In this paper we show that if $n\geq 5$ and $G$ is any of the groups $SU_n(q)$ with $n\neq 6,$ $Sp_{2n}(q)$ with $q$ odd, $\Omega_{2n+1}(q),$ $\Omega_{2n}^{\pm}(q),$ then $G$ and the simple group $\barG=G/Z(G)$ are not 2-coverable. Moreover the only 2-covering of $Sp_{2n}(q),$ with $q$ even, has components $ O^-_{2n}(q)$ and $O^{+}_{2n}(q) .$

The processing of polymers for blood contacting devices can have a major influence on surface properties. In this study, we fabricated poly(ether imide) (PEI) membranes and films to investigate the effects of the processing on physicochemical surface properties by atomic force microscopy (AFM), scanning electron microscopy, contact angle as well as zeta potential measurements. A static platelet adhesion test was performed to analyze the thrombogenicity of both devices. While contact angle measurements showed similar levels of hydrophobicity and zeta potential values were equivalent, mean surface roughness as well as surface energies in the dispersive part were found to be increased for the PEI membrane. The static platelet adhesion test showed a significantly decreased number of adherent platelets per surface area on the PEI film (178.98 ± 102.70/45000 μm2) compared to the PEI membrane (504 ± 314.27/45000μm2) and, consequently, revealed evidence for higher thrombogenicity of the PEI membrane. This study shows that processing can have a significant effect on platelet adhesion to biomaterials, even though, molar weight was identical. Thrombogenicity of polymer-based cardiovascular devices, therefore, have to be evaluated at the final product level, following the entire processing procedure.

Poly(ether imide) (PEI) membranes were modified with a linear low-molecular weight (PETIM_0.6) and a branched high-molecular weight poly(ethylene imine) (PETIM_60). The membrane surfaces became more hydrophilic and the zeta potentials were shifted from negative to positive zeta values after immobilisation of both PETIM. These measurements also indicated the presence of a swollen surface layer in the case of PETIM_60, while a regular structuring of the surface was observed with scanning force microscopy for PETIM_0.6. A human keratinocyte cell line HaCaT was cultured on the different membranes. It was found that HaCaT cell growth was stimulated by PETIM_0.6. Cells reached earlier confluence on this substratum, while their growth was inhibited on a PEI membrane modified with PETIM_60, which makes PEI membranes modified with PETIM_0.6 a promising material for in vitro culture of epidermal transplants.

Apheresis is an emerging technique to separate blood components from whole blood or plasma to remove pathologically elevated levels of proteins or toxins. Advantageously, the realization of apheresis by chromatographic techniques allows a selective or specific removal of blood components causing the disease. However, the particulate support material carrying the ligands is frequently not adapted to the necessities of large-volume, high molecular weight components, which have to be removed. Thus commercial support materials have the disadvantages of a too low accessibility of the internal pore system, a too poor flow-through behavior and/or a too high unspecific protein adsorption. Hence, novel support materials with optimally adapted properties profile have to be developed. Polyimides have been identified as novel blood compatible, steam-sterilizable materials that can be easily functionalized by wet-chemistry means. So far no suitable preparation process for the fabrication of highly porous beads is known.In this work, a novel support for apheresis application is presented which is based on microporous particles that were prepared from poly(ether imide) by a spraying/coagulation process. The polymer solution is sprayed through a hollow needle to form droplets and the droplets were vitrified by a nonsolvent induced phase separation. Results of the investigation of the spraying step and of the phase inversion step as well as characteristic data of the prepared particles are presented. Data of the particle characteristics verify that this technique is suitable to prepare highly porous support particles, which have a high accessibility of their internal pore system.

Poly(ether imide) asymmetric membranes can be covalently functionalized with aminic modifiers. When poly(ethylene imine), i.e., a polyvalent high molecular weight modifier, is used, the functionalization is connected with the support membrane pore-filling in a very thin layer. The poly(ethylene imine) layer is, however, not stables at increased temperatures and does not fill completely large pores. The layer can be stabilized by crosslinking with oligomeric poly(ethylene glycol) diglycidyl ether (PEGDGE), but this does not improve the coverage of large pores. The poly(ethylene imine) functionalized membrane can be stabilized, however, by reactive coating with copolymers of methacrolein with 1-vinylpyrrolidone instead stabilization with PEGDGE with a coverage of the large pores. The copolymers having various ratios of both polymeric units were prepared by free radical polymerization. The methacrolein units of copolymers, which comprised predominantly 1-vinyl-2-pyrrolidone units, had aldehyde groups in a free reactive form. These aldehyde groups react readily with the amine groups of the poly(ethylene imine) layer, while 1-vinylpyrrolidone units render the coating hydrophilic. The membranes coated under optimal conditions had nanofiltration separation properties at high water fluxes. Good adhesion between the coating layer and the support membrane, which results from the covalent binding, should allow separations under harsh conditions.

