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Biomedical subjects

A Bartkowiak

Publications and source records attributed to A Bartkowiak.

At least 19 recordsLinked to original sources
PubMed2005

Biocompatible oligochitosans as cationic modifiers of alginate/Ca microcapsules.

In the past, it has been proven that by properly adjusting the molecular mass of the oligochitosan samples, it is possible to optimize the formation of rigid, biocompatible capsules with semipermeable membranes under physiological conditions. In this study, the feasibility of four oligochitosan samples, with varying molar masses (M(n) in range 3-5 kDa), as biocompatible coatings of alginate/Ca capsules was investigated. By selection of appropriate depolymerization and purification methods we obtained oligochitosan samples that appeared to be noncytotoxic for C(2)C(12) myoblasts and did not influence the mammalian cell metabolism especially in relative short time during the process of capsule formation. Furthermore, oligochitosans can be used as a tool to reduce the membrane cut-off of the alginate capsules. However, such reduction, as well as mechanical resistance of formed microcapsules, depend on MM of the cationic polysaccharide and the chemical composition of the alginate (mannuronic/guluronic acid ratio). Here, we address that the use of low molar mass chitosan (< 5000 g/mol) permits the formation of mechanical stable capsules at physiological pH, which represents a strong advantage over other chitosan-based chemistries.

Alginates↗
PubMed2001

Carrageenan-oligochitosan microcapsules: optimization of the formation process(1).

The formation of new microcapsules based on polyelectrolyte complexes between carrageenans and oligochitosan has been investigated. The optimization of the process, which includes the selection of the most suitable solvent and investigation of the influence of reaction conditions on capsule properties, is presented. Iota-carrageenan (1.2-2% wt.) prepared in HEPES buffer was found to be the most suitable for the formation of mechanically stable capsules. These new capsules combine extremely high deformability (>90%) and elasticity with permeability control and can be applied in various bioencapsulation technologies. It has been shown that the reaction time influences the mechanical properties, whereas carrageenan concentration and the temperature during the capsule formation effect both mechanical and porosity characteristic of the membrane. Moreover, the temperature influences the kinetics of the diffusion through the complex iota-carrageenan/oligochitosan membrane. In general egress is faster above the sol-gel transition point, indicating applicability in thermo-induced releasing systems.

Journal Article↗
PubMed2001

Optimal conditions of transplantable binary polyelectrolyte microcapsules.

Binary polyanion/oligocation microcapsules, prepared in a one-step process, are proposed as an alternative to the common alginate/poly-L-lysine system used in bioencapsulation technology. The model system is based on natural polysaccharides and involves the anionic sodium alginate, or iota-carrageenan, complexed with cationic oligochitosan. This system has been characterized with respect to capsule formation, mechanical strength, and permeability. This paper provides a general description of the influence of the most pronounced parameters that can be used as a tool to modulate the properties of binary microcapsules. These parameters have been separated into two categories. The first, which includes molar mass of polyanion, pH, ionic strength, and concentration of both polyelectrolytes, can be used to simultaneously control capsule mechanical and structural properties. The second set, molar mass of polyanion and reaction time, influences only mechanical resistance without altering membrane permeability. Additional issues related to mechanical stability and the possible change of capsule properties following transplantation are discussed.

Animals↗
PubMed2000

Physical and mechanical behavior of electron-beam irradiated and ethylene oxide sterilized multiblock polyester.

The effect of two sterilization treatments (electron-beam radiation and ethylene oxide gas) on the structure and mechanical properties of a multiblock copolymer were investigated to establish the effects of the sterilizing procedures on potential biomedical material. The material was exposed for different radiation doses in order to find an optimum dose of electron-beam radiation. Characterization techniques employed include gel permeation chromatography, infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and tensile testing. The optimal dose of radiation at which no change in structure and mechanical properties occurred was found as 25 kGy. Ethylene oxide gas treatment also did not affect the structure and properties of the polymer and it can be recommended as an alternative sterilization route for the studied polymer.

Journal Article↗
PubMed1999

New microcapsules based on oligoelectrolyte complexation.

A new one-step microencapsulation procedure has been developed. For the alginate/oligochitosan system the molar mass of the chitosan is a key parameter in the formation of stable, elastic capsules with high modulus. Furthermore, the selection of an optimum molar mass provides an additional degree of freedom, permitting the simultaneous regulation of mechanical properties and permeability without the need for multicomponent organic-inorganic chemistries as have been previously employed. The effects of molar mass of chitosan, its concentration, the alginate molar mass and its metal salt on the preparation, physical properties, and release characteristics of the capsules have been studied.

Alginates↗
PubMed1999

New multicomponent capsules for immunoisolation.

