short side chains and unusual O3 substitution showed loose coils or star-like conformations. Primary cell wall RG-I, which included polygalacturonan (PGA) fragments, represented micellar objects and rare long chains. Pure RG-I with long galactan side chains, which was isolated as nascent polysaccharide before its incorporation into the tertiary cell wall of bast fibers was observed as long unbranched objects. RG-I entrapped by cellulose microfibrils in tertiary cell wall was visualized as compact micellar complexes. All types of flax RGs-I tended to aggregate. Relationships between RG-I structure and morphology are discussed.

Adhesive properties of calcium pectinate gels prepared from callus cultures pectins.

The aim of this research is to investigate the influence of the surface morphology of the calcium pectinate gel (CaPG) beads as well as the physicochemical characteristics of pectins and the CaPG beads on the adhesive properties of gels against the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Bacillus subtilis. The adhesion of the bacteria depends on the type of pectin and the surface morphology of the beads. The faster adhesion on CaPG beads appeared to be related to a lower degree of methyl esterification (DE), a higher molecular weight (Mw) and specific viscosity of the pectin and a higher gel strength. Surface roughness measurements were performed using an atomic force microscope. The beads from pectins with a higher Mw, a higher specific viscosity and a lower DE had a higher surface roughness. The surface roughness was one of the factors promoting adhesion of the bacteria onto the calcium pectinate gels. The surface morphology was observed under a scanning electron microscope (SEM). SEM images illustrated that E. coli and B. subtilis adhered on the beads with a rough surface. CaPG beads obtained from callus culture pectins can be proposed for the preparation of gels with adhesive and antiadhesive properties.

In vitro gastrointestinal-resistant pectin hydrogel particles for ß-glucuronidase adsorption.

Pectin hydrogel particles (PHPs) were prepared by ionotropic gelation of low methylesterified pectin of Tanacetum vulgare L. with calcium ions. Wet PHPs prepared from TVF exhibited a smaller diameter and the lower weight as well as exhibited the best textural properties in terms of hardness and elasticity compared to the PHPs prepared from commercial low methylesterified pectin (CU701) used for comparison. Upon air drying, PHPs prepared from CU701 became small and dense microspheres whereas the dry PHPs prepared from TVF exhibited a drop-like shape. The morphology of dry PHPs determined by scanning electron microscopy revealed that the surface of the TVF beads exhibited fibred structures, whereas the PHPs prepared from CU701 exhibited a smooth surface. The characterization of surface roughness using atomic force microscopy indicated less roughness profile of the PHPs prepared from TVF than CU701. PHPs prepared from TVF were found to possess in vitro resistance to successive incubations in simulated gastric (SGF), intestinal (SIF), and colonic fluid (SCF) at 37 °C for 2, 4 and 18 h, respectively. The PHPs prepared from CU701 swelled in SGF and then lost their spherical shape and were fully disintegrated after 4 h of incubation in SIF. The PHPs from TVF, which were subjected to treatment with SGF, SIF and SCF, were found to adsorb microbial ß-glucuronidase (ßG) in vitro. The data obtained offered the prospect for the development of the PHPs from TVF as sorbents of colonic ßG for the inhibition of re-absorption of estrogens.