Droplet Interface Bilayers Research Articles

Challenges and opportunities in achieving the full potential of droplet interface bilayers

Model membranes can be used to elucidate the intricacies of the chemical processes that occur in cell membranes, but the perfectly biomimetic, yet bespoke, model membrane has yet to be built. Droplet interface bilayers are a new type of model membrane able to mimic some features of real cell membranes better than traditional models, such as liposomes and black lipid membranes. In this Perspective, we discuss recent work in the field that is starting to showcase the potential of these model membranes to enable the quantification of membrane processes, such as the behaviour of protein transporters and the prediction of in vivo drug movement, and their use as scaffolds for electrophysiological measurements. We also highlight the challenges that remain to enable droplet interface bilayers to achieve their full potential as artificial cells, and as biological analytical platforms to quantify molecular transport.

Using Dynamic Impedance Spectroscopy to Deconvolute Memory Elements in Droplet Interface Bilayers

The underlying principles for generating and storing memory in living organisms differ significantly from traditional hard-matter-based circuits. Bio-inspired membranes are ideal platforms for exploring biomimetic neuromorphic equivalents as they offer novel forms of tunable plasticity and diverse mechanisms to control functionality. Droplet interface bilayers (DIBs) are inherently nanostructures that show electrical properties that are extremely sensitive to nano-scale perturbation. We will demonstrate how dynamic electrochemical impedance spectroscopy (dEIS) can follow molecular-level restructuring in DIBs that lead to hysteretic loops and mem-behaviors in lipid bilayers in response to electrical biasing. We deconvoluted the DIB system’s memristance and memcapacitance by measuring the time-dependent complex impedance to show that if the bilayer’s structure (thickness or area) changes, these quantities contain the same information; however, if a phase transition occurs, then these responses have additional information. Figure 1, demonstrates both the DIBs platform two major modes of voltage-inducing physical change that can occur in bilayers. Through correlation analysis of the capacitance/resistance, we show that memory processes caused by lipid bilayer expansion, or contraction, do not affect the observed electrical charge/discharge time constant. However, phase transitions resulting in new solvation or lipid structures affect the extracted electrical time constant. In short, dEIS coupled with time-constant analysis provides a means for extracting individual memory elements from a simple two-terminal device, thereby multiplexing the function and potential computational throughput. Figure 1

Investigating the effect of phospholipids on droplet formation and surface property evolution in microfluidic devices for droplet interface bilayer (DIB) formation.

Despite growing interest in droplet microfluidic methods for droplet interface bilayer (DIB) formation, there is a dearth of information regarding how phospholipids impact device function. Limited characterization has been carried out for phospholipids, either computationally (in silico) or experimentally (in situ) in polydimethylsiloxane (PDMS) microfluidic devices, despite recent work providing a better understanding of how other surfactants behave in microfluidic systems. Hence, microfluidic device design for DIB applications relies heavily on trial and error, with many assumptions made about the impact of phospholipids on droplet formation and surface properties. Here, we examine the effects of phospholipids on interfacial tension, droplet formation, wetting, and hence device longevity, using DPhPC as the most widely used lipid for DIB formation. We use a customized COMSOL in silico model in comparison with in situ experimental data to establish that the stabilization of droplet formation seen when the lipid is dosed in the aqueous phase (lipid-in) or in the oil phase (lipid-out) is directly dependent on the effects of lipids on the device surface properties, rather than on how fast they coat the droplet. Furthermore, we establish a means to visually characterize surface property evolution in the presence of lipids and explore rates of device failure in the absence of lipid, lipid-out, and lipid-in. This first exploration of the effects of lipids on device function may serve to inform the design of microfluidic devices for DIB formation as well as to troubleshoot causes of device failure during microfluidic DIB experiments.

Trans-Resveratrol Decreases Membrane Water Permeability: A Study of Cholesterol-Dependent Interactions.

