T. P. Tuyen Dao (a)(b)(c) , F. Fernandes (c,d) , E. Ibarboure (a)(b) , K. Ferji (a)(b) , M. Prieto (c) , O. Sandre (a)(b) and
J. F. Le Meins (a)(b)
Phase separation in hybridpolymer/lipid giant unillamelar vesicles (GHUVs) has been described over the last few years. However there is still a lack of understanding on the physical and molecular factors governing the phase separation in such systems. Among these parameters it has been suggested that in analogy to multicomponent lipidvesicles that hydrophobic mismatchs as well as lipid fludity play a role. In this work, we aim to map a global picture of phase separation and domain formation in membrane of GHUVs by using various copolymers based on poly(dimethylsiloxane) (PDMS) and poly(ethylene glycol) (PEO) with different architectures (grafted, triblock) and molar masses, combined with phospholipids at fluid (POPC) or gel state (DPPC) at room temperature. From confocal imaging and fluorescence lifetime imaging microscopy technique (FLIM), the phase separation into either micro- or nano- domains within GHVs were studied. In particular, our systematic studies demonstrate that in addition to lipid/polymer fraction or lipid physical state, important factors such as line tension at lipidpolymer/lipid boundaries can be finely modulated by the molar mass and architecture of the copolymer and lead to the formation of stable lipid domains with different sizes and morphologies in such GHUVs.
g: ILL Grenoble, DS LSS, CS20156, 71 Ave Martyrs, F-38042 Grenoble 9, France
h: Univ Bordeaux, CNRS, Ctr Rech Paul Pascal CRPP, UPR 8641, F-33600 Pessac, France
KEYWORDS: HybridPolymerLipid Unilamellar Vesicle, lipid nanodomains, membrane, polymersomes
ABSTRACT: Hybrid, i.e. intimately mixed polymer/phospholipid vesicles can potentially marry in a single membrane the best characteristics of the two separate components. The ability of amphiphilic copolymers and phospholipids to self- assemble into hybrid membranes has been studied until now at the sub-micron scale using optical microscopy on Giant Hybrid Unilamellar Vesicles (GHUVs), but limited information is available on Large Hybrid Unilamellar Vesicles (LHUVs). In this work, copolymers based on poly(dimethyl siloxane) and poly(ethylene oxide) with different molar mass- es and architectures (graft, triblock) were associated with 1,2-di-palmitoyl-sn-glycero-3-phosphocholine (DPPC). Classical protocols of LUV formation were used to obtain nano-sized self-assembled structures. Using Small Angle Neutron Scat- tering (SANS), Time Resolved Förster Resonance Energy Transfer (TR-FRET) and Cryo-Transmission Electron Microscopy (Cryo-TEM), we show that copolymer architecture and molar mass have a direct consequence on the formation of hybrid nanostructures that can range from worm-like hybrid micelles to hybridvesicles presenting small lipid nanodomains.
Interestingly, phase-separation inside these hy- brid/polymerlipidvesicles was previously observed (through stable micrometric lipid domains) for giant vesicles obtained from the same polymer/lipid composi- tion with lipid in a gel state 20 . However, with lipid in a fluid state for such composition, budding and fission phenomenon was observed after a few hours, leading to the formation of “pure” liposomes and polymersomes. There is no evidence of such a phenomenon in our exper- iments for LUVs. This suggests that membrane curvature could play a role also in the stabilization of nanodomains. A complete study in parallel on GUV, LUV and SUV vesi- cles, involving several block copolymers with different molar masses and a large compositional range is currently in progress to gain more insight into the parameters gov- erning the phase separation and the formation of nanodomains in hybridpolymer/lipidvesicles.
Author manuscript version of Chapter 27 published In book: The Giant Vesicle Book ,
Rumiana Dimova & Carlos Marques Eds. (CRC PRESS Taylor and Francis group, Oct. 7 th 2019)
7 necessary to obtain stable hybridvesicles with different membrane structural levels (homogenous distribution of the components, nano-domain or micro-domain formation) will be first summarized, followed by a description of the different preparation methods used to obtain hGUVs. It has to be noted that hybridvesicles reported over the last ten years were exclusively prepared by a one-step process by which a film composed of the desired amount of copolymer and phospholipid is hydrated. We will not describe previous approaches based on the modulation of lipid membrane properties by adsorption of amphiphilic polymers onto preformed giant liposomes. Although such a method leads in some cases to a reorganization of the lipid membrane and to the induction of polymer-rich domains – see for instance (Ladavière, Tribet et al. 2002; Tribet and Vial 2007), readers interested by these approaches will find relevant information in Chapter 25 that describes membrane-polymer interactions. Finally, an overview of what is known about membrane properties of hybridvesicles and especially hGUVs will be proposed. Tips and advices will be given in the two last sections about the preparation protocols of hGUVs and techniques used to characterize their membrane properties.
