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Breisig H.,RWTH Aachen | Breisig H.,DWI Leibniz Institute for Interactive Materials Research | Hoppe J.,RWTH Aachen | Melin T.,RWTH Aachen | And 2 more authors.
Journal of Membrane Science | Year: 2014

Hollow-fiber emulsification is a recent development that allows a continuous production of narrow-dispersed droplets with tunable diameter using hollow-fiber membranes. The to-be-dispersed phase is fed on one end through the lumen side while the continuous phase permeates through the membrane wall. After droplet formation, a droplet train leaves the hollow fiber on the other end. Droplet break-up has been assumed to occur inside a hollow-fiber membrane originating from Rayleigh-like instabilities; however proof has been missing yet due to missing visualization techniques inside the hollow fiber. Here we proof for the first time experimentally the droplet break-up mechanism and support these findings using computational fluid dynamics (CFD) simulations. Results of the CFD simulations are compared with experiments carried out using a glycerol-water solution as droplet phase and paraffin oil as continuous phase. The oil turns the porous hollow-fiber membrane transparent thus allowing direct observation of the droplet formation process inside the membrane. Comparisons were carried out by variation of the volume flow rate of the disperse phase and its viscosity as relevant influencing parameters and for the target parameters droplet size and droplet break-up length. Simulations capture the governing trends of the process such as the presence of a size maximum and allow the prediction of the required membrane lengths for droplet break-up. The droplet size maximum is explained using the understanding of droplet detachment in co-flowing streams. © 2014 Elsevier B.V.


David O.,DWI Leibniz Institute for Interactive Materials Research | Gendel Y.,DWI Leibniz Institute for Interactive Materials Research | Wessling M.,DWI Leibniz Institute for Interactive Materials Research | Wessling M.,RWTH Aachen
Journal of Membrane Science | Year: 2014

We present tubular macroporous titanium membranes prepared via a dry-wet spinning process from a polyethersulfone solution loaded with Ti particles (15. μm) and a subsequent sintering process at various sintering temperatures (1100-1500. °C) and sintering times (30-75. min). Outer diameter, wall thickness, average pore size and porosity of the Ti tubes were ~4.5. mm, ~350. μm, 1.6-2.8. μm and ~30%, respectively. These tubular membranes have excellent mechanical strength, electrical conductivity as well as nitrogen and water permeability. These properties, together with the inherent high corrosion and temperature resistance of titanium make them suitable for a wide range of membrane applications such as microfiltration, porous tubular electrodes for electrochemical membrane reactors; and gas-to-liquid diffuser. © 2014 Elsevier B.V.


Vuoriluoto M.,Aalto University | Orelma H.,Aalto University | Orelma H.,VTT Technical Research Center of Finland | Zhu B.,DWI Leibniz Institute for Interactive Materials Research | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2016

We passivated TEMPO-oxidized cellulose nanofibrils (TOCNF) toward human immunoglobulin G (hIgG) by modification with block and random copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA). The block copolymers reversibly adsorbed on TOCNF and were highly effective in preventing nonspecific interactions with hIgG, especially if short PDMAEMA blocks were used. In such cases, total protein rejection was achieved. This is in contrast to typical blocking agents, which performed poorly. When an anti-human IgG biointerface was installed onto the passivated TOCNF, remarkably high affinity antibody-antigen interactions were observed (0.90 ± 0.09 mg/m2). This is in contrast to the nonpassivated biointerface, which resulted in a significant false response. In addition, regeneration of the biointerface was possible by low pH aqueous wash. Protein A from Staphylococcus aureus was also utilized to successfully increase the sensitivity for human IgG recognition (1.28 ± 0.11 mg/m2). Overall, the developed system based on TOCNF modified with multifunctional polymers can be easily deployed as bioactive material with minimum fouling and excellent selectivity. © 2016 American Chemical Society.


Celikkin N.,RWTH Aachen | Jakubcova L.,RWTH Aachen | Zenke M.,RWTH Aachen | Hoss M.,RWTH Aachen | And 3 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2015

Engineered magnetic nanoparticles (MNPs) are emerging to be used as cell tracers, drug delivery vehicles, and contrast agents for magnetic resonance imaging (MRI) for enhanced theragnostic applications in biomedicine. In vitro labeling of target cell populations with MNPs and their implantation into animal models and patients shows promising outcomes in monitoring successful cell engraftment, differentiation and migration by using MRI. Dendritic cells (DCs) are professional antigen-presenting cells that initiate adaptive immune responses. Thus, DCs have been the focus of cellular immunotherapy and are increasingly applied in clinical trials. Here, we addressed the coating of different polyelectrolytes (PE) around ferumoxytol particles using the layer-by-layer technique. The impact of PE-coated ferumoxytol particles for labeling of DCs and Flt3+ DC progenitors was then investigated. The results from our studies revealed that PE-coated ferumoxytol particles can be readily employed for labeling of DC and DC progenitors and thus are potentially suitable as contrast agents for MRI tracking. © 2014 Elsevier B.V.


