154 results found
Hindley JW, Zheleva DG, Elani Y, et al., 2019, Building a synthetic mechanosensitive signaling pathway in compartmentalized artificial cells, Proceedings of the National Academy of Sciences, Vol: 116, Pages: 16711-16716, ISSN: 0027-8424
To date reconstitution of one of the fundamental methods of cell communication, the signaling pathway, has been unaddressed in the bottom-up construction of artificial cells (ACs). Such developments are needed to increase the functionality and biomimicry of ACs, accelerating their translation and application in biotechnology. Here we report the construction of a de novo synthetic signaling pathway in microscale nested vesicles. Vesicle cell models respond to external calcium signals through activation of an intracellular interaction between phospholipase A2 and a mechanosensitive channel present in the internal membranes, triggering content mixing between compartments and controlling cell fluorescence. Emulsion-based approaches to AC construction are therefore shown to be ideal for the quick design and testing of new signaling networks and can readily include synthetic molecules difficult to introduce to biological cells. This work represents a foundation for the engineering of multi-compartment-spanning designer pathways that can be utilised to control downstream events inside an artificial cell, leading to the assembly of micromachines capable of sensing and responding to changes in their local environment.
Supramaniam P, Ces O, Salehi-Reyhani A, 2019, Microfluidics for Artificial Life: Techniques for Bottom-Up Synthetic Biology, MICROMACHINES, Vol: 10, ISSN: 2072-666X
Khan H, Seddon JM, Law RV, et al., 2019, Effect of glycerol with sodium chloride on the Krafft point of sodium dodecyl sulfate using surface tension, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 538, Pages: 75-82, ISSN: 0021-9797
Friddin MS, Elani Y, Trantidou T, et al., 2019, New directions for artificial cells using rapid prototyped biosystems, Analytical Chemistry, Vol: 91, Pages: 4921-4928, ISSN: 0003-2700
Microfluidics has been shown to be capable of generating a range of single- and multi- compartment vesicles and bilayer delineated droplets that can be assembled in 2D and 3D. These model systems are becoming increasingly recognized as powerful biomimetic constructs for assembling tissue models, engineering therapeutic delivery systems and for screening drugs. One bottleneck in developing this technology is the time, expertise and equipment required for device fabrication. This has led to interest across the microfluidics community in using rapid prototyping to engineer microfluidic devices from Computer Aided Design (CAD) drawings. We highlight how this rapid prototyping revolution is transforming the fabrication of microfluidic devices for bottom-up synthetic biology. We provide an outline of the current landscape and present how advances in the field may give rise to the next generation of multifunctional biodevices, particularly with Industry 4.0 on the horizon. Successfully developing this technology and making it open-source could pave the way for a new generation of citizen-led science, fueling the possibility that the next multi-billion dollar start-up could emerge from an attic or a basement.
Ces O, Elani Y, 2019, Community building in synthetic biology., Exp Biol Med (Maywood), Vol: 244, Pages: 281-282
Friddin M, Bolognesi G, Salehi-Reyhani A, et al., Direct manipulation of liquid ordered lipid membrane domains using optical traps, Nature Communications Chemistry
Trantidou T, Friddin M, Gan KB, et al., 2018, Mask-free laser lithography for rapid and low-cost microfluidic device fabrication, Analytical Chemistry, Vol: 90, Pages: 13915-13921, ISSN: 0003-2700
Microfluidics has become recognized as a powerful platform technology associated with a constantly increasing array of applications across the life sciences. This surge of interest over recent years has led to an increased demand for microfluidic chips, resulting in more time being spent in the cleanroom fabricating devices using soft lithography—a slow and expensive process that requires extensive materials, training and significant engineering resources. This bottleneck limits platform complexity as a byproduct of lengthy delays between device iterations and affects the time spent developing the final application. To address this problem, we report a new, rapid, and economical approach to microfluidic device fabrication using dry resist films to laminate laser cut sheets of acrylic. We term our method laser lithography and show that our technique can be used to engineer 200 μm width channels for assembling droplet generators capable of generating monodisperse water droplets in oil and micromixers designed to sustain chemical reactions. Our devices offer high transparency, negligible device to device variation, and low X-ray background scattering, demonstrating their suitability for real-time X-ray-based characterization applications. Our approach also requires minimal materials and apparatus, is cleanroom free, and at a cost of around $1.00 per chip could significantly democratize device fabrication, thereby increasing the interdisciplinary accessibility of microfluidics.
