A mini-module with built-in spacers for high-throughput ultrafiltration

Ultrafiltration membrane modules suffer from a permeate flow decrease arising during filtration and caused by concentration polarization and fouling in, e.g., fermentation broth purification. Such performance losses are frequently mitigated by manipulating the hydrodynamic conditions at the membrane-fluid interface using, e.g., mesh spacers acting as static mixers. This additional element increases manufacturing complexity while improving mass transport in general, yet accepting their known disadvantages such as less transport in dead zones. However, the shape of such spacers is limited to the design of commercially available spacer geometries. Here, we present a methodology to design an industrially relevant mini-module with an optimized built-in 3D spacer structure in a flat-sheet ultrafiltration membrane module to eliminate the spacer as a separate part. Therefore, the built-in structures have been conceptually implemented through an in-silico design in compliance with the specifications for an injection molding process. Ten built-in structures were investigated in a digital twin of the mini-module by 3D-CFD simulations to select two options, which were then compared to the empty feed channel regarding mass transfer. Subsequently, the simulated flux increase was experimentally verified during bovine serum albumin (BSA) filtration. The new built-in sinusoidal corrugation outperforms conventional mesh spacer inlays by up to 30% higher permeation rates. The origin of these improvements is correlated to the flow characteristics inside the mini-module as visualized online and in-situ by low-field and high-field magnetic resonance imaging velocimetry (flow-MRI) during pure water permeation

3D Nanofabrication inside rapid prototyped microfluidic channels showcased by wet-spinning of single micrometre fibres

Microfluidics is an established multidisciplinary research domain with widespread applications in the fields of medicine, biotechnology and engineering. Conventional production methods of microfluidic chips have been limited to planar structures, preventing the exploitation of truly three-dimensional architectures for applications such as multi-phase droplet preparation or wet-phase fibre spinning. Here the challenge of nanofabrication inside a microfluidic chip is tackled for the showcase of a spider-inspired spinneret. Multiphoton lithography, an additive manufacturing method, was used to produce free-form microfluidic masters, subsequently replicated by soft lithography. Into the resulting microfluidic device, a threedimensional spider-inspired spinneret was directly fabricated in-chip via multiphoton lithography. Applying this unprecedented fabrication strategy, the to date smallest printed spinneret nozzle is produced. This spinneret resides tightly sealed, connecting it to the macroscopic world. Its functionality is demonstrated by wet-spinning of single-digit micron fibres through a polyacrylonitrile coagulation process induced by a water sheath layer. The methodology developed here demonstrates fabrication strategies to interface complex architectures into classical microfluidic platforms. Using multiphoton lithography for in-chip fabrication adopts a high spatial resolution technology for improving geometry and thus flow control inside microfluidic chips. The showcased fabrication methodology is generic and will be applicable to multiple challenges in fluid control and beyond

Wet-Spun PEDOT/CNT Composite Hollow Fibers as Flexible Electrodes for H2O2 Production

The electrochemical synthesis of hydrogen peroxide (H2O2) using the oxygen reduction reaction (ORR) requires highly catalytic active, selective, and stable electrode materials to realize a green and efficient process. The present publication shows for the first time the application of a facile one-step bottom-up wet-spinning approach for the continuous fabrication of stable and flexible tubular poly(3,4-ethylene dioxythiophene) (PEDOT : PSS) and PEDOT : PSS/carbon nanotube (CNT) hollow fibers. Additionally, electrochemical experiments reveal the catalytic activity of acid-treated PEDOT : PSS and its composites in the ORR forming hydrogen peroxide for the first time. Under optimized conditions, the composite electrodes with 40 wt % CNT loading could achieve a high production rate of 0.01 mg/min/cm2 and a current efficiency of up to 54 %. In addition to the high production rate, the composite hollow fiber has proven its long-term stability with 95 % current retention after 20 h of hydrogen peroxide production. © 2021 The Authors. ChemElectroChem published by Wiley-VCH Gmb

Rapid prototyping of microfluidic systems using two-photon lithography

Additive manufacturing is revolutionizing research and development activities as the pace for innovation increases with the fast formation of complex prototypes. Current lithography techniques prototype polymeric objects at the macro-, meso- and microscale with spatial resolutions spanning over several orders of magnitude. In this, the diffraction of light is limiting the resolution of linear optical lithography techniques. Two-photon lithography can even surpass the optical diffraction limit by confining nonlinear photon adsorption to an ellipsoid. The ability to control the movement of the ellipsoid in time and space enables additive polymerization inside a light-sensitive photoresist. In the present thesis, two-photon lithography is used to create truly three-dimensional microfluidic systems. The geometry of such systems manipulates the prevailing fluid dynamics and transport phenomena. To augment device functionality, even smaller prototyped objects are directly interfaced into the microfluidic channel using in situ two-photon lithography. These free-form objects reside tightly sealed and connected to the macroscopic world. The novel technique is demonstrated by continuous polyacrylonitrile coagulation that is forming single-digit micron fibers in an interfaced co-flow wet-spinning nozzle. Substantially smaller nanofibers are directly synthesised inside a horizontal-flow channel using in situ two-photon continuous-flow lithography. This continuous-flow lithography technique is extended to the real-time synthesis of complex free-standing porous microtubes inside a vertical-flow channel. The combined benefits of a controlled microfluidic environment with the precision of in situ two-photon lithography contributes to the generic formation of complex-shaped materials with rigorous control over the morphology and surface topology. The developed methodology is further transferred to investigate the advancement of the first continuous microfluidic cell-sorting device towards a thrombocyte bypass for extracorporeal membrane oxygenation. Within the cell-sorting device, whole blood with a clinical relevant hematocrit is sorted based on the joint effects of flow focusing and inertial lift forces resulting in lateral cell migration. The speed of migration is dependent on size and shape of the cellular components. The application of three-dimensional microfluidic systems in a clinical regulated environment demonstrates the potential and transferability of the developed methodology to a multitude of theoretical and practical problems in the natural sciences and technology

Controlled depolymerization of lignin in an electrochemical membrane reactor

The electrochemical oxidative cleavage of lignin is a promising approach to valorize lignin's monomeric subunits as bulk and fine chemicals. It is attractive since it does not require toxic solvents or expensive catalysts. However, due to the rather unselective nature of the electrochemical depolymerization, overoxidation of the generated products occurs. In order to prevent the degradation of the aromatic monomeric compounds into acids and CO2, a selective product removal strategy from the reaction environment is necessary. We report the use of an electrochemical membrane reactor for the continuous electrochemical cleavage of lignin integrated with an in-situ nanoporous filtration process. The generated cleavage products are removed through the nanofiltration membrane from the oxidative environment and product degradation is prevented. The reaction/separation unit comprises an unprecedented electrode configuration: electrode rods integrated into a 3D-printed turbulence-promoting mixer minimizing fouling and polarization phenomena at membrane and electrodes. Keywords: Electrochemical membrane reactor, Electrooxidation, Lignin, Nanofiltration, In-situ filtratio