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Biomedical subjects

P Vondrácek

Publications and source records attributed to P Vondrácek.

14 recordsLinked to original sources
PubMed2004

[A unique case of congenital muscular dystrophy].

The congenital muscular dystrophies (CMD, MDC) represent a heterogeneous group of autosomal recessive disorders manifesting in infancy by muscle weakness and hypotonia. Approximately 40% of patients with CMD have a primary deficiency of the laminin alpha 3. chain of merosin (laminin-2) due to mutations in LAMA2 gene. Laminin-2 bound to alpha-dystroglycan forms a link between actin--associated cytoskeletal proteins and the components of extracellular matrix. Disruption of this axis is responsible for several forms of muscular dystrophy. A unique case of congenital muscular dystrophy simulating a juvenile polymyositis in a muscle biopsy is presented. A profound reduction of alpha-dystroglycan and less pronounced secondary deficiency of alpha 2-laminin were found. All known forms of CMD were excluded, and the disorder was diagnosed as so far undescribed form of CMD. The mutation in a gene encoding the protein, that seems to play a role in a glycosylation of alpha-dystroglycan, is presumed.

Child↗
PubMed1993

Silicone rubber-hydrogel composites as polymeric biomaterials. IV. Silicone matrix-hydrogel filler interaction and mechanical properties.

Composite materials consisting of a silicone rubber matrix and particulate synthetic hydrogels were prepared and their mechanical properties were studied. The influence of the size, shape, aggregation of hydrogel particles, chemical reactions of polymer phases on tensile properties and tear strength of the composite materials were investigated. The relations between the properties, structure and chemical composition of polymer phases of the composite materials and their mechanical properties are discussed.

Biocompatible Materials↗
PubMed1991

Silicone rubber-hydrogel composites as polymeric biomaterials. III. An investigation of phase distribution by scanning electron microscopy.

The structure of silicone rubber-hydrogel composite materials was investigated by scanning electron microscopy (SEM) and light microscopy. The polymer phases in these materials composed of the polysiloxane matrix and very small particles of lightly cross-linked poly(2-hydroxyethylmethacrylate) or poly(2-hydroxyethylmethacrylate-co-methacrylic acid) were visualized using both methods. The distribution of polymer phases was studied by SEM of fracture surfaces of the materials. The results are discussed in relation to the transport properties of the materials.

Biocompatible Materials↗
PubMed1990

Silicone rubber-hydrogel composites as polymeric biomaterials. I. Biological properties of the silicone rubber-p(HEMA) composite.

A composite material was prepared consisting of silicone rubber matrix and particulate lightly cross-linked poly(2-hydroxyethyl methacrylate) (p(HEMA] hydrogel. The material resembling common silicone rubber is hydrophilic and swells in water like hydrogels. The effects of the implanted composite on tissues of the living organism were tested in rats by methods assessing local acute and chronic inflammatory reactions and calcification by means of radioactive indicators and by histological examination. Results of a 6 month implant study indicated no difference in reactions of the animal body on the silicone rubber-p(HEMA) composite and a non-toxic, non-irritant pure solid p(HEMA) control.

Animals↗
PubMed1990

Silicone rubber-hydrogel composites as polymeric biomaterials. II. Hydrophilicity and permeability to water-soluble low-molecular-weight compounds.

The surface and transport properties of water-swollen silicone rubber-hydrogel composites were investigated. Surface wettability of these materials, composed of a polysiloxane matrix and the hydrogel phase consisting of very fine particles of lightly cross-linked poly(2-hydroxyethylmethacrylate), increased markedly with increasing content of the hydrogel phase. For composite materials containing a lightly cross-linked 2-hydroxyethylmethacrylate (HEMA)-methacrylic acid (MAA) copolymer and polymethacrylic acid (PMAA) as the hydrogel phase, permeability to water-soluble organic compounds and drugs were measured. The permeability varied within a broad range depending on the composition and content of the hydrogel phase. High permeation rates could be obtained while still retaining relatively fair mechanical properties. Relationships between the composition of silicone rubber-hydrogel composites, their structure and the permeation coefficients of the individual permeates are discussed.

