20 research outputs found
Tailored Light Scattering through Hyperuniform Disorder in Self-Organized Arrays of High-Index Nanodisks
Arrays of nanoparticles exploited in light scattering applications commonly only feature either a periodic or a rather random arrangement of its constituents. For the periodic case, light scattering is mostly governed by the strong spatial correlations of the arrangement, expressed by the structure factor. For the random case, structural correlations cancel each other out and light scattering is mostly governed by the scattering properties of the individual scatterer, expressed by the form factor. In contrast to these extreme cases, it is shown here that hyperuniform disorder in self-organized large-area arrays of high refractive index nanodisks enables both structure and form factor to impact the resulting scattering pattern, offering novel means to tailor light scattering. The scattering response from the authors’ nearly hyperuniform interfaces can be exploited in a large variety of applications and constitutes a novel class of advanced optical materials
Effect of metal ions on the physical properties of multilayers from hyaluronan and chitosan, and the adhesion, growth and adipogenic differentiation of multipotent mouse fibroblasts
[EN] Polyelectrolyte multilayers (PEMs) consisting of the polysaccharides hyaluronic acid (HA) as the polyanion and chitosan (Chi) as the polycation were prepared with layer-by-layer technique (LbL). The [Chi/HA](5) multilayers were exposed to solutions of metal ions (Ca2+, Co2+, Cu2+ and Fe3+). Binding of metal ions to [Chi/HA](5) multilayers by the formation of complexes with functional groups of polysaccharides modulates their physical properties and the bioactivity of PEMs with regard to the adhesion and function of multipotent murine C3H10T1/2 embryonic fibroblasts. Characterization of multilayer formation and surface properties using different analytical methods demonstrates changes in the wetting, surface potential and mechanical properties of multilayers depending on the concentration and type of metal ion. Most interestingly, it is observed that Fe3+ metal ions greatly promote adhesion and spreading of C3H10T1/2 cells on the low adhesive [Chi/HA](5) PEM system. The application of intermediate concentrations of Cu2+, Ca2+ and Co2+ as well as low concentrations of Fe3+ to PEMs also results in increased cell spreading. Moreover, it can be shown that complex formation of PEMs with Cu2+ and Fe3+ ions leads to increased metabolic activity in cells after 24 h and induces cell differentiation towards adipocytes in the absence of any additional adipogenic media supplements. Overall, complex formation of [Chi/HA](5) PEM with metal ions like Cu2+ and Fe3+ represents an interesting and cheap alternative to the use of growth factors for making cell-adhesive coatings and guiding stem cell differentiation on implants and scaffolds to regenerate connective-type of tissues.This work was part of the High-Performance Center Chemical and Biosystems Technology Halle/Leipzig, supported by the European Regional Development Fund (ERDF), and a grant to HK from the Martin Luther University Halle-Wittenberg for female PhD students. The work was further supported by the Fraunhofer Internal Programs under Grant No. Attract 069-608203 (CEHS). TG acknowledges the kind support by the Ministry of Science and Higher Education of the Russian Federation within the framework of state support for the creation and development of World-Class Research Centers ``Digital biodesign and personalized healthcare'' 075-15-2020926. GGF acknowledges funding by the State Research Agency. Ministry of Science and Innovation of Spain, grant PID2019106000RB-C21/AEI/10.13039/501100011033 project. We are grateful for the kind support by Christian Willems for the help in formatting and proof reading the manuscript.Kindi, H.; Menzel, M.; Heilmann, A.; Schmelzer, CEH.; Herzberg, M.; Fuhrmann, B.; Gallego-Ferrer, G.... (2021). Effect of metal ions on the physical properties of multilayers from hyaluronan and chitosan, and the adhesion, growth and adipogenic differentiation of multipotent mouse fibroblasts. Soft Matter. 17(36):8394-8410. https://doi.org/10.1039/d1sm00405k83948410173
Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves
Nanoscale multifunctional perpendicular organic spin valves have been fabricated. The devices based on an La0.7Sr0.3MnO3/Alq3/Co trilayer show resistive switching of up to 4-5 orders of magnitude and magnetoresistance as high as -70% the latter even changing sign when voltage pulses are applied. This combination of phenomena is typically observed in multiferroic tunnel junctions where it is attributed to magnetoelectric coupling between a ferromagnet and a ferroelectric material. Modeling indicates that here the switching originates from a modification of the La0.7Sr0.3MnO3 surface. This modification influences the tunneling of charge carriers and thus both the electrical resistance and the tunneling magnetoresistance which occurs at pinholes in the organic layer
Elastic behavior of metal-assisted etched Si/SiGe superlattice nanowires containing dislocations
We systematically investigate structural parameters, such as shape, size, elastic strain, and relaxations, of metal-assisted etched vertically modulated Si/SiGe superlattice nanowires by using electron microscopy, synchrotron-based x-ray diffraction, and numerical linear elasticity theory. A vertical Si/Ge superlattice with atomically flat interfaces is grown by using molecular beam epitaxy on Si-buffered Si(001) substrates. The lattice constants for Si and Ge are 5.43 and 5.66 Ă…, respectively, which indicate a lattice mismatch of 4.2%. This results in a strained layer in the boundary between Si and Ge leading to dislocations. These substrates serve as the starting material for nanostructuring the surface by using metal-assisted etching. It is shown that the high quality crystalline structure is preserved in the fabrication process, while the lattice mismatch is partially relieved by dislocation formation. Despite this highly effective relaxation path, dislocations present in the parent superlattice do not vanish upon nanostructuring for wires with diameters of down to at least 80 nm. We relate these observations to the applicability of silicon-based nanowires for high-performance thermoelectric generators
