88 results found
Furse S, Brooks NJ, Woscholski R, et al., 2016, Pressure-dependent inverse bicontinuous cubic phase formation in a phosphatidylinositol 4-phosphate/phosphatidylcholine system, Chemical Data Collections, Vol: 3-4, Pages: 15-20, ISSN: 2405-8300
In this paper, we report the inositide-driven formation of an inverse bicontinuous cubic phase with space group Ia3d (QIIG, gyroid phase). The system under study consisted of distearoylphosphatidylinositol 4-phosphate (DSPIP) and dioleoylphosphatidylcholine at a molar ratio of 1:49, with a physiological concentration of magnesium ions at pH 7·4. The behaviour of the system was monitored as a function of temperature and pressure. The formation of the phase with Ia3d geometry was recorded repeatably at high pressure, and occurred more readily at higher temperatures. We conclude that the Ia3d phase formed is a thermodynamically stable structure, and that DSPIP is a potent source of membrane curvature that can drive the formation of mesophases with both 2- and 3D geometry.
Chan CL, Bolognesi G, Bhandarkar A, et al., 2016, DROPLAY: laser writing of functional patterns within biological microdroplet displays, Lab on a Chip, Vol: 16, Pages: 4621-4627, ISSN: 1473-0197
In this study, we introduce an optofluidic method for the rapid construction of large-area cell-sized droplet assemblieswith user-defined re-writable two-dimensional patterns of functional droplets. Light responsive water-in-oil dropletscapable of releasing fluorescent dye molecules upon exposure were generated and self-assembled into arrays in amicrofluidic device. This biological architecture was exploited by the scanning laser of a confocal microscope to ‘write’ userdefined patterns of differentiated (fluorescent) droplets in a network of originally undifferentiated (non-fluorescent)droplets. As a result, long lasting images were produced on a droplet fabric with droplets acting as pixels of a biologicalmonitor, which can be erased and re-written on-demand. Regio-specific light-induced droplet differentiation within a largepopulation of droplets provides a new paradigm for the rapid construction of bio-synthetic systems with potential as tissuemimics and biological display materials.
Dent MR, López-Duarte I, Dickson CJ, et al., 2016, Imaging plasma membrane phase behaviour in live cells using a thiophene-based molecular rotor, Chemical Communications, Vol: 52, Pages: 13269-13272, ISSN: 1364-548X
Molecular rotors have emerged as versatile probes of microscopic viscosity in lipid bilayers, although it has proved difficult to find probes that stain both phases equally in phase-separated bilayers. Here, we investigate the use of a membrane-targeting viscosity-sensitive fluorophore based on a thiophene moiety with equal affinity for ordered and disordered lipid domains to probe ordering and viscosity within artificial lipid bilayers and live cell plasma membranes.
Friddin MS, Bolognesi G, Elani Y, et al., 2016, Optically assembled droplet interface bilayer (OptiDIB) networks from cell-sized microdroplets, Soft Matter, Vol: 12, Pages: 7731-7734, ISSN: 1744-6848
We report a new platform technology to systematically assemble droplet interface bilayer (DIB) networks in user-defined 3D architectures from cell-sized droplets using optical tweezers. Our OptiDIB platform is the first demonstration of optical trapping to precisely construct 3D DIB networks, paving the way for the development of a new generation of modular bio-systems.
Kuimova MK, Mika JT, Thompson AJ, et al., 2016, Measuring the viscosity of the Escherichia coli plasma membrane using molecular rotors, Biophysical Journal, Vol: 111, Pages: 1528-1540, ISSN: 1542-0086
The viscosity is a highly important parameter within the cell membrane, affecting the diffusion ofsmall molecules and, hence, controlling the rates of intra-cellular reactions. There is significantinterest in the direct, quantitative assessment of membrane viscosity. Here we report the use offluorescence lifetime imaging microscopy (FLIM) of the molecular rotor BODIPY C10 in themembranes of live Escherichia coli (E. coli) bacteria to permit direct quantification of the viscosity.Using this approach we investigated the viscosity in live E. coli cells, spheroplasts and liposomesmade from E. coli membrane extracts. For live cells and spheroplasts the viscosity was measured atboth room temperature (23o C) and the E. coli growth temperature (37o C), while the membraneextract liposomes were studied over a range of measurement temperatures (5-40o C). At 37o C werecorded a membrane viscosity in live E. coli cells of 950 cP, which is considerably higher than thatpreviously observed in other live cell membranes (e.g., eukaryotic cells, membranes of Bacillusvegetative cells). Interestingly, this indicates that E. coli cells exhibit a high degree of lipid orderingwithin their liquid-phase plasma membranes.