Miller RM, Cabral J, Robles E, et al., 2018, Crystallisation of sodium dodecyl sulfate–water micellar solutions with structurally similar additives: counterion variation, CrystEngComm, Vol: 20, Pages: 6834-6843, ISSN: 1466-8033
The effects of a series of structurally similar sodium dodecyl sulfate (SDS) additives on the crystallisation of SDS–water micellar solutions were investigated using a combination of differential scanning calorimetry, dynamic light scattering, optical microscopy and inductively coupled plasma optical emission spectroscopy. Seven different counterions were chosen from groups 1 and 2 of the periodic table to replace the sodium on SDS: LDS, (SDS), KDS, RbDS, CsDS, Mg(DS)2, Ca(DS)2 and Sr(DS)2. Two representative temperature profileswere employed – linear cooling ramps at rate of 0.5 °C min−1 to determine near-equilibrium kinetics and transitions and isothermal holds at 6 °C to elucidate morphological changes. Crystallisation of the reference solution 20% SDS–H2O with 0.25, 1.0 and 2.5% additive was generally promoted or inhibited even at the lowest concentrations. Melting points however remained largely unchanged, suggesting that the additives predominantly had a kinetic rather than thermodynamic effect. ICP-OES measurements for the solutions containing 1% additive indicated that most of the additives were integrated into the SDS crystals which was reflected by morphological changes, including the formation of hexagonal and oval shaped crystals. Our results both quantify and provide a morphological insight into the effect of a series of additives on the crystallisation of micellar SDS solutions, which can readily form due to preferential Na exchange.
Barlow N, Kusumaatmaja H, Salehi-Reyhani A, et al., 2018, Measuring bilayer surface energy and curvature in asymmetric droplet interface bilayers, Journal of the Royal Society Interface, Vol: 15, ISSN: 1742-5662
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.
Trantidou T, Dekker L, Polizzi K, et al., 2018, Functionalizing cell-mimetic giant vesicles with encapsulated bacterial biosensors, Interface Focus, Vol: 8, ISSN: 2042-8901
The design of vesicle microsystems as artificial cells (bottom-up synthetic biology) has traditionally relied on the incorporation of molecular components to impart functionality. These cell mimics have reduced capabilities compared with their engineered biological counterparts (top-down synthetic biology), as they lack the powerful metabolic and regulatory pathways associated with living systems. There is increasing scope for using whole intact cellular components as functional modules within artificial cells, as a route to increase the capabilities of artificial cells. In this feasibility study, we design and embed genetically engineered microbes (Escherichia coli) in a vesicle-based cell mimic and use them as biosensing modules for real-time monitoring of lactate in the external environment. Using this conceptual framework, the functionality of other microbial devices can be conferred into vesicle microsystems in the future, bridging the gap between bottom-up and top-down synthetic biology.
Chatzimichail S, Supramaniam P, Ces O, et al., 2018, Micropatterning of planar metal electrodes by vacuum filling microfluidic channel geometries, Scientific Reports, Vol: 8, ISSN: 2045-2322
We present a simple, facile method to micropattern planar metal electrodes defined by the geometry of a microfluidic channel network template. By introducing aqueous solutions of metal into reversibly adhered PDMS devices by desiccation instead of flow, we are able to produce difficult to pattern “dead end” or discontinuous features with ease. We characterize electrodes fabricated using this method and perform electrical lysis of mammalian cancer cells and demonstrate their use as part of an antibody capture assay for GFP. Cell lysis in microwell arrays is achieved using the electrodes and the protein released is detected using an antibody microarray. We show how the template channels used as part of the workflow for patterning the electrodes may be produced using photolithography-free methods, such as laser micromachining and PDMS master moulding, and demonstrate how the use of an immiscible phase may be employed to create electrode spacings on the order of 25 – 50 μm, that overcome the current resolution limits of such methods. This work demonstrates how the rapid prototyping of electrodes for use in total analysis systems can be achieved on the bench with little or no need for centralized facilities.
