Cryo-electron tomography of nanoparticle transmigration into liposome

Hydrogen bonding-mediated interaction underlies the enhanced membrane toxicity of chemically transformed polystyrene microplastics by cadmium

The global attention on microplastic pollution and its implications for human health has grown in recent years. Additionally, the co-existence of heavy metals may significantly alter microplastics' physicochemical characteristics, potentially amplifying their overall toxicity-a facet that remains less understood. In this study, we focused the membrane toxicity of modified polystyrene microplastics (PS-MPs) following cadmium (Cd) pretreatment. Our findings revealed that Cd-pretreated PS-MPs exacerbated their toxic effects, including diminished membrane integrity and altered phase fluidity in simulated lipid membrane giant unilamellar vesicles (GUVs), as well as heightened membrane permeability, protein damage, and lipid peroxidation in red blood cells and macrophages. Mechanistically, these augmented membrane toxicities can be partially ascribed to modifications in the surface roughness and hydrophilicity of Cd-pretreated PS-MPs, as well as to interactions between PS-MPs and lipid bilayers. Notably, hydrogen bonds emerged as a crucial mechanism underlying the enhanced interaction of PS-MPs with lipid bilayers.

Evaluating Cryo-TEM Reconstruction Accuracy of Self-Assembled Polymer Nanostructures

Cryogenic transmission electron microscopy (cryo-TEM) combined with single particle analysis (SPA) is an emerging imaging approach for soft materials. However, the accuracy of SPA-reconstructed nanostructures, particularly those formed by synthetic polymers, remains uncertain due to potential packing heterogeneity of the nanostructures. In this study, the combination of molecular dynamics (MD) simulations and image simulations is utilized to validate the accuracy of cryo-TEM 3D reconstructions of self-assembled polypeptoid fibril nanostructures. Using CryoSPARC software, image simulations, 2D classifications, ab initio reconstructions, and homogenous refinements are performed. By comparing the results with atomic models, the recovery of molecular details is assessed, heterogeneous structures are identified, and the influence of extraction location on the reconstructions is evaluated. These findings confirm the fidelity of single particle analysis in accurately resolving complex structural characteristics and heterogeneous structures, exhibiting its potential as a valuable tool for detailed structural analysis of synthetic polymers and soft materials.

Dissolved metal ions and mineral-liposome hybrid systems: Underlying interactions, synthesis, and characterization

Liposomes are versatile lipid-based vesicles with interesting physicochemical properties, making them excellent candidates for interdisciplinary applications in the medicinal, biological, and environmental sciences. The synthesis of mineral-liposome hybrid systems lends normally inert vesicles with the catalytic, magnetic, electrical, and optical properties of the integrated mineral species. Such applications require an understanding of the physicochemical interactions between organic molecules and inorganic crystal structures. This review provides an overview on these interactions and details on synthesis and characterization methods for these systems.

Key Role of Choline Head Groups in Large Unilamellar Phospholipid Vesicles for the Interaction with and Rupture by Silica Nanoparticles

For highly abundant silica nanomaterials, detrimental effects on proteins and phospholipids are postulated as critical molecular initiating events that involve hydrogen-bonding, hydrophobic, and/or hydrophilic interactions. Here, large unilamellar vesicles with various well-defined phospholipid compositions are used as biomimetic models to recapitulate membranolysis, a process known to be induced by silica nanoparticles in human cells. Differential analysis of the dominant phospholipids determined in membranes of alveolar lung epithelial cells demonstrates that the quaternary ammonium head groups of phosphatidylcholine and sphingomyelin play a critical and dose-dependent role in vesicle binding and rupture by amorphous colloidal silica nanoparticles. Surface modification by either protein adsorption or by covalent coupling of carboxyl groups suppresses the disintegration of these lipid vesicles, as well as membranolysis in human A549 lung epithelial cells by the silica nanoparticles. Furthermore, molecular modeling suggests a preferential affinity of silanol groups for choline head groups, which is also modulated by the pH value. Biomimetic lipid vesicles can thus be used to better understand specific phospholipid-nanoparticle interactions at the molecular level to support the rational design of safe advanced materials.

Impact of Biogenic and Chemogenic Selenium Nanoparticles on Model Eukaryotic Lipid Membranes

Microbial nanotechnology is an expanding research area devoted to producing biogenic metal and metalloid nanomaterials (NMs) using microorganisms. Often, biogenic NMs are explored as antimicrobial, anticancer, or antioxidant agents. Yet, most studies focus on their applications rather than the underlying mechanism of action or toxicity. Here, we evaluate the toxicity of our well-characterized biogenic selenium nanoparticles (bSeNPs) produced by the Stenotrophomonas maltophilia strain SeITE02 against the model yeast Saccharomyces cerevisiae comparing it with chemogenic SeNPs (cSeNPs). Knowing from previous studies that the biogenic extract contained bSeNPs in an organic material (OM) and supported here by Fourier transform infrared spectroscopy, we removed and incubated it with cSeNPs (cSeNPs_OM) to assess its influence on the toxicity of these formulations. Specifically, we focused on the first stages of the eukaryotic cell exposure to these samples─i.e., their interaction with the cell lipid membrane, which was mimicked by preparing vesicles from yeast polar lipid extract or phosphatidylcholine lipids. Fluidity changes derived from biogenic and chemogenic samples revealed that the bSeNP extract mediated the overall rigidification of lipid vesicles, while cSeNPs showed negligible effects. The OM and cSeNPs_OM induced similar modifications to the bSeNP extract, reiterating the need to consider the OM influence on the physical-chemical and biological properties of bSeNP extracts.

