A membrane stirrer for product recovery and substrate feeding.

During fermentation processes, in situ product recovery (ISPR) using submerged membranes allows a continuous operation mode with effective product removal. Continuous recovery reduces product inhibition and organisms in the reactor are not exposed to changing reaction conditions. For an effective in situ product removal, submerged membrane systems should have a sufficient large membrane area and an anti-fouling concept integrated in a compact device for the limited space in a lab-scale bioreactor. We present a new membrane stirrer with integrated filtration membranes on the impeller blades as well as an integrated gassing concept in an all-in-one device. The stirrer is fabricated by rapid prototyping and is equipped with a commercial micromesh membrane. Filtration performance is tested using a yeast cell suspension with different stirring speeds and aeration fluxes. We reduce membrane fouling by backflushing through the membrane with the product stream.

Total ankle replacement in patients with haemophilia and virus infections--a safe alternative to ankle arthrodesis?

Despite reliable results of ankle fusion for advanced haemophilic arthropathy, total ankle replacement (TAR) may be functionally advantageous. There is only very limited literature data available on TAR in patients with haemophilia. The objective of this study is to evaluate the short- and mid-term results after TAR in patients with end-stage haemophilic ankle arthropathy and concomitant virus infections. In a retrospective study, results after eleven TAR in 10 patients with severe (n = 8) and moderate (n = 2) haemophilia (mean age: 49 ± 7 years, range, 37-59) were evaluated at a mean follow-up of 3.0 years (range, 1.2-5.4). Nine patients were positive for hepatitis C, five were HIV-positive. Range of motion (ROM), AOFAS-hindfoot-score, pain status (visual analogue scale, VAS) as well as patient satisfaction were evaluated. In two cases deep prosthesis infection occurred leading to the removal of the implant. In the remaining eight patients the mean AOFAS score improved significantly from 21.5 to 68.0 points (P < 0.0005), the VAS score decreased significantly from 7.6 to 1.9 points (P < 0.0005). ROM increased from 23.2 to 25.0 degrees (P = 0.51). At final follow-up all patients without any complications were satisfied with the postoperative results. Radiographic examination did not reveal any signs of prosthetic loosening. TAR is a viable surgical treatment option in patients with end-stage ankle osteoarthritis due to haemophilia. It provides significant pain relieve and high patient satisfaction. However, due to the increased risk of infection and lack of long-term results, TAR particularly in patients with severe haemophilia and virus infections should be indicated carefully.

Towards a carbon independent and CO2-free electrochemical membrane process for NH3 synthesis.

Ammonia is exclusively synthesized by the Haber-Bosch process starting from precious carbon resources such as coal or CH4. With H2O, H2 is produced and with N2, NH3 can be synthesized at high pressures and temperatures. Regrettably, the carbon is not incorporated into NH3 but emitted as CO2. Valuable carbon sources are consumed which could be used otherwise when carbon sources become scarce. We suggest an alternative process concept using an electrochemical membrane reactor (ecMR). A complete synthesis process with N2 production and downstream product separation is presented and evaluated in a multi-scale model to quantify its energy consumption. A new micro-scale ecMR model integrates mass, species, heat and energy balances with electrochemical conversions allowing further integration into a macro-scale process flow sheet. For the anodic oxidation reaction H2O was chosen as a ubiquitous H2 source. Nitrogen was obtained by air separation which combines with protons from H2O to give NH3 using a hypothetical catalyst recently suggested from DFT calculations. The energy demand of the whole electrochemical process is up to 20% lower than the Haber-Bosch process using coal as a H2 source. In the case of natural gas, the ecMR process is not competitive under today's energy and resource conditions. In future however, the electrochemical NH3 synthesis might be the technology-of-choice when coal is easily accessible over natural gas or limited carbon sources have to be used otherwise but for the synthesis of the carbon free product NH3.

Cassie-Baxter to Wenzel state wetting transition: scaling of the front velocity.