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T(switch). If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(epsilon-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25 degrees C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA x m(-1)). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.

Polymeric membranes have been well established in many separation processes since the introduction of a preparation technique generating asymmetric morphologies by Loeb and Sourirajan. If the separation layer of an asymmetric membrane is highly permeable, the support layer resistance can become significant. A highly asymmetric structure over the entire cross-section of a membrane is a prerequisite for the restriction of this resistance. With regard to hollow fiber membranes, a very open pore structure on the membrane surface opposite to the active layer is required.Scanning electron microscopy (SEM) analysis of the morphology of poly(ether imide) (PEI) hollow fiber membranes prepared by a dry-wet spinning technology have been carried out. The results show that the outer layer of the extruded polymer solution can be precipitated by vapor induced phase separation (VIPs) resulting in relatively dense structures. In order to avoid VIPs, a modified air gap spinning process was developed using a triple spinneret where the outer annulus was used for transport of fluids containing a high amount of solvent. As a consequence of the presence of fluid at the outer surface of the nascent hollow fiber, the polymer concentration was locally reduced and the fiber was protected against the sorption of water vapor from the ambient atmosphere in the air gap. The results show that highly asymmetric hollow fiber morphologies without any external skin can be reproducibly prepared. Their separation properties are similar to those of conventionally prepared membranes but the permeability could be improved considerably due to a distinctly reduced support layer resistance. (c) 2005 Elsevier B.V. All rights reserved.

The water/polymer interaction parameter plays an important role in the thermodynamic description of membrane-forming water/solvent/polymer solutions with the Flory-Huggins (FH) model. In order to discuss reasons for the wide variety of values for this parameter reported in the literature, interaction parameter was determined utilizing two different methods for polysulfone, poly(ether sulfone), cellulose acetate and poly(ether imide) (PSU, PES, CA, and PEI). In a “direct” determination, water sorption isotherms have been measured and analyzed with the FH model. In a second, “indirect”, method an optimal parameter value was found by fitting experimental cloud point data of ternary polymer systems with the FH model. Liquid–liquid equilibrium (LLE) calculations have been carried out under the assumption that the water/solvent and solvent/polymer interactions are correctly described by known composition dependent interaction parameters. For a given polymer, the water/polymer interaction parameters resulting from fits of ternary systems with different solvents agree well. But the obtained values are smaller than the ones resulting from the sorption experiment. The difference is smaller for a more hydrophilic polymer with a higher water uptake than for hydrophobic polymers with a lower uptake. Reasons for this difference will be discussed.

Contactors equipped with hydrophobic porous membranes were widely tested and operated in different separation processes. New applications, e.g. concentration of fruit juice or air conditioning, require a reliable separation of the two contacting phases at a higher level as for common applications in order to avoid product pollution by the liquid absorbent. The application of coated membranes as a liquid tight semipermeable barrier offers the best prerequisites in order to meet this requirement. Because the dense layer of such membranes acts as an additive transport resistance its thickness has to be as thin as possible which requires porous support membranes with the porosity profile of ultrafiltration membranes. Are such support membranes suitable for the application in gas/liquid contactors? In order to find an answer to this question at first a model gas/liquid contactor arrangement was installed and experimentally proved. Applying this arrangement the water vapor permeability of membrane types with ultrafiltration separation characteristics was determined. At the model development a well characterized hollow fiber with microfiltration properties was used. The results show that neglecting the temperature polarization would result in underestimated membrane permeability values. Hence the temperature polarization arising during the absorption process was determined experimentally. By taking the temperature polarization into consideration the calculated membrane permeabilities were in good accordance to literature data. Using this simple model different structured poly(ether imide) hollow fiber membranes with ultrafiltration separation profile were characterized with respect to the water vapor permeability. The results document that these ultrafiltration membranes provide equivalent or even distinctly higher permeabilities than commercial microfiltration membranes. The better performance is related to the asymmetric structure of these membranes. On basis of the obtained results it can be concluded that membranes with ultrafiltration separation profile – which are coatable with a thin coating layer – should be suitable for the preparation of effective contactor membranes without risk of remarkable losses in performance in comparison with uncoated microfiltration membranes. Furthermore the morphology of these membrane types can be tailored to special contactor applications, which require high heat transfer (e.g. osmotic distillation) or low heat transfer (e.g. membrane distillation).

