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Biomedical subjects

F Rypácek

Publications and source records attributed to F Rypácek.

17 recordsLinked to original sources
PubMed2004

Cell adhesion on artificial materials for tissue engineering.

Advanced interdisciplinary scientific field of tissue engineering has been developed to meet increasing demand for safe, functional and easy available substitutes of irreversibly damaged tissues and organs. First biomaterials were constructed as "two-dimensional" (allowing cell adhesion only on their surface), and durable (non-biodegradable). In contrast, biomaterials of new generation are characterized by so-called three dimensional porous or scaffold-like architecture promoting attachment, growth and differentiation of cells inside the material, accompanied by its gradual removal and replacement with regenerated fully functional tissue. In order to control these processes, these materials are endowed with a defined spectrum of bioactive molecules, such as ligands for adhesion receptors on cells, functional parts of natural growth factors, hormones and enzymes or synthetic regulators of cell behavior, incorporated in defined concentrations and spatial distribution against a bioinert background resistant to uncontrolled protein adsorption and cell adhesion.

Animals↗
PubMed2003

Functionalized surfaces of polylactide modified by Langmuir-Blodgett films of amphiphilic block copolymers.

To modify the surface of poly(L-lactide) (PLA) supports, we have investigated the feasibility to deposit on the PLA surface Langmuir-Blodgett films of amphiphilic block copolymers based on poly(L-lactide). AB and ABA block copolymers were prepared with PLA as the A block and either poly(ethylene oxide), alpha-methoxy-omega-hydroxy poly(ethylene oxide), alpha-carboxy-omega-hydroxy poly(ethylene oxide) or poly(L-aspartic acid) as the B blocks. Films with phase-separated hydrophilic and hydrophobic blocks in a bilayer "brush" structure were prepared by compression of the copolymer Langmuir films on the water/air interface. The interfacial behavior of the monolayers and the effect of the copolymer composition on the phase separation was followed by measurements of the surface-pressure/area isotherms using a Langmuir trough and by contact angle measurement of deposited Langmuir-Blodgett (LB) films. The phase separation of the hydrophilic and PLA blocks is more effective in diblock AB copolymers compared with triblock ABA copolymers. The presence of ionic groups in the hydrophilic chains facilitates penetration of hydrophilic segments into the water subphase. Dynamic contact angle measurements were used to study the stability of the LB-films transferred on the PLA support and the changes in the surface properties upon incubation of surfaces in water.

Journal Article↗
PubMed2000

Microdomain structure in polylactide-block-poly(ethylene oxide) copolymer films.

Structured surface is an important property of polymer biomaterials for tissue engineering, for its capacity to expose domains with different surface energy and functional groups. For this purpose, amphiphilic A-B-A block copolymers with polylactide (PLA) as A blocks and poly(ethylene oxide) (PEO 3, Mn = 3090; PEO6, Mn = 6110) as B block were synthesized by ring-opening polymerization of either L-lactide (L-LA) or DL-lactide (DL-LA), using poly(ethylene glycol)s as macroinitiators and tin(II) octanoate (Sn(Oct)2) as a catalyst. Differential scanning calorimetry (DSC) and electron microscopy were used to study the phase separation of the hydrophobic (PLA) and hydrophilic (PEO) segments in films made of the copolymers and their blends with high-molecular-weight PLA homopolymers. Hydrophilic (PEO) and hydrophobic (PLA) domains were formed at the polymer film surface due to the separation of phases. The phase separation was affected by the copolymer composition and the stereoregularity of PLA blocks in the copolymers.

Biocompatible Materials↗
PubMed1997

New radiopaque polyHEMA-based hydrogel particles.

New iodine-containing polymeric hydrogel particles were prepared by suspension radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), 3-(methacryloylamidoacetamido)-2,4,6-triiodobenzoic acid (MABA) and ethylene dimethacrylate (EDMA) in an aqueous medium using azobisisobutyronitrile as an initiator and magnesium hydroxide as a suspension stabilizer. To impart porosity to the product, cyclohexanol and 1-dodecanol were added as inert diluents to the polymerization mixture. Particles containing 27 wt % iodine produced radiopacity sufficient to observe a clearly visible X-ray image. The equilibrium swelling behavior of the particles in water was characterized. Swelling of the particles dramatically increased by converting the acid groups of MABA into their Na+ form. The more MABA the copolymer particle contain, the higher is their swelling in the Na+ form.

Biocompatible Materials↗
PubMed1994

A study of enzymic degradation of a macromolecular substrate, poly[N5-(2-hydroxyethyl)-L-glutamine], by gel permeation chromatography and kinetic modelling.