We experimentally study the dynamics of water in the Cassie-Baxter state to Wenzel state transition on surfaces decorated with assemblies of micrometer-size square pillars arranged on a square lattice. The transition on the micro-patterned superhydrophobic polymer surfaces is followed with a high-speed camera. Detailed analysis of the movement of the liquid during this transition reveals the wetting front velocity dependence on the geometry and material properties. We show that a decrease in gap size as well as an increase in pillar height and intrinsic material hydrophobicity result in a lower front velocity. Scaling arguments based on balancing surface forces and viscous dissipation allow us to derive a relation with which we can rescale all experimentally measured front velocities, obtained for various pattern geometries and materials, on one single curve.

Interplay between physical cleaning, membrane pore size and fluid rheology during the evolution of fouling in membrane bioreactors.

Fouling is one of the most pressing limitations during operation of membrane bioreactors, as it increases operating costs and is the cause of short membrane lifespans. Conducting effective physical cleanings is thus essential for keeping membrane operation above viable performance limits. The nature of organic foulants present in the sludge and the membrane properties are among the most influential factors determining fouling development and thus, efficiency of fouling mitigation approaches. The role of other factors like sludge viscosity on fouling is still unclear, given that contradictory effects have been reported in the literature. In the present study we use a new research approach by which the complex interplay between fouling type, levels of permeate flux, membrane material and feed properties is analyzed, and the influence of these factors on critical flux and membrane permeability is evaluated. A variety of systems including activated sludge and model solutions with distinct rheological behavior has been investigated for two membranes differing in pore size distribution. We present a novel method for assessing the efficiency of fouling removal by backwash and compare it with the efficiency achieved by means of relaxation. Results obtained have proven that backwash delays development of critical fouling as compared with relaxation and reduces fouling irreversibility regardless of fluid rheology. It was shown that backwash is especially effective for membranes for which internal fouling is the main cause of loss in permeability. Nonetheless, we found out that for membranes with tight pores, both relaxation and backwash are equally effective. The critical flux decreases significantly for high-viscosity fluids, such as activated sludge. This effect is mainly caused by an intensified concentration polarization at the feed side rather than by internal fouling events. However, membrane permeability has been proven to rely more on the permeate viscosity than on the feed viscosity: poor rejection of organic fractions showcasing high viscosity causes an acute decline in membrane permeability as a consequence of increased shear stress inside the membrane pores.

Morphology and microtopology of cation-exchange polymers and the origin of the overlimiting current.

In electrodialysis desalination processes, the operating current density is limited by concentration polarization. In contrast to other membrane processes such as ultrafiltration, in electrodialysis, current transport above the limiting current is possible. In this work, the origin of the overlimiting current at cation-exchange polymers is investigated. We show that, under certain experimental conditions, electroconvection is the origin of the overlimiting conductance. The theory concerning electroconvection predicts a shortening of the plateau length of membranes with increased conductive or geometrical heterogeneity. We investigate the influence of these two parameters and show that the creation of line undulations on the membrane surface normal to the flow direction, having distances in the range of approximately 50-200% of the boundary-layer thickness, lead to an earlier onset of the overlimiting current. The plateau length of the undulated membranes is reduced by up to 60% compared to that of a flat membrane. These results verify the existence of electroconvection as a mechanism destabilizing the laminar boundary layer at the liquid-membrane interface and causing ionic transport above the limiting current density.

Membranes and microfluidics: a review.

The integration of mass transport control by means of membrane functionality into microfluidic devices has shown substantial growth over the last 10 years. Many different examples of mass transport control have been reported, demonstrating the versatile use of membranes. This review provides an overview of the developments in this area of research. Furthermore, it aims to bridge the fields of microfabrication and membrane science from a membrane point-of-view. First the basic terminology of membrane science will be discussed. Then the integration of membrane characteristics on-chip will be categorized based on the used fabrication method. Subsequently, applications in various fields will be reviewed. Considerations for the use of membranes will be discussed and a checklist with selection criteria will be provided that can serve as a starting point for those researchers interested in applying membrane-technology on-chip. Finally, opportunities for microfluidics based on proven membrane technology will be outlined. A special focus in this review is made on the membrane properties of polydimethylsiloxane (PDMS), since this material is frequently used nowadays in master replication.

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties.

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.

Oestrogen removal from biological pretreated wastewater within decentralised sanitation and re-use concepts.

