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Biomedical subjects

R P Franke

Publications and source records attributed to R P Franke.

At least 19 recordsLinked to original sources
PubMed1997

[Hemocompatibility of various synthetic granulates].

The adherence of platelets to different polymer granulates was examined in a perfusion chamber filled with platelet-rich plasma. The surface area of each of the granulates was of a standardised size. The results were compared with those found for a non-thrombogenic and a highly thrombogenic foreign-body surface. The three polymers examined-Cryolite, Styrolux and Zylar-must be considered non-thrombogenic. Platelet adherence to these substances is significantly less (3%) than that to a highly thrombogenic surface such as glass (95%). The three materials did not differ in terms of platelet adherence, and would appear to be suitable potential materials for use in cell separators.

Biocompatible Materials↗
PubMed1996

Sensitivity of femoral strain pattern analyses to resultant and muscle forces at the hip joint.

An automated geometrical preprocessor was developed with the aim of creating three-dimensional finite element models (FEM) of the human femur. On the basis of postprocessed computed tomography data, this preprocessor makes possible rapid, flexible and regular meshing with 'brick' elements. Three different material properties were modelled at the present stage of development. Sensitivity analyses demonstrated that the strain energy density (SED) patterns of the different femoral parts were most sensitive to the implementation of an iliotibial tract force. The variation of the resultant hip force and abductor force direction within the sagittal plane demonstrated a SED minimum at an anterior inclination of 13 degrees; the variation of the resultant force direction within the frontal plane demonstrated a minimum SED at a medial inclination of 21 degrees relative to the mechanical axis of the lower limb. The orientation of the connecting line between the surface-SED-peaks in the horizontal view was found to be most sensitive to the variation of the resultant force within the sagittal plane.

Biomechanical Phenomena↗
PubMed1995

[Determination of the energy density of rapid periodic laser light patterns of homogeneous superficial coverage for medical applications].

The use of laser light in in vitro experiments on fibroblasts and osteoblasts and animal experiments has revealed similar thresholds the crossing of which is apparently necessary for achieving photobiological effects. Clinical observations suggested that such a threshold might apply to energy density, while further investigations seemed to indicate that a threshold for intensity (power density) might also be of importance. This was investigated in the clinical setting involving laser light applications to large areas. Initial measurements obtained with available measuring equipment pointed up the problems associated with the measurement of power and energy in different-speed radiation systems. Using a laser in conjunction with a "light chopper", a way of determining the range of a measuring system, in which useful measurements can be obtained is described.

Animals↗
PubMed1994

[Automatic generation of 3-D finite element codes of the human femur].

The extremely irregular geometry of bones makes it very difficult to develop and preprocess three-dimensional finite element models (FEM). In the field of biomechanics, the finite element simulation method is a research tool of increasing importance for the prediction of stresses and the stress-compatibility testing of endoprostheses. With this in mind, a FEM preprocessor was developed with the aim of creating three dimensional models of human femurs. On the basis of postprocessed computed tomography data, this preprocessor makes possible rapid, flexible and regular cross-linking. "Brick" elements are used, which are of advantage in terms of computing time, accuracy and computer storage requirements. The software simplifies the generation of models and facilitates the investigation of individual variations, thus providing the basis for utilizing the method in the clinical setting.

Biomechanical Phenomena↗
PubMed1993

Improved in vitro rheological system for studying the effect of fluid shear stress on cultured cells.

A rheological in vitro system has been developed to study and quantify cellular adhesion under precisely defined external shear forces. The system is similar to a cone-and-plate viscosimeter. A rotating transparent cone produces both steady and pulsatile flow profiles on cultured cells. Direct visualization of cells by phase-contrast or fluorescence optics and connection of the optical system to a computer-controlled x/y-linear stage allows automatic recording of any point of the cell cultures. With the use of up to 12 individual rheological units, this setup allows the quantitative analysis of cell substrate adhesion by determination of cell detachment kinetics. Two examples of application of this rheological system have been studied. First, we show that the extracellular matrix protein laminin strongly increases endothelial cell adhesion under fluid shear stress. In a second approach, we obtained further support for the concept that shear stress-induced formation of actin filament stress fibers is important for endothelial cells to resist the fluid shear stress; inhibition of stress fiber formation by doxorubicin resulted in significant detachment of endothelial cells exposed to medium levels of fluid shear stress (5 dyn/cm2). No detachment was seen under resting conditions.

Animals↗
PubMed1993

[Determining energy density distribution in laser irradiation fields, generated by the LILAB system].

Laser energy densities of less than 1 J/cm2 had no apparent effect on human tissues, while energy densities of more than 4 J/cm2 resulted in tissue damage. For non-punctiform laser applications, therefore, a laser beam distribution system that provides a homogeneous energy density distribution is of advantage, since such a system permits safe application of the laser in the effective therapeutic range. Conventional laser scanners for medical use have been reported to produce grossly inhomogeneous energy density distributions. The new LILAB system, which is a very fast laser beam distribution system, readily generates application fields of different configuration with high homogeneous energy density distribution. The article presents an example of a randomly selected application field, in which the energy densities at the edges and at the centre are compared.

