Microparticle Assembly Pathways on Lipid Membranes

Coupling liquid phases in 3D condensates and 2D membranes: Successes, challenges, and tools

This review describes the major experimental challenges researchers meet when attempting to couple phase separation between membranes and condensates. Although it is well known that phase separation in a 2D membrane could affect molecules capable of forming a 3D condensate (and vice versa), few researchers have quantified the effects to date. The scarcity of these measurements is not due to a lack of intense interest or effort in the field. Rather, it reflects significant experimental challenges in manipulating coupled membranes and condensates to yield quantitative values. These challenges transcend many molecular details, which means they impact a wide range of systems. This review highlights recent exciting successes in the field, and it lays out a comprehensive list of tools that address potential pitfalls for researchers who are considering coupling membranes with condensates.

Nonadditivity in interactions between three membrane-wrapped colloidal spheres

Many cell functions require a concerted effort from multiple membrane proteins, for example, for signaling, cell division, and endocytosis. One contribution to their successful self-organization stems from the membrane deformations that these proteins induce. While the pairwise interaction potential of two membrane-deforming spheres has recently been measured, membrane-deformation-induced interactions have been predicted to be nonadditive, and hence their collective behavior cannot be deduced from this measurement. We here employ a colloidal model system consisting of adhesive spheres and giant unilamellar vesicles to test these predictions by measuring the interaction potential of the simplest case of three membrane-deforming, spherical particles. We quantify their interactions and arrangements and, for the first time, experimentally confirm and quantify the nonadditive nature of membrane-deformation-induced interactions. We furthermore conclude that there exist two favorable configurations on the membrane: (1) a linear and (2) a triangular arrangement of the three spheres. Using Monte Carlo simulations, we corroborate the experimentally observed energy minima and identify a lowering of the membrane deformation as the cause for the observed configurations. The high symmetry of the preferred arrangements for three particles suggests that arrangements of many membrane-deforming objects might follow simple rules.

A colloidal viewpoint on the sausage catastrophe and the finite sphere packing problem

It is commonly believed that the most efficient way to pack a finite number of equal-sized spheres is by arranging them tightly in a cluster. However, mathematicians have conjectured that a linear arrangement may actually result in the densest packing. Here, our combined experimental and simulation study provides a physical realization of the finite sphere packing problem by studying arrangements of colloids in a flaccid lipid vesicle. We map out a state diagram displaying linear, planar, and cluster conformations of spheres, as well as bistable states which alternate between cluster-plate and plate-linear conformations due to membrane fluctuations. Finally, by systematically analyzing truncated polyhedral packings, we identify clusters of 56 ≤ N ≤ 70 number of spheres, excluding N = 57 and 63, that pack more efficiently than linear arrangements.

Wrapping Pathways of Anisotropic Dumbbell Particles by Giant Unilamellar Vesicles

Endocytosis is a key cellular process involved in the uptake of nutrients, pathogens, or the therapy of diseases. Most studies have focused on spherical objects, whereas biologically relevant shapes can be highly anisotropic. In this letter, we use an experimental model system based on Giant Unilamellar Vesicles (GUVs) and dumbbell-shaped colloidal particles to mimic and investigate the first stage of the passive endocytic process: engulfment of an anisotropic object by the membrane. Our model has specific ligand-receptor interactions realized by mobile receptors on the vesicles and immobile ligands on the particles. Through a series of experiments, theory, and molecular dynamics simulations, we quantify the wrapping process of anisotropic dumbbells by GUVs and identify distinct stages of the wrapping pathway. We find that the strong curvature variation in the neck of the dumbbell as well as membrane tension are crucial in determining both the speed of wrapping and the final states.

Transgenerational impacts of micro(nano)plastics in the aquatic and terrestrial environment

Plastic particles of diameters ranging from 1 to 1000 nm and > 1 µm to 5 mm are respectively known as nanoplastics and microplastics, and are collectively termed micro(nano)plastics (MNPs). They are ubiquitously present in aquatic and terrestrial environments, posing adverse multifaceted ecological impacts. Recent transgenerational studies have demonstrated that MNPs negatively impact both the exposed parents and their unexposed generations. Therefore, this review summarizes the available research on the transgenerational impacts of MNPs in aquatic and terrestrial organisms, induced by exposure to MNPs alone or in combination with other organic and inorganic chemicals. The most commonly reported transgenerational effects of MNPs include tissue bioaccumulation and transfer, affecting organisms' survival, growth, reproduction, and energy metabolism; inducing oxidative stress; enzyme and genetic responses; and causing tissue damage. Similarly, co-exposure to MNPs and chemicals (organic and inorganic pollutants) significantly impacts survival, growth, and reproduction and induces oxidative stress, thyroid disruption, and genetic toxicity in organisms. The characteristics of MNPs (degree of aging, size, shape, polymer type, and concentration), exposure type and duration (parental exposure vs. multigenerational exposure and acute exposure vs. chronic exposure), and MNP-chemical interactions are the main factors affecting transgenerational impacts. Selecting MNP properties based on their realistic environmental behavior, employing more diverse animal models, and considering chronic exposure and MNP-chemical mixture exposure are salient research prospects for an in-depth understanding of the transgenerational impacts of MNPs.