* Correspondence: email@example.com; Tel.: (33)556846194
Received: 17 October 2019; Accepted: 02 December 2019; Published: 4 December 2019
Abstract: In the emerging field of hybridpolymer/lipidvesicles, relatively few copolymers have
been evaluated regarding their ability to form these structures and the resulting membrane properties have been scarcely studied. Here, we present the synthesis and self-assembly in solution of poly(dimethylsiloxane)-block-poly(ethylene oxide) diblock copolymers (PDMS-b-PEO). A library of different PDMS-b-PEO diblock copolymers was synthesized using ring-opening polymerization of hexamethylcyclotrisiloxane (D3) and further coupling with PEO chains via click chemistry. Self- assembly of the copolymers in water was studied using Dynamic Light Scattering (DLS), Static Light Scattering (SLS), Small Angle Neutron Scattering (SANS), and Cryo-Transmission Electron Microscopy (Cryo-TEM). Giant polymersomes obtained by electroformation present high toughness compared to those obtained from triblock copolymer in previous studies, for similar membrane thickness. Interestingly, these copolymers can be associated to phospholipids to form Giant Hybrid Unilamellar Vesicles (GHUV); preliminary investigations of their mechanical properties show that tough hybridvesicles can be obtained.
to our knowledge the association of lipids and polymers has never been investigated so far to develop entirely asymmetric membranes.
We herein introduce a versatile method to produce asym- metric giant hybridpolymer–lipid unilamellar vesicles (aGHUV). In the present work, the vesicles are constituted of an inner leaflet of poly(butadiene)-b-poly(ethylene oxide) copoly mer and outer leaflet of lipid type via an emulsion-centrif- ugation method. We also show how we can prepare the reverse structures with the lipid leaflet facing the interior of the vesicle. We demonstrate the asymmetric character of the membrane and follow its stability by fluorescence quenching measurements. In addition, we further investigate lipid dynamic responses such as lateral and transverse diffusion (flip-flop). We thus provide an efficient method to afford aGHUV that exhibit close resem- blance to the architecture and membrane diffusion dynamics of biological cells. This system could serve as a tool and scaffold to better understand the importance of asymmetry and how it is maintained in biological systems.
In this study, we show how a cationic switchable lipid (CSL) impacts the membrane dynamics of a lipid or hybridlipid/polymer membrane in a pH-responsive manner. At a nanometer scale (LUV and LHUV), the incorporation of CSL resulted in decreased size and count rate, which was not observed for non-responsive vesicles. At a micrometer scale (GUV and GHUV), CSL incorporation resulted in pH-triggered membrane morphological changes and increased membrane permeability. This study gives additional insight to the biological behavior of CSL-based lipid nanoparticles previously reported  and open new perspectives in hybridlipid/polymer vesicle design . In future studies, it would be important to screen different polymers or lipid/polymer blends to investigate the possibility of domains formation, which could lead to a pH-responsive gate in synthetic vesicles. In this case, we need to further develop a fluorescent-tagged switchable lipid to address their distribution within lipid and hybrids polymer/lipid membranes. Moreover, anisotropic NMR could unveil whether the tweezer-like structure arisen from pH-triggered conformational change are responsible for a bilayer incompatible polymorphism .
which we interpret as a quite fluid-like behavior of the polymeric GUV membrane, which starts
“flowing” within the trap. This is consistent with the fact that the polymer is well above its glass
transition temperature, leading to mobile chains within the polymersome. On the contrary, pure
lipid DPPC GUVs deform in a transverse way while the flow intensity is increased (Figure 5c,
C hapt er 4. P reparat ion of giant hybridpolymer/ lipidvesicles 103
The electroformed vesicles are difficult to detach from the plate, this can be a consequence of electrostatic interactions between the charged copolymer and the conductive glass slide (this effect was also noticed in mixed vesicles PEO:PBD where the detachment was favoured with the addition of PBD:PEO- COOH 104 ). The selected experimental conditions made demanding the further
work will be reported separately. 62
In this paper we have presented a detailed characterization of thiophene terminated Si(111) surfaces and photoelectro- chemical growth of polythiophene on these surfaces. The process outlined here leads to the formation of robust conducting polymer/silicon junctions in which the polymer is covalently linked to the silicon substrate through an alkyl spacer. The resulting doped polythiophene/decyl/Si(111) structures exhibit properties similar to other more conventional MIS diodes. These results suggest that this approach is promising for constructing hybrid molecular/silicon devices. The use of conducting polymer as a top contact for these devices should avoid problems due to metal penetration and/or damage to the organic layer associated with the evaporation of metal contacts. Furthermore, covalent bonding of the top contact to the device has potential advantages in terms of stability and lowering contact resistances.
