Evaporation-induced monolayer compression improves droplet interface bilayer formation using unsaturated lipids

Venkatesan, Guru A.; Taylor, Graham J.; Basham, Colin; Brady, Nathan G.; Collier, C. Patrick; Sarles, Stephen A.

doi:10.1063/1.5016523

Cited by 23 publications

(23 citation statements)

References 53 publications

(75 reference statements)

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“…However, with lipids suspended in the aqueous phase at a lower concentration of 0.05 wt% to 0.2 wt%, it is necessary to wait at least 30 minutes to ensure an adequate interfacial concentration, or a bilayer will not nucleate upon thinning. An analogous factor to bilayer formation has been found using droplet interface bilayers (59),…”

Section: Comparison Between Lipid-in-oil and Lipid-in-aqueous Symmetrsupporting

confidence: 60%

Fabrication and electromechanical characterization of free-standing asymmetric membranes

Liu

Zabala-Ferrera

Beltramo

2020

Preprint

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All biological cell membranes maintain an electric transmembrane potential of around 100 mV, due in part to an asymmetric distribution of charged phospholipids across the membrane. This asymmetry is crucial to cell health and physiological processes such as intracell signaling, receptor-mediated endocytosis, and membrane protein function. Experimental artificial membrane systems incorporate essential cell membrane structures, such as the phospholipid bilayer, in a controllable manner where specific properties and processes can be isolated and examined. Here, we describe a new approach to fabricate and characterize planar, free-standing, asymmetric membranes and use it to examine the effect of headgroup charge on membrane stiffness. The approach relies on a thin film balance used to form a freestanding membrane by adsorbing aqueous phase lipids to an oil-water interface and subsequently thinning the oil to form a bilayer. We validate this lipid-in-aqueous approach by analyzing the thickness and compressibility of symmetric membranes with varying zwitterionic DOPC and anionic DOPG content as compared to previous lipid-in-oil methods. We find that as the concentration of DOPG increases, membranes become thicker and stiffer. By controlling the lipid composition in the aqueous compartments on either side of the oil within the thin film balance, asymmetric membranes are then examined. Membrane compositional asymmetry is qualitatively demonstrated using a fluorescence quenching assay and quantitatively characterized through voltage-dependent capacitance measurements. Stable asymmetric membranes with DOPC on one side and DOPC/DOPG mixtures on the other were created with transmembrane potentials ranging from 10 to 25 mV. Introducing membrane charge asymmetry also increases the stiffness of the membrane. These initial successes demonstrate a viable pathway to quantitatively characterize asymmetric bilayers that can be extended to accommodate more complex membrane processes in the future.SIGNIFICANCEA defining characteristic of the cell membrane is asymmetry in phospholipid composition between the interior and exterior bilayer leaflet. Although several methods have been used to artificially create membranes with asymmetry, there has not been extensive characterization of the impact of asymmetry on membrane material properties. Here, a technique to fabricate free-standing asymmetric membranes is developed which facilitates the visualization and electromechanical characterization of the bilayer. Asymmetry in anionic phospholipid concentration is quantified by measurements of membrane capacitance at varying voltages, which also allows for determination of the membrane compressibility. This method represents an advance in the development of artificial biomembranes by reliably creating phospholipid bilayers with asymmetry and facilitates the interrogation of more complex biological processes in the future.

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Section: Comparison Between Lipid-in-oil and Lipid-in-aqueous Symmetrsupporting

confidence: 60%

Fabrication and electromechanical characterization of free-standing asymmetric membranes

Liu

Zabala-Ferrera

Beltramo

2020

Preprint

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“…The polymer was dissolved in hexadecane at a concentration of 2 mg/mL, yielding an optically transparent oil phase. Measurements were made as described previously 10,46 using 1-2 μL inverted ODMS-MIM (+) in oil droplets generated at the tip of a stainless steel needle submerged in a cuvette containing 3-4 mL of water or buffer. The needle was pre-loaded with 20 μL of oligomer in hexadecane solution before being submerged in the cuvette containing water or buffer.…”

Section: Experimental Section Odms-mim (+) Synthesismentioning

confidence: 99%

Insight into the Mechanisms Driving the Self-Assembly of Functional Interfaces: Moving from Lipids to Charged Amphiphilic Oligomers