Surface-Functionalized Polystyrene Nanoparticles Alter the Transmembrane Potential via Ion-Selective Pores Maintaining Global Bilayer Integrity

Although nanoplastics have well-known toxic effects toward the environment and living organisms, their molecular toxicity mechanisms, including the nature of nanoparticle-cell membrane interactions, are still under investigation. Here, we employ dynamic light scattering, quartz crystal microbalance with dissipation monitoring, and electrophysiology to investigate the interaction between polystyrene nanoparticles (PS NPs) and phospholipid membranes. Our results show that PS NPs adsorb onto lipid bilayers creating soft inhomogeneous films that include disordered defects. PS NPs form an integral part of the generated channels so that the surface functionalization and charge of the NP determine the pore conductive properties. The large difference in size between the NP diameter and the lipid bilayer thickness (∼60 vs ∼5 nm) suggests a particular and complex lipid-NP assembly that is able to maintain overall membrane integrity. In view of this, we suggest that NP-induced toxicity in cells could operate in more subtle ways than membrane disintegration, such as inducing lipid reorganization and transmembrane ionic fluxes that disrupt the membrane potential.

Intergenerational and biological effects of roxithromycin and polystyrene microplastics to Daphnia magna

The influence of microplastics (MPs) on transgenerational effects of pharmaceuticals are drawing growing attention, however, whether aged process will alter the carrier effects of MPs were unknown. In this study, the intergenerational toxicity of single and combined exposure of polystyrene microplastics (PS-MPs) and roxithromycin (ROX) were investigated at the environmentally related concentrations, using Daphina magna as test organism. In the presence of UV-aged PS-MPs, the survival of D. magna for maternal generation (F0) at ROX concentration of 0.1 and 10 µg/L were increased by 20% and 40%, respectively. Meanwhile, the inhibition effects of ROX on the number of offspring and intrinsic rate of natural increase were obviously moderated. All these reproductive toxicity of ROX and PS-MPs in the first offspring (F1) were further aggravated both for the single and combined exposure. And the adverse effects disappeared much easier for the single exposure compared to the co-exposure through subsequent recovery. The combined exposure resulted in the change of inhibition of ROX on the swimming velocity and acceleration of D. magna into induction, while the feeding behavior kept inhibited. The AChE activity was distinctly increased by 1.61-3.25 times for the single and combined treatments, and the induction level of UV-aged MPs was higher than that of original MPs. Oxidative stress of the single exposure of ROX and original PS-MPs was observed with obvious induction of T-AOC and SOD activity, while the significant increase of MDA content was observed for the co-exposure. Among all indicators, the biochemical biomarkers and time of first brood were attributed to a class among all indicators, indicating that the time of first brood might be the most sensitive reproductive toxicity index. These results illustrated that both maternal impacts and offspring quality need to be considered for assessment of interaction of emerging contaminants.

Controlled adhesion, membrane pinning and vesicle transport by Janus particles

The interactions between biomembranes and particles are key to many applications, but the lack of controllable model systems to study them limits the progress in their research. Here, we describe how Janus polystyrene microparticles, half coated with iron, can be partially engulfed by artificial cells, namely giant vesicles, with the goals to control and investigate their adhesion and degree of encapsulation. The interaction between the Janus particles and these model cell membrane systems is mediated by electrostatic charge, offering a further mode of modulation in addition to the iron patches. The ferromagnetic particle coatings also enable manipulation and transport of the vesicles by magnetic fields.

Spatial arrangements of spherical nanoparticles on lipid vesicles

We report results of a numerical investigation of the modes of adhesion of two spherical nanoparticles (NPs) on lipid vesicles based on molecular dynamics simulations, in conjunction with the weighted histogram analysis method, of an implicit-solvent model of self-assembled membranes. Our investigation shows that the NPs exhibit a sequence of three modes of adhesion. For low adhesive interactions, the adhering NPs are apart from each other. As the adhesive interaction is increased, the NPs dimerize into in-plane dimers. As the adhesive interaction is further increased for relatively large vesicles, the NPs dimerize into tubular dimers. However, for small vesicles, the tubular dimer state is not observed. For higher values of the adhesive interaction, four endocytosis modes are observed, depending on the initial locations of the NPs on the vesicle and the relative size of the NPs with respect to that of the vesicle. For relatively large vesicles, the NPs are endocytosed individually or as a dimer. For relatively small vesicles, only one NP is endocytosed if the initial distance between the NPs is large, while the second NP remains adhered to the outer leaflet of the vesicle. However, if the initial distance between the NPs is small, one NP is endocytosed, while the other is internalized in the vesicle through a pore.