Machta BB, Gray E, Nouri M, et al., 2016, Conditions that Stabilize Membrane Domains Also Antagonize n-Alcohol Anesthesia, Biophysical Journal, Vol: 11, Pages: 537-545, ISSN: 1542-0086
Diverse molecules induce general anesthesia with potency strongly correlated with both their hydrophobicity and their effects on certain ion channels. We recently observed that several n -alcohol anesthetics inhibit heterogeneity in plasma-membrane-derived vesicles by lowering the critical temperature (Tc) for phase separation. Here, we exploit conditions that stabilize membrane heterogeneity to further test the correlation between the anesthetic potency of n -alcohols and effects on Tc. First, we show that hexadecanol acts oppositely to n -alcohol anesthetics on membrane mixing and antagonizes ethanol-induced anesthesia in a tadpole behavioral assay. Second, we show that two previously described “intoxication reversers” raise Tc and counter ethanol’s effects in vesicles, mimicking the findings of previous electrophysiological and behavioral measurements. Third, we find that elevated hydrostatic pressure, long known to reverse anesthesia, also raises Tc in vesicles with a magnitude that counters the effect of butanol at relevant concentrations and pressures. Taken together, these results demonstrate that ΔTc predicts anesthetic potency for n-alcohols better than hydrophobicity in a range of contexts, supporting a mechanistic role for membrane heterogeneity in general anesthesia.
Brooks NJ, Cates ME, Clegg PS, et al., 2016, Soft Interfacial Materials: from Fundamentals to Formulation, Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1364-503X
This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’.The science of soft interfaces (lipid membranes, emulsions, particle-stabilized droplets, etc.) is rapidly moving into an era of predictive capability that allows the design and development of advanced materials to be based on secure scientific knowledge. This Theme Issue reports papers presented at a Discussion Meeting intended not only to address the fundamental science, focusing on generic design principles for self-organization and interfacial structure, but also to explore the resulting prospects for ‘informed formulation’ of new and improved industrial products.At the end of this introductory essay, we briefly summarize some of the scientific progress reported in the individual research and review papers included in this volume. Before doing so, we take the opportunity to describe some of the background thinking that shaped the content and aims of the Meeting as conceived by the organizers.This essay is intended to be thought provoking, not definitive; much of it is based on a wrap-up discussion that two of us (Alex Lips and Wilson Poon) contributed at the end of the Meeting itself. In it, we focus on the relationship between science (‘fundamentals’) and technology (‘formulation’). At least in the soft materials area, this represents a subtler and more interesting form of symbiosis than is often assumed.
McCarthy NLC, Brooks NJ, 2016, Using high pressure to modulate lateral structuring in model lipid membranes, Advances in Biomembranes and Lipid Self-Assembly, Vol: 24, Pages: 75-89, ISSN: 2451-9634
© 2016 Elsevier Inc. All rights reserved. Cell membranes are highly complex fluid structures. They not only play a vital role in maintaining basic cellular integrity and compartmentalizing biological processes but also provide an active matrix within which reactions can take place and are vital for processes such as mediating protein function and signal transduction. The dynamic lateral organization of membranes is thought to be critical to their function and simplified lipid membranes offer a highly controllable model for probing the molecular interactions and assemblies that contribute to membrane function. Pressure has recently proved to be a highly important tool for triggering changes in lateral structure in model membranes at high speed and without risking thermal degradation of the membrane constituents.
Miller RM, Poulos AS, Robles ESJ, et al., 2016, Isothermal Crystallization Kinetics of Sodium Dodecyl Sulfate–Water Micellar Solutions, Crystal Growth & Design, Vol: 16, Pages: 3379-3388, ISSN: 1528-7505
The crystallization mechanisms and kinetics of micellar sodium dodecyl sulfate (SDS) solutions in water, under isothermal conditions, were investigated experimentally by a combination of reflection optical microscopy (OM), differential scanning calorimetry (DSC), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The rates of nucleation and growth were estimated from OM and DSC across temperatures ranging from 20 to −6 °C for 20% SDS-H2O, as well as for 10 and 30% SDS-H2O at representative temperatures of 6, 2, and −2 °C. A decrease in temperature increased both nucleation and growth rates, and the combined effect of the two processes on the morphology was quantified via both OM and ATR-FTIR. Needles, corresponding to the hemihydrate polymorph, become the dominant crystal form at ≤ −2 °C, while platelets, the monohydrate, predominate at higher temperatures. Above 8 °C, crystallization was only observed if seeded from crystals generated at lower temperatures. Our results provide quantitative and morphological insight into the crystallization of ubiquitous micellar SDS solutions and its phase stability below room temperature.
