pH-dependent lipid vesicle interactions with plasma polymerized thin films (original) (raw)
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Recent and Expected Roles of Plasma-Polymerized Films for Biomedical Applications
Chemical Vapor Deposition, 2007
This review aims to provide a summary of some of the challenges in correlating surface science and biology, with particular emphasis on areas where plasma polymerization has and will play an important role as a method to synthesize reproducible and well-defined surfaces. Since the range of possible applications of plasma polymer films in biomaterial applications is immense, this paper will focus on processes to develop various surface morphologies and chemical structures for the immobilization of proteins and cells. Functional, plasma-polymerized films are discussed as biosensitive interfaces that may ultimately be part of a multilayer system that aims at connecting inorganic/metallic transducers with biologically reactive surfaces. These topics will be reviewed with some experimental results taken from the authors' own work. Specific aspects such as adhesion improvement and solvent effects are also discussed.
Journal of Colloid and Interface Science, 2000
The adhesion of lipid vesicles (liposomes) having controlled chemical and physical structure to polymer supported human serum albumin (HSA) thin layers was investigated by a spectrofluorimetric technique. The vesicle lipid bilayer was labeled with a small amount of an apolar fluorescent probe (diphenylexathriene) and the vesicle suspension was set in contact with the protein film. After washing and drying, the adhering vesicles containing sample was dissolved in chloroform and the homogeneous solution was analyzed by standard spectrofluorimetric techniques. Different parameters of the lipid bilayer, suspending solution, and protein film were varied and their influence on the liposome binding was investigated. Concerning the lipid bilayer, we studied the effect of liposome surface charge by using different mixtures of neutral (dipalmitoyl-phosphatidylcholine) and charged dipalmitoylphosphatidic acid) phospholipids and the fluid or gel nature of the lipid bilayer (switched on and off by temperature variation). Variations of the local environment involve Ca 2+ and H + changes in the millimolar range as well as different hydrodynamical flows (in the range 0.1-10 cm/s). Preliminary measurements using different protein layers were also performed. Results show: (a) negligible adhesion without the protein layer, (b) the presence of a maximum for the liposome adhesion vs ion concentration (depending on the liposome composition and kind of the adsorbed ions), (c) a much stronger adhesion for vesicles in the fluid phase (overcoming the entropy-driven desorption increase with temperature), and (d) a dramatic lowering of the adhesion capability under hydrodynamic flow. Points a-c have been interpreted on the basis of a simple mechanoelectrical model. C 2000 Academic Press
Langmuir, 2003
Although fluid lipid films have been used widely in biosensing devices, they lack the high stability desired for technological implementation because the noncovalent forces between the constituent lipids are relatively weak. In this work, polymerized, planar supported lipid bilayers ((poly)PSLBs) composed of diene-functionalized lipids have been prepared and characterized. Several parameters relating (poly)-PSLB structure and stability to observations made in studies of polymerized bilayer vesicles were examined, including a comparison of UV photopolymerization and redox-initiated radical polymerization, the number and location of the polymerizable moieties in the lipid monomer, and a comparison to PSLBs produced with diacetylene lipids. Redox-initiated polymerization of films composed of bis-substituted diene lipids with at least one polymerizable moiety located near the acyl terminus produced dried PSLBs that were highly uniform and stable. All other conditions yielded PSLBs that contained a high density of defects after drying, including those formed from diacetylene lipids. In most cases, defect formation is attributed to desorption of unreacted monomers or low molecular weight polymers when the film was passed through the air/water interface. Studies on highly stable (poly)PSLBs doped with nonpolymerizable lipids showed that 40-80% of the dopants are retained when the film is dried. Thus to ensure quantitative lipid retention upon PSLB removal from water, all of the lipid monomers must be covalently anchored to the polymer network.
Langmuir, 2000
Lipid bilayer systems have been used extensively to study the structure and function of biomembranes including molecular recognition, permeation, adhesion, and fusion. 1-5 Further interest arises from their potential use as biosensors.6 , 7 While classical black lipid bilayer membranes are highly suitable as such model systems, they suffer from their limited long-term stability. 1 Additionally, to apply the broad range of surface sensitive experimental techniques developed in recent years for the characterization of ultrathin films, it is often necessary to immobilize lipid bilayers on solid supports. However, lateral fluidity of the lipid membrane is governed by the physical and chemical properties of the solid substrate. Thus, bilayer membranes prepared by the Langmuir-Blodgett (LB) technique or by vesicle fusion directly onto solid substrates are often polycrystalline or amorphous, and lateral lipid mobility within the membrane is restricted. While on hydrophilic oxidized silicon or glass a water layer (~1 nm thick) is formed which allows for free diffusion of phospholipid molecules (but not membrane-spanning proteins) within the bilayer,8 -10 on most other metals and metal oxides, lipid mobility is strongly suppressed.11 , 12 To preserve the membrane's natural properties, one promising approach is to rest it on a water-swellable (hydrophilic) polymer or polyelectrolyte cushion which can act as a deformable and mobile substrate6 , 13 , 14 like the cytoskeletal support in living cells. Such softly supported lipid bilayers can, in principle, exist in an entirely fluid state, nearly undisturbed by the presence of the supporting polymer gel which provides an aqueous compartment between the solid substrate and the membrane. In our recent work, we have studied DMPC bilayers on a highly branched cationic polymer (polyethylenimine, PEI). Important structural information about these polymer-supported bilayer systems formed by various preparation methods was provided by neutron scattering experiments.15 , 16 Furthermore, measuring the intermembrane interaction forces using the surface forces apparatus (SFA) technique has shown the effect of fluidity on membrane functionality.17