Trantidou T, Friddin M, Salehi-Reyhani S, et al., 2018, Droplet microfluidics for the construction of compartmentalised model membranes, Lab on a Chip, Vol: 18, Pages: 2488-2509, ISSN: 1473-0189
The design of membrane-based constructs with multiple compartments is of increasing importance given their potential applications as microreactors, as artificial cells in synthetic-biology, as simplified cell models, and as drug delivery vehicles. The emergence of droplet microfluidics as a tool for their construction has allowed rapid scale-up in generation throughput, scale-down of size, and control over gross membrane architecture. This is true on several levels: size, level of compartmentalisation and connectivity of compartments can all be programmed to various degrees. This tutorial review explains and explores the reasons behind this. We discuss microfluidic strategies for the generation of a family of compartmentalised systems that have lipid membranes as the basic structural motifs, where droplets are either the fundamental building blocks, or are precursors to the membrane-bound compartments. We examine the key properties associated with these systems (including stability, yield, encapsulation efficiency), discuss relevant device fabrication technologies, and outline the technical challenges. In doing so, we critically review the state-of-play in this rapidly advancing field.
Chatzimichail S, Supramaniam P, Ces O, et al., 2018, Counting proteins in single cells with addressable droplet microarrays, Jove-Journal of Visualized Experiments, Vol: 137, ISSN: 1940-087X
Often cellular behaviour and cellular responses are analysed at the population level where the responses of many cells are pooled together as an average result masking the rich single cell behaviour within a complex population. Single cell protein detection and quantification technologies have made a remarkable impact in recent years. Here we describe a practical and flexible single cell analysis platform based on addressable droplet microarrays. This study describes how the absolute copy numbers of target proteins may be measured with single cell resolution. The tumour suppressor p53 is the most commonly mutated gene in human cancer, with more than 50% of total cancer cases exhibiting a non-healthy p53 expression pattern. The protocol describes steps to create 10nL droplets within which single human cancer cells are isolated and the copy number of p53 protein is measured with single molecule resolution to precisely determine the variability in expression. The method may be applied to any cell type including primary material to determine the absolute copy number of any target proteins of interest.
Bolognesi G, Friddin MS, Salehi-Reyhani S, et al., 2018, Sculpting and fusing biomimetic vesicle networks using optical tweezers, Nature Communications, Vol: 9, ISSN: 2041-1723
Constructing higher-order vesicle assemblies has discipline-spanning potential from responsive soft-matter materials to artificial cell networks in synthetic biology. This potential is ultimately derived from the ability to compartmentalise and order chemical species in space. To unlock such applications, spatial organisation of vesicles in relation to one another must be controlled, and techniques to deliver cargo to compartments developed. Herein, we use optical tweezers to assemble, reconfigure and dismantle networks of cell-sized vesicles that, in different experimental scenarios, we engineer to exhibit several interesting properties. Vesicles are connected through double-bilayer junctions formed via electrostatically controlled adhesion. Chemically distinct vesicles are linked across length scales, from several nanometres to hundreds of micrometres, by axon-like tethers. In the former regime, patterning membranes with proteins and nanoparticles facilitates material exchange between compartments and enables laser-triggered vesicle merging. This allows us to mix and dilute content, and to initiate protein expression by delivering biomolecular reaction components.
