Cell-Derived Vesicles with Increased Stability and On-Demand Functionality by Equipping Their Membrane with a Cross-Linkable Copolymer

Cell-derived vesicles retain the cytoplasm and much of the native cell membrane composition. Therefore, they are attractive for investigations of membrane biophysics, drug delivery systems, and complex molecular factories. However, their fragility and aggregation limit their applications. Here, the mechanical properties and stability of giant plasma membrane vesicles (GPMVs) are enhanced by decorating them with a specifically designed diblock copolymer, cholesteryl-poly[2-aminoethyl methacrylate- b -poly(ethylene glycol) methyl ether acrylate]. When cross-linked, this polymer brush enhances the stability of the GPMVs. Furthermore, the pH-responsiveness of the copolymer layer allows for a controlled cargo loading/release, which may enable various bioapplications. Importantly, the cross-linked-copolymer GPMVs are not cytotoxic and preserve in vitro membrane integrity and functionality. This effective strategy to equip the cell-derived vesicles with stimuli-responsive cross-linkable copolymers is expected to open a new route to the stabilization of natural membrane systems and overcome barriers to biomedical applications

Wrapping of Microparticles by Floppy Lipid Vesicles

Lipid membranes, the barrier defining living cells and many of their sub-compartments, bind to a wide variety of nano- and micro-meter sized objects. In the presence of strong adhesive forces, membranes can strongly deform and wrap the particles, an essential step in crossing the membrane for a variety of health and disease-related processes. A large body of theoretical and numerical work has focused on identifying the physical properties that underly wrapping. Using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure a wrapping phase diagram and make quantitative comparisons to theoretical models. Our data is consistent with a model of membrane-particle interactions accounting for the adhesive energy per unit area, membrane bending rigidity, particle size, and vesicle radius

Magnetic versus crystal field linear dichroism in NiO thin films

We have detected strong dichroism in the Ni $L_{2,3}$ x-ray absorption spectra of monolayer NiO films. The dichroic signal appears to be very similar to the magnetic linear dichroism observed for thicker antiferromagnetic NiO films. A detailed experimental and theoretical analysis reveals, however, that the dichroism is caused by crystal field effects in the monolayer films, which is a non trivial effect because the high spin Ni $3d^{8}$ ground state is not split by low symmetry crystal fields. We present a practical experimental method for identifying the independent magnetic and crystal field contributions to the linear dichroic signal in spectra of NiO films with arbitrary thicknesses and lattice strains. Our findings are also directly relevant for high spin $3d^{5}$ and $3d^{3}$ systems such as LaFeO$_{3}$, Fe$_{2}$O$_{3}$, VO, LaCrO$_{3}$, Cr$_{2}$O$_{3}$, and Mn$^{4+}$ manganate thin films

Emission fluxes and atmospheric degradation of monoterpenes above a boreal forest: field measurements and modelling

The contribution of monoterpenes to aerosol formation processes within and above forests is not well understood. This is also true for the particle formation events observed during the BIOFOR campaigns in Hyytiälä, Finland. Therefore, the diurnal variation of the concentrations of several biogenic volatile organic compounds (BVOCs) and selected oxidation products in the gas and particle phase were measured on selected days during the campaigns in Hyytiälä, Finland. α-pinene and Δ3-carene were found to represent the most important monoterpenes above the boreal forest. A clear vertical gradient of their concentrations was observed together with a change of the relative monoterpene composition with height. Based on concentration profile measurements of monoterpenes, their fluxes above the forest canopy were calculated using the gradient approach. Most of the time, the BVOC fluxes show a clear diurnal variation with a maximum around noon. The highest fluxes were observed for α-pinene with values up to 20 ng m−2 s−1 in summer time and almost 100 ng m−2 s−1 during the spring campaign. Furthermore, the main oxidation products from α-pinene, pinonaldehyde, and from β-pinene, nopinone, were detected in the atmosphere above the forest. In addition to these more volatile oxidation products, pinic and pinonic acid were identified in the particle phase in a concentration range between 1 and 4 ng m−3. Beside these direct measurement of known oxidation products, the chemical sink term in the flux calculations was used to estimate the amount of product formation of the major terpenes (α-pinene, β-pinene, Δ3-carene). A production rate of very low volatile oxidation products (e.g., multifunctional carboxylic) from ·OH- and O3-reaction of monoterpenes of about 1.3·104 molecules cm−3 s−1 was estimated for daylight conditions during summer time. Additionally, model calculations with the one-dimensional multilayer model CACHE were carried out to investigate the diurnal course of BVOC fluxes and chemical degradation of terpenes

Potential contribution of ancient introgression to the evolution of a derived reproductive strategy in ricefishes

