Freeze-fracture electron microscopy of lipid membranes on colloidal polyelectrolyte multilayer coated supports

Rotary biomolecular motor-powered supramolecular colloidal motor

Cells orchestrate the motion and force of hundreds of protein motors to perform various mechanical tasks over multiple length scales. However, engineering active biomimetic materials from protein motors that consume energy to propel continuous motion of micrometer-sized assembling systems remains challenging. Here, we report rotary biomolecular motor-powered supramolecular (RBMS) colloidal motors that are hierarchically assembled from a purified chromatophore membrane containing F_OF₁-ATP synthase molecular motors, and an assembled polyelectrolyte microcapsule. The micro-sized RBMS motor with asymmetric distribution of F_OF₁-ATPases can autonomously move under light illumination and is collectively powered by hundreds of rotary biomolecular motors. The propulsive mechanism is that a transmembrane proton gradient generated by a photochemical reaction drives F_OF₁-ATPases to rotate for ATP biosynthesis, which creates a local chemical field for self-diffusiophoretic force. Such an active supramolecular architecture endowed with motility and biosynthesis offers a promising platform for intelligent colloidal motors resembling the propulsive units in swimming bacteria.

Peptide-functionalized supported lipid bilayers to construct cell membrane mimicking interfaces

Supported lipid bilayers (SLB) functionalized with bioactive molecules can be effectively used to study the interaction of cells with different molecules for fundamental research or to develop biosynthetic systems for various biomedical applications. In this study, RGD and Osteocalcin mimetic (OSN) peptides were used as model molecules for functionalization of otherwise passive SLBs to evaluate cell-surface interactions via real-time monitoring in quartz crystal microbalance with dissipation. Similar platforms were also used in cell culture environment. It was seen that low density of mobile RGD peptides on SLB platforms preserved their biological activity and promoted cell adhesion more efficiently than high number of immobile, physisorbed peptides. Even though nonspecific protein and cell attachment was promoted, cells did not spread well on OSN-coated control surfaces. The stability of SLBs produced with different lipids were evaluated in various medium conditions. Enrichment with different lipids increased the stability of SLB to pure PC bilayer.

Biodegradable, Tethered Lipid Bilayer-Microsphere Systems with Membrane-Integrated α-Helical Peptide Anchors

Supported lipid bilayers (SLBs) are ideally suited for the study of biomembrane-biomembrane interactions and for the biomimicry of cell-to-cell communication, allowing for surface ligand displays that contain laterally mobile elements. However, the SLB paradigm does not include three-dimensionality and biocompatibility. As a way to bypass these limitations, we have developed a biodegradable form of microsphere SLBs, also known as proteolipobeads (PLBs), using PLGA microspheres. Microspheres were synthesized using solvent evaporation and size selected with fluorescence activated cell sorting (FACS). Biomembranes were covalently tethered upon fusion to microsphere supports via short-chain PEG spacers connecting membrane-integrated α-helical peptides and the microsphere surface, affecting membrane diffusivity and mobility as indicated by confocal FRAP analysis. Membrane heterogeneities, which are attributed to PLGA hydrophobicity and rough surface topography, are curtailed by the addition of PEG tethers. This method allows for the presentation of tethered, laterally mobile biomembranes in three dimensions with functionally embedded attachment peptides for mobile ligand displays.

Role of Hydrogen Bonding and Polyanion Composition in the Formation of Lipid Bilayers on Top of Polyelectrolyte Multilayers

The self-assembly of mixed vesicles of zwitterionic phosphatidylcholine (PC) and anionic phosphatidylserine (PS) phospholipids on top of polyelectrolyte multilayers (PEMs) of poly(allylamine hydrochloride) (PAH), as a polycation, and polystyrenesulfonate (PSS), as a polyanion, is investigated as a function of the vesicle composition by means of the quartz crystal microbalance with dissipation (QCM-D), cryo-transmission electron microscopy (Cryo-TEM), atomic force microscopy (AFM), and atomic force spectroscopy (AFS). Vesicles with molar percentages of PS between 50% and 70% result in the formation of lipid bilayers on top of the PEMs. Vesicles with over 50% of PC or over 80% of PS do not assembly into bilayers. AFS studies performed with a PAH-modified cantilever approaching and retracting from the lipid assemblies reveal that the main interaction between PAH and the lipids takes place through hydrogen bonding between the amine groups of PAH and the carboxylate and phosphate groups of PS and with the phosphate groups of PC. The interaction of PAH with PS is much stronger than with PC. AFS measurements on assemblies with 50% PC and 50% PS revealed similar adhesion forces to pure PS assemblies, but the PAH chains can reorganize much better on the lipids as a consequence of the presence of PC. QCM-D experiments show that vesicles with a lipid composition of 50% PC and 50% PS do not form bilayers if PSS is replaced by alginate (Alg) or poly(acrylic acid) (PAA).