Two parallel researches were performed; one focused on the fate of oestrogens in the biological treatment systems within decentralised sanitation and re-use concepts (DESAR), the second related to the development of a suitable specific removal method. A new affinity membrane was developed using antibodies as specific binding sites for hormone removal. It was found that, especially in anaerobic treatment, the core technology in DESAR, the removal is insufficient and therefore an additional separation method is required. The affinity membrane with antibodies was found to be a suitable additional method, though in the current system it only removes one selected compound. Future research will focus on making this method more feasible in practise.

[Quality in Revision Arthroplasty: A Comparison between Claims Data Analysis and External Quality Assurance]. / Ergebnisqualität in der Revisionsendoprothetik: Eine Analyse von Routinedaten mit dem Vergleich zur externen Qualitätssicherung.

BACKGROUND: External quality assurance for revisions of total knee arthroplasty (TKA) and total hip arthroplasty (THA) are carried out through the AQUA institute in Germany. Data are collected by the providers and are analyzed based on predefined quality indicators from the hospital stay in which the revision was performed. The present study explores the possibility to add routine data analysis to the existing external quality assurance (EQS). Differences between methods are displayed. The study aims to quantify the benefit of an additional analysis that allows patients to be followed up beyond the hospitalization itself. MATERIAL AND METHODS: All persons insured in an AOK sickness fund formed the population for analysis. Revisions were identified using the same algorithm as the existing external quality assurance. Adverse events were defined according to the AQUA indicators for the years 2008 to 2011.The hospital stay in which the revision took place and a follow-up of 30 days were included. For re-operation and dislocation we also defined a 365 days interval for additional follow-up. The results were compared to the external quality control reports. RESULTS: Almost all indicators showed higher events in claims data analysis than in external quality control. Major differences are seen for dislocation (EQS SD: 1.87 vs. claims data [cd] SD: 2.06 %, cd+30 d: 2.91 %, cd+365 d: 7.27 %) and reoperation (hip revision: EQS SD: 5.88 % vs. claims data SD: 8.79 % cd+30 d: 9.82 %, cd+365 d: 15.0 %/knee revision: EQS SD: 3.21 % vs. claims data SD: 4.07 %, cd+30 d: 4.6 %, cd+365 d: 15.43 %). Claims data could show additional adverse events for all indicators after the initial hospital stay, rising to 77 % of all events. CONCLUSIONS: The number of adverse events differs between the existing external quality control and our claims data analysis. Claims data give the opportunity to complement existing methods of quality control though a longer follow-up, when many complications become evident.

Characterization and solubilization of the cytochalasin B binding component from human placental microsomes.

Human placental microsomes exhibit uptake of D-[3H]glucose which is sensitive to inhibition by cytochalasin B (apparent Ki = 0.78 microM). Characterization of [3H]cytochalasin B binding to these membranes reveals a glucose-sensitive site, inhibited by D-glucose with an ED50 = 40 mM. The glucose-sensitive cytochalasin B binding site is found to have a Kd = 0.15 microM by analysis according to Scatchard. Solubilization with octylglucoside extracts 60-70% of the glucose-sensitive binding component. Equilibrium dialysis binding of [3H]cytochalasin B to the soluble protein displays a pattern of inhibition by D-glucose similar to that observed for intact membranes, and the measurement of an ED50 = 37.5 mM D-glucose confirms the presence of the cytochalasin B binding component, putatively assigned as the glucose transporter. Further evidence is attained by photoaffinity labelling; ultraviolet-sensitive [3H]cytochalasin B incorporation into soluble protein (Mr range 42000-68000) is prevented by the presence of D-glucose. An identical photolabelling pattern is observed for incorporation of [3H]cytochalasin B into intact membrane protein, confirming the usefulness of this approach as a means of identifying the presence of the glucose transport protein under several conditions.

New replication technique for the fabrication of thin polymeric microfluidic devices with tunable porosity.

