Lipid Self-Spreading on Solid Substrates

This chapter is dedicated to wetting and fracturing processes involving molecular phospholipid films and high-energy solid surfaces. In these systems, wetting of planar surfaces occurs in an aqueous environment by means of self-spreading of phospholipid membranes from artificially generated lipid sources, which range from manually deposited single sources (multilamellar liposomes) to liposome suspensions of different particle sizes, which are directly pipetted onto the substrate. The most prominent of the molecular lipid films is the phospholipid bilayer, which constitutes the fundamental structure of the biological cell membrane. Lipid membranes have peculiar characteristics, are highly dynamic, feature two-dimensional fluidity, and can accommodate functional molecules. Understanding the interactions of lipid films with solid interfaces is of high importance in areas like cell biology, biomedical engineering, and drug delivery

Active colloidal particles in emulsion droplets: A model system for the cytoplasm

In living cells, molecular motors create activity that enhances the diffusion of particles throughout the cytoplasm, and not just ones attached to the motors. We demonstrate initial steps toward creating artificial cells that mimic this phenomenon. Our system consists of active, Pt-coated Janus particles and passive tracers confined to emulsion droplets. We track the motion of both the active particles and passive tracers in a hydrogen peroxide solution, which serves as the fuel to drive the motion. We first show that correcting for bulk translational and rotational motion of the droplets induced by bubble formation is necessary to accurately track the particles. After drift correction, we find that the active particles show enhanced diffusion in the interior of the droplets and are not captured by the droplet interface. At the particle and hydrogen peroxide concentrations we use, we observe little coupling between the active and passive particles. We discuss the possible reasons for lack of coupling and describe ways to improve the system to more effectively mimic cytoplasmic activity

A microfluidics-integrated impedance/surface acoustic resonance tandem sensor

We demonstrate a dual sensor concept for lab-on-a-chip in-liquid sensing through integration of surface acoustic wave resonance (SAR) sensing with electrochemical impedance spectroscopy (EIS) in a single device. In this concept, the EIS is integrated within the building blocks of the SAR sensor, but features a separate electrical port. The two-port sensor was designed, fabricated, and embedded in a soft polymer microfluidic delivery system, and subsequently characterized. The SAR-EIS tandem sensor features low cross-talk between SAR and EIS ports, thus promoting non-interfering gravimetric and impedimetric measurements. The EIS was characterized by means of the modified Randle\u27s cell lumped element model. Four sensitive parameters could be established from the tandem sensor readout, and subsequently employed in a proof of principle study of liposome layers and their interaction with Ca2+ ions, leading to transformation into molecular film structures. The associated shift of the sensing quantities is analysed and discussed. The combination of impedimetric and gravimetric sensing quantities provides a unique and detailed description of physicochemical surface phenomena as compared to a single mode sensing routine

Protocells: Milestones and Recent Advances

The origin of life is still one of humankind\u27s great mysteries. At the transition between nonliving and living matter, protocells, initially featureless aggregates of abiotic matter, gain the structure and functions necessary to fulfill the criteria of life. Research addressing protocells as a central element in this transition is diverse and increasingly interdisciplinary. The authors review current protocell concepts and research directions, address milestones, challenges and existing hypotheses in the context of conditions on the early Earth, and provide a concise overview of current protocell research methods

Peridynamic Modeling of Ruptures in Biomembranes

We simulate the formation of spontaneous ruptures in supported phospholipid double bilayer membranes, using peridynamic modeling. Experiments performed on spreading double bilayers typically show two distinct kinds of ruptures, floral and fractal, which form spontaneously in the distal (upper) bilayer at late stages of double bilayer formation on high energy substrates. It is, however, currently unresolved which factors govern the occurrence of either rupture type. Variations in the distance between the two bilayers, and the occurrence of interconnections (“pinning sites”) are suspected of contributing to the process. Our new simulations indicate that the pinned regions which form, presumably due to Ca2+ ions serving as bridging agent between the distal and the proximal bilayer, act as nucleation sites for the ruptures. Moreover, assuming that the pinning sites cause a non-zero shear modulus, our simulations also show that they change the rupture mode from floral to fractal. At zero shear modulus the pores appear to be circular, subsequently evolving into floral pores. With increasing shear modulus the pore edges start to branch, favoring fractal morphologies. We conclude that the pinning sites may indirectly determine the rupture morphology by contributing to shear stress in the distal membrane

Spontaneous Formation and Rearrangement of Artificial Lipid Nanotube Networks as a Bottom-Up Model for Endoplasmic Reticulum