4 3. Results and Discussion
3.1 Orbital motion of Janus active colloids around isolated giant vesicles
For diluted enough particle and vesicle concentrations, we were able to observe the interaction between single active Janus colloids and single GUVs. The colloids are sedimented on the substrate, along which both passive and self-propelled motion occur. GUVs are also sedimented on the substrate without any strong adhesion between the solid wall and the membrane. A 2% H 2 O 2 aqueous solution was always used to trigger the self-propulsion of the silica-platinum Janus colloids. 28,29 In most of our experiments, whenever the trajectory of the active particle reached the vesicle boundary, the active particle initiated a striking orbital motion around the GUV. Figure. 1A shows a typical trajectory of an active colloid orbiting around a GUV observed (see Supporting Information, Video S1). For this particular example the GUV has a larger but comparable size to the active particle of radius R P ≈ 2 µm. For times t < 1 s, the GUV is still not perturbed by the active particle. For 1 < t < 2 s, the silica face of the Janus particle pushes on the GUV membrane, which starts to translate a distance L with approximately constant speed
flushed with 18.2 MΩ cm -1 water (Milli-Q; Millipore) between samples, and visually examined
to ensure that no particles were carried over between samples. All data files for a given experiment were processed using identical settings (typical setting range: camera shutter 30- 45ms; camera gain 300-400; detection threshold 5-7; auto blur). The vesicle concentration in the sample was defined based on the measurement of total particles between 50 - 250 nm diameter. Vesicle concentrations from field samples were estimated based on the total number of particles in the most vesicle-enriched gradient fraction (as assessed visually by electron microscopy), normalized to the total amount of water originally concentrated for that sample. Thin filamentous features of these fractions, visible by electron microscopy, were below the detection limit of the NanoSight. We note that our field concentration measurements represent minimum estimates, as we do not consider vesicles present in other gradient fractions besides the maximal one. This approach was intentionally conservative and designed to minimize the potential impact of counting any non-vesicle particles in the enriched field samples.
In this paper, LPG planar waveguides have been designed and fabricated using a hybrid structure consisting of silica and polymer layers. A silica layer not only provides a low-loss and high-quality lower cladding, but also allows a corrugated periodic struc- ture to be formed with precise dimensions via photo- lithography and reactive ion etching. The corrugated patterns ensure that the period structure has good stability in tough environments, such as exposure to higher temperature, humidity, and organic solvents. A new polymer material based on a highly fluori- nated poly(arylether ketone) was selected to fabri- cate the waveguides and the upper cladding layer. The refractive index of this type of polymer can be adjusted during synthesis and it shows excellent thermal stability. It also has low optical absorption in the communication wavelength range than other optical polymers due to its high content of fluorine, and also has exhibited good photosensitivity to UV light. The latter property can be exploited to fabri- cate waveguide or grating structures by a simple and mature photolithography process. Several differ- ent photonic devices, including arrayed waveguide gratings [ 24 ] and Mach–Zehnder interferometers [ 25 ], have been demonstrated in our laboratory pre- viously using this kind of polymer. The hybrid struc-
The proposed hybrid NDT approach makes it possible to accurately characterize the mechanical damage of composite materials. Its bene- fit is a more efficient interpretation of the damage characteristics and their cross-validation in order to increase the reliability of the moni- toring strategy, based on an original definition of damage indicators that provides a quantitative evaluation of the material’s damage state.