Micelles as "fluorescence protector" for an europium complex in microcapsules

Microcapsules with excellent fluorescence enhancement are assembled by using cetyltrimethylammonium bromide (CTAB) micelles to enrich Eu(DBM)(3)Phen (DBM and Phen are dibenzoylmethane and 1,10-phenanthroline, respectively) on CaCO(3) particles by the LbL technique. Compared to microcapsules without micelles, the fluorescence intensity of microcapsules with micelles increases 9 times, larger than the 6 times increase of absorbance. This unexpected fluorescence enhancement is attributed to the "fluorescence protector" effect of CTAB micelles in microcapsules. Energy loss from nonradiative deactivation through energy transfer to high-energy O-H vibrations from the emissive (5)D(0) state of Eu(III) is greatly prohibited. The new strategy using micelles in this work not only enriches europium complexes during assembly in aqueous solution but also yields a fluorescence enhancement ratio larger than the enrichment ratio.

Patterned microcontainers as novel functional elements for microTAS and LOC

Using nanoimprint lithography, arrays of highly ordered patterns of polyelectrolyte multilayer microcapsules consisting of alternating layers of poly(allylamine hydrochloride) and poly(sodium 4-styrene sulfonate) have been achieved. Anchoring the capsules on a pre-patterned substrate facilitates the utilization of their various capabilities in lab-on-a chip devices. In this paper we have demonstrated a very effective method to entrap soft capsules into surface cavities. Supported microcapsules were applied as the depots for loading and storage of macromolecular cargo (glucose oxidase and peroxidase) and as preserved microvessels for the cascade of enzymatic reactions. The loading of capsules was achieved under a pre-determined pH environment. This development is potentially useful for the realization of novel multianalytical systems for catalytic, bio-affinity and pH detection with protected sensing molecules.

Molecular assembly and application of biomimetic microcapsules

The assembly of multifunctional biomimetic microcapsules at the molecular level is of tremendous interest for biophysical research and the biomedical field. Among the available molecular assembly techniques, layer-by-layer assembly has attracted extensive attention for the fabrication of biomimetic microcapsules because it possesses engineered features including size, shape, thickness, composition and permeation, and the capability of incorporating different types of biomolecules. In this tutorial review, we highlight how biomimetic microcapsules can be fabricated by directly applying lipids and proteins as assembly pairs and how layer-by-layer assembled polyelectrolyte microcapsules can be interfaced with biological components such as phospholipid membranes and proteins. The applications of these biomimetic microcapsules in drug delivery, biosensors, and hybrid nanodevices are also addressed.

Effect of the polymer nature on the structural organization of lipid/polymer particle assemblies

The nano-organized LipoParticle assemblies, consisting of polymer particles coated with lipid layers, are investigated with the aim of evidencing the impact of the particle chemical nature on their physicochemical behavior. To this end, these colloidal systems are elaborated from anionic submicrometer poly(styrene) (P(St)) or poly(lactic acid) (PLA) particles, and lipid mixtures composed of zwitterionic 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and cationic 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP). As revealed by various experimental techniques, such as quasielastic light scattering, zeta potential measurements, transmission electron microscopy, and 1H NMR spectroscopy, the features of both LipoParticle systems are similar when cationic lipid formulations (DPPC/DPTAP mixtures) are used. This result emphasizes the major role of electrostatic interactions as driving forces in the assembly elaboration process. Conversely, the assemblies prepared only with the zwitterionic DPPC lipid are strongly dependent on the particle chemical nature. The structural characteristics of the assemblies based on PLA particles are not controlled and correspond to aggregates, contrary to P(St) particles. To understand this specific phenomenon, and to consequently improve the final organization of these assemblies which are potentially of great interest in biotechnology and biomedicine, numerous investigations are carried out such as the studies of the impact of the ionic strength and the pH of the preparation media, as well as the presence of ethanol (involved in the PLA particle synthesis) or the mean size of the lipid vesicles. From the resulting data and according to the nature of spherical solid support, hydrophobic effects, hydrogen bonds, or dipole-dipole interactions would also appear to influence the LipoParticle elaboration in the case of zwitterionic lipid formulation.

An overview of lipid membrane supported by colloidal particles

In recent years, original hybrid assemblies composed of a particle core surrounded by a lipid shell emerged as promising entities for various biotechnological applications. Their broadened bio-potentialities, ranging from model membrane systems or biomolecule screening supports, to substance delivery reservoirs or therapeutic vectors, are furthered by their versatility of composition due to the possible wide variation in the particle nature and size, as well as in the lipid formulation. The synthesis, the characteristics, and the uses of these Lipid/Particle assemblies encountered in the literature so far are reviewed, and classified according to the spherical core size in order to highlight general trends. Moreover, several criteria are particularly discussed: i) the interactions involved between the particles and the lipids, and implicitly the assembly elaboration mechanism, ii) the most suited techniques for an accurate characterization of the entities from structural and physicochemical points of view, and iii) the remarkable properties of the solid-supported lipid membrane obtained.

