PubMed Health⌕ Search

Biomedical subjects

S Lora

Publications and source records attributed to S Lora.

28 records · Page 2Linked to original sources
PubMed1994

Glucose sensors based on enzyme immobilization onto biocompatible membranes obtained by radiation-induced polymerization.

Amperometric glucose biosensors based on glucose oxidase immobilized onto poly(2-hydroxyethylmethacrylate) membranes obtained by gamma radiation-induced polymerization were constructed. In a three-electrode configuration, smooth or platinized platinum electrodes with different shapes were used, in order to detect the amount of hydrogen peroxide produced in the glucose oxidation. A saturated calomel electrode and a platinum foil were used as a reference and counterelectrode, respectively. The biocompatible obtained sensors were characterized as regards the temperature effect, the response, and lifetime. The determination of glucose in standard solutions was carried out, and linear calibration curves were obtained. Depending on the electrode configuration, the sensor had a response time of 1-4 min, and the measuring range extended from 5 x 10(-5) to 4 x 10(-3) M.

Biosensing Techniques↗
PubMed1994

Radiation grafting of hydrophilic monomers onto poly[bis(trifluoroethoxy)phosphazene].

The hydrophilic monomers dimethylacrylamide (DMAA) and acrylamide (AAm) were radiation grafted onto poly[bis-(trifluoroethoxy)phosphazene] (PTFP) for biocompatibility enhancement through direct irradiation of the polymer films immersed in monomer-solvent mixtures, and the progress of grafting was followed up to a large monomer depletion. The water absorption of the samples was found to increase as the amount of the grafted chains increased. The grafted chains, mainly confined in the film surface at high dose rates, progressively extend to the interior of the sample as the dose rate decreases. In the grafted samples the ultimate mechanical properties epsilon r and sigma r were essentially preserved. The in vivo tests indicated an enhancement of surface biocompatibility in the PTFP-g-AAm samples and not in the PTFP-g-DMAA samples.

Absorption↗
PubMed1993

Polyphosphazenes as biomaterials: surface modification of poly(bis(trifluoroethoxy)phosphazene) with polyethylene glycols.

Investigations were carried out on the metathetical exchange reaction between the -O-CH2CF3 moieties of poly(bis(trifluoroethoxy)phosphazene) (PTFP), in the state of slightly swollen films, and the alkoxide ions derived from methoxypolyethylene glycol (MPEG) of molecular mass ranging from 350 to 5000 g/mol. The substitution of these hydrophilic chains, mostly confined to thin surface layers, was revealed by means of optical microscopy and scanning electron microscopy observations, surface elemental analysis by energy-dispersive X-ray analysis (EDXA), FTIR-ATR analysis and water contact angle measurements. The surface biocompatibility was enhanced in all cases, whilst the mechanical properties of the original PTFP films were substantially retained in the modified samples exhibiting low substitutions. Such samples were obtained especially when the metathetical reaction was carried out with MPEG5000.

Animals↗
PubMed1992

Controlled release of proteins and peptides from hydrogels synthesized by gamma ray-induced polymerization.

Hydrogels prepared by radiation-induced polymerization at a low temperature have been used as carriers for the controlled release of peptides and proteins. It was found that polymerization of 2-hydroxyethyl methacrylate in the presence of poly (ethylene glycol) methyl ether (MPEG) enabled the more porous and swellable matrics to be obtained, the higher the molecular weight of MPEG. As a consequence, protein release took place at an increasing extent and, provided that MPEG molecular weight was high enough, high molecular weight proteins could also be released. Such a state of affairs was not met in the case of hydrogels based on poly (2-hydroxyethyl acrylate). SEM analysis revealed that even high molecular weight MPEG did not give rise to any porosity, even though the degree of swelling was very high. As a result, no protein release was observed. It was therefore concluded that control of hydrogel porosity for the controlled release of large proteins is of overwhelming importance.

Alcohol Dehydrogenase↗
PubMed1991

Biocompatible polyphosphazenes by radiation-induced graft copolymerization and heparinization.