Tear of lipid membranes by nanoparticles

Health concerns associated with the advent of nanotechnologies have risen sharply when it was found that particles of nanoscopic dimensions reach the cell lumina. Plasma and organelle lipid membranes, which are exposed to both the incoming and the engulfed nanoparticles, are the primary targets of possible disruptions. However, reported adhesion, invagination and embedment of nanoparticles (NPs) do not compromise the membrane integrity, precluding direct bilayer damage as a mechanism for toxicity. Here it is shown that a lipid membrane can be torn by small enough nanoparticles, thus unveiling mechanisms for how lipid membrane can be compromised by tearing from nanoparticles. Surprisingly, visualization by cryo transmission electron microscopy (cryo-TEM) of liposomes exposed to nanoparticles revealed also that liposomal laceration is prevented by particle abundance. Membrane destruction results thus from a subtle particle-membrane interplay that is here elucidated. This brings into a firmer molecular basis the theorized mechanisms of nanoparticle effects on lipid bilayers and paves the way for a better assessment of nanoparticle toxicity.

Biomimetic Curvature and Tension-Driven Membrane Fusion Induced by Silica Nanoparticles

Fusion events in living cells are intricate phenomena that require the coordinate action of multicomponent protein complexes. However, simpler synthetic tools to control membrane fusion in artificial cells are highly desirable. Native membrane fusion machinery mediates fusion, driving a delicate balance of membrane curvature and tension between two closely apposed membranes. Here, we show that silica nanoparticles (SiO₂ NPs) at a size close to the cross-over between tension-driven and curvature-driven interaction regimes initiate efficient fusion of biomimetic model membranes. Fusion efficiency and mechanisms are studied by Förster resonance energy transfer and confocal fluorescence microscopy. SiO₂ NPs induce a slight increase in lipid packing likely to increase the lateral tension of the membrane. We observe a connection between membrane tension and fusion efficiency. Finally, real-time confocal fluorescence microscopy reveals three distinct mechanistic pathways for membrane fusion. SiO₂ NPs show significant potential for inclusion in the synthetic biology toolkit for membrane remodeling and fusion in artificial cells.

Triggered interactions between nanoparticles and lipid membranes: design principles for gel formation or disruption-and-release

Lipid bilayer vesicles offer exciting possibilities for stimulated response, taking advantage of the membrane's flexibility and impermeability. We show how synergistic interactions between vesicles and polymer-based nanoparticles can be triggered at the nanoscale using UV light. This interaction leads either to adhesion and a membrane-based gel, or to nanoscale wrapping of the particles by the membrane and then vesicle destruction. To map the response, we varied the particle-membrane interactions via their surface charge densities. We found a crossover from adhesion to destruction at a well-defined region in parameter space. We modeled these results by accounting for the electrostatic attraction and the energy of membrane bending. We then synthesized amphiphilic polymers containing a UV-responsive nitrobenzyl moiety that switches its charge, and showed how a trigger predictably led to either a vesicle gel or disruption and release. The results pave the way to a new triggering mechanism and new response modes in soft materials.

Interface interaction between high-siliceous/calcareous mineral granules and model cell membranes dominated by electrostatic force

High-siliceous/calcareous mineral granules may cause cytotoxicity by attaching to cell membranes. In this research, giant (GUVs) and small unilamellar vesicles (SUVs) were used as model membranes for studying the interaction between high-siliceous/calcareous mineral granules (micro calcite, micro quartz, nano calcium carbonate, and nano silica) and artificial membranes. Confocal laser scanning microscopy (CLSM) and fluorescence labeling experiments suggest that nano calcium carbonate (nano CaCO₃) and nano silica (nano SiO₂) induce gelation by disrupting the oppositely charged membranes, indicating the important role of electrostatic forces. Thereby, the mineral granule size affects the electrostatic interactions and thus leading to the damage of the membranes. FTIR spectra and molecular dynamics reveal that mineral granules mainly interact with -PO₂^-, -OH, and -C-N(CH₃)₃⁺ groups in phospholipids. The electrostatic force between nano minerals and phospholipids is greater in the case SiO₂ when compared to CaCO₃. Moreover, nano SiO₂ forms the strongest hydrogen bond with the -PO₂^- group as confirmed by FTIR. Thus, nano SiO₂ causes the greatest damage to membranes. This research provides a deeper understanding of the mechanism regarding the interaction between inhalable mineral granules and cell membranes.

Membrane Remodeling by DNA Origami Nanorods: Experiments Exploring the Parameter Space for Vesicle Remodeling

Inspired by the ability of cell membranes to alter their shape in response to bound particles, we report an experimental study of long, slender nanorods binding to lipid bilayer vesicles and altering the membrane shape. Our work illuminates the role of particle concentration, adhesion strength, and membrane tension in determining the membrane morphology. We combined giant unilamellar vesicles with oppositely charged nanorods, carefully tuning the adhesion strength, membrane tension, and particle concentration. With increasing adhesion strength, the primary behaviors observed were membrane deformation, vesicle-vesicle adhesion, and vesicle rupture. These behaviors were observed in well-defined regions in the parameter space with sharp transitions between them. We observed the deformation of the membrane resulting in tubulation, textured surfaces, and small and large lipid-particle aggregates. These responses are robust and repeatable and provide a new physical understanding of the dependence on the shape, binding affinity, and particle concentration in membrane remodeling. The design principles derived from these experiments may lead to new bioinspired membrane-based materials.

Rethinking CRITID Procedure of Brain Targeting Drug Delivery: Circulation, Blood Brain Barrier Recognition, Intracellular Transport, Diseased Cell Targeting, Internalization, and Drug Release

The past decades have witnessed great progress in nanoparticle (NP)-based brain-targeting drug delivery systems, while their therapeutic potentials are yet to be fully exploited given that the majority of them are lost during the delivery process. Rational design of brain-targeting drug delivery systems requires a deep understanding of the entire delivery process along with the issues that they may encounter. Herein, this review first analyzes the typical delivery process of a systemically administrated NPs-based brain-targeting drug delivery system and proposes a six-step CRITID delivery cascade: circulation in systemic blood, recognizing receptor on blood-brain barrier (BBB), intracellular transport, diseased cell targeting after entering into parenchyma, internalization by diseased cells, and finally intracellular drug release. By dissecting the entire delivery process into six steps, this review seeks to provide a deep understanding of the issues that may restrict the delivery efficiency of brain-targeting drug delivery systems as well as the specific requirements that may guarantee minimal loss at each step. Currently developed strategies used for troubleshooting these issues are reviewed and some state-of-the-art design features meeting these requirements are highlighted. The CRITID delivery cascade can serve as a guideline for designing more efficient and specific brain-targeting drug delivery systems.