The enzymatic degradation of poly[N5-(2-hydroxyethyl)-L-glutamine] (PHEG) by papain was investigated with the aim of evaluating the role of the random and/or a non-random mechanism of cleavage. The random degradation was modelled experimentally by the reaction of PHEG with ethanolamine. Assuming that different mechanisms of cleavage would yield different molecular weight distributions (MWDs) of the polymer degraded to the same degree, the evaluation was based on the comparison of experimental MWDs, measured by gel permeation chromatography, with MWDs simulated kinetically for the assumed mechanism of degradation. While a very good fit through a broad range of degradation conversions was obtained between the MWDs simulated for a random process and the experimental MWDs of the degradation of PHEG by ethanolamine, the enzymic degradation of PHEG by papain was certainly not a random process. Two models were found to be compatible with the chromatographic data: (i) a multiple attack assuming that the subsequent cleavage may proceed only on one of the two fragments produced by the previous attack, or (ii) a model which assumes that the degradation rate of one bond in a macromolecule of molecular weight M is proportional to M-1/3, i.e. a model which stresses the role of the surface of the polymer coil. In both simulations of enzymic degradation, the two bonds on each end of the PHEG chain were assumed not be cleavable.

Binding Sites↗
PubMed1992

Polymer-bound enzyme inhibitors: synthesis, properties, and physiological relevance.

For the most part, the pharmacological effect of an enzyme inhibitor results from its interaction with a single target molecule--the target enzyme. In many cases, the inhibitor moiety can interact effectively with the enzyme without necessarily being released from the polymer carrier. In the simplest form, i.e., the inhibition of an extracellular enzyme, this interaction can be understood as being two macromolecules in a solution--a reaction that can be readily modeled in vitro. Thus, enzyme inhibitors are very suitable for preparing polymer-bound drugs for investigative purposes or therapeutical applications. The macromolecular properties of polymers impact on the pharmacokinetic behavior of the compound because of the controlled intercompartmental transport. The physiological significance of the polymer-bound enzyme inhibitors is considered herein regarding the factors controlling the biodistribution of polymers among the physiological compartments. Extracellular proteinases and lysosomal enzymes are the most easily approachable targets. Strategies for preparation of polymer-bound inhibitors are discussed.

Animals↗
PubMed1990

Degradation of N5-(2-hydroxyethyl)-L-glutamine and L-glutamic acid homopolymers and copolymers by papain.

The rate of degradation of poly[N5-(2-hydroxyethyl)-L-glutamine] (PHEG), poly(L-glutamic acid) (PGA) and poly[HEG-co-GA] random copolymers by papain was measured in the pH range 4.0-7.5, employing the gel permeation chromatography method. The effect of the degree of ionization on the polymer conformation was measured by circular dichroism (c.d.). PHEG, which is uncharged, had a random coil conformation and an almost constant degradation rate within the whole pH interval. The ionization of PGA increased with increasing pH and was accompanied by conformational transition from helix to random coil. The hydrolysis of PGA by papain depended on pH with the optimum at about pH 5, indicating that both the high content of helix (at pH less than 5) and increasing charge density (at pH greater than 5), decreased the degradation rate. Contrary to PGA, pH profiles of the degradation rate of poly[HEG-co-GA] copolymers are monotonous and do not decrease at pH less than 5. In the copolymers the HEG residues act as a helix breaker and limit the formation of helical conformation. The role of structural features of a macromolecular substrate, i.e. the charge, helical conformation and the nature of amino acid residues, in the interaction between enzyme and polymer is discussed.

Chromatography, Gel↗
PubMed1990

Transport of novel ovum surrogates in the human fallopian tube: a clinical study.

Functional inadequacy of the fallopian tube cannot be adequately diagnosed by classical tubal patency tests. A new method using novel ova surrogates, microspheres transport test, is designed to diagnose dysfunctional tubal sterility. Biodegradable test microspheres with diameters matching that of the native ovum were used. According to the optimum procedure, the suspension of test microspheres was applied through the vaginal wall into the Douglas' space under local anesthesia, and the transported microspheres were collected in a modified cervical cap. The microspheres were readily identified in the sediment of cervical secretion by their fluorescence. The method was tested in 139 long-term infertility patients. Transport was observed in 100% of the control group, and positive correlation between the transport findings and the anticipated frequencies of dysfunctional tubal sterility cases in other groups was found. Optimum diameter of test microspheres was estimated at about 175 microns. The test appears to be useful for examination of functional disorders of the ovum transport in human practice.

Adult↗
PubMed1985

Characterization of the adsorptive pinocytic capture of a polyaspartamide modified by the incorporation of tyramine residues.

Previously it has been shown (Duncan, R., Starling, D., Rypácek, F., Drobník, J. and Lloyd, J.B. (1982) Biochim. Biophys. Acta 717, 248-254) that incorporation of tyramine residues into poly (alpha, beta-(N-2-hydroxyethyl]-DL-aspartamide (PHEA) greatly increases its rate of pinocytic uptake by rat visceral yolk sacs cultured in vitro. Here we describe the relationship between the tyramine content (1.2-21.9 mol%) of modified PHEA and its rate of uptake by yolk sacs. Above a level of substitution of approximately 10 mol% the rate of uptake rises rapidly, and the concentration-dependence of capture is indicative of uptake by adsorptive pinocytosis. Serum proteins were shown to compete effectively for membrane binding sites, indicating a nonspecific interaction of PHEA-derivatives with the yolk sac membrane. PHEA derivatives of the same tyramine content, but of different mean molecular weights (Mr), were captured at the same rates.

