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- ItemPorous PEDOT:PSS Particles and their Application as Tunable Cell Culture Substrate(Weinheim : Wiley, 2021) Rauer, Sebastian Bernhard; Bell, Daniel Josef; Jain, Puja; Rahimi, Khosrow; Felder, Daniel; Linkhorst, John; Wessling, MatthiasDue to its biocompatibility, electrical conductivity, and tissue-like elasticity, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) constitutes a highly promising material regarding the fabrication of smart cell culture substrates. However, until now, high-throughput synthesis of pure PEDOT:PSS geometries was restricted to flat sheets and fibers. In this publication, the first microfluidic process for the synthesis of spherical, highly porous, pure PEDOT:PSS particles of adjustable material properties is presented. The particles are synthesized by the generation of PEDOT:PSS emulsion droplets within a 1-octanol continuous phase and their subsequent coagulation and partial crystallization in an isopropanol (IPA)/sulfuric acid (SA) bath. The process allows to tailor central particle characteristics such as crystallinity, particle diameter, pore size as well as electrochemical and mechanical properties by simply adjusting the IPA:SA ratio during droplet coagulation. To demonstrate the applicability of PEDOT:PSS particles as potential cell culture substrate, cultivations of L929 mouse fibroblast cells and MRC-5 human fibroblast cells are conducted. Both cell lines present exponential growth on PEDOT:PSS particles and reach confluency with cell viabilities above 95 vol.% on culture day 9. Single cell analysis could moreover reveal that mechanotransduction and cell infiltration can be controlled by the adjustment of particle crystallinity.
- ItemMitigating Water Crossover by Crosslinked Coating of Cation‐Exchange Membranes for Brine Concentration(Weinheim : Wiley, 2021) Rommerskirchen, Alexandra; Roth, Hannah; Linnartz, Christian J.; Egidi, Franziska; Kneppeck, Christian; Roghmans, Florian; Wessling, MatthiasUndesired water crossover through ion-exchange membranes is a significant limitation in electrically driven desalination processes. The effect of mitigating water crossover is twofold: 1) The desalination degree is less reduced due to the unwanted removal of water, and 2) the brine concentration is increased due to decreased dilution by an unwanted crossover of water molecules. Hence, water crossover limits the desalination and concentration efficiency of the processes, while the energy demand to achieve a certain level of desalination or concentration increases. This effect is especially pronounced when treating high salinity solutions, which goes hand in hand with the crossover of many ions through the ion-exchange membranes. A crosslinked coating for cation-exchange membranes (CEMs) is presented in this work, which can significantly mitigate such undesired water crossover. The efficacy is demonstrated using the flow-electrode capacitive deionization process applied for desalination and concentration of saline brines at feed concentrations of 60 and 120 g L−1 NaCl. With just a single coated CEM, the water crossover was reduced by up to 54%.
- Item3D‐Printed Bioreactor with Integrated Impedance Spectroscopy for Cell Barrier Monitoring(Weinheim : Wiley, 2021) Linz, Georg; Rauer, Sebastian Bernhard; Kuhn, Yasmin; Wennemaring, Simon; Siedler, Laura; Singh, Smriti; Wessling, MatthiasCell culture experiments often suffer from limited commercial availability of laboratory-scale bioreactors, which allow experiments to be conducted under flow conditions and additional online monitoring techniques. A novel 3D-printed bioreactor with a homogeneously distributed flow field enabling epithelial cell culture experiments and online barrier monitoring by integrated electrodes through electrical impedance spectroscopy (EIS) is presented. Transparent and conductive indium tin oxide glass as current-injecting electrodes allows direct visualization of the cells, while measuring EIS simultaneously. The bioreactor's design considers the importance of a homogeneous electric field by placing the voltage pick-up electrodes in the electrical field. The device's functionality is demonstrated by the cultivation of the epithelial cell line Caco-2 under continuous flow and monitoring of the cell layer by online EIS. The collected EIS data were fitted by an equivalent electric circuit, resulting in the cell layer's resistance and capacitance. This data is used to monitor the cell layer's reaction to ethylene glycol-bis-(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid and forskolin. These two model substances show the power of impedance spectroscopy as a non-invasive way to characterize cell barriers. In addition, the bioreactor design is available as a print-ready file in the Appendix, enabling its use for other scientific institutions.