Adsorption Kinetics of Oppositely Charged Hard and Soft Nanoparticles with Phospholipid Membranes

Nanoparticles (NPs) have great potential for biological applications as typically they exhibit strongly size-dependent properties. Specifically, the interaction of NPs with phospholipid membranes is significantly relevant to nanomedicine and the related field of nanotoxicology. Therefore, the investigation of interactions of NPs with model membranes is not only fundamentally important but also practically valuable to understand interactions of NPs with more complex cell membranes. Here, we report on the interaction of anionic vesicles of different charge densities and cationic SiO₂ NPs, either covered by a bare surface functionalized with amino moieties (-NH₂) or covered by poly[2-(dimethylamino) ethyl methacrylate]. We studied the kinetics of binding of NPs to the vesicle surface by time-resolved scattering experiments. A key result of the study is that binding is favored in the presence of electrostatic attraction, but the polymer layer decreases the binding rate drastically.

Self-assembled mRNA vaccines

mRNA vaccines have evolved from being a mere curiosity to emerging as COVID-19 vaccine front-runners. Recent advancements in the field of RNA technology, vaccinology, and nanotechnology have generated interest in delivering safe and effective mRNA therapeutics. In this review, we discuss design and self-assembly of mRNA vaccines. Self-assembly, a spontaneous organization of individual molecules, allows for design of nanoparticles with customizable properties. We highlight the materials commonly utilized to deliver mRNA, their physicochemical characteristics, and other relevant considerations, such as mRNA optimization, routes of administration, cellular fate, and immune activation, that are important for successful mRNA vaccination. We also examine the COVID-19 mRNA vaccines currently in clinical trials. mRNA vaccines are ready for the clinic, showing tremendous promise in the COVID-19 vaccine race, and have pushed the boundaries of gene therapy.

Antibacterial Action of Nanoparticles by Lethal Stretching of Bacterial Cell Membranes

It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. It is demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP-membrane interactions is presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon is demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram-positive and Gram-negative bacteria. Hydrophilic and hydrophobic quasi-spherical and star-shaped gold (Au)NPs are synthesized to explore the antibacterial mechanism of non-translocating AuNPs. Direct observation of nanoparticle-induced membrane tension and squeezing is demonstrated using a custom-designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi-spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques are used to characterize the NP-bacterial-membrane interactions. This combination of experimental and theoretical results confirm the proposed mechanism of membrane-tension-induced (mechanical) killing of bacterial cells by non-translocating NPs.

Pulmonary surfactant inhibition of nanoparticle uptake by alveolar epithelial cells

Pulmonary surfactant forms a sub-micrometer thick fluid layer that covers the surface of alveolar lumen and inhaled nanoparticles therefore come in to contact with surfactant prior to any interaction with epithelial cells. We investigate the role of the surfactant as a protective physical barrier by modeling the interactions using silica-Curosurf-alveolar epithelial cell system in vitro. Electron microscopy displays that the vesicles are preserved in the presence of nanoparticles while nanoparticle-lipid interaction leads to formation of mixed aggregates. Fluorescence microscopy reveals that the surfactant decreases the uptake of nanoparticles by up to two orders of magnitude in two models of alveolar epithelial cells, A549 and NCI-H441, irrespective of immersed culture on glass or air-liquid interface culture on transwell. Confocal microscopy corroborates the results by showing nanoparticle-lipid colocalization interacting with the cells. Our work thus supports the idea that pulmonary surfactant plays a protective role against inhaled nanoparticles. The effect of surfactant should therefore be considered in predictive assessment of nanoparticle toxicity or drug nanocarrier uptake. Models based on the one presented in this work may be used for preclinical tests with engineered nanoparticles.

Adhesion and Aggregation of Spherical Nanoparticles on Lipid Membranes

We present a review of recent results on the adhesion, wrapping and aggregation of spherical nanoparticles (NPs) on lipid membranes via molecular dynamics simulations of an implicit solvent model. We show that the degree of wrapping of small NPs, by tensionless planar membranes, can increase continuously with the adhesion strength. However, the degree of wrapping exhibits a discontinuity for large NPs or short interaction range. The adhesion of NPs to small vesicles, without volume constraint, also exhibits a discontinuity between weakly wrapped states and fully endocytosed states. Multiple spherical NPs, bound to tensionless planar membranes are either in a gas state, at weak adhesion strength, or aggregate, at relatively high adhesion strength, into a multitude of structures, corresponding to in-plane chains, out-of-plane tubes and rings, and out-of-plane single-chain tubes. Annealing scans and free energy calculations show that the gas and tube phases are the predominantly stable phases. In-plane chains are only stable for small aggregates and the out-of-plane bitubes are long-lived metastable states.

Size dependency of gold nanoparticles interacting with model membranes

The rapid development of nanotechnology has led to an increase in the number and variety of engineered nanomaterials in the environment. Gold nanoparticles (AuNPs) are an example of a commonly studied nanomaterial whose highly tailorable properties have generated significant interest through a wide range of research fields. In the present work, we characterise the AuNP-lipid membrane interaction by coupling qualitative data with quantitative measurements of the enthalpy change of interaction. We investigate the interactions between citrate-stabilised AuNPs ranging from 5 to 60 nm in diameter and large unilamellar vesicles acting as a model membrane system. Our results reveal the existence of two critical AuNP diameters which determine their fate when in contact with a lipid membrane. The results provide new insights into the size dependent interaction between AuNPs and lipid bilayers which is of direct relevance to nanotoxicology and to the design of NP vectors.