Elastic behavior of metal-assisted etched Si/SiGe superlattice nanowires containing dislocations
We systematically investigate structural parameters, such as shape, size, elastic strain, and relaxations, of metal-assisted etched vertically modulated Si/SiGe superlattice nanowires by using electron microscopy, synchrotron-based x-ray diffraction, and numerical linear elasticity theory. A vertical Si/Ge superlattice with atomically flat interfaces is grown by using molecular beam epitaxy on Si-buffered Si(001) substrates. The lattice constants for Si and Ge are 5.43 and 5.66 Ă…, respectively, which indicate a lattice mismatch of 4.2%. This results in a strained layer in the boundary between Si and Ge leading to dislocations. These substrates serve as the starting material for nanostructuring the surface by using metal-assisted etching. It is shown that the high quality crystalline structure is preserved in the fabrication process, while the lattice mismatch is partially relieved by dislocation formation. Despite this highly effective relaxation path, dislocations present in the parent superlattice do not vanish upon nanostructuring for wires with diameters of down to at least 80 nm. We relate these observations to the applicability of silicon-based nanowires for high-performance thermoelectric generators
Ag-Mediated Charge Transport during Metal-Assisted Chemical Etching of Silicon Nanowires
The
charge transport mechanism during metal-assisted chemical etching
of Si nanowires with contiguous metal films has been investigated.
The experiments give a better insight how the charges and reaction
products can penetrate to the etching front. The formation of a layer
of porous Si between the metal film and the bulk Si is a prerequisite
for the etching process. The electronic holes (positive charges) necessary
for the etching of porous Si are generated at the surface of the metal
in contact with the oxidative agent. Because of the insulating character
of the thin walls of the porous Si, the transport of the electronic
holes through this layer is not possible. Instead, it is found that
the transport of electronic holes proceeds primarily by means of the
Ag/Ag<sup>+</sup> redox pair circulating in the electrolyte and diffusing
through the etched pores in the Si. The charge transport occurs without
the ionic contribution at the positions where the metal is in direct
contact with the Si. Here, an electropolishing process takes place,
leading to an extensive removal of the Si and sinking in of the film
into the Si substrate
Nanoscaled Surface Patterns Influence Adhesion and Growth of Human Dermal Fibroblasts
In general, there is a need for passivation
of nanopatterned biomaterial
surfaces if cells are intended to interact only with a feature of
interest. For this reason self-assembled monolayers (SAM), varying
in chain length, are used; they are highly effective in preventing
protein adsorption or cell adhesion. In addition, a simple and cost-effective
technique to design nanopatterns of various sizes and distances, the
so-called nanosphere lithography (NSL), is discussed, which allows
the control of cell adhesion and growth depending on the feature dimensions.
Combining both techniques results in highly selective nanostructured
surfaces, showing that single proteins selectively adsorb on activated
nanopatterns. Additionally, adhesion and growth of normal human dermal
fibroblasts (NHDF) is strongly affected by the nanostructure dimensions,
and it is proven that fibronectin (FN) matrix formation of these cells
is influenced, too. Moreover, the FN fibrils are linked to the hexagonally
close-packed nanopatterns. As a result, the system presented here
can be applied in tissue engineering and implant design due to the
fact that the nanopattern dimensions give rise to further modifications
and allow the introduction of chemical heterogeneity to guide stem
cell differentiation in the future
Introduction of Laser Interference Lithography to Make Nanopatterned Surfaces for Fundamental Studies on Stem Cell Response
The
extracellular matrix (ECM) is a nanostructured environment
that provides chemical, mechanical, and topographical stimuli for
various cellular functions. Here, we introduce the application of
laser interference lithography (LIL) to generate hexagonally arranged
gold nanostructures of three different dimensions on silicon to study
the effect of feature dimensions on human adipose-derived stem cells
(hADSC) in terms of adhesion, growth, and differentiation. Self-assembled
monolayers (SAM) were used to passivate the background silicon surface
with a long-chain polyethylene glycol (PEG), whereas the gold nanostructures
were activated with mercaptoundecanoic acid (MUDA) to direct protein
adsorption and cell adhesive structures to them, only. It was possible
to show that the size and distance of the nanostructures affected
the spreading of hADSC with a decrease of cell size with the increase
of feature dimensions, which corresponded also to the expression of
focal adhesions and presence of the small GTPase RhoA. Effects of
these early events, related to outside-in signal transduction, were
visible by an enhanced cell growth on smaller feature dimensions and
distinct effects on cell differentiation. Because of the precise control
of chemical and topographical cues, the presented system offers great
potential to study effects of material topography on stem cell behavior,
which may pave the way for applications in tailoring surfaces of implants
and tissue engineering scaffolds