Krzysztof Szczubiałka

pH-Sensitive Genipin-Cross-Linked Chitosan Microspheres For Heparin Removal

Chitosan hydrogel microspheres were obtained by cross-linking chitosan in its inverse emulsion using genipin as cross-linker. The genipin-cross-linked chitosan microspheres (ChGp) swell significantly in water at pH values below 6.5 and shrink to a smaller extent at pH values above 6.5. ChGp microspheres bind heparin in water. The kinetics of heparin binding was found to be pH dependent and was faster and more efficient at a lower pH. That can be also controlled by the weight of ChGp microspheres used. Rate and efficiency of heparin adsorption at pH 7.4, which is typical of blood, could be increased by quaternization of ChGp microspheres using glycidyltrimethylammonium chloride (GTMAC). The polymeric material obtained thus can be potentially useful for heparin removal in biomedical applications.

Photocatalytic degradation of sulfamethoxazole in aqueous solution using a floating TiO2-expanded perlite photocatalyst

Photocatalytic degradation of an antibiotic, sulfamethoxazole (SMX), in aqueous solution using a novel floating TiO2-expanded perlite photocatalyst (EP-TiO2-773) and radiation from the near UV spectral range was studied. The process is important considering that SMX is known to be a widespread and highly persistent pollutant of water resources. SMX degradation was described using a pseudo-first-order kinetic equation according to the Langmuir-Hinshelwood model. The products of the SMX photocatalytic degradation were identified. The effect of pH on the kinetics and mechanism of SMX photocatalytic degradation was explained.

Hydrogel membranes based on genipin-cross-linked chitosan blends for corneal epithelium tissue engineering.

Novel polymeric hydrogel scaffolds for corneal epithelium cell culturing based on blends of chitosan with some other biopolymers such as hydroxypropylcellulose, collagen and elastin crosslinked with genipin, a natural substance, were prepared. Physicochemical and biomechanical properties of these materials were determined. The in vitro cell culture experiments with corneal epithelium cells have indicated that a membrane prepared from chitosan–collagen blend (Ch–Col) provided the regular stratified growth of the epithelium cells, good surface covering and increased number of the cell layers. Ch–Col membranes are therefore the most promising material among those studied. The performance of Ch–Col membranes is comparable with that of the amniotic membrane which is currently recommended for clinical applications.

Chitosan Derivatives as Novel Potential Heparin Reversal Agents

In emergency cases anticoagulant action of heparin needs to be stopped instantaneously, which is usually achieved by intravenous administration of protamine sulfate (PS). However, PS shows many adverse effects. The objective of the present work was to find out if chitosan (Ch) and a cationically modified chitosan, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC), may be applied for heparin reversal. For chitosan the efficiency of unfractionated heparin (UFH) binding decreases with increasing pH while for cationically modified chitosan heparin binding is efficient even for high pH values. Complexation of UFH and low-molecular-weight heparin (LMWH) by cationically modified chitosan in the aqueous solution at pH = 7.4 was studied. Complexes of the modified chitosan with UFH are smaller and of lower dispersity than those with PS. Cationically modified chitosan was found to bind both UFH and LMWH. The complex formation capability of cationically modified chitosan is comparable to that of PS.

Cationic derivatives of dextran and hydroxypropylcellulose as novel potential heparin antagonists.

Cationic derivatives of dextran (Dex) and hydroxypropylcellulose (HPC) were studied as potential alternatives of protamine sulfate (PS) used in the reversal of anticoagulant activity of heparin. The modification was performed by the attachment of cationic groups to the Dex main chain or by grafting short side chains of a polycation onto HPC. The cationic derivatives of these polysaccharides were found to bind heparin with the efficiency increasing with growing degree of cationic modification. The degree of cationic modification and consequently the ζ potential of the polymers do not have to be high to achieve effective heparin binding. The size of the complexes of cationic Dex with unfractionated heparin (UFH) is a few micrometers. For complexes of cationic HPC and UFH the size is much below 1 μm, both below and above the lower critical solution temperature of HPC. None of the cationic polysaccharides studied caused hemolysis. The concentrations of the polymers inducing the aggregation of human erythrocytes in vitro were determined.