Karamdad K, Hindley J, Friddin MS, et al., 2018, Engineering thermoresponsive phase separated vesicles formed via emulsion phase transfer as a content-release platform, Chemical Science, Vol: 9, Pages: 4851-4858, ISSN: 2041-6520
Giant unilamellar vesicles (GUVs) are a well-established tool for the study of membrane biophysics and are increasingly used as artificial cell models and functional units in biotechnology. This trend is driven by the development of emulsion-based generation methods such as Emulsion Phase Transfer (EPT), which facilitates the encapsulation of almost any water-soluble compounds (including biomolecules) regardless of size or charge, is compatible with droplet microfluidics, and allows GUVs with asymmetric bilayers to be assembled. However, the ability to control the composition of membranes formed via EPT remains an open question; this is key as composition gives rise to an array of biophysical phenomena which can be used to add functionality to membranes. Here, we evaluate the use of GUVs constructed via this method as a platform for phase behaviour studies and take advantage of composition-dependent features to engineer thermally-responsive GUVs. For the first time, we generate ternary GUVs (DOPC/DPPC/cholesterol) using EPT, and by compensating for the lower cholesterol incorporation efficiencies, show that these possess the full range of phase behaviour displayed by electroformed GUVs. As a demonstration of the fine control afforded by this approach, we demonstrate release of dye and peptide cargo when ternary GUVs are heated through the immiscibility transition temperature, and show that release temperature can be tuned by changing vesicle composition. We show that GUVs can be individually addressed and release triggered using a laser beam. Our findings validate EPT as a suitable method for generating phase separated vesicles and provide a valuable proof-of-concept for engineering content release functionality into individually addressable vesicles, which could have a host of applications in the development of smart synthetic biosystems.
Trantidou T, Regoutz A, Voon X, et al., 2018, A “cleanroom-free” and scalable manufacturing technology for the microfluidic generation of lipid-stabilized droplets and cell-sized multisomes, Sensors and Actuators B: Chemical, Vol: 267, Pages: 34-41, ISSN: 0925-4005
There is a growing demand to construct artificial biomimetic structures from the bottom-up using simple chemical components in a controlled and high-throughput way. These cell mimics are encapsulated by lipid membranes and can reconstitute biological machinery within them. To date, such synthetic cells based upon droplet microfluidics are fabricated using non-scalable, expensive and time-consuming strategies, and are thus restricted to small-scale in-house manufacturing. Here, we report a “cleanroom-free” and highly scalable microfluidic manufacturing technology based on dry film resists and multilayer lamination. The technology facilitates the controlled and high-throughput generation of stable and monodisperse droplets using anionic surfactants and more biologically relevant phospholipids. We demonstrate the versatility of this approach by selectively patterning the surface chemistry of the device, enabling the production of compartmentalized lipid structures based on droplet interface bilayers (multisomes). This technology has the potential to simultaneously unlock the widespread exploitation of microfluidics to chemists and synthetic biologists not having access to controlled production environments and facilitate low-cost (< £1) high-volume fabrication of self-contained disposable devices with minimum feature sizes of 30 μm. The associated material and equipment costs approach those of other deskilled prototyping technologies, such as 3D printing that have made the transition into the mainstream.
Hindley JW, Elani Y, McGilvery CM, et al., 2018, Light-triggered enzymatic reactions in nested vesicle reactors, Nature Communications, Vol: 9, ISSN: 2041-1723
Cell-sized vesicles have tremendous potential both as miniaturised pL reaction vessels and in bottom-up synthetic biology as chassis for artificial cells. In both these areas the introduction of light-responsive modules affords increased functionality, for example, to initiate enzymatic reactions in the vesicle interior with spatiotemporal control. Here we report a system composed of nested vesicles where the inner compartments act as phototransducers, responding to ultraviolet irradiation through diacetylene polymerisation-induced pore formation to initiate enzymatic reactions. The controlled release and hydrolysis of a fluorogenic β-galactosidase substrate in the external compartment is demonstrated, where the rate of reaction can be modulated by varying ultraviolet exposure time. Such cell-like nested microreactor structures could be utilised in fields from biocatalysis through to drug delivery.