Animals↗
PubMed1993

[Evaluation of the biocompatibility of implant materials with human bone marrow cell cultures].

A cell culture biocompatibility test for implant materials is described. For the first time, the human bone marrow cells that actually come into direct contact with the implanted biomaterial can be employed. The usefulness of this method is shown for materials which have long been used in the clinical situation (hydroxyapatite, commercially pure titanium and ultra-high molecular weight polyethylene). After two weeks in culture, light- and fluorescence-microscopic and SEM studies revealed significant differences in cell growth. Maximum compatibility was shown by the hydroxyapatite specimen. In the case of commercially pure titanium we found somewhat decreased biocompatibility. Polyethylene was associated with distinct signs of cytotoxicity. These results are compatible with those of animal experiments and clinical experience. Our system would thus appear to be a useful screening test for some implantation materials, and may help reduce the need for animal tests.

Biocompatible Materials↗
PubMed1993

[Experimental determination of muscle coordination of the lower extremity].

In order to describe the lines of action of muscles acting on joints, data on the geometrical position of insertions and origins are needed. These are of fundamental relevance for the biomechanical analysis, in particular for the calculation of joint loading. A measuring device with an accuracy of 0.1 mm was designed and constructed for the collection of three-dimensional experimental data from wet anatomical specimens. The main design features of the device include a vertically adjustable stand on wheels and a rotatable scale ring with a radial pointer. After setting the reading, the apparatus permits the measurement of cylindrical coordinates The margins of the attachments of muscles acting on the hip and knee joints were measured in two specimens. Two extensive sets of morphological data are now available and can be used to create complex biomechanical computer models.

Biomechanical Phenomena↗
PubMed1992

Capillary occlusion and secondary angiogenesis: case report.

The first follow-up control 5 days later (14.1.1990) showed a fresh capillary occlusion with massive red blood cell diapedesis. The arteriolar limb of the capillary is filled with erythrocytes up to the occlusion. Since capillary occlusion probably allowed some plasma flow at first, blood cells distal to the occlusion were washed away. After 53 days (8.3.1990) extravasal cells could no longer be made out. At the upper margin of the image a newly formed capillary loop can be seen. The channel of the old capillary seemed to have disappeared. Seventy-three days after occlusion, on 28th of March, the tip of the capillary, already demonstrated on 8th of March, had further grown distally. The capillary had crossed the neighbouring diagonal capillary. Twelve days later (9.4.1990) a remarkable growth connected with formation of a collateral was observed. The new capillary grew in direction of the former capillary channel. On 22nd of April the new capillary had almost got back to its old form. The collateral vessel formed on 9th of April had also grown and could be well distinguished. The different branches were immediately well perfused (mean erythrocyte velocity is v = 0.74 mm/s). The capillary were growing at different speeds. The new capillary had visibly grown by 220 microns over a period of 47 days which corresponds to an average growth of 4.7 microns a day. The capillary was growing fastest between the 9th and 22nd of April. A minimum of growth of 2 microns was observed within the first 11 days of the observation period.

Adult↗
PubMed1989

Induction by sodium butyrate of cytomegalovirus replication in human endothelial cells.

Cultured endothelial cells are shown to be induced in regard to permissiveness to human cytomegalovirus by temporary treatment postinfection with sodium butyrate (1-2 mM). Drug-treated cells are demonstrated to exhibit expression of immediate early and early viral antigens, synthesis of viral DNA and viral structural glycoprotein B. Progeny virus could be visualized by electron microscopy.

Antigens, Viral↗
PubMed1989

[The filter effectiveness of common 15-micron filters (DIN 58362). II: Scanning electron microscopy and roentgen analysis].

When i.v. solutions are used, millions of foreign particles are washed into the organism. Our town studies could recently show that these particles may interact with the organism and thus cause injury. A new method is introduced here (energy dispersive X-ray analysis in scanning electron microscopy, SEM, Jeol 35 CF/EDX, EEDS II Ortec), with which the element combination of foreign particles can be analyzed qualitatively and quantitatively. As a first step an analysis of the particulate matter in filtrates of infusion solutions was carried out in the same way, materials used in infusion therapy (e.g. infusion sets, cannulas, etc.) were analyzed. The results show that most of the particulate matter consists of glass from ampoules, plastic materials from infusion sets and rubber from the rubber stoppers of infusion bottles.

Electron Probe Microanalysis↗
PubMed1989

[Particulate contamination of infusion solutions and drug additives within the scope of long-term intensive therapy. 1. Energy dispersion electron images in the scanning electron microscope-REM/EDX].