Loss of membrane asymmetry alters the interactions of erythrocytes with engineered silica nanoparticles

Disruption of plasma membrane integrity is a primary mechanism of nanoparticle toxicity in cells. Mechanistic studies on nanoparticle-induced membrane damage have been commonly performed using model membranes with a focus on symmetric bilayers, overlooking the fact that the membrane has an asymmetric phospholipid composition. In this study, erythrocytes with normal and scrambled membrane asymmetry were utilized to examine how the loss of membrane asymmetry and the resulting alterations in the outer leaflet lipid composition affect nanoparticle-membrane interactions. Unmodified, amine-modified, and carboxyl-modified silica (30 nm) were used as nanoparticle models. Loss of membrane asymmetry was achieved by induction of eryptosis, using a calcium ionophore. Erythrocyte membrane disruption (hemolysis) by unmodified silica nanoparticles was significantly reduced in eryptotic compared to healthy cells. Amine- and carboxyl-modified particles did not cause hemolysis in either cell. In agreement, a significant reduction in the binding of unmodified silica nanoparticles to the membrane was observed upon loss of membrane asymmetry. Unmodified silica particles also caused significant cell deformation, changing healthy erythrocytes into a spheroid shape. In agreement with findings in the cells, unmodified particles disrupted vesicles mimicking the erythrocyte outer leaflet lipid composition. The degree of disruption and nanoparticle binding to the membrane was reduced in vesicles mimicking the composition of scrambled membranes. Cryo-electron microscopy revealed the presence of lipid layers on particle surfaces, pointing to lipid adsorption as the mechanism for vesicle damage. Together, findings indicate an important role for the lipid composition of the membrane outer leaflet in nanoparticle-induced membrane damage in both vesicles and erythrocytes.

A Technical Introduction to Transmission Electron Microscopy for Soft-Matter: Imaging, Possibilities, Choices, and Technical Developments

With a significant role in material sciences, physics, (soft matter) chemistry, and biology, the transmission electron microscope is one of the most widely applied structural analysis tool to date. It has the power to visualize almost everything from the micrometer to the angstrom scale. Technical developments keep opening doors to new fields of research by improving aspects such as sample preservation, detector performance, computational power, and workflow automation. For more than half a century, and continuing into the future, electron microscopy has been, and is, a cornerstone methodology in science. Herein, the technical considerations of imaging with electrons in terms of optics, technology, samples and processing, and targeted soft materials are summarized. Furthermore, recent advances and their potential for application to soft matter chemistry are highlighted.

Revealing the pulmonary surfactant corona on silica nanoparticles by cryo-transmission electron microscopy

When inhaled, nanoparticles (NPs) deposit in alveoli and transit through the pulmonary surfactant (PS), a biofluid made of proteins and phospholipid vesicles. They form a corona reflecting the PS-nanomaterial interaction. Since the corona determines directly the NPs' biological fate, the question of its nature and structure is central. Here, we report on the corona architecture formed after incubation of positive or negative silica particles with Curosurf®, a biomimetic pulmonary surfactant of porcine origin. Using optical, electron and cryo-electron microscopy (cryo-TEM), we determine the pulmonary surfactant corona structure at different scales of observation. Contrary to common belief, the PS corona is not only constituted by phospholipid bilayers surrounding NPs but also by multiple hybrid structures derived from NP-vesicle interaction. Statistical analysis of cryo-TEM images provides interesting highlights about the nature of the corona depending on the particle charge. The influence of Curosurf® pre- or post-treatment is also investigated and demonstrates the need for protocol standardization.

Probing Nanoparticle/Membrane Interactions by Combining Amphiphilic Diblock Copolymer Assembly and Plasmonics

Understanding the interactions between nanoparticles (NPs) and boundaries of cells is crucial both for their toxicity and therapeutic applications. Besides specific receptor-mediated endocytosis of surface-functionalized NPs, passive internalization is prompted by relatively unspecific parameters, such as particle size and charge. Based on theoretical treatments, adhesion to and bending of the cell membrane can induce NP wrapping. Experimentally, powerful tools are needed to selectively probe possible membrane-NP motifs at very dilute conditions and avoid dye labeling. In this work, we employ surface resonance-enhanced dynamic light scattering, surface plasmon resonance, electron microscopy, and simulations for sensing interactions between plasmonic AuNPs and polymersomes. We distinguish three different interaction scenarios at nanomolar concentrations by tuning the surface charge of AuNPs and rationalize these events by balancing vesicle bending and electrostatic/van der Waals AuNP and vesicle adhesion. The clarification of the physical conditions under which nanoparticles passively translocate across membranes can aid in the rational design of drugs that cannot exploit specific modes of cellular uptake and also elucidates physical properties that render nanoparticles in the environment particularly toxic.

Property-Activity Relationship of Black Phosphorus at the Nano-Bio Interface: From Molecules to Organisms

As a novel member of the two-dimensional nanomaterial family, mono- or few-layer black phosphorus (BP) with direct bandgap and high charge carrier mobility is promising in many applications such as microelectronic devices, photoelectronic devices, energy technologies, and catalysis agents. Due to its benign elemental composition (phosphorus), large surface area, electronic/photonic performances, and chemical/biological activities, BP has also demonstrated a great potential in biomedical applications including biosensing, photothermal/photodynamic therapies, controlled drug releases, and antibacterial uses. The nature of the BP-bio interface is comprised of dynamic contacts between nanomaterials (NMs) and biological systems, where BP and the biological system interact. The physicochemical interactions at the nano-bio interface play a critical role in the biological effects of NMs. In this review, we discuss the interface in the context of BP as a nanomaterial and its unique physicochemical properties that may affect its biological effects. Herein, we comprehensively reviewed the recent studies on the interactions between BP and biomolecules, cells, and animals and summarized various cellular responses, inflammatory/immunological effects, as well as other biological outcomes of BP depending on its own physical properties, exposure routes, and biodistribution. In addition, we also discussed the environmental behaviors and potential risks on environmental organisms of BP. Based on accumulating knowledge on the BP-bio interfaces, this review also summarizes various safer-by-design strategies to change the physicochemical properties including chemical stability and nano-bio interactions, which are critical in tuning the biological behaviors of BP. The better understanding of the biological activity of BP at BP-bio interfaces and corresponding methods to overcome the challenges would promote its future exploration in terms of bringing this new nanomaterial to practical applications.