More than just a barrier: using physical models to couple membrane shape to cell function

The correct execution of many cellular processes, such as division and motility, requires the cell to adopt a specific shape. Physically, these shapes are determined by the interplay of the plasma membrane and internal cellular driving factors. While the plasma membrane defines the boundary of the cell, processes inside the cell can result in the generation of forces that deform the membrane. These processes include protein binding, the assembly of protein superstructures, and the growth and contraction of cytoskeletal networks. Due to the complexity of the cell, relating observed membrane deformations back to internal processes is a challenging problem. Here, we review cell shape changes in endocytosis, cell adhesion, cell migration and cell division and discuss how by modeling membrane deformations we can investigate the inner working principles of the cell.

Understanding the interactions of poly(methyl methacrylate) and poly(vinyl chloride) nanoparticles with BHK-21 cell line

Microplastic and nanoplastic particles are prevalent in the environment and are beginning to enter the living system through multiple channels. Currently, little is known about the impact of plastic nanoparticles in living organisms. In order to investigate the health impact of micro- and nanoparticles of common polymers in a systematic way, luminescent plastic nanoparticles from two common polymers, polyvinyl chloride (PVC) and poly (methyl methacrylate) (PMMA) with relatively narrow size distribution are prepared using a nanoprecipitation method. As a model system, BHK-21 cells were exposed to polymer nanoparticles to understand the mode of uptake, internalization and biochemical changes inside the cells. The cellular effects of the nanoparticles were evaluated by monitoring the changes in cell viability, cell morphology, concentrations of reactive oxygen species (ROS), adenine triphosphate (ATP) and lactate dehydrogenase at different concentrations of the nanoparticles and time of exposure. PVC and PMMA nanoparticles induced a reduction in the cell viability along with a reduction of ATP and increase of ROS concentrations in a dose- and time-dependent manner. The plastic nanoparticles are internalized into the cell via endocytosis, as confirmed by Dynasore inhibition assay and colocalization with latex beads. Our findings suggest that plastic nanoparticle internalization could perturb cellular physiology and affect cell survival under laboratory conditions.

Wrapping of Microparticles by Floppy Lipid Vesicles

Lipid membranes, the barrier defining living cells and many of their subcompartments, bind to a wide variety of nano- and micrometer sized objects. In the presence of strong adhesive forces, membranes can strongly deform and wrap the particles, an essential step in crossing the membrane for a variety of healthy and disease-related processes. A large body of theoretical and numerical work has focused on identifying the physical properties that underly wrapping. Using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure a wrapping phase diagram and make quantitative comparisons to theoretical models. Our data are consistent with a model of membrane-particle interactions accounting for the adhesive energy per unit area, membrane bending rigidity, particle size, and vesicle radius.

Interactions of particulate matter and pulmonary surfactant: Implications for human health

Particulate matter (PM), which is the primary contributor to air pollution, has become a pervasive global health threat. When PM enters into a respiratory tract, the first body tissues to be directly exposed are the cells of respiratory tissues and pulmonary surfactant. Pulmonary surfactant is a pivotal component to modulate surface tension of alveoli during respiration. Many studies have proved that PM would interact with pulmonary surfactant to affect the alveolar activity, and meanwhile, pulmonary surfactant would be adsorbed to the surface of PM to change the toxic effect of PM. This review focuses on recent studies of the interactions between micro/nanoparticles (synthesized and environmental particles) and pulmonary surfactant (natural surfactant and its models), as well as the health effects caused by PM through a few significant aspects, such as surface properties of PM, including size, surface charge, hydrophobicity, shape, chemical nature, etc. Moreover, in vitro and in vivo studies have shown that PM leads to oxidative stress, inflammatory response, fibrosis, and cancerization in living bodies. By providing a comprehensive picture of PM-surfactant interaction, this review will benefit both researchers for further studies and policy-makers for setting up more appropriate regulations to reduce the adverse effects of PM on public health.