Karamdad K, Law R, Seddon J, et al., 2016, Studying the effects of asymmetry on the bending rigidity of lipid membranes formed by microfluidics, Chemical Communications (London), Vol: 52, Pages: 5277-5280, ISSN: 0009-241X
In this article we detail a robust high-throughput microfluidic platform capable of fabricating either symmetric or asymmetric giant unilamellar vesicles (GUVs) and characterise the mechanical properties of their membranes.
Zhang Y, Carter JW, Lervik A, et al., 2016, Structural organization of sterol molecules in DPPC bilayers: a coarse-grained molecular dynamics investigation, Soft Matter, Vol: 12, Pages: 2108-2117, ISSN: 1744-6848
Martin HP, Brooks NJ, Seddon JM, et al., 2016, Microfluidic processing of concentrated surfactant mixtures: online SAXS, microscopy and rheology, Soft Matter, Vol: 12, Pages: 1750-1758, ISSN: 1744-6848
Ces O, Elani Y, Karamdad K, et al., 2016, Novel microfluidic technologies for the bottom-up construction of artificial cells
© 2016 Institution of Engineering and Technology. All rights reserved. This talk will outline novel microfluidic strategies for biomembrane engineering that are capable of fabricating vesicles , droplet interface bilayer networks , multisomes  and artificial tissues  where parameters such as membrane asymmetry, membrane curvature, compartment connectivity and individual compartment contents can be controlled. Various bulk methods, such as extrusion, gentle hydration and electroformation, have been synonymous with the formation of lipid vesicles over recent years. However these strategies suffer from significant shortcomings associated with these processes including limited control of vesicle structural parameters such as size, lamellarity, membrane composition and internal contents. To address this technological bottleneck we have developed novel microfluidic platforms to form lipid vesicles in high-Throughput with full control over the composition of both the inner and outer leaflet of the membrane thereby enabling the manufacture of symmetric and asymmetric vesicles. This is achieved by manufacturing microfluidic channels with a step junction, produced by double-layer photolithography, which facilitates the transfer of a W/O emulsion across an oil-water phase boundary and the self-Assembly of a phospholipid bilayer. These platforms are being used to explore the role of asymmetry in biological systems  and study the engineering rules that regulate membrane mediated protein-protein interactions . In addition, these technologies are enabling the construction of biological machines capable of acting as micro-reactors , environmental sensors and smart delivery vehicles  as well as complex multi-compartment artificial cells where the contents and connectivity of each compartment can be controlled. These compartments are separated by biological functional membranes that can facilitate transport between the compartments themselves and between
Friddin MS, Bolognesi G, Elani Y, et al., 2016, Light-driven drag and drop assembly of micron-scale bilayer networks for synthetic biology, Pages: 545-546
We have developed a new method to assemble single- or multi-layered networks of droplet interface bilayers (DIBs) from cell-sized droplets using a single beam optical trap (optical tweezers). The novelty of our approach is the ability to directly trap the microdroplets with the laser and manipulate them in 3D to construct DIB networks of user-defined architectures. Our method does not require a complex optical setup, is versatile, contactless, benefits from both high spatial and temporal resolution, and could set a new paradigm for the assembly of smart, synthetic biosystems.
Carreras P, Elani Y, Law RV, et al., 2015, A microfluidic platform for size-dependent generation of droplet interface bilayer networks on rails, Biomicrofluidics, Vol: 9, ISSN: 1932-1058
Dropletinterface bilayer (DIB) networks are emerging as a cornerstone technology for the bottom up construction of cell-like and tissue-like structures and bio-devices. They are an exciting and versatile model-membrane platform, seeing increasing use in the disciplines of synthetic biology, chemical biology, and membrane biophysics. DIBs are formed when lipid-coated water-in-oil droplets are brought together—oil is excluded from the interface, resulting in a bilayer. Perhaps the greatest feature of the DIB platform is the ability to generate bilayer networks by connecting multiple droplets together, which can in turn be used in applications ranging from tissue mimics, multicellular models, and bio-devices. For such applications, the construction and release of DIB networks of defined size and composition on-demand is crucial. We have developed a droplet-based microfluidic method for the generation of different sized DIB networks (300–1500 pl droplets) on-chip. We do this by employing a droplet-on-rails strategy where droplets are guided down designated paths of a chip with the aid of microfabricated grooves or “rails,” and droplets of set sizes are selectively directed to specific rails using auxiliary flows. In this way we can uniquely produce parallel bilayer networks of defined sizes. By trapping several droplets in a rail, extended DIB networks containing up to 20 sequential bilayers could be constructed. The trapped DIB arrays can be composed of different lipid types and can be released on-demand and regenerated within seconds. We show that chemical signals can be propagated across the bio-network by transplanting enzymatic reaction cascades for inter-droplet communication.