Investigations were carried out on the radiation-induced graft copolymerization by direct irradiation of dimethylaminoethyl methacrylate on to poly(bis(trifluoroethoxy)phosphazene) and on to poly (bis(phenoxy)phosphazene). Kinetics of grafting were followed with the polyphosphazenes immersed in monomer - methanol mixtures of various composition. The grafted film samples were quaternized with methyl iodide and, to the produced ammonium group, heparin was ionically bonded with high yield. On the grafted and heparinized-grafted film samples an evaluation of hydrophilicity, mechanical properties, biocompatibility and anticoagulating properties was carried out.

Animals↗
PubMed1991

In vitro and in vivo behaviour of narciclasine released from matrices based on poly (2-hydroxyethyl methacrylate).

Narciclasine (1,2,3,7-tetrahydroxy-8,9-methylendioxy-1,2,3,4-tetrahydrophena ntridone) is a natural substance with strong antimitotic effects on cells and potential antitumor activity. Its release form a hydrogel matrix was studied with the purpose of avoiding the concentration spikes of the parenteral administration. The matrix prepared by gamma ray polymerization of a mixture of 2-hydroxyethyl methacrylate (85%) and trimethylolpropane trimethacrylate (15%) was found to release narciclasine for several days, according to a diffusion controlled mechanism. In agreement with its antimitotic effect, narciclasine inhibited the growth rate of healthy mice, when the drug-loaded matrix was introduced subcutaneously. Antitumor effect was observed in an experimental model of Erlich ascitic tumor when low amounts of tumor cells were inoculated. No effect was observed at high concentrations of inoculum or towards solid tumors (Sarcoma 180). This behaviour was related to the rapid clearance of narciclasine from the body which prevented the reaching of sufficient therapeutical concentrations. A pharmacokinetic investigation carried out by an original method of assay demonstrated that narciclasine was accumulated in significant amounts in the kidney only and eliminated in urine with a half time of less than 20 min.

Alkaloids↗
PubMed1987

Radiation-induced polymerization for the immobilization of penicillin acylase.

The immobilization of Escherichia coli penicillin acylase (EC 3.5.1.11) was investigated by radiation-induced polymerization of 2-hydroxyethyl methacrylate at low temperature. A leak-proof composite that does not swell in water was obtained by adding the cross-linking agent trimethylolpropane trimethacrylate to the monomer-aqueous enzyme mixture. Penicillin acylase, which was immobilized with greater than 70% yield, possessed a higher Km value toward the substrate 6-nitro-3-phenylacetamidobenzoic acid than the free enzyme form (Km = 1.7 X 10(-5) and 1 X 10(-5) M, respectively). The structural stability of immobilized penicillin acylase, as assessed by heat, guanidinium chloride, and pH denaturation profiles, was very similar to that of the free-enzyme form, thus suggesting that penicillin acylase was entrapped in its native state into aqueous free spaces of the polymer matrix.

Amidohydrolases↗
PubMedDate not supplied

[Polymer biomaterials (polyphosphazenes) in the repair of peripheral nervous system].

Biodegradable polymers gives interesting perspectives of use in making artificial conduits for peripheral nerve reconstruction. Poliphosphazenes are materials highly biocompatible and have a controllable reabsorption rate. According to the substitutes that are introduced in the molecule, they can also be used as a framework for drug release. Conduits obtained with poli [bis(etilalanate) phosphazene] were evaluated as guides for nerve regeneration in an experimental animal model. In six Wistar rats, under general anesthesia and with microsurgical technique, the ischiatic nerve was isolated. On the right side a segment of the nerve was removed in order to create a 10 mm gap. The defect was then repaired using the conduit. On the controlateral limb the nerve continuity was restored using as an autograft the segment removed from the right. Control were performed at 30, 90, 180 days and consisted in histological and electron microscopy investigations. They showed the gradual degradation of the conduit without signs of local and general toxicity. The regeneration of the nerve fibers in the lumen of the conduit was not significantly different from the one obtained with the autologous grafts. So poliphosphazene conduits may be considered effective as a guide for nerve regeneration, above all for the possibility of use the polymer as a carrier for neurite-promoting factors.

Animals↗