Chowdhury¹,

Taylor²,

Bocharova³

et al. 2019

Preprint

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Polymer-stabilized liquid-liquid interfaces are an important and growing class of bioinspired materials that combine the structural and functional capabilities of advanced synthetic materials with naturally evolved biophysical systems. These platforms have the potential to serve as selective membranes for chemical separations, molecular sequencers, and to even mimic neuromorphic computing elements. Despite the diversity in function, basic insight into the assembly of well-defined amphiphilic polymers to form functional structures remains elusive, which hinders the continued development of these technologies. In this work we provide new mechanistic insight into the assembly of an amphiphilic polymer-stabilized oil/aqueous interface, in which the headgroups consist of positively charged methylimidazolium ionic liquids, and the tails are short, monodisperse oligodimethylsiloxanes covalently attached to the headgroups. We demonstrate using vibrational sum frequency generation spectroscopy and pendant drop tensiometery that the composition of the bulk aqueous phase, particularly the ionic strength, dictates the kinetics and structures of the amphiphiles in the organic phase as they decorate the interface. These results show that H-bonding and electrostatic interactions taking place in the aqueous phase bias the grafted oligomer conformations that are adopted in the neighboring oil phase. The kinetics of self-assembly were ionic strength dependent and found to be surprisingly slow, being composed of distinct regimes where molecules adsorb and reorient on relatively fast time scales, but where conformational sampling and frustrated packing takes place over longer timescales. These results set the stage for understanding related chemical phenomena of bioinspired materials in diverse technological and fundamental scientific fields and provide a solid physical foundation on which to design new functional interfaces.

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“…(46) Additionally, it is important to note that attaining thermodynamic equilibrium can be somewhat troublesome for DIBs as they continually lose water mass due to evaporation, this is a particular problem for DIBs with diameters on a micron length scale. (5) The effect of evaporation on DIBs was characterized recently by Venkatesan et al, (47) and this effect is mitigated by using droplets on the order of 300 micron in diameter covered by a thick layer of oil, however the effect of gravity on droplet shape prevents the use of much larger DIBs without adding another level of complexity to the model. ( 48) Indeed, the model system is limited in scalability by the Bond number (see Section 2.4).…”

Section: Limitations In Scalabilitymentioning

confidence: 99%

Measuring bilayer surface energy and curvature in asymmetric droplet interface bilayers

Barlow

Kusumaatmaja

Salehi-Reyhani

et al. 2018

J. R. Soc. Interface.

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For the past decade, droplet interface bilayers (DIBs) have had an increased prevalence in biomolecular and biophysical literature. However, much of the underlying physics of these platforms is poorly characterized. To further our understanding of these structures, lipid membrane tension on DIB membranes is measured by analysing the equilibrium shape of asymmetric DIBs. To this end, the morphology of DIBs is explored for the first time using confocal laser scanning fluorescence microscopy. The experimental results confirm that, in accordance with theory, the bilayer interface of a volume-asymmetric DIB is curved towards the smaller droplet and a lipid-asymmetric DIB is curved towards the droplet with the higher monolayer surface tension. Moreover, the DIB shape can be exploited to measure complex bilayer surface energies. In this study, the bilayer surface energy of DIBs composed of lipid mixtures of phosphatidylgylcerol (PG) and phosphatidylcholine are shown to increase linearly with PG concentrations up to 25%. The assumption that DIB bilayer area can be geometrically approximated as a spherical cap base is also tested, and it is discovered that the bilayer curvature is negligible for most practical symmetric or asymmetric DIB systems with respect to bilayer area.

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Evaporation-induced monolayer compression improves droplet interface bilayer formation using unsaturated lipids

Cited by 23 publications

References 53 publications

Fabrication and electromechanical characterization of free-standing asymmetric membranes

Fabrication and electromechanical characterization of free-standing asymmetric membranes

Insight into the Mechanisms Driving the Self-Assembly of Functional Interfaces: Moving from Lipids to Charged Amphiphilic Oligomers

Measuring bilayer surface energy and curvature in asymmetric droplet interface bilayers

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