Figure 2. Mechanisms involved in the modulation of Angiogenesis by MSC-derived extracellular vesicles (EVs). In response to hypoxia,
mesenchymal stem/stromal cells release EVs containing active pSTAT3 and nuclear factor (NF)-κB pathway–associated proteins, which are transferred to recipient endothelial cell (EC) and promote the transcription of proangiogenic proteins. EVs contain and transfer several growth factors to EC (PDGF, FGF, EGF, VEGF, SCF, and c-kit). Wnt is present in the EVs and through interaction with its receptor, promotes the transcription of several molecules involved in angiogenesis. EVs stimulate vessel formation through the transfer of various micro-RNA. Among them, miR-31 acts by suppressing the factor inhibiting HIF-1α, and miR-125 promotes tip cell specification by suppressing Delta-like 4 (Dll4). ? indicates that the exact mechanisms of their transfer and the underlying signaling pathways are not completely described; EGF, epidermal growth factor; FGF, fibroblast growth factor; FIH, factor inhibiting HIF-1α; HIF, hypoxia inducible factor; PCNA, proliferating cell nuclear antigen; PDGF, platelet-derived growth factor; SCF, stem cell factor; and VEGF, vascular endothelial growth factor.
In the first section, we introduce the principles of sensors based on a single interferometric structure consisting of one MR or one MZ. The fundamental characteristics and the measurement method based on wavelength shift linked to these kinds of sensors are introduced as well. We then discuss the interest of the two proposed structures, which are based on the Vernier effect, for overcoming the limitations of sensors based on only one MR or one MZ. In a second section, we consider the appropriate choice of materials for these complex structures. This choice include for example, a porous material such as PSi, which is sensitive to refractive index variation induced by analytes grafting on its internal surface for the core of the sensing device; while a material such as a polymer, which leads to low waveguide propagation losses, can be used for the access waveguides and for the reference part of the sensing device. In the last section, we compare two different complex structures to select the best one for sensor applications and finally we point out the interest of the hybrid Vernier effect sensor.
I.2 From Hydrophobic to Hydrophilic: Coating of UCNP with Polymer Materials
In general, UCNP are synthesized by a thermolysis approach, which produces UCNP with high crystallinity, high UCL efficiency and low polydispersity. Unfortunately, the as-synthesized UCNP can only be dispersed in non-polar organic solvents (e.g., cyclohexane) due to their surface hydrophobic ligands, like oleic acid (OA) and oleylamine (OM). These organic ligands significantly restrict UCNP applications. So, it is necessary to modify their surface for preparing novel functional materials. For instance, decoration of UCNP can improve their dispersity and compatibility in composites (20, 30), which is favorable for fabricating materials with high transparency (31). Moreover, particularly in the biomaterials fields, adjusting the surface of UCNP from hydrophobic to hydrophilic is required because of the aqueous environment in biological tissues. Besides the modified UCNP should also be biocompatible, biodegradable and multi-functional (protein conjunction, drug loading and release) in some cases to meet various needs. Undoubtedly, surface coating of UCNP is the first step to explore their further usage. Several comprehensive reviews related to this topic have been published in the past few years (32-34).
adjust to their loss of surface area ( 28% between the L fluid and the P 0 rippled phases [ 14 ]) by adding a controlled sucrose solution in the external solution. Gel- phase GUVs obtained with this protocol were spherical and presented no observable defects in the membrane. Finally, GUVs sedimented in an iso-osmolar glucose solution were kept at 15 C and osmotically deflated by adding con- trolled amounts of glucose solution of suitable concentra- tion in the external solution. GUVs were observed by phase contrast microscopy. The obtained shapes displayed in Fig. 1 line (a) show obvious differences with the classical shapes observed on vesicles in the fluid state [ 15 ]. Subjected to the osmotic shock, gel-phase GUVs shrink and develop a large variety of morphologies, from stoma- tocytes to concave polyhedra (i.e., sphere paved with de- pressions). The final faceted state is reached around 40 min after the beginning of the deflation (the whole process is limited by diffusion of glucose molecules in the surround- ing medium), and, thereafter, no shape modification is observed over several hours, when temperature and osmo- larity are kept constant.
Observation. Aliquots of the giant unilamellar vesicles suspen- sion are incubated with 1% v兾v of 560 M Di 10 ASP-PS in ethanol
for half an hour in order to insert the dye at 4 mol% into the DOPC bilayers. Then they are diluted and in some cases settled in two volumes of equiosmolar solution. The samples are ob- served in a closed chamber (two glass slides spaced by 200 m and sealed with hot paraffin) to avoid streams caused by evaporation. A conventional upright fluorescence microscope with an immer- sion objective [⫻100兾1.25 oil Zeiss Achroplan or ⫻63兾0.90 water Olympus (New Hyde Park, NY) LUMPlanF1] and a motorized focus is used. Excitation in epiillumination is provided by a 200-W mercury lamp through a 455-490-nm band pass filter, and the fluorescence (peak at 580 nm) is detected with a standard