Elani Y, Trantidou T, Wylie D, et al., 2018, Constructing vesicle-based artificial cells with embedded living cells as organelle-like modules, Scientific Reports, Vol: 8, ISSN: 2045-2322
There is increasing interest in constructing artificial cells by functionalisinglipid vesicles with biological and synthetic machinery. Due to their reduced complexity and lack of evolved biochemical pathways, the capabilities of artificial cells are limitedin comparison to their biologicalcounterparts. We show that encapsulating living cells in vesicles provides a means for artificial cells to leverage cellular biochemistry, with the encapsulated cells serving organelle-like functions as living modules inside a larger syntheticcell assembly. Using microfluidic technologies to construct such hybrid systems, we demonstrate that the vesicle host and the encapsulated cell operate in concert. The external architecture of the vesicle shields the cell from toxic surroundings, whilethe cellacts as a bioreactor module that processes encapsulated feedstock which is further processedby a synthetic enzymatic cascadeco-encapsulated in the vesicle.
Heide C, Ces O, Polizzi K, et al., Creating cell-free protein synthesis factories, Pharmaceutical Bioprocessing, ISSN: 2048-9145
Heide C, Ces O, Polizzi K, et al., Creating cell-free protein synthesis factories, Pharmaceutical Bioprocessing, ISSN: 2048-9145
Barlow NE, Bolognesi G, Haylock S, et al., 2017, Rheological Droplet Interface Bilayers (rheo-DIBs): Probing the Unstirred Water Layer Effect on Membrane Permeability via Spinning Disk Induced Shear Stress, Scientific Reports, Vol: 7, ISSN: 2045-2322
A new rheological droplet interface bilayer (rheo-DIB) device is presented as a tool to apply shear stress on biological lipid membranes. Despite their exciting potential for affecting high-throughput membrane translocation studies, permeability assays conducted using DIBs have neglected the effect of the unstirred water layer (UWL). However as demonstrated in this study, neglecting this phenomenon can cause significant underestimates in membrane permeability measurements which in turn limits their ability to predict key processes such as drug translocation rates across lipid membranes. With the use of the rheo-DIB chip, the effective bilayer permeability can be modulated by applying shear stress to the droplet interfaces, inducing flow parallel to the DIB membranes. By analysing the relation between the effective membrane permeability and the applied stress, both the intrinsic membrane permeability and UWL thickness can be determined for the first time using this model membrane approach, thereby unlocking the potential of DIBs for undertaking diffusion assays. The results are also validated with numerical simulations.
Thomas JM, Friddin MS, Ces O, et al., 2017, Programming membrane permeability using integrated membrane pores and blockers as molecular regulators, Chemical Communications, Vol: 53, Pages: 12282-12285, ISSN: 1359-7345
We report a bottom-up synthetic biology approach to engineering vesicles with programmable permeabilities. Exploiting the concentration-dependent relationship between constitutively active pores (alpha-hemolysin) and blockers allows blockers to behave as molecular regulators for tuning permeability, enabling us to systematically modulate cargo release kinetics without changing the lipid fabric of the system.
de Bruin A, Friddin MS, Elani Y, et al., 2017, A transparent 3D printed device for assembling droplet hydrogel bilayers (DHBs), RSC Advances, Vol: 7, Pages: 47796-47800, ISSN: 2046-2069
We report a new approach for assembling droplet hydrogel bilayers (DHBs) using a transparent 3D printed device. We characterise the transparency of our platform, confirm bilayer formation using electrical measurements and show that single-channel recordings can be obtained using our reusable rapid prototyped device. This method significantly reduces the cost and infrastructure required to develop devices for DHB assembly and downstream study.