Resveratrol (RSV), a biologically active plant phenol, has been extensively investigated for cancer prevention and treatment due to its ability to regulate intracellular targets and signaling pathways which affect cell growth and metastasis. The non-specific interactions between RSV and cell membranes can modulate physical properties of membranes, which in turn can affect the conformation of proteins and perturb membrane-hosted biological functions. This study examines non-specific interactions of RSV with model membranes having varying concentrations of cholesterol (Chol), mimicking normal and cancerous cells. The perturbation of the model membrane by RSV is sensed by changes in water permeability parameters, using Droplet Interface Bilayer (DIB) models, thermotropic properties from Differential Scanning Calorimetry, and structural properties from confocal Raman spectroscopy, all of which are techniques not complicated by the use of probes which may themselves perturb the membrane. The nature and extent of interactions greatly depend on the presence and absence of Chol as well as the concentration of RSV. Our results indicate that the presence of RSV decreases water permeability of lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), indicating a capability for RSV in stiffening fluidic membranes. When Chol is present, however, (at 4:1 and 2:1mol ratio DOPC to cholesterol), the addition of RSV has no significant effect upon the water permeability. DSC thermograms show that RSV interacts with DOPC and DOPC/Chol bilayers and influences their thermotropic phase behavior in a concentration-dependent manner, by decreasing the main phase transition temperature and enthalpy, with a phase separation shown at the higher concentrations of RSV. Raman spectroscopic studies indicate an ordering effect of RSV on DOPC supported bilayer, with a lesser extent of ordering in the presence of Chol. Combined results from these investigations highlight a differential effect of RSV on Chol-free and Chol-enriched membranes, respectively, which results constitute a bellwether for increased understanding and effective use of resveratrol in disease therapy including cancer.

Homogeneous hybrid droplet interface bilayers assembled from binary mixtures of DPhPC phospholipids and PB-b-PEO diblock copolymers

Hybrid membranes built from phospholipids and amphiphilic block copolymers seek to capitalize on the benefits of both constituents for constructing biomimetic interfaces with improved performance. However, hybrid membranes have not been formed or studied using the droplet interface bilayer (DIB) method, an approach that offers advantages for revealing nanoscale changes in membrane structure and mechanics and offers a path toward assembling higher-order tissues. We report on hybrid droplet interface bilayers (hDIBs) formed in hexadecane from binary mixtures of synthetic diphytanoyl phosphatidylcholine (DPhPC) lipids and low molecular weight 1,2 polybutadiene-b-polyethylene oxide (PBPEO) amphiphilic block copolymers and use electrophysiology measurements and imaging to assess the effects of PBPEO in the membrane. This work reveals that hDIBs containing up to 15 mol% PBPEO plus DPhPC are homogeneously mixtures of lipids and polymers, remain highly resistive to ion transport, and are stable—including under applied voltage. Moreover, they exhibit hydrophobic thicknesses similar to DPhPC-only bilayers, but also have significantly lower values of membrane tension. These characteristics coincide with reduced energy of adhesion between droplets and the formation of alamethicin ion channels at significantly lower threshold voltages, demonstrating that even moderate amounts of amphiphilic block copolymers in a lipid bilayer provide a route for tuning the physical properties of a biomimetic membrane.

Influence of salt on the formation and separation of droplet interface bilayers

Phospholipid bilayers are a major component of the cell membrane that is in contact with physiological electrolyte solutions including salt ions. The effect of salt on the phospholipid bilayer mechanics is an active research area due to its implications for cellular function and viability. In this manuscript, we utilize droplet interface bilayers (DIBs), a bilayer formed artificially between two aqueous droplets, to unravel the bilayer formation and separation mechanics with a combination of experiments and numerical modeling under the effects of K+, Na+, Li+, Ca2+, and Mg2+. Initially, we measured the interfacial tension and the interfacial complex viscosity of lipid monolayers at a flat oil–aqueous interface and show that both properties are sensitive to salt concentration, ion size, and valency. Subsequently, we measured DIB formation rates and show that the characteristic bilayer formation velocity scales with the ratio of the interfacial tension to the interfacial viscosity. Next, we subjected the system to a step strain by separating the drops in a stepwise manner. By tracking the evolution of the bilayer contact angle and radius, we show that salt influences the bilayer separation mechanics, including the decay of the contact angle, the decay of the bilayer radius, and the corresponding relaxation time. Finally, we explain the salt effect on the observed bilayer separation by means of a mathematical model comprising the Young–Laplace and evolution equations.