Stability and fusion of lipid layers on polyelectrolyte multilayer supports studied by colloidal force spectroscopy

The interaction between lipid layers supported by polyelectrolyte multilayer cushions has been studied by means of colloidal force spectroscopy. In a typical experiment, a colloidal probe engineered with a layer-by-layer film and a lipid bilayer on top is approached to a planar surface coated in a symmetrical way. Kinks of a few nanometres in width appear when lipid layers are pressed together--reflecting either fusion processes between lipid layers or membranes, or the penetration of polymer blobs into or through the lipid layers. Retracting curves show a stepwise shape, which results from lipid tether formation or from polymer stretching, the latter suggesting that polyelectrolyte multilayers make contact as a result of penetration or lipid fusion.

Bioinspired colloidal systems via layer-by-layer assembly

This paper provides an overview of our recent work in the area of bioinspired colloidal particles. We highlight how modifying the basic polyelectrolyte multilayer shell with materials such as light-absorbing gold nanoparticles, lipid bilayer membranes, and targeting ligands can functionalize colloids prepared the layer-by-layer assembly technique. These nanoengineered colloids are expected to show promise in areas ranging from drug and gene delivery to cell membrane modeling.

Arrays of lipid bilayers and liposomes on patterned polyelectrolyte templates

This paper presents novel methods to produce arrays of lipid bilayers and liposomes on patterned polyelectrolyte multilayers. We created the arrays by exposing patterns of poly(dimethyldiallylammonium chloride) (PDAC), polyethylene glycol (m-dPEG) acid, and poly(allylamine hydrochloride) (PAH) on polyelectrolyte multilayers (PEMs) to liposomes of various compositions. The resulting interfaces were characterized by total internal reflection fluorescence microscopy (TIRFM), fluorescence recovery after pattern photobleaching (FRAPP), quartz crystal microbalance (QCM), and fluorescence microscopy. Liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phosphate (monosodium salt) (DOPA) were found to preferentially adsorb on PDAC and PAH surfaces. On the other hand, liposome adsorption on sulfonated poly(styrene) (SPS) surfaces was minimal, due to electrostatic repulsion between the negatively charged liposomes and the SPS-coated surface. Surfaces coated with m-dPEG acid were also found to resist liposome adsorption. We exploited these results to create arrays of lipid bilayers by exposing PDAC, PAH and m-dPEG patterned substrates to DOPA/DOPC vesicles of various compositions. The patterned substrates were created by stamping PDAC (or PAH) on SPS-topped multilayers, and m-dPEG acid on PDAC-topped multilayers, respectively. This technique can be used to produce functional biomimetic interfaces for potential applications in biosensors and biocatalysis, for creating arrays that could be used for high-throughput screening of compounds that interact with cell membranes, and for probing, and possibly controlling, interactions between living cells and synthetic membranes.

Analysis of photoinitiated polymerization in a membrane mimetic film using infrared spectroscopy and near-IR Raman microscopy

A method has been developed to investigate the extent of polymer cross-linking that results following in situ photopolymerization of an acrylate-functionalized phospholipid assembly adsorbed onto a stabilized, membrane-mimetic film produced from a polyelectrolyte multilayer (PEM) on polytetrafluoroethylene (PTFE) grafts. The acrylate phospholipid monomer was synthesized, prepared as a unilamellar vesicle, and fused onto closed-packed acyl chains that make up the PEM membrane-mimetic barrier on the PTFE graft. Both broad band white light and 514.5 nm laser radiation were used as excitation sources for photoinitiation; eosin Y was used as the photoinitiator. The use of 514.5 nm excitation reduced the time for maximum polymerization of the acrylate lipid from 60 min to 240 s. Infrared spectroscopy was successfully used to analyze the extent of photopolymerization in simplified model acrylate lipid systems; however, this method could not be used to analyze acrylate polymerization in heterogeneous, multicomponent PEM membrane-mimetic barriers on PTFE grafts. A near-infrared Raman microscopy method based on the ratio of the integrated areas of the CC and CN vibrations was shown to provide equivalent information to the IR method for analysis of the extent of polymerization efficiency in acrylate lipids. In addition, it proved feasible to extend this near-IR Raman method to the in situ analysis of the extent of polymerization in a stabilized acrylate lipid membrane on a PEM film in a PTFE vascular graft. This work describes a new approach for generating and analyzing the robustness of a membrane-mimetic coating on biomaterial surfaces, and may improve our ability to predict the long-term stability of polymeric membrane-mimetic films on implantable medical devices.

