INMdok (Leibniz Institute for New Materials)
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Fingertip friction and tactile rating of wrapping papers
Get PDFThe tactile explorartion and perception of wrapping papers is investigated in terms of fingertip friction and rating of sensory, affective, and evaluative adjectives. Friction coefficients, which vary significantly between samples, are correlated with factors such as valence which are identified in a principal component analysis of subjective ratings. We found that affective appraisals of valence and arousal as well as evaluations of novelty, but not of value, decreased with increasing friction
On the adhesion between thin sheets and randomly rough surfaces
Get PDFThin, elastic sheets are well known to adapt to rough counterfaces, whereby adhesive interactions and pull-off stresses σp can be significant, yet no generally applicable, quantitative guideline has been suggested hitherto as to when a sheet should be considered thin enough to be sticky. Using computer simulations, we find that the dependence of σp on surface energy γ has a high and a low-pull-off-stress regime. For randomly rough surfaces, we locate the dividing line at the point, where γ is approximately half the elastic energy per unit area needed to make conformal contact, which is the same ratio as for semi-infinite elastic solids. This rule of thumb also applies to a certain degree for single-wavelength roughness, in which case the transition from low to high stickiness occurs when at the moment of maximum tension contact is not only broken at the height maxima but also at the saddle points
Flexible and transparent electrodes imprinted from Au nanowires: stability and ageing
Get PDFWe study the stability of flexible transparent electrodes (FTEs) that were self-assembled from ultra-thin gold nanowires (AuNW) by direct nanoimprinting of inks with different particle concentrations (1 to 10 mg mL−1). The resulting lines were less than 3 μm wide and contained bundles of AuNW with oleylamine (OAm) ligand shells. Small-angle X-ray scattering confirmed a concentration-independent bundle structure. Plasma sintering converted the wire assemblies into lines with a thin metal shell that contributes most to electrical conductivity and covers a hybrid core. We studied the relative change in sheet resistance and the morphology of the FTEs with time. The sheet resistance increased at all concentrations, but at different rates. The metal shell aged by de-wetting and pore formation. The hybrid core de-mixed and densified, which led to a partial collapse of the shell. Residual organics migrated through the shell via its pores. Lines formed at low concentration (cAu = 2 to 3 mg mL−1) contained less residual organics and aged slower than those formed at high cAu ≥ 5 mg mL−1. We passivated the conductive shell with thin, adsorbed layers of PEDOT:PSS and found that it decelerated degradation by slowing surface diffusion and hindering further rupture of the shell. Thick capping layers prevented degradation entirely and stopped pore formation
3D Printed Tubular Scaffolds with Massively Tailorable Mechanical Behavior
Get PDFMelt electrowriting (MEW) is a promising additive manufacturing technique for tissue scaffold biofabrication. Successful application of MEW scaffolds requires strictly controlled mechanical behavior. This requires scaffold geometry be optimized to match native tissue properties while simultaneously supporting cell attachment and proliferation. The objective of this work is to investigate how geometric properties can be exploited to massively tailor the mechanical behavior of tubular crosshatch scaffolds. An experimentally validated finite element (FE) model is developed and 441 scaffold geometries are investigated under tension, compression, bending, and radial loading. A range of pore areas (4–150 mm2) and pore angles (11°–134°) are investigated. It is found that scaffold mechanical behavior is massively tunable through the control of these simple geometric parameters. Across the ranges investigated, scaffold stiffness varies by a factor of 294× for tension, 204× for compression, 231× for bending, and 124× for radial loading. Further, it is discussed how these geometric parameters can be simultaneously tuned for different biomimetic material applications. This work provides critical insights into scaffold design to achieve biomimetic mechanical behavior and provides an important tool in the development of biomimetic tissue engineered constructs
Rhodamine 6G and 800 intermolecular heteroaggregates embedded in PMMA for near-infrared wavelength shifting
Get PDFThe opto-electronic properties of small-molecules and functional dyes usually differ when incorporated into solid matrices with respect to their isolated form due to an aggregation phenomenon that alters their optical and fluorescent properties. These spectroscopic modifications are studied in the framework of the exciton theory of aggregates, which has been extensively applied in the literature for the study of molecular aggregates of the same type of molecules (homoaggregation). Despite the demonstrated potential of the control of the heteroaggregation process (aggregation of different types of molecules), most of the reported works are devoted to intramolecular aggregates, complex molecules formed by several chromophores attached by organic linkers. The intramolecular aggregates are specifically designed to hold a certain molecular structure that, on the basis of the exciton theory, modifies their optical and fluorescent properties with respect to the isolated chromophores that form the molecule. The present article describes in detail the incorporation of Rhodamine 6G (Rh6G) and 800 (Rh800) into polymeric matrices of poly-(methyl methacrylate), PMMA. The simultaneous incorporation of both dyes results in an enhanced fluorescent emission in the near-infrared (NIR), originating from the formation of ground-state Rh6G–Rh800 intermolecular heteroaggregates. The systematic control of the concentration of both rhodamines provides a model system for the elucidation of the heteroaggregate formation. The efficient energy transfer between Rh6G and Rh800 molecules can be used as wavelength shifters to convert effectively the light from visible to NIR, a very convenient wavelength range for many practical applications which make use of inexpensive commercial detectors and systems