Transitions from no parental care to extensive care are costly and involve major changes in life history, behaviour and morphology. Nevertheless, in Sulawesi ricefishes, pelvic brooding evolved from transfer brooding in two distantly related lineages within the genera Adrianichthys and Oryzias, respectively. Females of pelvic brooding species carry their eggs attached to their belly until the fry hatches. Despite their phylogenetic distance, both pelvic brooding lineages share a set of external morphological traits. A recent study found no direct gene flow between pelvic brooding lineages, suggesting independent evolution of the derived reproductive strategy. Convergent evolution can, however, also rely on repeated sorting of pre-existing variation of an admixed ancestral population, especially when subjected to similar external selection pressures. We thus used a multi-species coalescent (MSC) model and D-statistics to identify gene-tree - species-tree incongruencies, to evaluate the evolution of pelvic brooding with respect to inter-specific gene flow not only between pelvic brooding lineages, but between pelvic brooding lineages and other Sulawesi ricefish lineages. We found a general network-like evolution in Sulawesi ricefishes and as previously reported, no gene flow between the pelvic brooding lineages. Instead, we found hybridization between the ancestor of pelvic brooding Oryzias and the common ancestor of the Oryzias species from the Lake Poso area. We further detected signs of introgression within the confidence interval of a quantitative trait locus (QTL) associated with pelvic brooding in O. eversi. Our results hint towards a contribution of ancient standing genetic variation to the evolution of pelvic brooding in Oryzias

All-optical routing and switching for three-dimensional photonic circuitry

The ability to efficiently transmit and rapidly process huge amounts of data has become almost indispensable to our daily lives. It turned out that all-optical networks provide a very promising platform to deal with this task. Within such networks opto-optical switches, where light is directed by light, are a crucial building block for an effective operation. In this article, we present an experimental analysis of the routing and switching behaviour of light in two-dimensional evanescently coupled waveguide arrays of Y- and T-junction geometries directly inscribed into fused silica using ultrashort laser pulses. These systems have the fundamental advantage of supporting three-dimensional network topologies, thereby breaking the limitations on complexity associated with planar structures while maintaining a high dirigibility of the light. Our results show how such arrays can be used to control the flow of optical signals within integrated photonic circuits

Wrapping of Microparticles by Lipid Membranes

Lipid membranes play an essential role in both the morphology and functionality of living cells. They not only delineate the inside and outside of all eukaryotic cells but also define a number of organelles inside these cells. Cells come into contact with many different objects like particles, pathogens or smaller compartments confined by a lipid membrane, such as vesicles. It is thus essential to understand how membranes interact with such objects and how this interaction is impacted by the physical properties of the membranes. In this thesis, a novel model system to study particle-membrane interactions in proposed. This model system consists of micron-sized particles and giant unilamellar vesicles (GUVs) that interact via nonspecific depletion interactions. In the first part of this thesis, we address the specific conditions for the wrapping of single particles by the membrane. We found three distinct regimes of wrapping: While at low particle-membrane adhesion energies, the membrane does not wrap around the particle, at high adhesion energies particles are spontaneously wrapped. At intermediate adhesion energies particles are wrapped only when an external force is applied. This regime is stabilized by membrane curvature. In the second part of this thesis the dynamics of particle wrapping is investigated in the spontaneous wrapping regime at high adhesion energies. The wrapping dynamics are found to be largely independent of the particle size. Dissipation at the contact line appears to be the dominant process determining the wrapping velocity. However, we observe discrepancies in the experimentally observed wrapping velocities when compared to expected wrapping velocities in a quasistatic model of the system. These discrepancies suggest another process at play on top of dissipation at the contact line. A possible explanation of this phenomena is that the membrane is deformed on a size and timescale in these experiments that the membrane shear viscosity comes into play. The findings of this thesis provide new experimental insights into particle-membrane interactions. Particularly, the proposed novel model system allows for a large number of new experiments offering deeper understanding of membrane mechanics, how cells interact with their environment and how cells shape themselves

The blab of the pave/d: Ethnographic encounters in a choice school

This narrative ethnography adopts a literary lens to relay the various lived experiences of a non-traditional, Midwestern public high school during its final year in its original building. Extending upon previous research of high school dropouts (Cameron, 2012), I examine how this one particular high school incorporated a self-paced curriculum with a focus on family to address the unique learning needs of students at risk of not graduating. By employing elements of grounded theory, narrative inquiry, and autoethnography, I share the stories of Walgut High School\u27s (a pseudonym) roughly sixty students as they struggle to navigate their respective roles in a dominant cultural narrative to which they\u27ve never felt like they belonged. Through the extensive and organic voices of the primary participants--as well as my observations of my own participation in the school culture over the course of a year--this project serves to offer insights not only into the school experiences of marginalized adolescents, but also into Walgut\u27s myriad successes and failures. In particular, this piece highlights the vitality of unconditionally caring or hospitable teachers (Derrida, 2000), while also ultimately questioning the presumed utility of a high school diploma. The story concludes not by lauding the alternative mine created for Walgut\u27s canaries, but by questioning the purpose and stability of all scholastic mines

Understanding phase transformations in steels using modern electron microscopy techniques

The advantages and limitations of electron back-scattering diffraction coupled with energy dispersive X-ray spectroscopy and of transmission Kikuchi diffraction in relation to the in-depth characterisation of steel microstructures containing phases with similar lattice parameters and/or precipitates are discussed. An in-house developed EBSD map post-processing methodology provided insights into the mechanisms of bainite formation

Dynamics of spontaneous wrapping of microparticles by floppy lipid membranes

Lipid membranes form the barrier between the inside and outside of cells and many of their subcompartments. As such, they bind to a wide variety of nano- and micrometer sized objects and, in the presence of strong adhesive forces, strongly deform and envelop particles. This wrapping plays a key role in many healthy and disease-related processes. So far, little work has focused on the dynamics of wrapping. Here, using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure the velocity of the particle during wrapping as well as the forces exerted on it by the lipid membrane. Dissipation near the contact line appears to be the main factor determining the wrapping velocity and time to wrap an object