During use of i.v. solutions, particulate matter may be introduced into the patient. X-ray analyses have shown that the particulate matter consists mainly of glass from ampules, rubber from stoppers of infusion bottles, and plastic from infusion sets. A new method is introduced: scanning electron microscopy-SEM- in combination with energy-dispersive X-ray analysis-EDX. using this technique all foreign particles larger than 0.8 microns can be detected and analyzed in any tissue. Especially in critically ill patients, particularly matter is deposited in the microcirculation of the lung. The particles cause a variety of pathologic changes (formation of thrombi, thromboembolization of the microcirculation, destruction of the vascular endothelium, formation of granulomas and foreign body giant cells). The adult respiratory distress syndrome could be produced or respiratory insufficiency might be aggravated following circulatory shock. It is therefore recommended that terminal in-line filters with small pore sizes be used for all i.v. solutions.

Adult↗
PubMed1989

Role of the endothelial actin filament cytoskeleton in rheology and permeability.

We have provided evidence for the existence of two distinct sets of actin filaments in endothelial cells, the stress fibers, and the peripheral filament band. Both sets of actin filaments also contain myosin, alpha-actinin, and other associated proteins of the contractile apparatus in muscle. We have shown that both systems of actin filaments in endothelial cells can contract. Stress fibers probably serve to prevent the endothelium from hydrodynamic injury and detachment, whereas the peripheral band of actin filaments appears to be important for the regulation of certain aspects of endothelial permeability.

Actin Cytoskeleton↗
PubMed1989

[The significance of laminin for the stability of endothelial-substrate adhesion in rheologic conditions].

The glycoprotein laminin is a component of the extracellular matrix and seems to be of considerable importance for cellular adhesion. In static cell cultures laminin revealed a profound influence on migration and proliferation of cultured endothelial cells. Coating of coverslips with laminin was found to have a profound and long-lasting effect on the adhesiveness of endothelial cells exposed to experimental fluid shear stress. By changing the seeding density of the cells per cm2 we could stimulate endogenous laminin production to a level that increased resistance of the monolayer against rheological shear stress by 200%.

Cell Adhesion↗
PubMed1989

[Particulate contamination of infusion solutions and drug additives in the framework of long-term intensive therapy. 2. An animal model].

When IV solutions are used, particulate matter may be introduced into the patient. Using X-ray studies we could demonstrate particulate matter consisting mainly of glass from ampules, rubber from rubber stoppers of infusion bottles, and plastic material from IV sets. With a recently introduced method of back-scatter pictures in scanning electron microscopy combined with X-ray studies--Jeol 35 CF/EEDS II Ortec (REM EDX)--we analyzed this phenomenon using an animal model (rabbit). It appears that particulate matter is deposited in the interstitial lung tissue and especially the pulmonary microcirculation. Pathogenetic effects could also be demonstrated (formation of thrombi, etc.).

Animals↗
PubMed1989

[Filtering effectiveness of conventional 15 m micron filters (DIN 58362) and newly developed 15 m micron and 5 m micron filters. I: Particle count].

When i.v. solutions are used, a considerable amount of particulate matter is washed into the patient. This particulate matter consists mainly of glass from ampoules, plastic materials from infusion sets, rubber from the rubber stoppers of infusion bottles and various materials, partly derived from the manufacturing process of the solutions. A new method of particle counting is introduced here (modified thrombocyte counter, Becton Dickinson), whereby particulate matter (less than 2 microns, greater 0.8 microns) could be counted for the first time. Using this counting method, the efficiency of the standard filtration (DIN 58362) was tested. Also tested were 2 new final filtration systems (with 15 microns and 5 microns pore-size). All 3 filtration methods were shown to be ineffective; especially small particles (less than 2 microns) cannot be eliminated by these filtration methods.

Drug Contamination↗
PubMed1988

Ultrastructural organization of contractile and cytoskeletal proteins in glomerular podocytes of chicken, rat, and man.

By immunoelectron microscopy the podocyte foot processes of the rat and human kidney have been shown to contain three major proteins of the contractile apparatus in muscle, i.e., actin, myosin, and the Z-line protein, alpha-actinin. Gel electrophoresis and immunoblot analysis of isolated glomeruli suggests that these proteins constitute an important part of the total glomerular protein contents. In the chicken kidney, the plasmalemmal portion of the foot processes that abuts the glomerular basement membrane was specifically labeled with antibodies against chicken gizzard vinculin and talin, two proteins thought to be important for the linkage of actin filaments to the lipid bilayer and to the receptor for fibronectin and laminin. Such a linkage may not only be important for the attachment of actin filaments to the plasma membrane, but could also be of functional significance for restricting the fibronectin-laminin receptor in its lateral diffusion in the plane of the lipid bilayer and to localize it at the basis of the podocytic foot processes. Assuming that actin, myosin, and alpha-actinin are arranged in a way that would allow the foot processes to generate contractile force this filament system might help the glomerular capillaries to resist the high intraluminal hydrostatic pressure as well as to actively modify the surface area for filtration. Vimentin and tubulin, the main protein subunits of intermediate filaments and microtubules, respectively, were confined to the podocyte cell body and the major processes but were virtually absent from the foot processes. This suggests that both proteins and their polymers are not important for the structure and function of the foot processes.

Actinin↗