Barriga HMG, Law RV, Seddon JM, et al., 2015, The effect of hydrostatic pressure on model membrane domain composition and lateral compressibility, Physical Chemistry Chemical Physics, ISSN: 1463-9084
Phase separation in ternary model membranes is known to occur over a range of temperatures and compositions and can be induced by increasing hydrostatic pressure. We have used small angle X-ray scattering (SAXS) to study phase separation along pre-determined tie lines in dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC) and cholesterol (CHOL) mixtures. We can unequivocally distinguish the liquid ordered (Lo) and liquid disordered (Ld) phases in diffraction patterns from biphasic mixtures and compare their lateral compressibility. The variation of tie line endpoints with increasing hydrostatic pressure was determined, at atmospheric pressure and up to 100 MPa. We find an extension and shift of the tie lines towards the DOPC rich region of the phase diagram at increased pressure, this behaviour differs slightly from that reported for decreasing temperature.
Pommella A, Brooks NJ, Seddon JM, et al., 2015, Selective flow-induced vesicle rupture to sort by membrane mechanical properties, Scientific Reports, Vol: 5, ISSN: 2045-2322
Dent MR, López-Duarte I, Dickson CJ, et al., 2015, Imaging phase separation in model lipid membranes through the use of BODIPY based molecular rotors., Phys Chem Chem Phys, Vol: 17, Pages: 18393-18402
In order to fully understand the dynamics of processes within biological lipid membranes, it is necessary to possess an intimate knowledge of the physical state and ordering of lipids within the membrane. Here we report the use of three molecular rotors based on meso-substituted boron-dipyrrin (BODIPY) in combination with fluorescence lifetime spectroscopy to investigate the viscosity and phase behaviour of model lipid bilayers. In phase-separated giant unilamellar vesicles, we visualise both liquid-ordered (Lo) and liquid-disordered (Ld) phases using fluorescence lifetime imaging microscopy (FLIM), determining their associated viscosity values, and investigate the effect of composition on the viscosity of these phases. Additionally, we use molecular dynamics simulations to investigate the orientation of the BODIPY probes within the bilayer, as well as using molecular dynamics simulations and fluorescence correlation spectroscopy (FCS) to compare diffusion coefficients with those predicted from the fluorescence lifetimes of the probes.
Purushothaman S, Cicuta P, Ces O, et al., 2015, The Influence of high pressure on the bending rigidity of model membranes, Journal of Physical Chemistry B, Vol: 119, Pages: 9805-9810, ISSN: 1520-6106
Curvature is a fundamental lipid membrane property that influences many membrane-mediated biological processes and dynamic soft materials. One of the key parameters that determines the energetics of curvature change is the membrane bending rigidity. Understanding the intrinsic effect of pressure on membrane bending is critical to understanding the adaptation and structural behavior of bio-membranes in deep-sea organisms, as well as soft material processing. However, it has not previously been possible to measure the influence of high hydrostatic pressure on membrane bending energetics and this bottleneck has primarily been due to a lack of technology platforms for performing such measurements. We have developed a new high pressure microscopy cell which, combined with vesicle fluctuation analysis, has allowed us to make the first measurements of membrane bending rigidity as a function of pressure. Our results show a significant increase in bending rigidity at pressures up to 40 MPa. Above 40 MPa, the membrane mechanics become more complex. Corresponding small and wide angle X-ray diffraction shows an increase in density and thickness of the bilayer with increasing pressure which correlates with the micro-mechanical measurements and these results are consistent with recent theoretical predictions of the bending rigidity as a function of hydrocarbon chain density. This technology has the potential to transform our quantitative understanding of the role of pressure in soft material processing, the structural behavior of bio-membranes and the adaptation mechanisms employed by deep-sea organisms.
McCarthy NLC, Ces O, Law RV, et al., 2015, Separation of liquid domains in model membranes induced with high hydrostatic pressure., Chem Commun (Camb), Vol: 51, Pages: 8675-8678
We have imaged the formation of membrane microdomains immediately after their induction using a novel technology platform coupling high hydrostatic pressure to fluorescence microscopy. After formation, the ordered domains are small and highly dynamic. This will enhance links between model lipid assemblies and dynamic processes in cellular membranes.