A new generation of microcapsules based on the use of oligomers which participate in polyelectrolyte complexation reactions has been developed. These freeze-thaw stable capsules have been applied as a bioartificial pancreas and have resulted in normoglycemia for periods of six months in concordant xenotransplantations. The new chemistry permits the control of permeability and mechanical properties over a wide range and can be adapted both to microcapsule and hollow fiber geometries rendering it a robust tool for encapsulation in general. Methods, and metrics, for the characterization of the mechanical properties and permeability of microcapsules are presented.

Artificial Organs↗
PubMed1990

[Effect of superoxide dismutase on the number of chromosome aberrations in lymphocytes after irradiation of human blood preparations].

The aim of the present study was to determine the radioprotective effects of endo- and exogenous SOD on the number of post-radiation chromosomal aberrations in human lymphocytes from irradiated samples of whole blood. Blood samples from 17 donors were irradiated with the dose of 1 Gy of neutron radiation or with 2 Gy of gamma radiation. Specific endogenous activity of SOD was assessed in lymphocytes from both irradiated and non-irradiated blood samples. Lymphocytes were then cultured in standard conditions with the application of PHA as a stimulator of cell divisions. The rate of chromosomal aberrations was determined in lymphocytes obtained from these cultures. Preliminary results revealed relatively low SOD activity in lymphocytes from normal (non-irradiated) blood samples, though it could vary among individuals from 1.19 to 8.81 U/mg of protein (in extreme cases the differences are even eight-fold). In further experiments, however, no relationship between the level of endogenous SOD activity and number of postradiation chromosomal aberrations was found (exposure of blood samples to the dose of 1 Gy of neutron high LET radiation.

Chromosome Aberrations↗
PubMed1984

Aging of the erythrocyte. XIX. Decrease in surface charge density of bovine erythrocytes.

Decrease in electrophoretic mobility of erythrocytes, increase in Km of erythrocyte membrane acetylcholinesterase and decrease in the binding constant of 8-anilino-1-naphthalene sulfonate to erythrocyte membranes demonstrate a decrease in surface charge density of bovine erythrocytes during in vivo aging. This phenomenon seems to be species-specific; it may be due to a diminution of the sialic acid content but may also be contributed by conformational changes of membrane proteins.

Acetylcholinesterase↗
PubMed1983

Aging of the erythrocyte--XVII. Changes in the properties of superoxide dismutase.

1. An increase in the sensitivity of superoxide dismutase (SOD) to the action of diethyldithio-carbamate and cyanide was observed in red cell fractions of greater age. 2. It suggests that SOD inactivation during erythrocyte aging is not an "all or none" process but involves transition(s) between enzyme forms of different properties. 3. An increase in the ratio of less mobile to the more mobile SOD bands was observed by polyacrylamide-gel-electrophoresis in older erythrocytes.

Animals↗
PubMed1982

The crypto-OH radical in the damage of DNA by bleomycin-Fe2+?

1. Effects of various OH scavengers, superoxide dismutase and catalase on the formation of malondialdehyde-like products from DNA by bleomycin-Fe2+ were studied. In no case was a protective effect observed. 2. These results can be interpreted on the basis that a crypto-OH radical mediates the damage to DNA by bleomycin-Fe2+.

Bleomycin↗
PubMed1982

Study of the effects of paraquat on the peroxide metabolism enzymes in guinea-pig.

1. Guinea-pigs, which exhibit a similar metabolism to that of man insofar as they are incapable of synthesizing ascorbic acid, were poisoned with Gramoxon containing the LD50 or LD100 of paraquat. 2. A study was made of how the paraquat poisoning affected previously investigated tissue parameters, the superoxide dismutase, catalase and glutathione peroxidase activities and the lipid peroxidation. 3. In accordance with earlier results, the paraquat influences these parameters in different ways in all the tissues examined, depending on its concentration. 4. These parameters comprise primarily affected systems as regards paraquat toxicity.

Animals↗
PubMed1982

Effect of .OH scavengers on radiation damage to the erythrocyte membrane.

Thiourea, and .OH scavenger, reduced the gamma-radiation-induced changes in the rigidity of erythrocyte membrane lipids, the state of membrane proteins, and lipid peroxidation. Several .OH scavengers, but not superoxide dismutase, also inhibited the radiation-induced acceleration of the transport of a hydrophilic non-electrolyte spin label TEMPOL across the erythrocyte membrane. The effects of scavengers were usually biphasic with a maximum of the protective effect. Higher concentrations of the scavengers were less effective, as in the case of radioprotection of erythrocytes to haemolysis studied previously.

Animals↗