W. Marconi

New polyurethane compositions able to bond high amounts of both albumin and heparin: Part I

In order to prepare polymers provided with better haemocompatibility with respect both to the coagulative cascade and to platelet aggregation and activation, we have synthesized new polyurethanes containing in the chain-extender [di(2-hydroxyethyl)hexadecylamine] both a long chain alkyl group (able to bond albumin) and a tertiary ammonium group able, after suitable quaternization reaction, to bind ionically significant amounts of heparin. The amounts of heparin and albumin bonded to the polymer films were determined spectrophotometrically. A biological in vitro evaluation of the heparinized and albuminized films was also carried out with respect to blood coagulation factors (by activated partial thromboplastin time measurements) and to platelet adhesion and activation (by platelet count and scanning electron microscopy examination). It was seen that the type of adsorption sequence for albumin and heparin, respectively, onto the various homo- and copolymer films, plays an important role on their biological properties; the possible mechanisms involved are also discussed on the basis of X-ray photoelectron spectroscopy and attenuated transmission reflectance evaluation of the polymer surfaces.

Synthesis and physicochemical characterization of a hydrophilic Polyurethane able to bind heparin

The synthesis of a new segmented polyurethane containing quaternary ammonium groups in the side-chain is reported. The quaternization was carried out both on the polymer dissolved in an organic solvent and on polymer films. Polymeric films quaternized by both techniques were heparinized. The amount of bonded heparin, determined by spectrophotometry, was remarkably higher than previously described. Polymer quaternized in solution bonded more heparin than that heparinized directly on film. In vitro evaluations of antithrombogenicity by activated partial thromboplastin time (APTT) carried out on the films confirmed these data. The polymers were also characterized by chemical, i.r., n.m.r., differential scanning calorimetry and viscometric techniques.

Direct synthesis of carboxylated polyurethanes

Abstract The first direct synthesis of a carboxylated polyurethane is described. The polyurethane, of the segmented type, was obtained by reaction of 4,4′-diphenylmethane diisocyanate with poly(propylene oxide) and the tributylammonium salt of dihydroxymethylpropionic acid. The polymer was characterized by viscometry, DSC, i.r. and NMR spectroscopy. The reactivity of the free carboxylic group in the polymer was evaluated for esterification and amidation.

Sulfation and preliminary biological evaluation of ethylene-vinyl alcohol copolymers

Full Paper: In order to obtain polymers provided with improved haemocompatibility a commercial ethylene-vinyl alcohol copolymer (EVAL) was chemically modified by introduction of different amounts of sulfate groups. The sulfation reaction was carried out by the reaction was carried out by the reaction of hydroxy groups with two different sulfating reagents (CISO 3 H and PySO 3 ). The influence of the molar ratio of the reagents and the reaction time on the functionalization degree was evaluated also for elevated substitution degrees. No difference in the sulfation agents efficiency was noted. the new terpolymers (EVAL-SO 3 H) have been characterized by chemical and physico-chemical techniques as: titration of the acidic groups, Fourier Transform IR reflectrance spectroscopy (FTIR-ATR), differential scanning calometry (DSC), X-ray photoelectron spectroscopy (XPS° and 1 H-NMR. The haemocompatibility was evaluated by in vitro plasma coagulation (APTT) and platelet aggregation tests and is proved to be excellent for sulfation degrees higher than 35% of the hydroxylgroups of the polymer.

New polyurethane compositions able to bond high amounts of both albumin and heparin: II: Copolymers and polymer blends

Haemocompatible new urethane copolymers and polymer blends containing, in the chain extender, a long chain alkyl group (able to bond albumin) or a tertiary ammonium group able, after suitable quaternization reaction, to bind ionically significant amounts of heparin, were prepared. The copolymers were characterized by differential scanning calorimetry, intrinsic viscosity determinations, infrared spectroscopy and nuclear magnetic resonance (1H and 13C). Biological in vitro evaluation has shown that the adsorption sequence for albumin and heparin, respectively, onto films of the various copolymers and blends, exerts a great influence. From scanning electron microscopy measurements it was seen that the bonding type of albumin to the polymer films plays a determining role on the platelet activation. A phase segregation occurring on the polymer blends surface was demonstrated by X-ray photoelectron spectroscopy measurements.

Synthesis and characterization of novel carboxylated ethylene-vinyl alcohol polymers

Abstract In order to obtain polymers provided with improved haemocompatibility a commercial ethylene-vinyl alcohol copolymer (EVAL) was chemically modified by the introduction of different amounts of carboxylated groups. The carboxylation was carried out by reaction of the EVAL hydroxy groups with three different anhydrides. The influence of the reagents molar ratio on the functionalization degree was evaluated. The new terpolymers (EVAL–COOH) have been characterized by chemical and physico-chemical techniques as titration of the acidic groups, elemental analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and 1 H-NMR.

Immobilized enzymes: their catalytic behaviour and their industrial and analytical applications☆

Abstract This state-of-the-art report reviews the history of enzyme fixation, methods for immobilization, kinetics of reactions catalyzed by immobilized enzymes, their practical applications as catalysts in organic chemistry and as agents in analytical chemistry, and the technique of immobilization of whole cells and its use in industrial practice. Future prospects are pointed out.

Synthesis and characterization of new amphiphilic polyurethane compositions

Abstract New segmented polyurethanes containing in the chain extender molecule (dihydroxyethyl- n -hexadecylamine, DHHA) both a hydrophobic long alkyl group and a tertiary ammonium group (whose polarity was further increased by quaternization reaction), are described. In order to evaluate the influence of the chain extender content on the polymer properties, also polymers containing DHHA and 1,4 butanediol at different molar ratios have been prepared. The obtained polymers were characterized by i.r., NMR, DSC, viscometry and water swelling measurements.

The Absorption of Cephalosporin on Vinyl Polymers to Form Antibacterial Surfaces

In order to obtain antimicrobial polymer compositions potentially suitable for catheter fabrication, a cephalosporin was bonded to ethylene-vinyl alcohol copolymers and to their derivatives containing hydrophilic positively or negatively charged groups. The polymers were characterized by chemical and physico-chemical techniques. The antibiotic was adsorbed at a density of 1.3 mg/cm2 onto the unaffected polymer surface. The density was increased up to 1.78 mg/cm2 when the polymer was derivatized. The elution rate of the antibiotic from the surfaces and its antimicrobial activity were determined. The underivatized polymer has shown antimicrobial activity for 24 h whereas the carboxylated polymer was active for 72 h. During this time 32% of the antibiotic was eluted from the underivatized polymer and approximately 15% from the derivatized polymer.

Study of fumarase activity in non-conventional media. Part II

Abstract The hydration of fumarase and the dehydration of l -malate catalysed by fumarase were investigated in water/methanol and water/formamide one phase systems. The effects of the amount of organic solvent on the maximum velocity ( V max ), the Michael is-Menten constant ( K M ) and the equilibrium constant ( K eq ) were studied for both the reaction media. The denaturing power of both methanol and formamide was observed together with the familiar decrease of the K M . Fumarase catalysis in water/methanol systems was further investigated by evaporating the organic solvent and evaluating the degree of reversibility of the inactivation. Reversibility of formamide denaturation was also investigated. The effects of phosphate concentration in the reaction medium with different amounts of methanol was investigated following the variation of the kinetic parameters of the hydration reaction. At high concentrations of phosphate an inhibiting effect appeared. Time-dependent denaturation was also investigated and a remarkable instability of fumarase in systems with percentages ( v/v ) of formamide higher than 10% was observed. 10% formamide proved to be less deactivating than the other non-conventional reaction media so far employed.