Quantitative membrane loading of polymer vesicles
Soft Matter, 2006
We utilize a series of structurally homologous, multi-porphyrin-based, fluorophores (PBFs) in order to explore the capacity of polymer vesicles (polymersomes) to stably incorporate large hydrophobic molecules, non-covalently within their thick lamellar membranes. Through aqueous hydration of dry, uniform thin-films of amphiphilic polymer and PBF species deposited on Teflon, self-assembled polymersomes are readily generated incorporating the hydrophobic fluorophores in prescribed molar ratios within their membranes. The size-dependent spectral properties of the PBFs allow for ready optical verification (via steady-state absorption and emission spectroscopy) of the extent of vesicle membrane loading and enable delineation of intermembranous molecular interactions. The resultant effects of PBF membrane-loading on polymersome thermodynamic and mechanical stability are further assessed by cryogenic transmission electron microscopy (cryo-TEM) and micropipet aspiration, respectively. We demonstrate that polymersomes can be loaded at up to 10 mol/wt% concentrations, with hydrophobic molecules that possess sizes comparable to those of large pharmaceutical conjugates (e.g. ranging 1.4-5.4 nm in length and Mw = 0.7-5.4 kg mol -1 ), without significantly compromising the robust thermodynamic and mechanical stabilities of these synthetic vesicle assemblies. Due to membrane incorporation, hydrophobic encapsulants are effectively prevented from selfaggregation, able to be highly concentrated in aqueous solution, and successfully shielded from deleterious environmental interactions. Together, these studies present a generalized paradigm for the generation of complex multi-functional materials that combine both hydrophilic and hydrophobic agents, in mesoscopic dimensions, through cooperative self-assembly.
On the distinct molecular architectures of dipping- and spray-LbL films containing lipid vesicles
Materials Science and Engineering: C, 2014
The introduction of spraying procedures to fabricate layer-by-layer (LbL) films has brought new possibilities for the control of molecular architectures and for making the LbL technique compliant with industrial processes. In this study we show that significantly distinct architectures are produced for dipping and spray-LbL films of the same components, which included DODAB/DPPG vesicles. The films differed notably in their thickness and stratified nature. The electrical response of the two types of films to aqueous solutions containing erythrosin was also different. With multidimensional projections we showed that the impedance for the DODAB/DPPG spray-LbL film is more sensitive to changes in concentration, being therefore more promising as sensing units. Furthermore, with surface-enhanced Raman scattering (SERS) we could ascribe the high sensitivity of the LbL films to adsorption of erythrosin.
Polymerization in Polymerizable Vesicle Bilayer Membranes
Langmuir, 2000
Polymerization reactions in lyotropic liquid crystalline phases have opened the way to the development of many novel materials. Inter alia, the two-dimensional self-assembly of amphiphiles in vesicle bilayers has attracted considerable interest as an ordered reaction medium. In this study we follow three different routes to polymerize within vesicle bilayer membranes with a view to preparing novel vesicle-polymer colloids. First, we study the vesicle formation and the polymerization of functional amphiphiles carrying one or two styryl groups. A combination of characterization techniques gives insights into bilayer properties, polymerization kinetics, and vesicle morphology of these (polymerized) vesicles. On the basis of this reference system, we explore the copolymerization of monomers inserted in the matrix of polymerizable amphiphiles. On the basis of kinetic and morphological data we prove that the copolymerization is viable if the polymerizable moieties are adequately chosen with respect to reactivity and location within the amphiphile matrix. Extremely deformed, albeit stable, vesicles are induced by cross-linking inserted monomers with monofunctional amphiphiles. In a last step, we attempt the synthesis of two-dimensional interpenetrating networks employing the previously polymerized amphiphile networks as templates. The cross-linking of divinylbenzene within cross-linked membranes affords peculiar orange-skin-like bilayer morphologies and gives evidence of the feasibility of the concept. Throughout the study, cryogenic electron microscopy appears as an indispensable means to unravel the morphology of the obtained vesicle-polymer architectures.
Hybrid polymer/lipid vesicles: state of the art and future perspectives
Materials Today, 2013
Hybrid vesicles resulting from the combined self-assembly of both amphiphilic copolymers and lipids have attracted particular interest from chemists and (bio)physicists over the last five years. Such assemblies may be viewed as an advanced vesicular structure compared to their liposome and polymersome forerunners as the best characteristics from the two different systems can be integrated in a new, single vesicle. To afford such a design, the different parameters controlling both self-assembly and membrane structure must be tuned. This highlight aims to present a comprehensive overview of the fundamental aspects related to these structures, and discuss emerging developments and future applications in this field of research.
Spontaneous formation of interfacial lipid-protein monolayers during adsorption from vesicles
Biophysical Journal, 1996
Spread and adsorbed monolayers of lipid-protein mixtures have served as models for biomembranes and pulmonary surfactant, but their similarity was unclear. Epifluorescence microscopy of monolayers spontaneously adsorbed from vesicles of dipalmitoylphosphatidylcholine or dipalmitoylphosphatidylcholine plus surfactant protein C (SP-C) showed gas, liquid expanded, and liquid condensed (LC) domains. The shapes and distribution of LC domains in the adsorbed and solvent-spread monolayers were quite similar. Labeled SP-C adsorbed into the air-water interface in the company of the lipids. In both forms of monolayers, SP-C occupied the fluid phase and reduced the size and amount of the LC domains. The properties suggest that these adsorbed and spread monolayers are analogous to one another.