Richens JL, Tyler AII, Barriga HMG, et al., 2017, Spontaneous charged lipid transfer between lipid vesicles, Scientific Reports, Vol: 7, ISSN: 2045-2322
An assay to study the spontaneous charged lipid transfer between lipid vesicles is described. A donor/acceptor vesicle system is employed, where neutrally charged acceptor vesicles are uorescentlylabelled with the electrostatic membrane probe Fluoresceinphosphatidylethanolamine (FPE).Upon addition of charged donor vesicles, transfer of negatively charged lipid occurs, resulting ina uorescently detectable change in the membrane potential of the acceptor vesicles. Using this approach we have studied the transfer properties of a range of lipids, varying both the headgroup and the chain length. At the low vesicle concentrations chosen, the transfer follows a rst-order process where lipid monomers are transferred presumably through the aqueous solution phase from donor to acceptor vesicle. The rate of transfer decreases with increasing chain length which is consistent with energy models previously reported for lipid monomer vesicle interactions. Our assay improves on existing methods allowing the study of a range of unmodi ed lipids, continuous monitoring of transfer and simpli ed experimental procedures.
Trantidou T, Friddin M, Elani Y, et al., 2017, Engineering compartmentalized biomimetic micro- and nanocontainers, ACS Nano, Vol: 11, Pages: 6549-6565, ISSN: 1936-086X
Compartmentalization of biological content and function is a key architectural feature in biology, where membrane bound micro- and nanocompartments are used for performing a host of highly specialized and tightly regulated biological functions. The benefit of compartmentalization as a design principle is behind its ubiquity in cells and has led to it being a central engineering theme in construction of artificial cell-like systems. In this review, we discuss the attractions of designing compartmentalized membrane-bound constructs and review a range of biomimetic membrane architectures that span length scales, focusing on lipid-based structures but also addressing polymer-based and hybrid approaches. These include nested vesicles, multicompartment vesicles, large-scale vesicle networks, as well as droplet interface bilayers, and double-emulsion multiphase systems (multisomes). We outline key examples of how such structures have been functionalized with biological and synthetic machinery, for example, to manufacture and deliver drugs and metabolic compounds, to replicate intracellular signaling cascades, and to demonstrate collective behaviors as minimal tissue constructs. Particular emphasis is placed on the applications of these architectures and the state-of-the-art microfluidic engineering required to fabricate, functionalize, and precisely assemble them. Finally, we outline the future directions of these technologies and highlight how they could be applied to engineer the next generation of cell models, therapeutic agents, and microreactors, together with the diverse applications in the emerging field of bottom-up synthetic biology.
Salehi-Reyhani A, Ces O, Elani Y, 2017, Artificial cell mimics as simplified models for the study of cell biology, Experimental Biology and Medicine, Vol: 242, Pages: 1309-1317, ISSN: 1535-3702
Living cells are hugely complex chemical systems composed of a milieu of distinct chemical species (including DNA, proteins, lipids, and metabolites) interconnected with one another through a vast web of interactions: this complexity renders the study of cell biology in a quantitative and systematic manner a difficult task. There has been an increasing drive towards the utilization of artificial cells as cell mimics to alleviate this, a development that has been aided by recent advances in artificial cell construction. Cell mimics are simplified cell-like structures, composed from the bottom-up with precisely defined and tunable compositions. They allow specific facets of cell biology to be studied in isolation, in a simplified environment where control of variables can be achieved without interference from a living and responsive cell. This mini-review outlines the core principles of this approach and surveys recent key investigations that use cell mimics to address a wide range of biological questions. It will also place the field in the context of emerging trends, discuss the associated limitations, and outline future directions of the field.
Trantidou T, Elani Y, Parsons E, et al., 2017, Hydrophilic surface modification of PDMS for droplet microfluidics using a simple, quick, and robust method via PVA deposition, Microsystems and Nanoengineering, Vol: 3, ISSN: 2055-7434
Polydimethylsiloxane (PDMS) is a dominant material in the fabrication of microfluidic devices to generate water-in-oil droplets, particularly lipid-stabilized droplets, because of its highly hydrophobic nature. However, its key property of hydrophobicity has hindered its use in the microfluidic generation of oil-in-water droplets, which requires channels to have hydrophilic surface properties. In this article, we developed, optimized, and characterized a method to produce PDMS with a hydrophilic surface via the deposition of polyvinyl alcohol following plasma treatment and demonstrated its suitability for droplet generation. The proposed method is simple, quick, effective, and low cost and is versatile with respect to surfactants, with droplets being successfully generated using both anionic surfactants and more biologically relevant phospholipids. This method also allows the device to be selectively patterned with both hydrophilic and hydrophobic regions, leading to the generation of double emulsions and inverted double emulsions.