Biocompatible Materials↗
PubMed1989

In vivo degradation of polymers. I. Change of mechanical properties in polyethylene pacemaker lead insulations during long-term implantation in the human body.

The results of mechanical testing and microscopic examination of explanted clinically-used polyethylene pacemaker lead insulations are presented. An experimental set of 98 lead insulations implanted for times ranging from 7 d to 11 yr was evaluated for changes in mechanical properties during clinical use. The results showed that the polyethylene tubing suffered a gradual structural change, due to its exposure to the physiological environment of the human body. The decline of the mechanical properties with implantation time is described by empirical formulae. Abrasive deterioration was also observed and is discussed.

Electrodes, Implanted↗
PubMed1989

In vivo degradation of polymers. II. Change of mechanical properties and cross-link density in silicone rubber pacemaker lead insulations during long-term implantation in the human body.

The results of mechanical testing, microscopic examinations and swelling of the explanted clinically used silicone rubber pacemaker lead insulations are presented. An experimental set of 100 lead insulations implanted for times ranging from 3 d to 11 yr were evaluated for change of mechanical properties and cross-link density during clinical use. The results show that the silicone rubber tubing suffers a gradual structural change due to its exposure to the physiological environment of the human body. A spiral deformation pattern due to the permanent set of the silicone rubber tubing in contact with the electrode leading wire was observed.

Equipment Failure↗
PubMed1989

The role of sulfation in the metabolic activation of N-hydroxy-4'-fluoro-4-acetylaminobiphenyl.

The role of sulfation in the metabolic activation of the liver carcinogen N-hydroxy-4'-fluoro-4-acetylaminobiphenyl (N-OH-FAABP) in male rat liver was investigated. N-OH-FAABP was a substrate for sulfotransferases in vitro and sulfation was inhibited by the sulfotransferase inhibitors pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DCNP). The main metabolite of N-OH-FAABP excreted in bile in vivo, and in the isolated perfused liver, was identified as the N-O-glucuronide conjugate. Inhibition of sulfation in vivo by PCP or DCNP, or in vitro by omission of inorganic sulfate, resulted in a large increase in the excretion of the N-O-glucuronide conjugate. It was estimated that at least 21% of the dose was sulfated in control animals. Inhibition of sulfation in vivo by PCP or DCNP prevented the covalent binding of N-OH-FAABP to liver (and kidney) macromolecules by 70% and 20% respectively. HPLC analysis of the fluorobiphenyl DNA and RNA adducts showed that the formation of both N-acetylated and deacetylated (deoxy)-guanosine adducts was prevented. Furthermore, omission of inorganic sulfate in the isolated perfused liver prevented the formation of all fluorobiphenyl DNA adducts by 70-80%. It is concluded that two sulfotransferase-dependent pathways exist for the metabolic activation of N-OH-FAABP in male rat liver: (i) direct sulfation of the hydroxamic acid, resulting, upon decomposition of the FAABP-N-sulfate ester, in the formation of N-acetylated DNA adducts and (ii) deacetylation followed by sulfation of the hydroxylamine to FABP-N-sulfate, leading to the formation of deacetylation DNA adducts.

Aminobiphenyl Compounds↗
PubMed1984

Biostability of medical elastomers: a review.

Biostability of synthetic elastomers used for manufacturing artificial replacements of human organs or their parts is a critical property of such materials as it determines the long-term function of a specific biomedical device. This paper presents a critical review of the present knowledge of biostability of elastomeric biomedical materials used as artifacts functioning under the simultaneous effects of dynamic flexing and contact with body fluids. The main topics discussed are silicone rubber, elastomers for artificial blood pumps, and the methodology of model fatigue-life testing.

Animals↗