We present a convenient method to form a bottom-up structural organelle model for the endoplasmic reticulum (ER). The model consists of highly dense lipidic nanotubes that are, in terms of morphology and dynamics, reminiscent of ER. The networks are derived from phospholipid double bilayer membrane patches adhering to a transparent Al2O3 substrate. The adhesion is mediated by Ca2+ in the ambient buffer. Subsequent depletion of Ca2+ by means of BAPTA/EDTA causes retraction of the membrane, resulting in spontaneous lipid nanotube network formation. The method only comprises phospholipids and microfabricated surfaces for simple formation of an ER model and does not require the addition of proteins or chemical energy (e.g., GTP or ATP). In contrast to the 3D morphology of the cellular endoplasmic reticulum, the model is two-dimensional (albeit the nanotube dimensions, geometry, structure, and dynamics are maintained). This unique in vitro ER model consists of only a few components, is easy to construct, and can be observed under a light microscope. The resulting structure can be further decorated for additional functionality, such as the addition of ER-associated proteins or particles to study transport phenomena among the tubes. The artificial networks described here are suitable structural models for the cellular ER, whose unique characteristic morphology has been shown to be related to its biological function, whereas details regarding formation of the tubular domain and rearrangements within are still not completely understood. We note that this method uses Al2O3 thin-film-coated microscopy coverslips, which are commercially available but require special orders. Therefore, it is advisable to have access to a microfabrication facility for preparation

Did Solid Surfaces Enable the Origin of Life?

In this perspective article, I discuss whether and how solid surfaces could have played a key role in the formation of membranous primitive cells on the early Earth. I argue why surface energy could have been used by prebiotic amphiphile assemblies for unique morphological transformations, and present recent experimental findings showing the surface-dependent formation and behavior of sophisticated lipid membrane structures. Finally, I discuss the possible unique contributions of such surface-adhered architectures to the transition from prebiotic matter to living systems

The Relatıon Between Women Poverty And Informal Employment: An Empırıcal Research

Tez çalışmasının asıl amacı, enformel istihdamda yer alan yoksul kadınların, enformel istihdama yönelmesinde etkili olan nedenleri, enformel istihdamdaki çalışma koşullarını ve enformel istihdamın kadının psikolojik, sosyal, kültürel yaşantısına olan etkilerini belirlemektir. Sayılan bu amaç doğrultusunda, Ankara ili içerisinde enformel istihdamda bulunan 388 yoksul kadın ile görüşülmüştür. Görüştüğümüz yoksul kadınların çoğunluğu birinci tercihleri olmamasına karşın, aile bütçesine katkı ve çocukların eğitimini sağlayabilmek için enformel istihdama yönelmişlerdir. Yoksullukla baş etmeye çalışan bu kadınların sosyal katılımları tam olarak gerçekleştiremedikleri, gelecekleri ile ilgili kaygı duydukları görülmüştür. Ayrıca görüştüğümüz kadınlar, kendilerinden farklı olarak çocuklarının devlette; garantili olarak tabir ettikleri bir işte çalışmasını arzu etmektedirler.The main purpose of thesis is to determine the reasons that are effective on poor women inclining to informal employment, working conditions in informal employment and the impacts on women's pyscological, social, cultural life of informal employment. In accordance with this purpose, 388 poor women in the city of Ankara were interviewed. The majority of the poor women we interviewed have choosen informal employment to ensure the education of their children and to contribute to family budget although it is not their primary preference. It has been seen that these women who try to cope with poverty can not have social participation and are concerned about their future. Additionally the women we interviewed, unlike themselves, wish for their children to work in public sector which they express as guaranteed employment

The self-spreading double bilayer/Advances in lipid membrane nanotechnology

In my thesis I describe the generation, characterization and uses of self-spreading double bilayers. This new type of solid-supported model membrane combines features and properties of the 2D lipid bilayer membrane, and the 3D phospholiposome. The double bilayer membrane, i.e., a fully closed, parallel stack of two lipid bilayers, is essentially a surface-adhered flat giant unilamellar vesicle (FGUV) with a very small internal volume. It possesses features of supported membranes, such as flatness, large area coverage and high mechanical stability, and of giant vesicles, such as the ability to encapsulate nanoparticles in its interior volume. In the experimental work towards this thesis, I have probed the response of the FGUV to chemical or physical cues, and studied dynamic features reminiscent of complex cell behavior. A number of examples are discussed, including protrusion formation as a response to a chemical gradient, directed and reversible movement in a temperature gradient, spontaneous nanotube formation in response to the adhesion of virus-like particles, and repair of large area membrane pores. An important outcome of my work is the discovery of two non-trivial pore formation modes in membranes, which links biomembrane materials properties to fundamental properties of thin solid materials. One of the modes displays crackling noise dynamics, featuring sudden intermittent bursts over a broad size range (avalanches), similar to earthquakes. I consider the FGUV to be an experimental model system for studying various aspects of cell like behavior on intact model membranes, as well as a nanotechnological platform, useful to construct mesoscale membrane architectures and networks