Characterization and manipulation of lipid self-assembly to construct stable, portable synthetic lipid bilayers

The overarching goal of this research work is to further our understanding of lipid self-assembly and its organization at an oil-water interface to support the development of synthetic lipid bilayer systems that can be used in biologically relevant fields such as membrane biophysics, protein electrophysiology, development of synthetic biomolecules, drugs, nanoparticles and other applications. Self-assembly kinetics and interfacial properties of lipid monolayers formed at a liquid-air and liquid-liquid interface are characterized using Langmuir-Blodgett trough and pendant drop tensiometer. Insights gained from these studies not only allow us to answer questions related to droplet interface bilayer (DIB; a promising technique to assemble artificial lipid membranes) formation but also enable us to manipulate properties of monolayer in order to improve the potential of droplet interface bilayer by, a) increasing the number of phospholipids that can form DIBs, b) improving the success rate of DIB formation, and c) enhancing the electrical stability of bilayers formed. Owing to its wide range of applicability, novel efforts towards improving the durability and portability of DIB system are presented. In addition, this research work aims at using Nanoscribe direct laser writing — a state-of-the-art 3D printing device, to build 3D micro-scaffolds that can support lipid monolayers and bilayers that are suitable for high resolution optical studies

Efectos de las proteínas SP-B y SP-C del surfactante pulmonar en las propiedades físicas de membranas biológicas

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Aplicada III, leída el 10/07/2013Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Calculation of the Phase Behavior of Lipids

The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.Comment: to appear in Phys.Rev.

Physical principles of membrane organization

Membranes are the most common cellular structures in both plants and animals. They are now recognized as being involved in almost all aspects of cellular activity ranging from motility and food entrapment in simple unicellular organisms, to energy transduction, immunorecognition, nerve conduction and biosynthesis in plants and higher organisms. This functional diversity is reflected in the wide variety of lipids and particularly of proteins that compose different membranes. An understanding of the physical principles that govern the molecular organization of membranes is essential for an understanding of their physiological roles since structure and function are much more interdependent in membranes than in, say, simple chemical reactions in solution. We must recognize, however, that the word &lsquo;understanding&rsquo; means different things in different disciplines, and nowhere is this more apparent than in this multidisciplinary area where biology, chemistry and physics meet.<br /

Effects of fullerene on lipid bilayers displaying different liquid ordering: a coarse-grained molecular dynamics study

Background The toxic effects and environmental impact of nanomaterials, and in particular of Fullerene particles, are matters of serious concern. It has been reported that fullerene molecules enter the cell membrane and occupy its hydrophobic region. Understanding the effects of Carbon-based nanoparticles on biological membranes is therefore of critical importance to determine their exposure risks. Methods We report on a systematic coarse-grained molecular dynamics study of the interaction of fullerene molecules with simple model cell membranes. We have analyzed bilayers consisting of lipid species with different degrees of unsaturation and a variety of cholesterol fractions. Addition of fullerene particles to phase-segregated ternary membranes is also investigated in the context of the lipid raft model for the organization of the cell membrane. Results Fullerene addition to lipid membranes modifies their structural properties like thickness, area and internal ordering of the lipid species, as well as dynamical aspects such as molecular diffusion and cholesterol flip-flop. Interestingly, we show that phase-segregating ternary lipid membranes accumulate fullerene molecules preferentially in the liquid-disordered domains promoting phase-segregation and domain alignment across the membrane. Conclusions Lipid membrane internal ordering determines the behavior and distribution of fullerene particle, and this, in turn, determines the influence of fullerene on the membrane. Lipid membranes are good solvents of fullerene molecules, and in particular those with low internal ordering. General Significance Preference of fullerene molecules to be dissolved in the more disordered hydrophobic regions of a lipid bilayer and the consequent alteration of its phase behavior may have important consequences on the activity of biological cell membranes and on the bioconcentration of fullerene in living organisms.Peer ReviewedPostprint (author's final draft