Adsorption↗
PubMed1985

Retention and biliary excretion of poly-alpha, beta-[N(2-hydroxyethyl)-D,L-aspartamide] (PHEA) and its tyramine derivative (PHEA-Tyr) by isolated perfused rat liver. The role of molecular weight and chemical structure.

Isolated rat liver was perfused with fractions of fluorescent labelled poly-alpha,beta-[N(2-hydroxyethyl)-D,L-aspartamide] (PHEA), (Mw:8000, 51 400 and 70 000) and its tyramine derivative, PHEA-Tyr (19 mol% tyramine side chains; Mw:8000 and 35 000) under conditions approximating an "in vivo" situation. By an analysis of the recovered polymers it was shown, firstly that accumulation of polymers, which occurred most apparently in the Kupffer cells, was neither affected by the presence of tyramine side chains nor influenced by the molecular weight of polymers; secondly that the tyramine side chains slightly increased the biliary excretion of PHEA-Tyr, and thirdly with both types of polymers the excretion of high-molecular-weight fractions in the bile was strongly suppressed.

Animals↗
PubMed1984

Cisplatin-induced tubular injury studied by water-soluble synthetic polymers.

Accumulation of a synthetic water-soluble polymer, poly-alpha, beta-[N(2-hydroxyethyl)-D,L-aspartamide-co-N(4-hydroxyphenethyl )- D,L-aspartamide] in the cells of kidney proximal tubules was used as an indicator for the functional localization of Cisplatin (CDDP) induced tubular injury in rats. Tubular accumulation of polymer was examined using 131I and fluorescence labelling for quantitative as well as morphological evaluation. It was found that reabsorption of the polymer, in which mainly the epithelium of proximal convolutions is involved, remains unaffected upon CDDP treatment in the course of one to six days after the drug administration. This finding supports on the functional level the morphological localization of CDDP injury into the straight segment of the proximal tubule.

Animals↗
PubMed1982

Pinocytosis of poly (alpha, beta-(N-2-hydroxyethyl))-DL-aspartamide and a tyramine derivative by rat visceral yolk sacs cultured in vitro. Ability of phenolic residues to enhance the rate of pinocytic capture of a macromolecule.

Incorporation of 20% tyramine residues into its structure greatly increased the rate of pinocytosis of poly(alpha, beta-(N-2-hydroxyethyl))-DL-aspartamide (PHEA) by rat visceral yolk sacs cultured in vitro. Both the parent macromolecule and the tyramine derivative (PHEA-tyramine) were captured by adsorptive pinocytosis, the higher affinity of the derivative for the yolk sac plasma membrane being responsible for its greater rate of capture. Using 125I-labelled PHEA-tyramine, the relationship between substrate concentration and rate of capture was determined, it was also shown that following internalization, the PHEA-tyramine linkage is resistant to intracellular hydrolysis. Fluorescence micrographs were consistent with capture of both substrates being by pinocytosis and illustrated the highly efficient concentration of the tyramine derivative by yolk sac endodermal cells.

Animals↗
PubMed1982

The renal excretion and retention of macromolecules: The chemical structure effect.

Five derivatives of polyaspartamide were used as macromolecular models to study the effect of chemical structure of macromolecules on their renal excretion and retention. The parent polymer was formed solely by N(2-hydroxyethyl)aspartamide units (I) and in its derivatives about 20% of 2-hydroxyethyl groups were randomly replaced by either n-butyl- (II), 2(4-hydroxyphenyl)ethyl- (III, N- dimethylamino propyl- (IV) or the aspartamide unit was modified to free aspartic acid carboxyl (V). The rate of clearance from the serum, the deposition in the kidney tissue in comparison with the deposition in reticuloendothelial system organs-liver and spleen, as well as tissue and cellular localisation of deposits were studied on rabbits and mice taking advantage of fluorescence labelling. The clearance of macromolecular models from the serum compartment by the glomerular filtration is mainly molecular weight controlled, while the retention of macromolecules possessing the same molecular weight by the kidney tubular epithelium is strongly affected chemical modification. About thirty and hundred times higher retentions due to reabsorption in proximal tubule were found with macromolecular models II and III respectively.

Animals↗
PubMed1982

Effect of polyethylene glycol on the rate of immune complex formation by non-precipitating antibody.

A kinetic study formation of large size complexes of non-precipitating pig-Dnp anti-Dnp antibody and multivalent dinitrophenylated serum albumin was performed using light scattering and absorption spectroscopy of the Dnp-group. A very rapid phase of the process resulted in the formation of complexes having molecular weight of about 2 X 10(6). Further increase of the complex size was much slower. Addition of PEG affected positively the rate of complex growth even in concentrations below 1%. The spectroscopic kinetic curves also showed a rapid and a slow phase, sensitive to the presence of PEG. The character of the kinetic data does not support the simple view that polymers enhance precipitate-formation by the steric exclusion of complexes from the polymer domains. It can be assumed that the interaction of the polymer with the antigen-antibody system consists of a subtle temporary attachment of the polymer to the antibody molecule resulting in a change of the shape and/or flexibility of the antibody molecule, favouring its cross-linking capacity.

Absorption↗