Primary and Secondary Plastic Particles Exhibit Limited Acute Toxicity but Chronic Effects on Daphnia magna

Nanoplastics (NPs; <0.1 μm) are speculated to be a bigger ecological threat due to their predicted wider distribution, higher concentrations, and bioavailability. Primary NPs are manufactured to be that size, while secondary NPs originate from fragmentation of bigger debris. To date, the long-term impact of NPs in freshwater systems, particularly secondary NPs, is not well-understood. Thus, we employed a freshwater invertebrate, Daphnia magna, to investigate the chronic effects of model primary NPs, fluorescent polystyrene nanospheres (PS-NPs; 20 nm), and water leachate of weathered single-use plastics that contained micro- and nanosized particles. In experiment 1, parent Daphnia (F0) were exposed to 1 and 50 mg/L PS-NPs until the production of the neonates (F1) followed by a two-generation recovery. PS-NPs were mainly detected in the intestine and brood chamber in F0 and transferred to F1 and F2. PS-NPs significantly decreased the appendage curling and heartbeat rate in F0 and reduced reproduction in F2. In experiment 2, the plastic leachate also reduced the appendage curling rate but increased growth and reproduction. The results suggest that the acute toxicity of primary and secondary plastic particles is low even at high concentrations, but their chronic and sublethal effects should not be overlooked.

Programmable interactions with biomimetic DNA linkers at fluid membranes and interfaces

At the heart of the structured architecture and complex dynamics of biological systems are specific and timely interactions operated by biomolecules. In many instances, biomolecular agents are spatially confined to flexible lipid membranes where, among other functions, they control cell adhesion, motility and tissue formation. Besides being central to several biological processes, multivalent interactions mediated by reactive linkers confined to deformable substrates underpin the design of synthetic-biological platforms and advanced biomimetic materials. Here we review recent advances on the experimental study and theoretical modelling of a heterogeneous class of biomimetic systems in which synthetic linkers mediate multivalent interactions between fluid and deformable colloidal units, including lipid vesicles and emulsion droplets. Linkers are often prepared from synthetic DNA nanostructures, enabling full programmability of the thermodynamic and kinetic properties of their mutual interactions. The coupling of the statistical effects of multivalent interactions with substrate fluidity and deformability gives rise to a rich emerging phenomenology that, in the context of self-assembled soft materials, has been shown to produce exotic phase behaviour, stimuli-responsiveness, and kinetic programmability of the self-assembly process. Applications to (synthetic) biology will also be reviewed.

Poly(Ionic Liquid) Nanoparticles Selectively Disrupt Biomembranes

Polymer-based nanoparticles have an increasing presence in research due to their attractive properties, such as flexible surface functionality design and the ability to scale up production. Poly(ionic liquid) (PIL) nanoparticles of size below 50 nm are very unique in terms of their high charge density and internal onion-like morphology. The interaction between PIL nanoparticles and giant unilamellar vesicles (GUVs) of various surface charge densities is investigated. GUVs represent a convenient model system as they mimic the size and curvature of plasma membranes, while simultaneously offering direct visualization of the membrane response under the microscope. Incubating PIL nanoparticles with GUVs results in poration of the lipid membrane in a concentration- and charge-dependent manner. A critical poration concentration of PILs is located and the interactions are found to be analogous to those of antimicrobial peptides. Microbial mimetic membranes are already affected at submicromolar PIL concentrations where contrast loss is observed due to sugar exchange across the membrane, while at high concentrations the collapse of vesicles is observed. Finally, a confocal microscopy-based approach assessing the particle permeation through the membrane is reported and a mechanism based on bilayer frustration and pore stabilization via particle integration in the membrane is proposed.

Surfactant-free Colloidal Particles with Specific Binding Affinity

Colloidal particles with specific binding affinity are essential for in vivo and in vitro biosensing, targeted drug delivery, and micrometer-scale self-assembly. Key to these techniques are surface functionalizations that provide high affinities to specific target molecules. For stabilization in physiological environments, current particle coating methods rely on adsorbed surfactants. However, spontaneous desorption of these surfactants typically has an undesirable influence on lipid membranes. To address this issue and create particles for targeting molecules in lipid membranes, we present here a surfactant-free coating method that combines high binding affinity with stability at physiological conditions. After activating charge-stabilized polystyrene microparticles with EDC/Sulfo-NHS, we first coat the particles with a specific protein and subsequently covalently attach a dense layer of poly(ethyelene) glycol. This polymer layer provides colloidal stability at physiological conditions as well as antiadhesive properties, while the protein coating provides the specific affinity to the targeted molecule. We show that NeutrAvidin-functionalized particles bind specifically to biotinylated membranes and that Concanavalin A-functionalized particles bind specifically to the glycocortex of Dictyostelium discoideum cells. The affinity of the particles changes with protein density, which can be tuned during the coating procedure. The generic and surfactant-free coating method reported here transfers the high affinity and specificity of a protein onto colloidal polystyrene microparticles.