PD36-08 BLOOD TESTIS BARRIER-MIMETIC DROPLET INTERFACE BILAYERS (DIBS) FOR PASSIVE PERMEABILITY PREDICTION

You have accessJournal of UrologyCME1 May 2022PD36-08 BLOOD TESTIS BARRIER-MIMETIC DROPLET INTERFACE BILAYERS (DIBS) FOR PASSIVE PERMEABILITY PREDICTION Jaime Korner, Meghan Robinson, Katherine Elvira, Ryan Flannigan, and Stephanie Willerth Jaime KornerJaime Korner More articles by this author , Meghan RobinsonMeghan Robinson More articles by this author , Katherine ElviraKatherine Elvira More articles by this author , Ryan FlanniganRyan Flannigan More articles by this author , and Stephanie WillerthStephanie Willerth More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002594.08AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The blood testis barrier (BTB) serves as a “gatekeeper” for the apical compartment of the seminiferous epithelium where spermatogenesis takes place. Tight junctions between adjacent Sertoli cells create the BTB, regulate transport of molecules, and protect the luminal compartment from toxins and pathogens. Investigating the impact of toxins and drugs, and the regulation of human spermatogenesis requires realistic in vitro models. The purpose of this study was to develop an artificial cellular membrane to mimic the BTB using droplet interface bilayers (DIBs) derived from human Sertoli cell lipid extracts. METHODS: Human Sertoli cells were collected from a dissociated human testicular biopsy using magnetic activated sorting for Follicle-Stimulating Hormone Receptor (FSHR). Sertoli cells were expanded in vitro and lipids were extracted using a Lipid Extraction Kit (Cell Biolabs). Permeability experiments were conducted using a poly(dimethylsiloxane) (PDMS) microfluidic device which allows for the controlled formation of pairs of differing droplet compartments connected by a phospholipid bilayer. A solution of Sertoli lipids in squalene (10 mg/mL) was used as the outer phase. Donor droplets contained fluorophore (100 µM in buffer) and acceptor droplets contained only buffer (both pH 7.4). The DIB-connected droplet pairs were formed at 50 °C and the temperature was decreased to 37 °C for observation. RESULTS: These results represent the first DIBs to be made using human lipid extracts and the first use of DIBs to model permeability of the BTB. We found that the BTB-mimetic DIBs were impermeable to both fluorophores tested: fluorescein and calcein. Calcein is normally membrane-impermeable and serves as a control experiment to confirm the presence of an intact phospholipid bilayer. Fluorescein has been observed to permeate DIBs made using single, synthetic lipids and intestine-mimetic DIBs but not most blood-brain barrier-mimetic DIBs. CONCLUSIONS: DIBs can be made from human Sertoli cell lipid extracts and show great potential to more accurately model BTB permeability. Source of Funding: Collaborative Healthy Grant © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e635 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Jaime Korner More articles by this author Meghan Robinson More articles by this author Katherine Elvira More articles by this author Ryan Flannigan More articles by this author Stephanie Willerth More articles by this author Expand All Advertisement PDF DownloadLoading ...

Impact of Cyclization and Methylation on Peptide Penetration through Droplet Interface Bilayers.

Cell-penetrating peptides enter cells via diverse mechanisms, such as endocytosis, active transport, or direct translocation. For the design of orally delivered cell-penetrating peptides, it is crucial to know the contribution of these different mechanisms. In particular, the ability of a peptide to translocate through a lipid bilayer remains a key parameter for the delivery of cargos. However, existing approaches used to assess translocation often provide discrepant results probably because they have different sensitivities to the distinct translocation mechanisms. Here, we focus on the passive permeation of a range of hydrophobic cyclic peptides inspired by somatostatin, a somatotropin release-inhibiting factor. Using droplet interface bilayers (DIB), we assess the passive membrane permeability of these peptides and study the impact of the peptide cyclization and backbone methylation on translocation rates. Cyclization systematically improved the permeability of the tested peptides while methylation did not. By studying the interaction of the peptides with the DIB interfaces, we found membrane insertion and peptide intrinsic diffusion to be two independent factors of permeability. Compared to the industrial gold standard Caco-2 and parallel artificial membrane permeability assay (PAMPA) models, DIBs provide intermediate membrane permeability values, closer to Caco-2. Even for conditions where Caco-2 and PAMPA are discrepant, the DIB approach also gives results closer to Caco-2. Thereupon, DIBs represent a robust alternative to the PAMPA approach for predicting the permeability of peptides, even if the latter present extremely small structural differences.