Armstrong A, Ces O, Compte RV, 2017, All aboard for chemistry, CHEMISTRY & INDUSTRY, Vol: 81, Pages: 14-15, ISSN: 0009-3068
Miller RM, Ces O, Brooks NJ, et al., 2017, Crystallization of Sodium Dodecyl Sulfate-Water Micellar Solutions under Linear Cooling, CRYSTAL GROWTH & DESIGN, Vol: 17, Pages: 2428-2437, ISSN: 1528-7483
The crystallization kinetics of sodium dodecyl sulfate (SDS)-water micellar solutions, under linear cooling conditions, were experimentally investigated using optical microscopy, differential scanning calorimetry, and infrared spectroscopy. Cooling rates were systematically varied, from 0.1 to 50 °C min–1, encompassing environmental to near-“isothermal” temperature changes, between 22 and −5 °C, for a reference concentration of 20% SDS-H2O. The cooling rate was shown to determine the dominant crystal morphologies, with platelets and needles predominating at the lowest and highest rates, respectively. The results were rationalized in terms of isothermal crystallization data and the time–temperature cooling profile. Rates 0.1, 5.0, and 10 °C min–1 yield morphologies and kinetics analogous to those of isothermal quenches at the corresponding crystallization temperature window. Nontrivial deviations were observed for intermediate rates (0.5, 1.0 °C min–1), due to commensurate changes in temperature and crystallization mechanism, accompanied by solute depletion. The polythermal metastable zone width was estimated, and the non-isothermal nucleation described by the Nývlt equation, while the Avrami and Kissinger models described overall crystallization kinetics. Our measurements quantify the impact of temperature gradients in the crystallization of ubiquitous SDS micellar solutions, for a range of practically relevant profiles incurred during manufacturing and storage.
Barlow NE, Smpokou E, Friddin MS, et al., 2017, Engineering plant membranes using droplet interface bilayers, Biomicrofluidics, Vol: 11, ISSN: 1932-1058
Droplet interface bilayers (DIBs) have become widely recognised as a robust platform for constructing model membranes and are emerging as a key technology for the bottom-up assembly of synthetic cell-like and tissue-like structures. DIBs are formed when lipid-monolayer coated water droplets are brought together inside a well of oil, which is excluded from the interface as the DIB forms. The unique features of the system, compared to traditional approaches (e.g., supported lipid bilayers, black lipid membranes, and liposomes), is the ability to engineer multi-layered bilayer networks by connecting multiple droplets together in 3D, and the capability to impart bilayer asymmetry freely within these droplet architectures by supplying droplets with different lipids. Yet despite these achievements, one potential limitation of the technology is that DIBs formed from biologically relevant components have not been well studied. This could limit the reach of the platform to biological systems where bilayer composition and asymmetry are understood to play a key role. Herein, we address this issue by reporting the assembly of asymmetric DIBs designed to replicate the plasma membrane compositions of three different plant species; Arabidopsis thaliana, tobacco, and oats, by engineering vesicles with different amounts of plant phospholipids, sterols and cerebrosides for the first time. We show that vesicles made from our plant lipid formulations are stable and can be used to assemble asymmetric plant DIBs. We verify this using a bilayer permeation assay, from which we extract values for absolute effective bilayer permeation and bilayer stability. Our results confirm that stable DIBs can be assembled from our plant membrane mimics and could lead to new approaches for assembling model systems to study membrane translocation and to screen new agrochemicals in plants.
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