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Biomedical subjects

D Falkenhagen

Publications and source records attributed to D Falkenhagen.

At least 37 records · Page 2Linked to original sources
PubMed1997

Permeability and adsorption capacity of dialysis membranes to lipid A.

Hemodialysis membranes were tested in vitro for possible penetration by low molecular weight endotoxins containing lipid A. Using lipid A from Escherichia coli as a model substance for this kind of pyrogen, different dialyzers (F4, E3. Acepal 1300, Altraflux, F 40, Polyflux 110, Filtral 12, F 60) were challenged by tangential filtration in aqueous medium. All membranes exhibited impermability to lipid A (as well as to LPS from Pseudomonas aeruginosa), which was proved by additional experiments using culture filtrates of Pseudomonas aeruginosa in bicarbonate dialysis fluid, as well as by employing miniaturized dialyzers with synthetic lipid A as a contaminant. Furthermore, the highest adsorption capacities were found for polysulfone and polyamide membranes.

Adsorption↗
PubMed1997

A novel field generator for magnetic stimulation in cell culture experiments.

A novel field generator specially designed to examine the influence of low frequency magnetic fields on specific cell material was constructed and characterized. The exposure unit described in this paper consists of a controller unit and three sets of coils. The field generator permits a precious definition of the revelant signal parameters and allows the superposition of alternating current (AC) and direct current (DC) magnetic fields. Critical system parameters were monitored continuously. The three sets of coils, each arranged in the Helmholtz Configuration were characterized. After data processing and visualization the results showed a constant and homogeneous field within the experimental area. The special coil design also allows their use in an incubator.

Cell Physiological Phenomena↗
PubMed1996

Microspheres based detoxification system: a new method in convective blood purification.

A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.

Adsorption↗
PubMed1996

Protein A carrying monosize PMMA microbeads for the removal of HIgG from human plasma.

Protein A-incorporated polymethylmethacrylate (PMMA) microbeads were investigated for specific removal of HIgG from human plasma. The microbeads were prepared by a phase inversion polymerization, and activated by periodate oxidation. Protein A was then incorporated by covalent binding onto these microbeads through hydroxyl groups coming from the stabilizer. The amount of incorporated protein A was controlled by the initial concentrations of protein A in the immobilization medium and pH. The maximum protein A immobilization of 0.615 mg protein A/g PMMA, was observed at a pH of 9.5 corresponding to an initial protein A concentration of 0.1 mg/ml. There was no HIgG adsorption onto the plain PMMA microbeads, while high HIgG adsorptions of up to 32 mg HIgG/g PMMA were achieved with human plasma.

Adsorption↗
PubMed1994

The Microspheres based Detoxification System (MDS). A new extracorporeal blood purification technology based on recirculated microspherical adsorbent particles.

Plasma sorption processes have so far been performed with filters and appropriate adsorption columns. In this paper, we introduce a newly developed plasma sorption system, which is based on the high adsorption capacity of microspheres in a recirculation system. The technology has been applied successfully in vitro to eliminate endotoxins, low density lipoproteins (LDL) and barbiturates from human plasma.

Animals↗
PubMed1993

Behaviour of white blood cells and the complement system.

Seven different types of dialysers were investigated in five dialysis centres in four countries with respect to behaviour of white blood cells and the complement system. The results of this controlled crossover study demonstrated significant differences in the dialysers. Those containing cuprammonium cellulose (G10-3N and G120 M) showed the greatest changes in white blood cell count, including monocytes and neutrophils, as well as the greatest complement activation. With regard to lymphocytes the subpopulation of low-mobility cells, which were predominantly the B-cells, showed the greatest mobility with dialysers containing cuprammonium cellulose. The PAN copolymer- and PMMA-containing dialysers Filtral and T 150 clearly caused the least changes in white blood cells and complement factors. Dialysers containing cellulose acetate and polysulphone membranes (Duo-Flux Artificial Kidney, CD 4000, and F 60) produced only a moderate decrease of WBC, monocyte, neutrophil, and lymphocyte counts, and this result corresponded to a relatively small change in complement factors.

Acrylic Resins↗
PubMed1993

Biocompatibility of a new high-permeability modified cellulose membrane for haemodialysis.

The biocompatibility and solute permeability characteristics of a high-permeability modified cellulose membrane (Hemophan-HP) (He-HP) were compared with those of two synthetic membranes (poly(ethylene-co-vinyl alcohol) (EVAL) and poly(acrylonitrile-co-sodium methallyl sulphonate) (AN69)) and Cuprophan in a multicentre, four-way cross-over clinical trial. Cuprophan membranes caused significant complement activation, leukopenia, and granulocyte elastase release. He-HP membranes demonstrated a lesser effect, which was similar to that observed for the EVAL membrane, although less than that seen with the AN69 membrane. A similar order for the four membranes was seen for their effect on platelets. Cuprophan membranes provided superior small-molecule removal to the other three membranes. In contrast, Cuprophan was essentially impermeable to beta 2-microglobulin, whereas He-HP, EVAL, and AN69 allowed the removal of 60-90 mg of beta 2-microglobulin per treatment. However, a decrease in the plasma concentration of beta 2-microglobulin was observed only with the AN69 membrane, most probably as a result of the ability of that membrane to adsorb proteins. Our results demonstrate that high-permeability membranes of comparable biocompatibility to some synthetic membranes can be fabricated from cellulose derivatives.

Adult↗
PubMed1993

Extracorporeal endotoxin removal by immobilized polyethylenimine.