Dynamic Light Scattering on Nanoparticles in Microgravity in a Drop Tower
Get PDFGravity affects colloidal dispersions via sedimentation and convection. We used dynamic light scattering (DLS) to quantify the mobility of nanoparticles on ground and in microgravity. A DLS instrument was adapted to withstand the accelerations in a drop tower, and a liquid handling set-up was connected in order to stabilize the liquid temperature and enable rapid cooling or heating. Light scattering experiments were performed in the drop tower at ZARM (Bremen, Germany) during a microgravity interval of 9.1 s and compared to measurements on ground. Particle dynamics were analyzed at constant temperature and after a rapid temperature drop using a series of DLS measurements with 1 s integration time. We observed nanoparticles with average gold core diameters of 7.8 nm and non-polar oleylamine shells that were dispersed in tetradecane and had an average hydrodynamic diameter of 21 nm. The particles did not change their diameter in the observed temperature range. The particle dynamics inferred from DLS on ground and in microgravity were in good agreement, demonstrating the possibility to perform reliable DLS measurements in a drop tower
Gelation kinetics of thiol-methylsulfone (MS) hydrogel formulations for 3D cell culture
Get PDFCrosslinking chemistries that allow hydrogel formation within minutes are essential to achieve homogeneous networks and cell distributions in 3D cell culture. Thiol-methylsulfone (MS) crosslinking chemistry offers minutes-scale gelation under near-physiological conditions showing many desirable attributes for 3D cell encapsulation. Here we investigate the gelation kinetics and mechanical properties of PEG-based hydrogels formed by thiol-tetrazole methylsulfone (TzMS) crosslinking as a function of buffer, crosslinker structure, and degree of TzMS functionalization. Appropriate buffer selection ensured constant pH throughout crosslinking. The formulation containing cell adhesive ligand RGD and enzymatically-degradable peptide VPM gelled in ca. 4 min at pH 7.5, and stiffness could be increased from hundreds of Pascals to > 1 kPa by using excess VPM. The gelation times and stiffnesses for these hydrogels are highly suitable for 3D cell encapsulations, and pave the way for reliable 3D cell culture workflows in pipetting robots
Nanoparticle-cell interactions in a dynamic in vitro lung model
Get PDFThe effects of engineered nanomaterials on human health are intensively studied in order to facilitate their safe application. However, relatively little is known how me-chanical strain (stretching), as induced in alveolar epithelial cells by breathing dynam-ics, modifies biological responses to nanoparticles. In this study, A549 cells as a model for human type II alveolar epithelial cells were exposed to 25 nm amorphous colloidal silica nanoparticles (Si25) under dynamic or static culture conditions. Gene array data, qPCR, and ELISA revealed that stretching, in order to mimic breathing, can amplify the inflammatory responses to nanoparticle exposure. Treatment of cells with either stretching or nanoparticles alone led to minor changes in gene expression or cytokine secretion. The amplifying effect from stretching was not influenced by nanoparticle size or an intensified stretching, but by varying fetal bovine sera for medium supple-mentation. The type of fetal bovine serum used as medium supplement determined the occurrence of the amplifying effect, affecting both baseline cytokine production, as well as cellular response to nanoparticles. Gene expression alterations induced by combined exposure to nanoparticles plus stretching showed a high similarity to those known to be induced by TNF and mediated by NFkB. However, translocation of NFkB-p65, NF-κB2-p100/p52, and NF-κB1-p105/p50 subunits upon Si25, stretch, or a combined treatment could not be observed. Confocal microscopy revealed that stretching did not lead to an increased internalization of nanoparticles in this simplified lung model, indicating that the observed response amplification was not caused secondary to an elevated intracellular nanoparticle accumulation. This study suggests that mechanical strain, which constantly affects lung epithe-lial cells in vivo, significantly determines cell response and should therefore be imple-mented in all in vitro models for pulmonary toxicity tests.Die Auswirkungen menschengemachter Nanopartikel sind im Fokus vieler wissenschaftlicher Studien, um zukünftig deren sichere Handhabung und Anwendung zu gewährleisten. Wenig ist bisher darüber bekannt, wie sich mechanische Belastung, die beispielsweise während der Atmung in unseren Lungen stattfindet, auf die zelluläre Reaktion gegenüber inhalierter Nanopartikel auswirkt. In dieser Arbeit wurden A549 Zellen als Modell für humane alveoläre Typ II Epithelzellen mit kolloidalen amorphen Siliziumdioxid-Nanopartikeln behandelt und währenddessen entweder mit oder ohne mechanische Dehnung kultiviert. Genexpressionsanalysen mittels Microarrays und quantitativer Echtzeit-Polymerase-Kettenreaktion (qPCR) sowie Sekretionsanalysen durch Enzymimmunoassays (ELISA) zeigten, dass atmungssimulierende mechanische Dehnung in vitro die inflammatorische Zellantwort auf Nanopartikelexposition verstärken kann. Die Behandlung der Zellen mit entweder mechanischer Dehnung oder Nanopartikeln allein verursachte nur schwache Veränderungen der Genexpression und Sekretion bestimmter Zytokine. Der beobachtete verstärkende Effekt der mechanischen Dehnung auf die Zytokinexpression schien unabhängig von der Größe der eingesetzten Nanopartikel zu sein. Auch das Steigern der mechanischen Dehnung von 15% auf 25% Flächenexpansion veränderte den verstärkenden Effekt nicht. Jedoch führte die Verwendung eines anderen fötalen Kälberserums (FBS) in der Zellkultur zum Ausbleiben dieses Effekts von mechanischer Dehnung. Sowohl die grundlegende Zytokinproduktion, als auch die Reaktion auf die Nanopartikel waren vom Einfluss des FBS betroffen. Das durch Siliziumdioxid-Nanopartikel plus mechanische Dehnung veränderte Genexpressionsmuster der Zellen wies Ähnlichkeit mit der Zellantwort auf, die NFkB-abhängig durch den Tumornekrosefaktor (TNF) induziert wird. Mithilfe von Konfokalmikroskopie konnte die Translokation der NFkB-p65, NF-κB2-p100/p52 und NF-κB1-p105/p50 Untereinheiten durch Behandlung mit Nanopartikeln, Dehnung oder einer Kombination aus beidem nicht nachgewiesen werden. Die Vermutung, dass mechanische Dehnung die zelluläre Aufnahme von Siliziumdioxid-Nanopartikeln steigert und damit indirekt zu einer stärkeren inflammatorischen Reaktion führt, konnte für dieses Lungenmodell mithilfe von Konfokalmikroskopie widerlegt werden. Diese Arbeit bestätigt, dass mechanische Belastung ein integraler Bestandteil der in vivo Situation von alveolaren Epithelzellen ist und deren Zellantwort auf Nanopartikel signifikant beeinflusst. Mechanische Belastung sollte daher in allen in vitro-Modellen für Pneumotoxizitätstests implementiert werden
Redox-triggerable Luciferin-Bioinspired Hydrogels as Injectable and Cell-encapsulating Matrices
Get PDFOver the past few decades there has been a great interest in developing smart hydrogels that are stimuli-responsive, due to their ability to respond to variations caused by external stimuli. These materials are exploited for biomedical applications such as biosensors, injectable scaffolds, drug delivery and tissue engineering. Recently, our group reported firefly-inspired hydrogel matrices for 3D cell culture. This platform exhibited certain advantages like rapid gelation rate and tunability of mechanical and biological properties. However, this firstly reported system did not allow for fine control of the gelation onset because the crosslinking reaction started as soon as the two precursors were mixed. Moreover, one of its precursors demonstrated poor storage stability in aqueous solution. These limitations restrict its application as injectable matrices. In this article, we endow the luciferin-inspired hydrogels with redox-triggering capability, to overcome the limitations of the previous system and to widen its application range. We achieve this goal by introducing protected macromers as hydrogel polymeric precursors that can be activated in the presence of a mild reductant, to trigger gel formation in situ with high degree of control. We demonstrate that the regulation of intrinsic (e.g., structure of protecting group, reductant type) and extrinsic (e.g., pH, temperature) parameters of the triggering reaction can be used to modulate key materials properties. This novel upgraded redox-triggerable system enables precise control over gelation onset and kinetics, thus facilitating its utilization as injectable hydrogel without negatively impacting its cytocompatibility. Our findings expand the current toolkit of chemically-based stimuli-responsive hydrogels
Achieving the theoretical limit of strength in shell-based carbon nanolattices
Get PDFRecent developments in mechanical metamaterials exemplify a new paradigm shift called mechanomaterials, in which mechanical forces and designed geometries are proactively deployed to program material properties at multiple scales. Here, we designed shell-based micro-/nanolattices with I-WP (Schoen’s I-graph–wrapped package) and Neovius minimal surface topologies. Following the designed topologies, polymeric microlattices were fabricated via projection microstereolithography or two-photon lithography, and pyrolytic carbon nanolattices were created through two-photon lithography and subsequent pyrolysis. The shell thickness of created lattice metamaterials varies over three orders of magnitude from a few hundred nanometers to a few hundred micrometers, covering a wider range of relative densities than most plate-based micro-/nanolattices. In situ compression tests showed that the measured modulus and strength of our shell-based micro-/nanolattices with I-WP topology are superior to those of the optimized plate-based lattices with cubic and octet plate unit cells and truss-based lattices. More strikingly, when the density is larger than 0.53 g cm−3, the strength of shell-based pyrolytic carbon nanolattices with I-WP topology was found to achieve its theoretical limit. In addition, our shell-based carbon nanolattices exhibited an ultrahigh strength of 3.52 GPa, an ultralarge fracture strain of 23%, and an ultrahigh specific strength of 4.42 GPa g−1 cm3, surpassing all previous micro-/nanolattices at comparable densities. These unprecedented properties can be attributed to the designed topologies inducing relatively uniform strain energy distributions and avoiding stress concentrations as well as the nanoscale feature size. Our study demonstrates a mechanomaterial route to design and synthesize micro-/nanoarchitected materials