- ItemPorous PVDF Monoliths with Templated Geometry(Weinheim : Wiley, 2021) Djeljadini, Suzana; Bongartz, Patrick; Alders, Michael; Hartmann, Nils; Oing, Alexander; Cornelissen, Christian; Hesselmann, Felix; Arens, Jutta; Steinseifer, Ulrich; Linkhorst, John; Wessling, MatthiasAdditive manufacturing of complex porous polymer geometries is a new field of advanced materials processing. Such new geometries can be used to fabricate porous polymer monoliths serving as a support for other material functions. Here, a novel fabrication technology to manufacture tailored 3D porous monoliths via additive manufacturing and templating is presented. The method is based on replicating a 3D-printed mold with a polymer solution of polyvinylidenfluorid-triethyl phosphate (PVDF-TEP) and induce phase separation of the polymer solution subsequently. In a second step, the mold is removed without affecting the porous PVDF phase. As a result, porous monoliths with a templated 3D architecture are successfully fabricated. The manufacturing process is successfully applied to complex structures and can be applied to any conceivable geometry. Coating the porous 3D monoliths with another PVDF solution allows applying a skin layer yielding an asymmetric membrane monolith. As a showcase, a polydimethylsiloxane coating even leads to a smooth and dense layer of micrometer size. The methodology enables a new generation of complex porous polymer monoliths with tailored surface coatings. For the combination of poly(dimethylsiloxane) on a porous support, gas/liquid mass transfer is used in blood oxygenation with reduced diffusion limitation is within reach.
- ItemOn the Dynamical Regimes of Pattern-Accelerated Electroconvection([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Davidson, Scott M.; Wessling, Matthias; Mani, AliRecent research has established that electroconvection can enhance ion transport at polarized surfaces such as membranes and electrodes where it would otherwise be limited by diffusion. The onset of such overlimiting transport can be influenced by the surface topology of the ion selective membranes as well as inhomogeneities in their electrochemical properties. However, there is little knowledge regarding the mechanisms through which these surface variations promote transport. We use high-resolution direct numerical simulations to develop a comprehensive analysis of electroconvective flows generated by geometric patterns of impermeable stripes and investigate their potential to regularize electrokinetic instabilities. Counterintuitively, we find that reducing the permeable area of an ion exchange membrane, with appropriate patterning, increases the overall ion transport rate by up to 80%. In addition, we present analysis of nonpatterned membranes and find a novel regime of electroconvection where a multivalued current is possible due to the coexistence of multiple convective states.
- ItemDirect Observation of Deformation in Microgel Filtration([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Linkhorst, John; Rabe, Jonas; Hirschwald, Lukas T.; Kuehne, Alexander J. C.; Wessling, MatthiasColloidal filtration processes using porous membranes suffer from productivity loss due to colloidal matter retention and continuous build-up by the retained matter. Especially during filtration of soft matter, the deformation of the individual colloids that make up the filter cake may be significant; however, this deformation and its impact remain unresolved so far. Yet, understanding the deformation on the single colloid level as well as on the ensemble level is important to be able to deconvolute filter cake properties from resistance increase of the membrane either by simultaneous internal adsorption or blocking of pores. Here, we report on the compression of a filter cake by filtrating soft microgels in a microfluidic channel in front of a model membrane. To study the single colloid deformation amorphous and crystalline domains were built up in front of the membrane and visualized on-line using confocal fluorescence microscopy while adjusting the degree of permeation, i.e., the transmembrane flux. Results show locally pronounced asymmetric deformation in amorphous domains, while the microgels in colloidal crystals approached regular polyeder shape. Increasing the flux beyond the maximum colloid deformation results in non-isochoric microgel behavior. The presented methodology enables a realistic description of complex colloidal matter deposits during filtration.