Tiwari R.,DWI Leibniz Institute for Interactive Materials Research | Honders D.,DWI Leibniz Institute for Interactive Materials Research | Schipmann S.,RWTH Aachen | Schulte B.,DWI Leibniz Institute for Interactive Materials Research | And 4 more authors.
Macromolecules | Year: 2014

Advances in the understanding of microgel properties and exploitation of their full potential for applications require control of the extent and type of functionalization, while at the same time providing control of particle shape, that is, size and uniformity, and intrinsic particle properties such as hardness and degree of crosslinking. However, versatile and simple synthetic approaches to prepare highly uniform and densely functionalized microgels based on functional groups unsuitable for aqueous precipitation polymerization are still scarce. As an alternative platform approach, herein we report on the synthesis of uniform particles based on classical batch emulsion polymerization, which are later postfunctionalized via Cu-mediated Huisgen-type alkyne/azide click chemistry. We use propargyl acrylate (PGA) as a monomer and ethylene glycol dimethacrylate (EGDMA) as a crosslinker for the synthesis of narrowly dispersed latex particles in the size regime of 50-200 nm in radius. We demonstrate how particle hardness and swelling can be tuned as a function of the used ratio of monomer/crosslinker. Postmodifications in the interior of the particles are conducted in the swollen state in DMSO, and we add pH-responsive cationic moieties as a first attractive model functionality. Combined Raman spectroscopy and elemental analysis reveal the kinetics and degree of modification. Both depend on the degree of crosslinking, and we find densely functionalized particles exhibiting a conversion of the alkyne functionalities of up to 90%. After modification, the resulting microgels display a pH-dependent ionization and swelling behavior in water. The suggested route opens up new and versatile ways to prepare narrowly dispersed water-dispersible microgels with tailored hardness and high density of functional groups, based on readily available building blocks. © 2014 American Chemical Society.


Begemann J.,RWTH Aachen | Spiess A.C.,RWTH Aachen | Spiess A.C.,DWI Leibniz Institute for Interactive Materials Research
Biotechnology Journal | Year: 2015

pH-shifts are a serious challenge in cofactor dependent biocatalytic oxidoreductions. Therefore, a pH control strategy was developed for reaction systems, where the pH value is not directly measurable. Such a reaction system is the biphasic aqueous-organic reaction system, where the oxidoreduction of hydrophobic substrates in organic solvents is catalysed by hydrogel-immobilized enzymes, and enzyme-coupled cofactor regeneration is accomplished via formate dehydrogenase, leading to a pH-shift. Dual lifetime referencing (DLR), a fluorescence spectroscopic method, was applied for online-monitoring of the pH-value within the immobilizates during the reaction, allowing for a controlled dosage of formic acid. It could be shown that by applying trisodium 8-hydroxypyrene-1, 3, 6-trisulfonate as pH indicator and Ru(II) tris(4, 7-diphenyl-1, 10-phenantroline) (Ru[dpp]) as a reference luminophore the control of the pH-value in a macroscopic gel-bead-stabilized aqueous/organic two phase system in a range of pH 6.5 to 8.0 is possible. An experimental proof of concept could maintain a stable pH of 7.5 ± 0.15 during the reaction for at least 105 h. With these results, it could be shown that DLR is a powerful tool for pH-control within reaction systems with no direct access for conventional pH-measurement. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Stiefel S.,RWTH Aachen | Stiefel S.,DWI Leibniz Institute for Interactive Materials Research | Marks C.,RWTH Aachen | Schmidt T.,DWI Leibniz Institute for Interactive Materials Research | And 4 more authors.
Green Chemistry | Year: 2016

The cleaving of technical lignin by different technologies is a promising but complex approach for the production of value-added compounds from biomass. A rigorous description of the underlying mechanisms and influencing parameters is complicated by lignin's heterogeneity, hampering comparability and reproducibility. This frequently leads to contradicting data and theories in the scientific community. By applying a statistical design of experiment approach to the electro-oxidation of Kraft lignin, the statistical variation of the experimental data can be separated from the systematic effects of reaction parameters on lignin properties. The data allow a clear quantification of the effect of temperature, alkalinity, catalyst, lignin concentration and current density on the molecular weight, monomer production, UV absorbance as well as acid-solubility of the treated lignin. The method described can be applied to reliably investigate the whole range of lignin cleavage technologies in spite of the pronounced heterogeneity of lignin. © 2016 The Royal Society of Chemistry.