Self-Exploding Lipid-Coated Microgels

Self-exploding microparticles show potential for advanced delivery of certain therapeutics. This study evaluates (1) whether degrading biodegradable dextran hydroxyethyl methacrylate (dex-HEMA) microgels can be coated by a lipid membrane and (2) whether the surrounding membrane can be ruptured by the increasing swelling pressure of the degrading microgel. We found that adsorption of charged liposomes to oppositely charged dex-HEMA microgels provides efficient coating of the microgels, whereby microparticles with a "core-shell" structure were clearly obtained. Especially, we could confirm experimentally that the swelling pressure increase of degrading dex-HEMA microgels can destroy the lipid membrane surrounding the microgels.

New insights into self-organization of a model lipid mixture and quantification of its adsorption on spherical polymer particles

The adsorption of lipids onto spherical polymer colloids led to original assemblies presenting structural characteristics adjustable with the lipid formulation. The model system selected for this work involved sulfate-charged poly(styrene) submicrometer particles and zwitterionic/cationic lipid mixtures composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP). According to the theoretical packing parameter calculations and whatever the DPPC/DPTAP ratio, the two lipids self-assembled in aqueous media to spontaneously form vesicles. A phase transition investigation of these DPPC/DPTAP vesicles using differential scanning calorimetry revealed particular thermotropic behaviors, especially for the equimolar formulation where very strong interactions occurred between DPPC and DPTAP. Furthermore, the coating of the lipids around particles was monitored versus DPPC/DPTAP ratio by means of numerous appropriate techniques. First, a thermogravimetric analysis, providing decomposition profiles of lipid/polymer particle assemblies with temperature, was atypically carried out for such nanostructures. Then, 1H NMR spectroscopy enabled the exact DPPC/DPTAP molar ratios adsorbed on particles to be determined by differentiating both lipids. Subsequently, it also pointed out the major role of electrostatic interactions as driving forces in the assembly elaboration process. In addition to these findings, quantitative information has been collected and correlated with chemical lipid assays and permitted the statement of a lipid bilayer coverage for the assemblies prepared in water, in agreement with quasi-elastic light scattering data.

Colloid stability of sodium dihexadecyl phosphate/poly(diallyldimethylammonium chloride) decorated latex

The colloid stability of supramolecular assemblies composed of the synthetic anionic lipid sodium dihexadecyl phosphate (DHP) on cationic poly(diallyldimethylammonium chloride) (PDDA) supported on polystyrene sulfate (PSS) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DHP adsorption on PDDA-covered particles. At 0.05 g/L PDDA and 5 x 10(9) PSS particles/mL, PDDA did not induce significant particle flocculation and a vast majority of PDDA covered single particles were present in the dispersion so that this was the condition chosen for determining DHP concentration (C) effects on particle size and zeta-potentials. At 0.8 mM DHP, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DHP/PDDA/PSS assembly. At 0.05 g L(-1) PDDA, isotherms of high affinity for DHP adsorption on PDDA-covered particles presented a plateau at a limiting adsorption of 135 x 10(19) DHP molecules adsorbed per square meter PSS which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy yielding ca. 6 +/- 1.5 nm hydrodynamic thickness. Maximal and massive adsorption of DHP lipid onto this layer produced polydisperse DHP/PDDA/PSS colloidal particles with low colloid stability and which, at best, remained aggregated as doublets over a range of large lipid concentrations so that it was not possible to evaluate the mean total thickness for the deposited film. The assembly anionic lipid/cationic PDDA layer/polymeric particle was relatively stable as particle doublets only well above charge neutralization of the polyelectrolyte by the anionic lipid, at relatively large lipid concentrations (above 1 mM DHP) with charge neutralization leading to extensive particle aggregation.

Controlling Ionic Conductivity in Lipid Polyelectrolyte Composite Capsules by Cholesterol

The effect of cholesterol on the formation and properties of bilayer lipid membranes deposited on polyelectrolyte multilayered capsules was studied. The permeability of lipid/cholesterol coated capsules for NaCl was derived from osmotic response experiments and ranged from 1.45 x 10(-8) to 2.9 x 10(-8) m.s(-1), which corresponds to a lipid layer conductivity of (0.7-1.4) x 10(-8) S.m(-1). These conductivity values were in good agreement with the value of 0.8 x 10(-8) S.m(-1) obtained by electrorotation and were by 3 orders of magnitude lower than those found earlier for lipid layers on polyelectrolyte capsules in the absence of cholesterol.

Lipid modified polyelectrolyte microcapsules with controlled diffusion

The lipid coating introduced directly on (polystyrene sulfonate/polyallylamine hydrochloride)5 polyelectrolyte microcapsule surfaces significantly reduces the permeability of capsule walls estimated by fluorescence recovery after photobleaching (FRAP).

Colloid stability of lipid/polyelectrolyte decorated latex

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.