Nanoparticles binding to lipid membranes: from vesicle-based gels to vesicle tubulation and destruction

While cells offer numerous inspiring examples in which membrane morphology and function are controlled by interactions with viruses or proteins, we still lack design principles for controlling membrane morphology in synthetic systems. With experiments and simulations, we show that spherical nanoparticles binding to lipid-bilayer membrane vesicles results in a remarkably rich set of collective morphologies that are controllable via the particle binding energy. We separately study cationic and anionic particles, where the adhesion is tuned by addition of oppositely charged lipids to the vesicles. When the binding energy is weak relative to a characteristic membrane-bending energy, vesicles adhere to one another and form a soft solid gel, a novel and useful platform for controlled release. With larger binding energy, a transition from partial to complete wrapping of the nanoparticles causes a remarkable vesicle destruction process culminating in rupture, nanoparticle-membrane tubules, and an apparent inversion of the vesicles. These findings help unify the diverse phenomena observed previously. They also open the door to a new class of vesicle-based, closed-cell gels that are more than 99% water and can encapsulate and release on demand, and show how to drive intentional membrane remodeling for shape-responsive systems.

Membrane-Mimetic Dendrimersomes Engulf Living Bacteria via Endocytosis

There is much interest in developing vesicular microcompartments from natural and synthetic amphiphiles, enabling programmable interactions with living matter. Of particular interest is the development of vesicles capable of endocytosis of living bacteria. Despite the complexity of this process, theoretical studies predict that the endocytosis of prolate micro-objects is possible without the need of active cell machinery if the energy released upon bacterial adhesion to the membrane surpasses the energy required to bend the membrane. Nonetheless, natural liposomes and synthetic polymersomes fail to sufficiently recapitulate membrane properties to perform this advanced function. Here we report the engulfment of living bacteria into endosomes by cell-like dendrimersomes assembled from Janus dendrimers. Full engulfment occurred in less than a minute after contact. The process is driven by the adhesion of the bacterium to the dendrimersome's membrane by ultraweak interactions, comparable to those utilized by nature. The key to success relies on the combination of high flexibility and stability of the dendrimersomes. The key properties of the dendrimersomes are programmed into the molecular structures of their building blocks. The ability to support endocytosis highlights opportunities for the design and programming of dendrimersomes in biomedical research.

Coarse-grained molecular dynamics simulation for uptake of nanoparticles into a charged lipid vesicle dominated by electrostatic interactions

We use a coarse-grained molecular dynamics simulation to investigate the interaction between neutral or charged nanoparticles (NPs) and a vesicle consisting of neutral and negatively charged lipids. We focus on the interaction strengths of hydrophilic and hydrophobic attraction and electrostatic interactions between a lipid molecule and an NP. A neutral NP passes through the lipid membrane when the hydrophobic interaction is sufficiently strong. As the valence of the positively charged NP increases, the membrane permeation speed of the NP is increased compared with the neutral NP and charged lipids are accumulated around the charged NP. A charged NP with a high valence passes through the lipid membrane via a transient channel formed by charged lipids or transportlike endocytosis. These permeation processes can be classified based on analyses of the density correlation function. When the nonelectrostatic interaction parameters are large enough, a negatively charged NP can be adsorbed on the membrane and a neutral lipid-rich region is formed directly below the NP. The NP is spontaneously incorporated into the vesicle under various conditions and the incorporation is mediated by the membrane curvature. We reveal how the NP's behavior depends on the NP valence, size, and the nonelectrostatic interaction parameters.

Tailoring Cell Morphomechanical Perturbations Through Metal Oxide Nanoparticles

The nowadays growing use of nanoparticles (NPs) in commercial products does not match a comprehensive understanding of their potential harmfulness. More in vitro investigations are required to address how the physicochemical properties of NPs guide their engulfment within cells and their intracellular trafficking, fate, and toxicity. These nano-bio interactions have not been extensively addressed yet, especially from a mechanical viewpoint. Cell mechanic is a critical indicator of cell health because it regulates processes like cell migration, tissue integrity, and differentiation via cytoskeleton rearrangements. Here, we investigated in vitro the elasticity perturbation of Caco-2 and A549 cell lines, in terms of Young's modulus modification induced by SiO2NPS and TiO2NPS. TiO2NPs demonstrated stronger effects on cell elasticity compared to SiO2NPs, as they induced significant morphological and morphometric changes in actin network. TiO2NPS increased the elasticity in Caco-2 cells, while opposite effects have been observed on A549 cells. These results demonstrate the existence of a correlation between the alteration of cell elasticity and NPs toxicity that depends, in turn, on the NPs physicochemical properties and the specific cell tested.

Biomechanical characterization of TIM protein-mediated Ebola virus-host cell adhesion

Since the most recent outbreak, the Ebola virus (EBOV) epidemic remains one of the world’s public health and safety concerns. EBOV is a negative-sense RNA virus that can infect humans and non-human primates, and causes hemorrhagic fever. It has been proposed that the T-cell immunoglobulin and mucin domain (TIM) family proteins act as cell surface receptors for EBOV, and that the interaction between TIM and phosphatidylserine (PS) on the surface of EBOV mediates the EBOV–host cell attachment. Despite these initial findings, the biophysical properties of the TIM-EBOV interaction, such as the mechanical strength of the TIM-PS bond that allows the virus-cell interaction to resist external mechanical perturbations, have not yet been characterized. This study utilizes single-molecule force spectroscopy to quantify the specific interaction forces between TIM-1 or TIM-4 and the following binding partners: PS, EBOV virus-like particle, and EBOV glycoprotein/vesicular stomatitis virus pseudovirion. Depending on the loading rates, the unbinding forces between TIM and ligands ranged from 40 to 100 pN, suggesting that TIM-EBOV interactions are mechanically comparable to previously reported adhesion molecule–ligand interactions. The TIM-4–PS interaction is more resistant to mechanical force than the TIM-1–PS interaction. We have developed a simple model for virus–host cell interaction that is driven by its adhesion to cell surface receptors and resisted by membrane bending (or tension). Our model identifies critical dimensionless parameters representing the ratio of deformation and adhesion energies, showing how single-molecule adhesion measurements relate quantitatively to the mechanics of virus adhesion to the cell.