Wiese S.,RWTH Aachen | Tsvetkova Y.,RWTH Aachen | Daleiden N.J.E.,RWTH Aachen | Spiess A.C.,RWTH Aachen | And 4 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

Here, we report on how to stabilize and break emulsions that are compatible with enzymatic reaction conditions. Many substrates of enzymatic reactions are soluble in unpolar organic solvents whereas the enzymes themselves often need an aqueous environment. We use a buffer solution (triethanolamine hydrochloride) as aqueous and MtBE (tert-butyl methyl ether) as organic phase which provide good enzyme compatibility. We are able to break emulsions in a desired temperature range by using NiPAM-NiPMAM microgels with different monomer compositions and architecture, respectively. Our microgels need to deswell to about 55% of its swollen size at room temperature to let the emulsion break. Emulsions can be broken such that the microgels are either colloidally stable in the aqueous phase or flocculated. The temperature interval in which the microgels stay colloidally stable while the emulsion is broken is broader for the core-shell microgel than for the copolymer microgel. The behavior of the microgels in aqueous solution allows predicting: (i) the temperature at which the emulsion breaks and (ii) whether microgels flocculate or not during breaking the emulsion. However, the partial miscibility of the organic phase with the aqueous phase has to be taken into account. Thus, we are able to stabilize and break emulsions by employing microgels as responsive emulsifiers and to adapt the microgels to the requirements of biocatalytic processes. © 2016 Elsevier B.V.


PubMed | DWI Leibniz Institute for Interactive Materials Research and Aalto University
Type: Journal Article | Journal: ACS applied materials & interfaces | Year: 2016

We passivated TEMPO-oxidized cellulose nanofibrils (TOCNF) toward human immunoglobulin G (hIgG) by modification with block and random copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA). The block copolymers reversibly adsorbed on TOCNF and were highly effective in preventing nonspecific interactions with hIgG, especially if short PDMAEMA blocks were used. In such cases, total protein rejection was achieved. This is in contrast to typical blocking agents, which performed poorly. When an anti-human IgG biointerface was installed onto the passivated TOCNF, remarkably high affinity antibody-antigen interactions were observed (0.90 0.09 mg/m(2)). This is in contrast to the nonpassivated biointerface, which resulted in a significant false response. In addition, regeneration of the biointerface was possible by low pH aqueous wash. Protein A from Staphylococcus aureus was also utilized to successfully increase the sensitivity for human IgG recognition (1.28 0.11 mg/m(2)). Overall, the developed system based on TOCNF modified with multifunctional polymers can be easily deployed as bioactive material with minimum fouling and excellent selectivity.


PubMed | DWI Leibniz Institute for Interactive Materials Research and Aalto University
Type: Journal Article | Journal: The journal of physical chemistry. B | Year: 2015

Block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) with varying block sizes were synthesized by consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization and then exposed to cellulose substrates with different anionic charge density. The extent and dynamics of quaternized PDMAEMA-b-POEGMA adsorption on regenerated cellulose, cellulose nanofibrils (CNF), and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) was determined by using electromechanical and optical techniques, namely, quartz crystal microbalance (QCM-D) and surface plasmon resonance (SPR), respectively. PDMAEMA-b-POEGMA equilibrium adsorption increased with the anionic charge of cellulose, an indication of electrostatic interactions. Such an observation was further confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Depending on their architecture, adsorption on TOCNF of some of the PDMAEMA-b-POEGMA copolymers produced a significant reduction in QCM frequency, as expected from large mass uptake, while surprisingly, other copolymers induced the opposite effect. This latter, remarkable behavior was ascribed to coupled water expulsion from the interface upon charge neutralization of anionic surface sites with adsorbing cationic polymer segments. These observations were further investigated with SPR and QCM-D measurements using deuterium oxide solvent exchange to determine the amount of coupled water at the TOCNF-block copolymer interface. Finally, random copolymers with similar composition adsorbed to a larger extent compared to the respective block copolymers, revealing the effect of adsorbed loops and tails as well as hydration.

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