Disentangling Memristive and Memcapacitive Effects in Droplet Interface Bilayers Using Dynamic Impedance Spectroscopy

AbstractThe underlying principles for generating intelligent behavior in living organisms are fundamentally different from those in traditional solid‐state circuits. Biomimetic neuromorphic equivalents based on biological membranes offer novel implementation of tunable plasticity and diverse mechanisms to control functionality. Here, dynamic electrochemical impedance spectroscopy (dEIS) to probe diphytanoylphosphatidylcholine (DPhPC) droplet interface bilayers (DIBs) to better understand the differences in molecular level structure/dynamics that give rise to hysteretic loops and neuromorphic, memelement behaviors in lipid bilayers in response to electrical biasing is used. Importantly, this system does not have ion‐conducting channels and is, therefore, not expected to show memristive behavior. Surprisingly, both memristive and memcapacitive behaviors by measuring the time‐dependent complex impedance of DPhPC DIBs are detected. It is shown that nonlinear memristance can originate from structural changes in the bilayer, affecting its dielectric properties. This novel dEIS application allows for the simultaneous analysis of the system's changing memristive and memcapacitive properties, which originate from different molecular restructuring processes. Moreover, and importantly, access to this type of information increases the number of neuromorphic processes supported simultaneously in a single two‐terminal device.

Differential Interaction of Cannabidiol with Biomembranes Dependent on Cholesterol Concentration.

Cannabidiol (CBD), the major nonpsychoactive component of plant-derived cannabinoids, has been reported to have a broad range of potential beneficial pharmacological effects on the central nervous system (CNS). In this study, the droplet interface bilayer, a model cell membrane, is used to examine the effects of CBD on passive water permeability, a fundamental membrane biophysical property. The presence of CBD decreases the water permeability of model lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and at low concentrations of cholesterol (Chol) (20 mol %) in DOPC, whereas when higher concentrations of Chol are present (33 mol %), CBD has an opposing effect, increasing water permeability. The diametric effect in water permeability change upon addition of CBD to Chol-low and Chol-high bilayers signifies a variant interaction of CBD, depending on the initial state of bilayer packing and fluidity. Additionally, differential scanning calorimetry studies provide evidence that there are selective changes in thermotropic behavior for CBD with DOPC and with DOPC/Chol membranes, respectively, supportive of these varying membrane interactions of CBD dependent upon cholesterol. The intriguing ability of CBD to sensitively respond to membrane Chol concentrations in modifying physical properties highlights the significant impact that CBD can have on heterogeneous biomembranes including those of the CNS, the neurons of which are enriched in Chol to a point where up to a quarter of the body's total Chol is in the brain, and defective brain Chol homeostasis is implicated in neurodegenerative diseases.

Reconstruction of the Gram-Negative Bacterial Outer-Membrane Bilayer.

The outer membrane (OM) of gram-negative bacteria is highly asymmetric. The outer leaflet comprises lipopolysaccharides (LPS) and the inner leaflet phospholipids. Here, it is shown that the outer membrane lipid bilayer (OMLB) of Escherichia coli can be reconstructed as a droplet interface bilayer (DIB), which separates two aqueous droplets in oil. The trimeric porin OmpF is inserted into the model OMLB and the translocation of the bacteriocin colicin E9 (colE9) through it is monitored. By contrast with LPS-free bilayers, it is found that colE9 made multiple failed attempts to engage with OmpF in an OMLB before successful translocation occurred. In addition, the observed rate for the second step of colE9 translocation is 3-times smaller than that in LPS-free bilayers, and further, the colE9 dissociates when the membrane potential is reversed. The findings demonstrate the utility of the DIB approach for constructing model OMLBs from physiologically realistic lipids and that the properties of the model OMLBs differ from those of a simple lipid bilayer. The model OMLB offers a credible platform for screening the properties of antibiotics.

Enhancing membrane-based soft materials with magnetic reconfiguration events

Adaptive and bioinspired droplet-based materials are built using the droplet interface bilayer (DIB) technique, assembling networks of lipid membranes through adhered microdroplets. The properties of these lipid membranes are linked to the properties of the droplets forming the interface. Consequently, rearranging the relative positions of the droplets within the network will also alter the properties of the lipid membranes formed between them, modifying the transmembrane exchanges between neighboring compartments. In this work, we achieved this through the use of magnetic fluids or ferrofluids selectively dispersed within the droplet-phase of DIB structures. First, the ferrofluid DIB properties are optimized for reconfiguration using a coupled experimental-computational approach, exploring the ideal parameters for droplet manipulation through magnetic fields. Next, these findings are applied towards larger, magnetically-heterogeneous collections of DIBs to investigate magnetically-driven reconfiguration events. Activating electromagnets bordering the DIB networks generates rearrangement events by separating and reforming the interfacial membranes bordering the dispersed magnetic compartments. These findings enable the production of dynamic droplet networks capable of modifying their underlying membranous architecture through magnetic forces.