Interactions Between Silver Nanoparticles/Silver Ions and Liposomes: Evaluation of the Potential Passive Diffusion of Silver and Effects of Speciation

Silver nanoparticles, used mainly for their antibacterial properties, are among the most common manufactured nanomaterials. How they interact with aquatic organisms, especially how they cross biological membranes, remains uncertain. Free Ag⁺ ions, released from these nanoparticles, are known to play an important role in their overall bioavailability. In this project, we have studied the uptake of dissolved and nanoparticulate silver by liposomes. These unilamellar vesicles, composed of phospholipids, have long been used as models for natural biological membranes, notably to study the potential uptake of solutes by passive diffusion through the phospholipid bilayer. The liposomes were synthesized using extrusion techniques and were exposed over time to dissolved silver under different conditions where Ag⁺, AgS₂O₃^-, or AgCl⁰ were the dominant species. Similar experiments were conducted with the complexes HgCl ₂ ⁰ and Cd(DDC) ₂ ⁰ , both of which are hydrophobic and known to diffuse passively through biological membranes. The uptake kinetics of Ag⁺, HgCl ₂ ⁰ , and Cd(DDC) ₂ ⁰ show no increase in internalized concentrations over time, unlike AgS₂O₃^- and AgCl⁰, which appear to pass through the phospholipid bilayer. These results are in contradiction with our initial hypothesis that lipophilic Hg and Cd complexes would be able to cross the membrane, whereas silver would not. Encapsulated tritiated water inside the liposomes was shown to rapidly diffuse through the lipid bilayer, suggesting a high permeability. We hypothesize that monovalent anions or complexes as well as small neutral complexes with a strong dipole can diffuse through our model membrane. Finally, liposomes were exposed to 5-nm polyvinylpyrrolidone-coated silver nanoparticles over time. No significant uptake of nanoparticulate silver was observed. Neither disruption of the membrane nor invagination of nanoparticles into the liposomes was observed. This suggests that the main risk caused by AgNPs for nonendocytotic biological cells would be the elevation of the free silver concentration near the membrane surface due to adsorption of AgNPs and subsequent oxidation/dissolution.

Nanoparticle-Lipid Interaction: Job Scattering Plots to Differentiate Vesicle Aggregation from Supported Lipid Bilayer Formation

The impact of nanomaterials on lung fluids, or on the plasma membrane of living cells, has prompted researchers to examine the interactions between nanoparticles and lipid vesicles. Recent studies have shown that nanoparticle-lipid interaction leads to a broad range of structures including supported lipid bilayers (SLB), particles adsorbed at the surface or internalized inside vesicles, and mixed aggregates. Currently, there is a need to have simple protocols that can readily evaluate the structures made from particles and vesicles. Here we apply the method of continuous variation for measuring Job scattering plots and provide analytical expressions for the scattering intensity in various scenarios. The result that emerges from the comparison between experiments and modeling is that electrostatics play a key role in the association, but it is not sufficient to induce the formation of supported lipid bilayers.

Structure and behaviour of vesicles in the presence of colloidal particles

This review highlights recent studies that investigate the structural changes and behaviour of synthetic vesicles when they are exposed to colloidal particles. We will show examples to demonstrate the power of combining particles and vesicles in generating exciting supracolloidal structures. These suprastructures have a wide range of often responsive behaviours that take advantage of both the mechanical and morphological support provided by the vesicles and the associated particles with preset functionality. This review includes applications spanning a variety of disciplines, including chemistry, biology, physics and medicine.

The role of surface charge in the interaction of nanoparticles with model pulmonary surfactants

Inhaled nanoparticles traveling through the airways are able to reach the respiratory zone of the lungs. In such an event, the incoming particles first come into contact with the liquid lining the alveolar epithelium, the pulmonary surfactant. The pulmonary surfactant is composed of lipids and proteins that are assembled into large vesicular structures. The question of the nature of the biophysicochemical interaction with the pulmonary surfactant is central to understand how the nanoparticles can cross the air-blood barrier. Here we explore the phase behavior of sub-100 nm particles and surfactant substitutes under controlled conditions. Three types of surfactant mimetics, including the exogenous substitute Curosurf®, a drug administered to infants with respiratory distress syndrome, are tested together with aluminum oxide (Al2O3), silicon dioxide (SiO2) and polymer (latex) nanoparticles. The main result here is the observation of spontaneous nanoparticle-vesicle aggregation induced by coulombic attraction. The role of the surface charges is clearly established. We also evaluate the supported lipid bilayer formation recently predicted and find that in the cases studied these structures do not occur. Pertaining to the aggregate internal structure, fluorescence microscopy shows that the vesicles and particles are intermixed at the nano- to microscale. With particles acting as stickers between vesicles, it is anticipated that the presence of inhaled nanomaterials in the alveolar spaces could significantly modify the interfacial and bulk properties of the pulmonary surfactant and interfere with lung physiology.

Advantages and Limitations of Current Imaging Techniques for Characterizing Liposome Morphology

There are currently a number of imaging techniques available for evaluating the morphology of liposomes and other nanoparticles, with each having its own advantages and disadvantages that should be considered when interpreting data. Controlling and validating the morphology of nanoparticles is of key importance for the effective clinical translation of liposomal formulations. There are a number of physical characteristics of liposomes that determine their in vivo behavior, including size, surface characteristics, lamellarity, and homogeneity. Despite the great importance of the morphology of nanoparticles, it is generally not well-characterized and is difficult to control. Appropriate imaging techniques provide important details regarding the morphological characteristics of nanoparticles, and should be used in conjunction with other methods to assess physicochemical parameters. In this review, we will discuss the advantages and limitations of available imaging techniques used to evaluate liposomal formulations.