The neutralization of bacterial endotoxins (ET) is still an unsolved problem in therapeutic medicine. The efficacy of anti-endotoxin antibodies or receptor antagonists and other substances interfering with the endotoxin-induced pathomechanisms is dependent on an intact cellular degradation system of the host. However, the phagocytosis function of that system seems to be impaired regularly in patients with intense or long-lasting endotoxemia or septic shock and in patients undergoing hemodialysis. Extracorporeal adsorption of ET might well be an effective support in the anti-ET therapy by lowering the amount of circulating ET and thus relieving the defense system of the body. In this work a new ET-adsorbent based on macroporous cellulosic beads with immobilized polyethylenimine (PEI) was tested for its ET-removal capacity in vitro. A test solution with 100 ng/ml ET from Escherichia coli 055:B5 was recirculated in a system containing the adsorbent beads. Polymyxin B immobilized to the same carrier was used for comparison. PEI as well as polymyxin B showed complete removal of ET from plasma and water as was measured by the Limulus Amebocyte Lysate (LAL) test (Chromogenix). The biocompatibility of the PEI absorber was superior to that of polymyxin B. The results indicate that the PEI absorber is of high efficacy and possibly of interest for the treatment of endotoxemia.

Adsorption↗
PubMed1991

Sterile and endotoxin free dialysis fluid for hemodialysis.

As the quality of water in dialysis fluid varies considerably, and, in view of the fact that endotoxin or active derivates can cause acute and chronic side effects in patients under hemodialysis treatment, the dialysis fluid must be sterile and endotoxin-free. The predialyzer fluid in 20 hemodialysis patients was investigated. The bacterial loading was between 5/ml and 12,000/ml, the endotoxin concentration was high and extremely variable. Therefore we introduced the ultrafiltration of the dialysis fluid by a polyamide hollow fiber membrane before entering the dialyzer. All samples were free of bacteria, and the concentration of endotoxin was lower than the detectable limit. With this procedure we can obtain sterile dialysis fluid, which is endotoxin free. Our preliminary results showed that Interleukin-1 in the patients was significantly (p less than 0.005) lower under ultrafiltration of the dialysis fluid than without ultrafiltration.

Colony Count, Microbial↗
PubMed1991

Detection of charges and their distribution on dialysis membranes with cationic/anionic dyes using confocal laser scanning microscopy.

Methods for the detection of positive or negative charges on the surface of biomaterials/membranes and inside a membrane are important for the characterisation of such materials. We tested different dyes and optimized staining procedures. Under standardized conditions negatively charged membranes were stained with cationic triarylmethane compounds such as crystal violet and positively charged membranes with the anionic anthraquinone dye anthralan blue B. There was no staining of uncharged cellulose membranes. The applicability of these methods was demonstrated on membranes coated to varying degrees with charged compounds such as heparin, these changes in charge being detectible quantitatively by photometry. The distribution of charges inside a membrane was detected by optical sectioning across the stained (FITC labelled poly-L-lysine) membrane using confocal laser scanning microscopy (LSM). LSM offers a completely new application possibility in biomaterial and biocompatibility research.

Biocompatible Materials↗
PubMed1991

Phagocytosis activity of polymorphonuclear cells of normal persons and dialysis patients is influenced by different dialysis membranes.

Leukocyte (PMN) functional capacity has been investigated through evaluation of phagocytosis of opsonised yeast cells in a radiometric test system. The PMN of dialysis patients (DP) had a slightly lower ability to ingest opsonised yeast cells in comparison with normal persons (NP), suggesting that an intrinsic cellular defect may exist. Under the influence of six membranes (cellulose acetate, regenerated cellulose, modified cellulose, cuprophane, polysulphone, and polymethylmethacrylate) the phagocytosis index decreased significantly between 10 and 17% in NP and between 13 and 23% in DP. There is a clear correlation with the membrane surface area. These results are not explained by the number of dead leukocytes (4-6.5% in DP and also in NP independently of membrane contact). The direct membrane effect could be responsible for the diminished phagocytic activity of leukocytes in NP and DP. Aqueous extracts of membranes alone resulted in no change of the phagocytic ability of PMN. Extracellular or 'uraemic factors' were excluded by the test procedure. The killing rate of yeast cells by PMN in NP and DP was not influenced in any of the membranes tested.

Adult↗
PubMed1991

Importance of endotoxins in high-flux dialysis.

Endotoxins are not only important for inducing pyrogenic reactions during haemodialysis but also for the stimulation of different blood cells. This is followed by the release of interleukin-1 and other powerful biological active substances, resulting in a broad spectrum of biological activities. Permeation of LPS (endotoxins) through dialysis and haemofiltration membranes is of great importance. Using a quantitative turbidimetric method based on the LAL (limulus amoebocyte lysate) test LPS concentrations were measured in a closed in vitro system for 11 different dialysers and haemofilters. To assess the passage of endotoxin through the membrane, permeation was measured from the dialysate to the blood side as well as from the blood compartment to the dialysate side.

Endotoxins↗
PubMed1990

Chemical modification of cellulosic membranes and their blood compatibility.

Blood compatibility is determined by interactions at the blood-material interface that depend on the material surface chemical structure. Through selective modifications of the chemically reactive hydroxyl groups of cellulose, the aim was to improve the biocompatibility of cellulose membranes. The number of potentially reactive hydroxyl groups on the cellulose membrane surface were reduced through isocyanate cross-links or through the introduction of hydrophilic, hydrophobic, or ionic functionalities by graft copolymerization. To assess blood compatibility, levels of C3a desArg were determined in plasma after membrane contact. Using the electrophoretic mobility test, the release of cytokines were measured after in-vitro incubation of mononuclear cells with membranes. Adsorption of 131J-human fibrinogen was additionally investigated. With respect to the biocompatibility parameters selected, the modified cellulose membranes show improved in-vitro blood compatibility in comparison to unmodified cellulose membranes.

Biocompatible Materials↗