Heavy water influences memcapacitive behavior of droplet interface bilayers

Memory resistors (memristors) and capacitors (memcapacitors) are circuit elements whose behavior depends on their prior history and are the result of different combinations of nonlinear electric responses. Currently, only a few systems have been shown to exhibit memcapacitive behavior. One of them is the droplet interface bilayer (DIB), developed to study membrane and membrane protein properties in a planar lipid bilayer system. DIBs are formed by suspending two aqueous lipid droplets attached to Ag/AgCl electrodes in an alkane oil reservoir with a lipid monolayer forming at the water-oil interface, where the lipid headgroups interact with water and the acyl chains with the oil phase.

Studying the Mechanics of Membrane Permeabilization through Mechanoelectricity.

In this research, real-time monitoring of lipid membrane disruption is made possible by exploiting the dynamic properties of model lipid bilayers formed at oil-water interfaces. This involves tracking an electrical signal generated through rhythmic membrane perturbation translated into the adsorption and penetration of charged species within the membrane. Importantly, this allows for the detection of membrane surface interactions that occur prior to pore formation that may be otherwise undetected. The requisite dynamic membranes for this approach are made possible through the droplet interface bilayer (DIB) technique. Membranes are formed at the interface of lipid monolayer-coated aqueous droplets submerged in oil. We present how cyclically alternating the membrane area leads to the generation of mechanoelectric current. This current is negligible without a transmembrane voltage until a composition mismatch between the membrane monolayers is produced, such as a one-sided accumulation of disruptive agents. The generated mechanoelectric current is then eliminated when an applied electric field compensates for this asymmetry, enabling measurement of the transmembrane potential offset. Tracking the compensating voltage with respect to time then reveals the gradual accumulation of disruptive agents prior to membrane permeabilization. The innovation of this work is emphasized in its ability to continuously track membrane surface activity, highlighting the initial interaction steps of membrane disruption. In this paper, we begin by validating our proposed approach against measurements taken for fixed composition membranes using standard electrophysiological techniques. Next, we investigate surfactant adsorption, including hexadecyltrimethylammonium bromide (CTAB, cationic) and sodium decyl sulfate (SDS, anionic), demonstrating the ability to track adsorption prior to disruption. Finally, we investigate the penetration of lipid membranes by melittin, confirming that the peptide insertion and disruption mechanics are, in part, modulated by membrane composition.

Cell-Free Synthesis Strategies to Probe Co-translational Folding of Proteins Within Lipid Membranes.

In order to comprehend the molecular basis of transmembrane protein biogenesis, methods are required that are capable of investigating the co-translational folding of these hydrophobic proteins. Equally, in artificial cell studies, controllable methods are desirable for in situ synthesis of membrane proteins that then direct reactions in the synthetic cell membrane. Here we describe a method that exploits cell-free expression systems and tunable membrane mimetics to facilitate co-translational studies. Alteration of the lipid bilayer composition improves the efficiency of the folding system. The approach also enables membrane transport proteins to be made and inserted into artificial cell platforms such as dropletinterface bilayers. Importantly, this gives a new facet to the droplet networks by enabling specific transport of molecules across the synthetic bilayer against a concentration gradient. This method also includes a protocol to pause and restart translation of membrane proteins at specified positions during their co-translational folding. This stop-start strategy provides an avenue to investigate whether the proteins fold in sequence order, or if the correct fold of N-terminal regions is reliant on the synthesis of downstream residues.

UV-DIB: label-free permeability determination using droplet interface bilayers.

Simple diffusion of molecular entities through a phospholipid bilayer, is a phenomenon of great importance to the pharmaceutical and agricultural industries. Current model lipid systems to probe this typically only employ fluorescence as a readout, thus limiting the range of assessable chemical matter that can be studied. We report a new technology platform, the UV-DIB, which facilitates label free measurement of small molecule translocation rates. This is based upon the coupling of droplet interface bilayer technology with implemented fiber optics to facilitate analysis via ultraviolet spectroscopy, in custom designed PMMA wells. To improve on current DIB technology, the platform was designed to be reusable, with a high sampling rate and a limit of UV detection in the low μM regime. We demonstrate the use of our system to quantify passive diffusion in a reproducible and rapid manner where the system was validated by investigating multiple permeants of varying physicochemical properties across a range of lipid interfaces, each demonstrating differing kinetics. Our system permits the interrogation of structural dependence on the permeation rate of a given compound. We present this ability from two structural perspectives, that of the membrane, and the permeant. We observed a reduction in permeability between pure DOPC and DPhPC interfaces, concurring with literature and demonstrating our ability to study the effects of lipid composition on permeability. In relation to the effects of permeant structure, our device facilitated the rank ordering of various compounds from the xanthine class of compounds, where the structure of each permeant differed by a single group alteration. We found that DIBs were stable up to 5% DMSO, a molecule often used to aid solubilisation of pharmaceutical and agrochemical compounds. The ability of our device to rank-order compounds with such minor structural differences provides a level of precision that is rarely seen in current, industrially applied technologies.