In this article we present a new versatile replication method to produce thin polymeric microfluidic devices with tunable porosity. This method is based on phase separation of a polymer solution on a microstructured mold. Compared to existing microfabrication techniques, such as etching and hot embossing, our technique offers four advantages: (a) simple and cheap process that can be performed at room temperature outside clean room facilities; (b) very broad range of applicable materials (including materials that could not be processed before); (c) ability to make thin flexible chips; (d) ability to introduce and tune porosity in the chip. By introducing porosity, the channel walls can be used for selective transport of gasses, liquids and solutes. A proof-of-concept will be given, by showing fast CO2 transport through the channel walls of a porous polymer chip. Furthermore, it will be demonstrated that the gas permeation performance of chips can be enhanced dramatically by a decrease in chip thickness and incorporation of porosity. We expect that the development of porous chips can lead to the on-chip integration of multiple unit operations, such as reaction, separation, gas liquid contacting and membrane emulsification.

The effect of colloid stability of wastewater treatment plants effluent on nanofiltration performance.

Laboratory-scale filtration tests utilizing wastewater treatment plants (WWTP) effluent were conducted to investigate fouling and filtration behaviour, especially the influence of colloidal stability on nanofiltration performance. Acidification and coagulant dosage were used to create unstable colloidal conditions. Colloidal stability of the effluent was analysed on by zeta potential measurements. A statistical design method, full factorial design with blocking, has been used to account for effluent composition variations and to account for interaction between experimental parameters. The results show a high correlation between unstable colloidal natural organic matter and the formation of dense fouling layers. The reversibility of the fouling process was shown to be independent from colloidal stability. Irreversible fouling was show to be promoted by mild acidic (pH 5) effluent conditions, whereas coagulant addition showed an increase in the reversibility of the fouling.

Adsorptive membranes for bilirubin removal.

In this study, we employed ethylene vinyl alcohol (EVAL) adsorptive membranes with bovine serum albumin (BSA) as bioligand for affinity supports for bilirubin (BR) retention. Microfiltration membranes were prepared from ternary or quaternary water/(1-octanol)/DMSO/EVAL systems. To obtain active binding sites for BSA, the EVAL membranes were either chemically functionalized in aqueous and organic medium and by plasma dischargement or physically activated by entrapping of active particles. Static BR removal was determined for all EVAL-BSA membranes. BR retentions relevant for human plasma were gained for the mixed adsorber membranes and additionally investigated in the dynamic mode.

Tailoring the properties of asymmetric cellulose acetate membranes by gas plasma etching.

Cellulose triacetate (CTA) ultrafilters and cellulose acetate blend (CAB) desalination membranes were treated with a radiofrequency gas plasma (tetrafluoromethane (CF(4)) or carbon dioxide (CO(2)), 47-49 W, 0.04-0.08 mbar). Treatment times were varied between 15 s and 120 min. The plasma-treated top layer of the membranes was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements to obtain information about surface structure, chemistry, and wettability, respectively. The membrane properties (e.g., permeability, selectivity, fouling) were studied by waterflux measurements, molecular weight cutoff measurements, and fouling experiments with bovine serum albumin. CO(2) plasma treatment resulted in gradual etching of the membrane's dense top layer. Permeation and selectivity changed significantly for treatment times of 0-15 min for CTA and 5-60 min for CAB membranes. Moreover, CTA membranes were hydrophilized during CO(2) plasma treatment whereas CF(4) plasma treatment led to hydrophobic surfaces due to strong fluorination of the top layer. This study shows that gas plasma etching can tailor the properties of asymmetric cellulose acetate membranes by simultaneously modifying the chemistry and structure of the top layer. The low fouling properties of CTA membranes were thereby largely maintained.

Nanometer-thick lateral polyelectrolyte micropatterns induce macrosopic electro-osmotic chaotic fluid instabilities.

Electro-convective vortices in ion concentration polarization under shear flow have been of practical relevance for desalination processes using electrodialysis. The phenomenon has been scientifically disregarded for decades, but is recently embraced by a growing fluid dynamics community due its complex superposition of multi-scale gradients in electrochemical potential and space charge interacting with emerging complex fluid momentum gradients. While the visualization, quantification and fundamental understanding of the often-chaotic fluid dynamics is evolving rapidly due to sophisticated simulations and experimentation, little is known whether these instabilities can be induced and affected by chemical topological heterogeneity in surface properties. In this letter, we report that polyelectrolyte layers applied as micropatterns on ion exchange membranes induce and facilitate the electro-osmotic fluid instabilities. The findings stimulate a variety of fundamental questions comparable to the complexity of today's turbulence research.