The effect of the porosity of acrylonitrile-N-vinylpyrrolidone copolymer membranes on human C3A hepatoblastoma cell adhesive interaction and functioning is investigated on four membranes with an average pore size ranging between 6 and 12 nm. Adhesion of C3A cells was quantified and characterized by studying overall cell morphology and focal adhesion formation. Cell-cell interactions were characterized by E-cadherin expression and organization. Cell growth, fibronectin synthesis and cytochrome P450 activity were estimated as criteria of functional cell activity. The results suggest that membrane porosity influences the initial cell-surface interactions since an increasing pore size augmented cell adhesion and aggregate formation. Cell growth after 7 d was diminished on membranes with an average pore size of 12 nm. The activity of P450 measured by 7-ethoxycoumarin conversion at day 7 was influenced by membrane topography representing a clear optimum in the range of 7-10 nm pore size. These results indicate that membrane porosity is a determinant for the function of hepatocytes in extracorporal liver assist devices.

A hollow fiber-in-fiber-based bioreactor system was tested for the applicability to host kidney epithelial cells as a model system for a bioartificial kidney. Hollow fibers were prepared from polyacrylonitrile (PAN), polysulfone-polyvinylpyrollidinone (PVP) blend (PSU) and poly(acrylonitrile-N-vinylpyrollidinone) copolymer P(AN-NVP). Hollow fibers with smaller and larger diameters were prepared so that the smaller fitted into the larger, with a distance of 50-100 microm in between. The following material combinations as outer and inner fiber were applied: PAN-PAN; PSU-PSU, PSU-P(AN-NVP). Madin-Darby kidney epithelial cells (MDCK) were seeded in the interfiber space and cultured for a period up to 14 days. Light, scanning, and transmission electron microscopy were used to follow the adhesion and growth of cells, and to characterize their morphology. As a result, we found that MDCK cells were able to grow in the interfiber space in mono- and multilayers without signs of systemic degeneration. Comparison of the different materials showed that PAN and P(AN-NVP) provided the best growth conditions, indicated by a tight attachment of cells on hollow fiber membrane, and subsequent proliferation and development of structural elements of normal epithelia, such as tight junctions and microvilli. In conclusion, the fiber-in-fiber design seems to be an interesting system for the construction of a bioartificial kidney.

Polyethylenterephtalat track-etched membranes were plasma-modified to increase cell-adhesion and tissue-compatibility. Amine functionalities were grafted onto the surfaces by means of ammonia-plasma treatment, and plasma deposition of allylamine. Changes of chemical and physical properties of the samples were followed and in vitro evaluation of biocompatibility was carried out by studying human skin fibroblast interaction with surfaces. We found that fibroblasts adhered and grew better on poly-allylamine coated surfaces with higher amine concentration than on ammonia-plasma treated ones, but both had better cell-adhesive properties than the original membrane.

Allylamine was plasma polymerised onto a polyester (PET) membrane to obtain a surface with good cell adhesive properties. Samples were coated using a microwave plasma source operating at different process parameters. The effect of process parameters on the physical, and chemical properties of plasma-polymerised-allylamine (PPAa) was evaluated by studying elemental composition, amine concentration, wettability, and surface morphology. A relatively high amine concentration was measured (up to 50nmol/cm2). In parallel, nitrogen enrichment was observed after exposure to high-energetic plasma. Irrespective of the treatment conditions, oxygen was incorporated into the polymer structure. PPAa surfaces were found to be more hydrophilic than PET. The wettability of the samples increased with increasing amine concentration. Pictures from scanning electron microscopy indicated that homogeneous pinhole-free PPAa layers were deposited on PET membranes, without a significant change of permeability. In vitro evaluation of biocompatibility was carried out by studying human skin fibroblast interaction with surfaces. Cell attachment and viability on PPAa layers were found to be more intensive than on the control PET, based on the higher metabolic activity of adhering cells, but also on morphological criteria including overall cell morphology.