Size-dependent uptake of electrically neutral amphipathic polymeric nanoparticles by cell-sized liposomes and an insight into their internalization mechanism in living cells

The size-dependent uptake of amphipathic uncharged-nanoparticles in cell-sized liposomes is emerging as a new insight into their internalization mechanism in living cells.

Determination of Nonspherical Morphology of Doxorubicin-Loaded Liposomes by Atomic Force Microscopy

The 3-D morphology of doxorubicin (DOX)-loaded liposomes with a size of circa 100 nm was characterized by atomic force microscopy in an aqueous environment. Prolate liposomes appear in accordance with linear expansion of DOX fiber bundles precipitated inside liposomes. Oblate and concave liposomes were simultaneously observed with increased DOX concentrations; however, their morphologies were not readily determined by 2-D cryo-TEM imaging. Precise data analysis of the 3-D parameters of each liposome allowed semiquantitative evaluation of the transformation of spherical liposomes into nonspherical-prolate, oblate, and concave liposomes. In addition, nonspherical liposomes became spherical on the replacement of the liposomal outer phase consisting of a sucrose solution, with water and subsequent water influx. All spherical liposomes transformed into oblate and concave liposomes with a return to hyperosmotic conditions, when transferred from water to sucrose solution. Furthermore, the concave liposomes did not appear under DOX incubation conditions (65°C), which could be due to the amorphous and supersaturated DOX inside the liposomes that restrained liposomal shrinkage. As atomic force microscopy has improved our ability to image 3-D morphologies of liposomes in various conditions, it is an alternative analytical tool to cryo-TEM and may have future applications in regulatory tests for quality control and assurance.

Supported pulmonary surfactant bilayers on silica nanoparticles: formulation, stability and impact on lung epithelial cells

Studies have shown that following exposure to particulate matter, ultrafine fractions (<100 nm) may deposit along the respiratory tract down to the alveolar region. To assess the effects of nanoparticles on the lungs, it is essential to address the question of their biophysicochemical interaction with the different pulmonary environments, including the lung lining fluids and the epithelia. Here we examine one of these interactive scenarios and study the role of supported lipid bilayers (SLB) in the effect of 40 nm fluorescent silica particles on living cells. We first study the particle phase behavior in the presence of Curosurf®, a pulmonary surfactant substitute used in replacement therapies. It is found that Curosurf® vesicles interact strongly with the nanoparticles, but do not spontaneously form SLBs. To achieve this goal, we use sonication to reshape the vesicular membranes and induce lipid fusion around the particles. Centrifugal sedimentation and electron microscopy are carried out to determine the optimum coating conditions and layer thickness. We then explore the impact of surfactant SLBs on the cytotoxic potential and interactions towards a malignant epithelial cell line. All in vitro assays indicate that SLBs mitigate the particle toxicity and internalization rates. In the cytoplasm, the particle localization is also strongly coating dependent. It is concluded that SLBs profoundly affect cellular interactions and functions in vitro and could represent an alternative strategy for particle coating. The current data also shed some light on the potential mechanisms pertaining to the particle or pathogen transport through the air-blood barrier.

Membrane interactions and antimicrobial effects of inorganic nanoparticles

Interactions between nanoparticles and biological membranes are attracting increasing attention in current nanomedicine, and play a key role both for nanotoxicology and for utilizing nanomaterials in diagnostics, drug delivery, functional biomaterials, as well as combinations of these, e.g., in theranostics. In addition, there is considerable current interest in the use of nanomaterials as antimicrobial agents, motivated by increasing resistance development against conventional antibiotics. Here, various nanomaterials offer opportunities for triggered functionalites to combat challenging infections. Although the performance in these diverse applications is governed by a complex interplay between the nanomaterial, the properties of included drugs (if any), and the biological system, nanoparticle-membrane interactions constitute a key initial step and play a key role for the subsequent biological response. In the present overview, the current understanding of inorganic nanomaterials as antimicrobial agents is outlined, with special focus on the interplay between antimicrobial effects and membrane interactions, and how membrane interactions and antimicrobial effects of such materials depend on nanoparticle properties, membrane composition, and external (e.g., light and magnetic) fields.

Design of Multivalent Inhibitors for Preventing Cellular Uptake

Cellular entry, the first crucial step of viral infection, can be inhibited by molecules adsorbed on the virus surface. However, apart from using stronger affinity, little is known about the properties of such inhibitors that could increase their effectiveness. Our simulations showed that multivalent inhibitors can be designed to be much more efficient than their monovalent counterparts. For example, for our particular simulation model, a single multivalent inhibitor spanning 5 to 6 binding sites is enough to prevent the uptake compared to the required 1/3 of all the receptor binding sites needed to be blocked by monovalent inhibitors. Interestingly, multivalent inhibitors are more efficient in inhibiting the uptake not only due to their increased affinity but mainly due to the co-localization of the inhibited receptor binding sites at the virion's surface. Furthermore, we show that Janus-like inhibitors do not induce virus aggregation. Our findings may be generalized to other uptake processes including bacteria and drug-delivery.

Morphology visualization of irregular shape bacteria by electron holography and tomography

In the current work, irregular morphology of Staphylococcus aureus bacteria has been visualized by phase retrieval employing off-axis electron holography (EH) and 3D reconstruction electron tomography using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Bacteria interacting with gold nanoparticles (AuNP) acquired a shrunken or irregular shape due to air dehydration processing. STEM imaging shows the attachment of AuNP on the surface of cells and suggests an irregular 3D morphology of the specimen. The phase reconstruction demonstrates that off-axis electron holography can reveal with a single hologram the morphology of the specimen and the distribution of the functionalized AuNPs. In addition, EH reduces significantly the acquisition time and the cumulative radiation damage (in three orders of magnitude) over biological samples in comparison with multiple tilted electron expositions intrinsic to electron tomography, as well as the processing time and the reconstruction artifacts that may arise during tomogram reconstruction.