Barriga HMG, Parsons ES, McCarthy NLC, et al., 2015, Pressure–Temperature Phase Behavior of Mixtures of Natural Sphingomyelin and Ceramide Extracts, Langmuir, Vol: 31, Pages: 3678-3686, ISSN: 0743-7463
Tang T-YD, Brooks NJ, Ces O, et al., 2015, Structural studies of the lamellar to bicontinuous gyroid cubic (Q(II)(G)) phase transitions under limited hydration conditions, SOFT MATTER, Vol: 11, Pages: 1991-1997, ISSN: 1744-683X
Tyler AII, Barriga HMG, Parsons ES, et al., 2015, Electrostatic swelling of bicontinuous cubic lipid phases, Soft Matter, Vol: 11, Pages: 3279-3286, ISSN: 1744-6848
Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in-vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by a) increasing the bilayer stiffness by adding cholesterol and b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å.
Barriga HMG, Tyler AII, McCarthy NLC, et al., 2015, Temperature and pressure tuneable swollen bicontinuous cubic phases approaching nature's length scales, SOFT MATTER, Vol: 11, Pages: 600-607, ISSN: 1744-683X
Casey D, Wylie D, Gallo J, et al., 2015, A novel, all-optical tool for controllable and non-destructive poration of cells with single-micron resolution, Bio-Optics: Design and Application 2015, Publisher: Optical Society of America
We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near-IR laser interacting with thin-layer amorphous silicon substrates. This technique will allow new experiments in single-cell biology, particularly in neuroscience.
Elani Y, Purushothaman S, Booth PJ, et al., 2015, Measurements of the effect of membrane asymmetry on the mechanical properties of lipid bilayers, Chemical Communications, Vol: 51, Pages: 6976-6979, ISSN: 1359-7345
<p>We detail an approach for constructing asymmetric membranes and characterising their mechanical properties, leading to the first measurement of the effect of asymmetry on lipid bilayer mechanics.</p>
Karamdad K, Law RV, Seddon JM, et al., 2014, Preparation and mechanical characterisation of giant unilamellar vesicles by a microfluidic method, Lab on a Chip, ISSN: 1473-0197
Giant unilamellar vesicles (GUVs) have a wide range of applications in biology and synthetic biology. As a result, new approaches for constructing GUVs using microfluidic techniques are emerging but there are still significant shortcomings in the control of fundamental vesicle structural parameters such as size, lamellarity, membrane composition and internal contents. We have developed a novel microfluidic platform to generate compositionally-controlled GUVs. Water-in-oil (W/O) droplets formed in a lipid-containing oil flow are transferred across an oil- water interface, facilitating the self-assembly of a phospholipid bilayer. In addition, for the first time we have studied the mechanical properties of the resultant lipid bilayers of the microfluidic GUVs. Using fluctuation analysis we were able to calculate the values for bending rigidity of giant vesicles assembled on chip and demonstrate that these correlate strongly with those of traditional low throughput strategies such as electroformation.
Brooks NJ, Seddon JM, 2014, High Pressure X-ray Studies of Lipid Membranes and Lipid Phase Transitions, Zeitschrift für Physikalische Chemie, Vol: 228, Pages: 987-1004, ISSN: 0942-9352
Hydrostatic pressure has dramatic effects on biomembrane structure and stability and is a key thermodynamic parameter in the context of the biology of deep sea organisms. Furthermore, high-pressure and pressure-jump studies are very useful tools in biophysics and biotechnology, where they can be used to study the mechanism and kinetics of lipid phase transitions, biomolecular transforma- tions, and protein folding/unfolding. Here, we first give an overview of the tech- nology currently available for X-ray scattering studies of soft matter systems under pressure. We then illustrate the use of this technology to study a variety of lipid membrane systems.
Brooks NJ, 2014, Pressure effects on lipids and bio-membrane assemblies., IUCrJ, Vol: 1, Pages: 470-477, ISSN: 2052-2525
Membranes are amongst the most important biological structures; they maintain the fundamental integrity of cells, compartmentalize regions within them and play an active role in a wide range of cellular processes. Pressure can play a key role in probing the structure and dynamics of membrane assemblies, and is also critical to the biology and adaptation of deep-sea organisms. This article presents an overview of the effect of pressure on the mesostructure of lipid membranes, bilayer organization and lipid-protein assemblies. It also summarizes recent developments in high-pressure structural instrumentation suitable for experiments on membranes.
Carreras P, Elani Y, Law R, et al., A droplet trapping microfluidic device for the study of mass-transport across droplet interface bilayers, MicroTAS 2014
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