In the wet-chemical treatment of polyimide (PI) membranes with aminic modifiers, the modifier molecules will be covalently bound to the membrane polymer. Using modifiers with high aminic nitrogen the amination is combined with a degradation process, which shifts separation properties from ultrafiltration characteristics (untreated membrane) to microfiltration characteristics (treated membrane). Under optimal treatment conditions the steepness of separating curves of the aminated membranes is comparable with the steepness of separating curves of commercial microfilters. Characteristic data of membranes such as water permeability, amine content, SEM morphology, wettability and the dependence of membrane thickness on treatment conditions were presented. Data show that membrane properties are insensitive to modifier concentration in the treatment bath with respect to degradation reaction but sensitive to reaction rate. From the data of amine content per unit surface area of membrane and amine content per unit membrane weight, it was concluded that the functionalization/degradation process is divided in two steps. In the first step functionalization dominates, whereas in the second step functionalization and degradation are simultaneous processes resulting in an equilibrium state. The expected reaction sequence of degradable functionalization is proposed and discussed. Initial membrane morphology seems to be the key parameter for further investigations to optimize membrane preparation processes.

Covalently aminated polyimide membranes are prepared by wet chemistry using different amines as modifiers. During this synthesis process carbonyl groups of the imide ring react with amine groups forming amide groups maintaining the macromolecular structure and an additional amide group bearing free amine groups. The reaction sequence was verified by FTIR-ATR and XPS measurements. Using poly(ethylene imine)s, highly aminated polyimide membranes with amine contents higher than 500 nmol/cm(2) membrane can be produced which can be used as basic functions for further modification. As a result of amination, the hydrophobic polyimide membranes were strongly hydrophilized. Depending on the process parameters for functionalization and the applied modifier, a symmetric or an asymmetric distribution of amine functions across the membrane was observed. The distributions of amine functions were determined by SEM microscopy (EDX mode) and by AR-XPS (take-off angle resolved XPS). Calculations suggest that in the case of an asymmetric distribution the pores of the surface layer are almost completely filled with a swollen network of the modifier, which allows the covalent binding of second modifiers in order to obtain new types of composite membranes.

OBJECTIVEInnovative treatments are needed for metastatic disease involving the pleura. NV1020 is a novel, multimutated, replication-restricted herpes simplex virus under investigation for its ability to selectively kill tumors by means of direct cell lysis. This study examines NV1020 in a rat model of pleura-based lung cancer.METHODSCytotoxicity and viral proliferation were evaluated in vitro by exposure of the human non-small cell lung cancer cell line A549 to virus. NV1020 was also tested in an in vivo pleura-based cancer model established by injecting 1 x 10(7) A549 cells into the thoracic cavity of nude rats. Intrapleural treatments (1 x 10(7) viral particles) were given 3 hours or 3 days after tumor injection to model treatment of microscopic or macroscopic disease (n = 8-9/group). Tumor burden was assessed at 5 weeks. NV1020 infection and dissemination within the thoracic cavity was determined by means of immunohistochemistry.RESULTSIn vitro, at multiplicities of infection (viral particles per tumor cell) of 0.01, 0.1, and 1.0, cell killing of A549 by NV1020 was 66%, 90%, and 97%, respectively, at 7 days after infection. Viral burst occurred by day 2. Intrapleural treatment was effective for both the microscopic (P <.001) and macroscopic (P <.05) in vivo tumor models. Virus was detectable by means of immunohistochemistry in tumors but not in adjacent normal intrathoracic tissues.CONCLUSIONSNV1020 is not only highly cytotoxic to the human lung cancer line A549 in vitro but can be delivered in a clinically relevant fashion to safely and effectively treat pleura-based tumor in vivo in a rat model.

Support membranes in bioartificial organs contact blood or plasma on one-side and adhesion dependent cells on the other side. Since membranes for biomedical applications, such as for haemodialysis, are optimised for blood contact and membranes for biotechnological applications for cell contact, there are no membranes available addressing the requirements of artificial organ technology. One approach is the preparation of porous bilayer membranes with a wall consisting of two chemical different polymer layers. Results of the preparation of such membrane types using triple spinnerets and a wet phase inversion process are shown here. It is demonstrated that one of the most important parameter is the structural integrity of the membrane wall at the interface between both layers. A new spinneret construction is presented where the membrane forming polymer solutions are layered in the spinneret before extrusion. As a result porous bilayer hollow fibre membranes with a high structural integrity could be manufactured using different composed polysulfone (PSu) polymer solutions for model investigation.