Optical control of lipid interaction in photolipid membranes

The physics of biological membranes is governed to a great extent by the interaction between the lipid molecules. Even slight changes of the interaction exerts a drastic effect on the properties of a membrane. Photoswitchable phospholipids, also called “photolipids”, provide an ideal opportunity to control the intermolecular interaction with light. Photolipids can be switched contactless and on fast timescales, allowing for reversible membrane manipulation with a high degree of spatiotemporal control. In this thesis, the physical properties of bilayer membranes consisting of an azobenzene-containing phosphatidylcholine, azo-PC, have been investigated. The photolipid incorporates an azobenzene group in its sn2 acyl chain that undergoes reversible photoisomerization on illumination with ultraviolet and blue light, respectively. Additionally, the main absorption peak of azo-PC in the trans state experiences a blue-shift when aggregated in a lipid membrane. The magnitude of the shift is sensitive to the local concentration of lipids and the phase state of the membrane. These optical properties are used to monitor phase separation in multicomponent membranes. Macroscopic domain formation results in anisotropic photolipid distribution, affecting both the optical and the mechanical properties of the membrane. Because of the blue-shift, the assembly and disassembly of photolipids in the trans state into lipid domains can be monitored by UV−vis spectroscopy. On top of that, isomerization of azo-PC is used to reversibly control domain formation and membrane stiffness with light. The presence of nanoscopic domains governs the behavior of the bending rigidity of binary azo-PC containing membranes. The photoisomerization of azo-PC allows furthermore to tune the lateral diffusion coefficient of a supported photolipid membrane by a factor of two. Similar to the effect of heat, conformational changes of the lipid tails lead to a modification of the area per lipid and hence a different diffusion coefficient. By using structured illumination, it is possible to generate compartments with specific diffusion coefficients on demand. Finally, the permeability of photolipid membranes is explored. Isomerization of azo-PC vesicles leads to a change of the surface to volume ratio. The resulting tension is released either by vesicle splitting or by exchange of liquid through transient pores. By measuring the ionic current through the membrane, the pore dynamics are observed as step like current spikes. The results presented in this thesis are valuable for understanding the effect of intermolecular interaction on the physical lipid bilayer properties. Using light as an immediate and precise stimulus for lipid membranes provides an ideal platform to study the dynamic response of lipid membranes themselves or the dynamics of receptors embedded in the membrane.Physikalische Eigenschaften von biologischen Membranen sind weitgehend durch die Interaktion zwischen den Lipidmolekülen bestimmt. Bereits kleine Änderungen der Wechselwirkung können sich drastisch auf die Eigenschaften einer Membrane auswirken. Photoschaltbare Phospholipide, auch „Photolipide“ genannt, eignen sich hervorragend, um die Wechselwirkung zwischen den Molekülen mit Licht zu steuern. Photolipide können berührungslos und schnell geschaltet werden, wodurch eine Membran reversibel und mit einer hohen räumlichen und zeitlichen Auflösung manipuliert werden kann. In dieser Arbeit wurden die physikalischen Eigenschaften von Lipidmembranen untersucht, die aus einem photoschaltbaren Molekül aus der Gruppe der Lecithine, genannt azo-PC, bestehen. Dieses Photolipid enthält eine Azobenzol Gruppe in der Acylkette an der sn2 Position, welche mit UV und mit blauem Licht reversibel isomerisiert werden kann. Zusätzlich wird die Absorptionswellenlänge des trans Zustandes von azo-PC blauverschoben, wenn das Molekül in einer Lipidmembrane aggregiert ist. Die Größenordnung der Verschiebung ist von der lokalen Konzentration und dem Phasenzustand der Membran abhängig. Mit diesen optischen Eigenschaften kann man die Phasenseparation in mehrkomponentigen Membranen beobachten. Makroskopischer Domänen führen zu einer anisotropen Verteilung der Photolipide, die sowohl die optischen als auch die mechanischen Eigenschaften der Membran beeinflusst. Durch die Blauverschiebung kann die Bildung von Domänen mit Photolipiden im trans Zustand mit optischer Spektroskopie überwacht werden. Darüber hinaus können die Bildung von Domänen und die Membransteifigkeit mit Hilfe von Licht reversibel gesteuert werden. Nanoskopische Domänen beeinflussen das Verhalten der Biegesteifigkeit von zweikomponentigen Membranen, die azo-PC enthalten. Außerdem kann durch die Isomerisierung von azo-PC der laterale Diffusionskoeffizient von Photolipidmembranen verdoppelt werden. Konformationsänderungen der Lipidschwänze führen, ähnlich wie bei Wärmeeinwirkung, zu einer Veränderung der Lipidfläche und damit auch einer Veränderung des Diffusionskoeffizienten. Mit strukturierter Beleuchtung ist es möglich, nach Bedarf Bereiche mit definierten Diffusionskoeffizienten zu erzeugen. Abschließend wird die Permeabilität von Photolipidmembranen untersucht. Photoschalten von Vesikeln bestehend aus azo-PC Lipiden führt zu einer Veränderung des Verhältnisses von der Vesikeloberfläche und dessen Volumen. Die resultierende Spannung wird entweder durch Spaltung von Vesikeln oder durch Flüssigkeitsaustausch durch transiente Poren reduziert. Bei Messungen des Stroms durch die Membrane wird die Entstehung einer Pore durch einen diskreten Anstieg der Stromstärke beobachtet. Die Ergebnisse, die in dieser Arbeit vorgestellt werden, heben den Einfluss von intermolekularen Wechselwirkungen auf die physikalischen Eigenschaften von Lipidmembranen hervor. Licht als unmittelbarer und präziser Stimulus für Lipidmembranen erlaubt es, die dynamischen Eigenschaften von Lipidmembranen oder von Rezeptoren, die in eine Membran eingebettet sind, zu untersuchen

Recent advances in smart biotechnology: Hydrogels and nanocarriers for tailored bioactive molecules depot

Over the past ten years, the global biopharmaceutical market has remarkably grown, with ten over the top twenty worldwide high performance medical treatment sales being biologics. Thus, biotech R&D (research and development) sector is becoming a key leading branch, with expanding revenues. Biotechnology offers considerable advantages compared to traditional therapeutic approaches, such as reducing side effects, specific treatments, higher patient compliance and therefore more effective treatments leading to lower healthcare costs. Within this sector, smart nanotechnology and colloidal self-assembling systems represent pivotal tools able to modulate the delivery of therapeutics. A comprehensive understanding of the processes involved in the self assembly of the colloidal structures discussed therein is essential for the development of relevant biomedical applications. In this review we report the most promising and best performing platforms for specific classes of bioactive molecules and related target, spanning from siRNAs, gene/plasmids, proteins/growth factors, small synthetic therapeutics and bioimaging probes.Istituto Italiano di Tecnologia (IIT)COST Action [CA 15107]People Program (Marie Curie Actions) of the European Union's Seventh Framework Program under REA [606713 BIBAFOODS]Portuguese Foundation for Science and Technology (FCT) [PTDC/AGR-TEC/4814/2014, IF/01005/2014]Fundacao para a Ciencia e Tecnologia [SFRH/BPD/99982/2014]Danish National Research Foundation [DNRF 122]Villum Foundation [9301]Italian Ministry of Instruction, University and Research (MIUR), PRIN [20109PLMH2]"Fondazione Beneficentia Stiftung" VaduzFondo di Ateneo FRAFRAinfo:eu-repo/semantics/publishedVersio