Cellular uptake of nanoparticles: journey inside the cell

Nanoscale materials are increasingly found in consumer goods, electronics, and pharmaceuticals. While these particles interact with the body in myriad ways, their beneficial and/or deleterious effects ultimately arise from interactions at the cellular and subcellular level. Nanoparticles (NPs) can modulate cell fate, induce or prevent mutations, initiate cell-cell communication, and modulate cell structure in a manner dictated largely by phenomena at the nano-bio interface. Recent advances in chemical synthesis have yielded new nanoscale materials with precisely defined biochemical features, and emerging analytical techniques have shed light on nuanced and context-dependent nano-bio interactions within cells. In this review, we provide an objective and comprehensive account of our current understanding of the cellular uptake of NPs and the underlying parameters controlling the nano-cellular interactions, along with the available analytical techniques to follow and track these processes.

Anionic and Cationic Silver Nanoparticle Binding Restructures Net-Anionic PC/PG Monolayers with Saturated or Unsaturated Lipids

We have examined the interactions between polymer-coated anionic (Ag-COOH) and cationic (Ag-NH) silver nanoparticles, and net-anionic lipid monolayers using dynamic surface pressure measurements. Monolayers composed of saturated or monounsaturated mixtures of anionic phosphatidylglycerol (PG) and zwitterionic phosphatidylcholine (PC) lipids (3:1 molar ratio) were used to determine how lipid packing and monolayer phase state influence the extent of nanoparticle binding and the monolayer response. Anionic Ag-COOH inserted into saturated dipalmitoyl-PC/PG (DPPC/DPPG) and dioleoyl-PC/PG (DOPC/DOPG) monolayers at a low initial surface pressure (10 mN m^-1) and caused lipid condensation at high initial surface pressures (20 and 30 mN m^-1). Hydrophobic interactions were responsible for insertion, while electrostatic and charge-dipole interactions with PCs were responsible for condensation. In contrast, cationic Ag-NH inserted only into saturated DPPC/DPPG monolayers and otherwise led to lipid condensation. For Ag-NH, adsorption was driven primarily by electrostatic interactions with PGs. Analysis of the subphase Ag and phosphorus concentrations confirmed that Ag-NH had a higher degree binding compared to Ag-COOH, and that the monolayer response was not due to lipid extraction.

Membrane-mediated aggregation of anisotropically curved nanoparticles

Using systematic numerical simulations, we study the self-assembly of elongated curved nanoparticles on lipid vesicles. Our simulations are based on molecular dynamics of a coarse-grained implicit-solvent model of self-assembled lipid membranes with a Langevin thermostat. Here we consider only the case wherein the nanoparticle-nanoparticle interaction is repulsive, only the concave surface of the nanoparticle interacts attractively with the lipid head groups and only the outer surface of the vesicle is exposed to the nanoparticles. Upon their adhesion on the vesicle, the curved nanoparticles generate local curvature on the membrane. The resulting nanoparticle-generated membrane curvature leads in turn to nanoparticle self-assembly into two main types of aggregates corresponding to chain aggregates at low adhesion strengths and aster aggregates at high adhesion strength. The chain-like aggregates are due to the fact that at low values of adhesion strength, the nanoparticles prefer to lie parallel to each other. As the adhesion strength is increased, a splay angle between the nanoparticles is induced with a magnitude that increases with increasing adhesion strength. The origin of the splay angles between the nanoparticles is shown to be saddle-like membrane deformations induced by a tilt of the lipids around the nanoparticles. This phenomenon of membrane mediated self-assembly of anisotropically curved nanoparticles is explored for systems with varying nanoparticle number densities, adhesion strength, and nanoparticle intrinsic curvature.

Effects of charge and surface defects of multi-walled carbon nanotubes on the disruption of model cell membranes

The direct contact between multi-walled carbon nanotubes (MWCNTs) and cell membranes causes membrane disruption, potentially leading to cytotoxicity. However, the role of electrostatic forces and MWCNT properties is still open to debate. In this study, the influences of charge and MWCNT surface defects on membrane disruption were investigated by microscopy and a quartz crystal microbalance with dissipation monitoring (QCM-D). Positively/negatively charged giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs) were made as model cell membranes. Negatively charged MWCNTs disrupted the GUVs containing positively charged lipids, which confirmed the electrostatically mediated interaction. However, the mass loss was detected from the negatively charged SLBs after MWCNT exposure, which suggests the extraction of phospholipids. The defect degree of MWCNTs correlated with their adhesion amount on the membranes. Both the oxygenated functional groups and unoxidized dangling carbon bonds were active sites for MWCNT-membrane interactions. The MWCNTs were observed to be engulfed inside the GUVs. The results clearly demonstrate that phospholipid extraction by MWCNTs could occur in electrostatically repulsive conditions, and MWCNT defects were active binding sites whether or not they were oxygenated. Our findings should be helpful in the design and safe applications of carbon nanomaterials.

Incorporation of Soft Particles into Lipid Vesicles: Effects of Particle Size and Elasticity

The interaction between particles and lipid biomembranes plays an essential role in many fields such as endocytosis, drug delivery, and intracellular traffic. Here we conduct a theoretical study on the incorporation of elastic particles of different sizes and rigidities into a lipid vesicle through adhesive wrapping. It is shown that while the incorporation of relatively small particles involves smooth shape evolution, the vesicle wrapping of large particles exhibits a discontinuous shape transition, followed by a protrusion of the vesicle membrane at infinitesimal cost of elastic deformation energy. Moreover, softer particles require stronger adhesion energy to achieve successful internalization and delay the onset of discontinuous shape transition to a higher wrapping degree. Depending on the adhesion energy, particle-vesicle size, and rigidity ratios, and the spontaneous curvature of the vesicle, a rich variety of wrapping phase diagrams consisting of stable and metastable states of no-wrapping, partial-wrapping, and full-wrapping are established. The underlying mechanism of the discontinuous shape transformation of the vesicle and the relation between the uptake proneness and uptake efficiency are discussed. These results shed further light on the elasticity effects in cellular uptake of elastic particles and may provide rational design guidelines for controlled endocytosis and diagnostics delivery.