- ItemMicrofluidic colloid filtration([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, MatthiasFiltration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.
- ItemMicrofluidic cell sorting: Towards improved biocompatibility of extracorporeal lung assist devices([London] : Macmillan Publishers Limited, part of Springer Nature, 2018) Bleilevens, Christian; Lölsberg, Jonas; Cinar, Arne; Knoben, Maren; Grottke, Oliver; Rossaint, Rolf; Wessling, MatthiasExtracorporeal lung assist technology is one of the last options in critical care medicine to treat patients suffering from severe oxygenation and decarboxylation disorders. Platelet activation along with the consequent thrombus formation is a potentially life-threatening complication of this technique. To avoid platelet-dependent clot formation, this study aims at developing a microfluidic cell sorting chip that can bypass platelets prior to the membrane oxygenator of the extracorporeal lung assist device. The cell sorting chips were produced by maskless dip-in laser lithography, followed by soft lithography replication using PDMS. Citrated porcine whole blood with a clinically relevant haematocrit of 17% was used for the cell sorting experiments involving three different blood flow rates. The joint effects of flow focusing and hydrodynamic lifting forces within the cell sorting chip resulted in a reduction of up to 57% of the baseline platelet count. This cell sorting strategy is suitable for the continuous and label-free separation of red blood cells and platelets and is potentially applicable for increasing the biocompatibility and lifetime of current extracorporeal lung assist devices.
- ItemTemplating the morphology of soft microgel assemblies using a nanolithographic 3D-printed membrane([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Linkhorst, John; Lölsberg, Jonas; Thill, Sebastian; Lohaus, Johannes; Lüken, Arne; Naegele, Gerhard; Wessling, MatthiasFilter cake formation is the predominant phenomenon limiting the filtration performance of membrane separation processes. However, the filter cake’s behavior at the particle scale, which determines its overall cake behavior, has only recently come into the focus of scientists, leaving open questions about its formation and filtration behavior. The present study contributes to the fundamental understanding of soft filter cakes by analyzing the influence of the porous membrane’s morphology on crystal formation and the compaction behavior of soft filter cakes under filtration conditions. Microfluidic chips with nanolithographic imprinted filter templates were used to trigger the formation of crystalline colloidal filter cakes formed by soft microgels. The soft filter cakes were observed via confocal laser scanning microscopy (CLSM) under dead-end filtration conditions. Colloidal crystal formation in the cake, as well as their compaction behavior, were analyzed by optical visualization and pressure data. For the first time, we show that exposing the soft cake to a crystalline filter template promotes the formation of colloidal crystallites and that soft cakes experience gradient compression during filtration.
- ItemParticle movements provoke avalanche-like compaction in soft colloid filter cakes([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Lüken, Arne; Stüwe, Lucas; Lohaus, Johannes; Linkhorst, John; Wessling, MatthiasDuring soft matter filtration, colloids accumulate in a compressible porous cake layer on top of the membrane surface. The void size between the colloids predominantly defines the cake-specific permeation resistance and the corresponding filtration efficiency. While higher fluxes are beneficial for the process efficiency, they compress the cake and increase permeation resistance. However, it is not fully understood how soft particles behave during cake formation and how their compression influences the overall cake properties. This study visualizes the formation and compression process of soft filter cakes in microfluidic model systems. During cake formation, we analyze single-particle movements inside the filter cake voids and how they interact with the whole filter cake morphology. During cake compression, we visualize reversible and irreversible compression and distinguish the two phenomena. Finally, we confirm the compression phenomena by modeling the soft particle filter cake using a CFD-DEM approach. The results underline the importance of considering the compression history when describing the filter cake morphology and its related properties. Thus, this study links single colloid movements and filter cake compression to the overall cake behavior and narrows the gap between single colloid events and the filtration process.