Photoactive Modified Chitosan

A water-soluble polymeric photosensitizer that contains naphthyl chromophores and absorbs light in the near UV region was obtained by modification of chitosan. The excitation energy can be used to induce photochemical reactions via energy and electron transfer.

Cationic derivative of dextran reverses anticoagulant activity of unfractionated heparin in animal models of arterial and venous thrombosis.

Heparin is a natural polymer widely used in medicine especially during the treatment of cardiovascular diseases since it is a potent blood anticoagulant. In case of emergency, e.g., massive hemorrhage, the anticoagulant activity of heparin has to be quickly stopped by the administration of a heparin reversing agent. Currently protamine sulfate, an allergenic protein, is used for this purpose. We are reporting the studies on a new polymeric substance, a cationic dextran derivative, which is able to form complexes with heparin. Dextran is a blood compatible polymer which is also frequently applied in medicine. By substituting dextran with glycidyltrimethylammonium chloride a cationic polymer was obtained that in vitro binds to heparin with an efficiency similar to that of protamine. To investigate the influence of modified dextran on the reversal of conventional heparin we used the models of experimental arterial thrombosis induced by electrical stimulation and chemically induced venous thrombosis. A decrease in bleeding time and activated partial thromboplastin time after administration of the cationic dextran to heparinized rats was found. Moreover, other routinely measured blood parameters are significantly affected. Modified dextran, in contrast to protamine sulfate, significantly increases red blood cell counts, hemoglobin level, and hematocrit value. The data we obtained show that the modified dextran may reduce anticoagulative heparin activity both under in vivo and in vitro conditions. Further clinical studies are needed to estimate whether modified dextran could replace protamine sulfate, especially in dialyzed patients with the end-stage renal disease associated with anemia.

Interactions of temperature-responsive anionic polyelectrolytes with a cationic surfactant

The interactions of temperature-responsive copolymers of sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with a cationic surfactant, dodecyltrimethylammonium chloride (DTAC), have been studied. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol%. The surface activity was higher for the polymers with lower AMPS content. It was found that DTAC undergoes association with the polymer chain, forming mixed polymer-surfactant micelles. The values of cac for the polymers were found in fluorescence studies using pyrene as the fluorescent probe. They were in the range 0.9-3.6x10(-3) M and were lower for polymers with higher AMPS content. An increase in DTAC concentration up to about its cmc results in a decrease of the LCST (lower critical solution temperature) of the copolymers, while further increase above the cmc results in an increase of the LCST. The minimum value of LCST in the presence of the surfactant is lower than the LCST of NIPAM homopolymer.

Photosensitized dechlorination of polychlorinated benzenes. 1. Carbazole-photosensitized dechlorination of hexachlorobenzene

Abstract Photosensitized dechlorination of hexachlorobenzene (HCBz) in hexane and in acetonitrile (MeCN) solutions as well as in aqueous solutions of poly(sodium styrenesulfonate-co-N-vinylcarbazole) (PSSS-VCz) copolymer has been studied. It was found that the reaction was photosensitized by both molecular and polymeric carbazole (Cz) chromophores. The products have been identified using GC, NMR and MS analyses. The detected products were: pentachlorobenzene, tetrachlorobenzenes, trichlorobenzenes, dichlorobenzenes, chlorobenzene and benzene. It was postulated that dechlorination process is mediated by an electron transfer from the excited carbazole chromophores to the molecule of chlorinated benzene with subsequent heterolytic cleavage of the CCl bond. The photosensitized by Cz dechlorination process is a stepwise reaction. The rate of photosensitized degradation of HCBz in aqueous PSSS-VCz solution was considerably higher than in organic solvents.

TiO2-coated EP as a floating photocatalyst for water purification

A water-floating photocatalyst composed of TiO2 deposited on perlite granules was synthesized and characterized. TiO2 was deposited by direct precipitation of titanium(IV) isopropoxide in the presence of perlite granules followed by calcination at three different temperatures. Temperature induced structural changes were monitored using UV-Vis, infrared and Raman spectroscopy, powder X-ray diffraction, BET surface adsorption, and scanning electron microscopy. The photocatalytic activity of the obtained materials was determined using a model reaction of the oxidative degradation of phenol. The ability of the obtained photocatalyst to float, combined with its ability to absorb solar light, makes it particularly well suited for the purification of shallow water reservoirs and industrial waste stabilization ponds.