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Porous PEDOT:PSS Particles and their Application as Tunable Cell Culture Substrate
Due 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.
A physicochemical perspective of aging from single-cell analysis of ph, macromolecular and organellar crowding in yeast
Cellular aging is a multifactorial process that is characterized by a decline in homeostatic capacity, best described at the molecular level. Physicochemical properties such as pH and macromolecular crowding are essential to all molecular processes in cells and require maintenance. Whether a drift in physicochemical properties contributes to the overall decline of homeostasis in aging is not known. Here we show that the cytosol of yeast cells acidifies modestly in early aging and sharply after senescence. Using a macromolecular crowding sensor optimized for long-term FRET measurements, we show that crowding is rather stable and that the stability of crowding is a stronger predictor for lifespan than the absolute crowding levels. Additionally, in aged cells we observe drastic changes in organellar volume, leading to crowding on the µm scale, which we term organellar crowding. Our measurements provide an initial framework of physicochemical parameters of replicatively aged yeast cells. © 2020, eLife Sciences Publications Ltd. All rights reserved.
4D Printing of a Light-Driven Soft Actuator with Programmed Printing Density
There is a growing interest in the concept of four-dimensional (4D) printing that combines a three-dimensional (3D) manufacturing process with dynamic modulation for bioinspired soft materials exhibiting more complex functionality. However, conventional approaches have drawbacks of low resolution, control of internal micro/nanostructure, and creation of fast, complex actuation due to a lack of high-resolution fabrication technology and suitable photoresist for soft materials. Here, we report an approach of 4D printing that develops a bioinspired soft actuator with a defined 3D geometry and programmed printing density. Multiphoton lithography (MPL) allows for controlling printing density in gels at pixel-by-pixel with a resolution of a few hundreds of nanometers, which tune swelling behaviors of gels in response to external stimuli. We printed a 3D soft actuator composed of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) and gold nanorods (AuNRs). To improve the resolution of printing, we synthesized a functional, thermoresponsive macrocrosslinker. Through plasmonic heating by AuNRs, nanocomposite-based soft actuators undergo nonequilibrium, programmed, and fast actuation. Light-mediated manufacture and manipulation (MPL and photothermal effect) offer the feasibility of 4D printing toward adaptive bioinspired soft materials. Copyright © 2020 American Chemical Society.
Oligothiophene-Based Phosphonates for Surface Modification of Ultraflat Transparent Conductive Oxides
The self-assembly of electroactive organic molecules on transparent conductive oxides is a versatile strategy to engineer the interfacial energy-level alignment and to enhance charge carrier injection in optoelectronic devices. Via chemical grafting of an aromatic oligothiophene molecule by changing the position of the phosphonic acid anchoring group with respect to the organic moiety (terminal and internal), the direction of the main molecular dipole is changed, i.e., from parallel to perpendicular to the substrate, to study the molecular arrangement and electronic properties at the organic–inorganic interface. It is found that the observed work function increase cannot solely be predicted based on the calculated molecular dipole moment of the oligothiophene-based phosphonates. In addition, charge transfer from the substrate to the molecule has to be taken into account. Molecular assembly and induced electronic changes are analogous for both indium-tin oxide (ITO) and zinc oxide (ZnO), demonstrating the generality of the approach and highlighting the direct correlation between molecular coverage and electronic effects. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Wet-Spinning of Biocompatible Core–Shell Polyelectrolyte Complex Fibers for Tissue Engineering
Polyelectrolyte complex fibers (PEC fibers) have great potential with regard to biomedical applications as they can be fabricated from biocompatible and water-soluble polyelectrolytes under mild process conditions. The present publication describes a novel method for the continuous fabrication of PEC fibers in a water-based wet-spinning process by interfacial complexation within a core–shell spinneret. This process combines the robustness and flexibility of nonsolvent-induced phase separation (NIPS) spinning processes conventionally used in the membrane industry with the complexation between oppositely charged polyelectrolytes. The produced fibers demonstrate a core–shell structure with a low-density core and a highly porous polyelectrolyte complex shell of ≈800 μm diameter. In the case of chitosan and polystyrene sulfonate (PSS), mechanical fiber properties could be enhanced by doping the PSS with poly(ethylene oxide) (PEO). The resulting CHI/PSS-PEO fibers present a Young modulus of 3.78 GPa and a tensile strength of 165 MPa, which is an excellent combination of elongation at break and break stress compared to literature. The suitability of the CHI/PSS-PEO fibers as a scaffold for cell culture applications is verified by a four-day cultivation of human HeLa cells on PEO-reinforced fibers with a subsequent analysis of cell viability by fluorescence-based live/dead assay. © 2020 The Authors. Published by Wiley-VCH GmbH
Modulating the luminance of organic light-emitting diodes: Via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode
Self-assembled monolayers (SAMs) deposited on bottom electrodes are commonly used to tune charge carrier injection or blocking in optoelectronic devices. Beside the enhancement of device performance, the fabrication of multifunctional devices in which the output can be modulated by multiple external stimuli remains a challenging target. In this work, we report the functionalization of an indium tin oxide (ITO) electrode with a SAM of a diarylethene derivative designed for optically control the electronic properties. Following the demonstration of dense SAM formation and its photochromic activity, as a proof-of-principle, an organic light-emitting diode (OLED) embedding the light-responsive SAM-covered electrode was fabricated and characterized. Optically addressing the two-terminal device by irradiation with ultraviolet light doubles the electroluminescence. The original value can be restored reversibly by irradiation with visible light. This expanded functionality is based on the photoinduced modulation of the electronic structure of the diarylethene isomers, which impact the charge carriers' confinement within the emissive layer. This approach could be successfully exploited in the field of opto-communication technology, for example to fabricate opto-electronic logic circuits. © 2020 The Royal Society of Chemistry.
3D‐Printed Bioreactor with Integrated Impedance Spectroscopy for Cell Barrier Monitoring
Cell 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.
Mitigating Water Crossover by Crosslinked Coating of Cation‐Exchange Membranes for Brine Concentration
Undesired 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%.
Tunable Photomechanics in Diarylethene-Driven Liquid Crystal Network Actuators
The response of soft actuators made of stimuli-responsive materials can be phenomenologically described by a stimulus-deformation curve, depicting the controllability and sensitivity of the actuator system. Manipulating such stimulus-deformation curve allows fabricating soft microrobots with reconfigurable actuation behavior, which is not easily achievable using conventional materials. Here, we report a light-driven actuator based on a liquid crystal polymer network containing diarylethene (DAE) photoswitches as cross-links, in which the stimulus-deformation curve under visible-light illumination is tuned with UV light. The tuning is brought about by the reversible electrocyclization of the DAE units. Because of the excellent thermal stability of the visible-absorbing closed-form DAEs, the absorbance of the actuator can be optically fixed to a desired value, which in turn dictates the efficiency of photothermally induced deformation. We employ the controllability in devising a logical AND gate with macroscopic output, i.e., an actuator that bends negligibly under UV or visible light irradiation, but with profound shape change when addressed to both simultaneously. The results provide design tools for reconfigurable microrobotics and polymer-based logic gating. © 2020 American Chemical Society. All rights reserved.
Porous PVDF Monoliths with Templated Geometry
Additive 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.