Layer-by-layer assembly of multi-layered droplet interface bilayers (multi-DIBs).

Droplet interface bilayers (DIBs) have tremendous promise as platforms for fundamental biomembrane studies and in biotechnology. Being composed of a single bilayer however limits their biomimetic potential, as many cell membrane motifs are composed of multiple aligned bilayers. We describe a technology to manufacture cell-sized multi-layered DIBs (multi-DIBs) by coating giant unilamellar vesicles with a further monolayer, and allowing such structures to make contact with themselves or a monolayer coated droplet. This easily customisable strategy will pave the way for an expanded repertoire of DIB functionality, for example by facilitating the incorporation of multiple-bilayer spanning protein complexes.

Encapsulated droplet interface bilayers as a platform for high-throughput membrane studies.

Whilst it is highly desirable to produce artificial lipid bilayer arrays allowing for systematic high-content screening of membrane conditions, it remains a challenge due to the combined requirements of scaled membrane production, simple measurement access, and independent control over individual bilayer experimental conditions. Here, droplet bilayers encapsulated within a hydrogel shell are output individually into multi-well plates for simple, arrayed quantitative measurements. The afforded experimental throughput is used to conduct a 2D concentration screen characterising the synergistic pore-forming peptides Magainin2 and PGLa. Maximal enhanced activity is revealed at equimolar peptide concentrations via a membrane dye leakage assay, a finding consistent with models proposed from NMR data. The versatility of the platform is demonstrated by performing in situ electrophysiology, revealing low conductance pore activity (∼15 to 20 pA with 4.5 pA sub-states). In conclusion, this array platform addresses the aforementioned challenges and provides new and flexible opportunities for high-throughput membrane studies. Furthermore, the ability to engineer droplet networks within each construct paves the way for “lab-in-a-capsule” approaches accommodating multiple assays per construct and allowing for communicative reaction pathways.

Drop coalescence during condensation on viscous slippery and viscoelastic coatings

Coatings of viscous oil or viscoelastic polymer on a rigid surface transform the condensation phenomena differently. When the viscous oil is infused on low-energy rigid surfaces, the surface shows excellent water repellent behavior. On the other hand, the viscoelastic material coating exhibits a high affinity with water drop resulting in more contact angle hysteresis (CAH). We focused on the drop coalescence phenomena during condensation on viscous slippery and viscoelastic coated metallic samples in this work. We have observed that the drop coalescence on lubricant infused surfaces (LIS) significantly depends on the viscosity of the lubricant and the stability of droplet interface bilayers between the drops. The lifetime of the non-coalescence event of the droplets during condensation on high viscous liquid infused surfaces (50 cst and 500 cst) surfaces was found to be in 1–3 orders of magnitude longer compared to low viscous liquid infused surface (5 cst). Coalescence induced motion during condensation was significantly observed in high viscous liquid infused surfaces (50 cst and 500 cst) compared to low viscous lubricant infused surface (5 cst). On soft viscoelastic coating, drop coalescence during condensation event undergoes through merging of the droplets followed by relaxation of the coalesced drop by the capillary induced movement of the contact line. Key findings of this work would be helpful to comprehend the drop coalescence phenomena on viscous slippery and viscoelastic coatings in a detailed manner.

Challenges and Methods for the Study of CPP Translocation Mechanisms.

Fluorescence-based methods are widely used to detect crossing of peptides across model or biological membranes. For membrane-active peptides, i.e., peptides that have strong membrane tropism, fluorescence experiments must be accompanied by relevant controls, otherwise they can lead to inconsistent interpretation and underestimation of their limitations. Here we describe how to prepare samples to study fluorescent peptide crossing droplet interface bilayer (model membrane) or cell membrane (biological membrane) and the pitfalls that can affect observational qualitative and quantitative data.