Development of multilayer constructs for tissue engineering.

The rapidly developing field of tissue engineering produces living substitutes that restore, maintain or improve the function of tissues or organs. In contrast to standard therapies, the engineered products become integrated within the patient, affording a potentially permanent and specific cure of the disease, injury or impairment. Despite the great progress in the field, development of clinically relevantly sized tissues with complex architecture remains a great challenge. This is mostly due to limitations of nutrient and oxygen delivery to the cells and limited availability of scaffolds that can mimic the complex tissue architecture. This study presents the development of a multilayer tissue construct by rolling pre-seeded electrospun sheets [(prepared from poly (l-lactic acid) (PLLA) seeded with C2C12 pre-myoblast cells)] around a porous multibore hollow fibre (HF) membrane and its testing using a bioreactor. Important elements of this study are: 1) the medium permeating through the porous walls of multibore HF acts as an additional source of nutrients and oxygen to the cells, which exerts low shear stress (controllable by trans membrane pressure); 2) application of dynamic perfusion through the HF lumen and around the 3D construct to achieve high cell proliferation and homogenous cell distribution across the layers, and 3) cell migration occurs within the multilayer construct (shown using pre-labeled C2C12 cells), illustrating the potential of using this concept for developing thick and more complex tissues.

Corrugated round fibers to improve cell adhesion and proliferation in tissue engineering scaffolds.

Optimal cell interaction with biomaterial scaffolds is one of the important requirements for the development of successful in vitro tissue-engineered tissues. Fast, efficient and spatially uniform cell adhesion can improve the clinical potential of engineered tissue. Three-dimensional (3-D) solid free form fabrication is one widely used scaffold fabrication technique today. By means of deposition of polymer fibers, scaffolds with various porosity, 3-D architecture and mechanical properties can be prepared. These scaffolds consist mostly of solid round fibers. In this study, it was hypothesized that a corrugated fiber morphology enhances cell adhesion and proliferation and therefore leads to the development of successful in vitro tissue-engineered constructs. Corrugated round fibers were prepared and characterized by extruding poly(ethylene oxide terephthalate)-co-poly(butylene terephthalate) (300PEOT55PBT45) block co-polymer through specially designed silicon wafer inserts. Corrugated round fibers with 6 and 10 grooves on the fiber surface were compared with solid round fibers of various diameters. The culture of mouse pre-myoblast (C2C12) cells on all fibers was studied under static and dynamic conditions by means of scanning electron microscopy, cell staining and DNA quantification. After 7days of culturing under static conditions, the DNA content on the corrugated round fibers was approximately twice as high as that on the solid round fibers. Moreover, under dynamic culture conditions, the cells on the corrugated round fibers seemed to experience lower mechanical forces and therefore adhered better than on the solid round fibers. The results of this study show that the surface architecture of fibers in a tissue engineering scaffold can be used as a tool to improve the performance of the scaffold in terms of cell adhesion and proliferation.

[Basic principles of surgical treatment of bone metastases]. / Grundlagen der operativen Behandlung von Knochenmetastasen.

Due to an increased life expectancy and improved oncological treatment, the necessity for surgical treatment of bone metastases has increased as well. Ideally, therapy should concentrate on the improvement of the patient's quality of life while preferably being interdisciplinary. The type and extent of surgical therapy depend on the prognosis, tumor entity, localization of the tumor as well as on the patient's general condition. The main aims of surgical treatment is to reduce pain and preserve or restore function and mobility. After the contribution on spinal metastases in the last volume, this article focusses on metastases of the extremities and the pelvis. Pathologic fractures with an unclear oncological situation should be examined thoroughly before any surgical treatment is performed. In case of doubt, a biopsy should be performed. Depending on the individual prognosis, possible options for extremity surgery are (compound) osteosynthesis and implantation of a tumor endoprosthesis. The latter should be preferred for patients with a favorable prognosis and long life expectancy. To avoid revision surgery, the selected implant should outlast the patient's remaining life expectancy.