Interaction modes between nanosized graphene flakes and liposomes: Adsorption, insertion and membrane fusion

Differences in interaction of graphene/graphene oxide with bacterial and mammalian cell membranes

Graphene, a single layer, hexagonally packed two-dimensional carbon sheet is an attractive candidate for diverse applications including antibacterial potential and drug delivery. One of the knowledge gaps in biomedical application of graphene is the interaction of these materials with the cells. To address this, we investigated the interaction between graphene materials (graphene and graphene oxide) and plasma membranes of cells (bacterial and mammalian cells). The interactions of four of the most abundant phospholipids in bacteria and mammalian plasma membranes with graphene materials were studied using density functional theory (DFT) at the atomic level. The calculations showed that the mammalian phospholipids have stronger bonding to each other compared to bacterial phospholipids. When the graphene/graphene oxide sheet is approaching the phospholipid pairs, the bacterial pairs exhibit less repulsive interactions, thereby a more stable system with the sheets was found. We also assembled bacterial and mammalian phospholipids into liposomes. We further observed that the bacterial liposomes and cells let the graphene flakes penetrate the membrane. The differential scanning calorimetry measurements of liposomes revealed that the bacterial liposomes have the lowest heat capacity; this strengthens the theoretical predictions of weaker interaction between the bacterial phospholipids compared to the mammalian phospholipids. We further demonstrated that graphene oxide could be internalized into the mammalian liposomes without disrupting the membrane integrity. The results suggest that the weak bonding among bacteria phospholipids and less repulsive force when graphene materials approach, result in graphene materials interacting differently with the bacteria compared to mammalian cells.

Cellular Uptake of Engineered Extracellular Vesicles: Biomechanisms, Engineered Strategies, and Disease Treatment

Extracellular vesicles (EVs), lipid-enclosed nanosized membrane vesicles, are regarded as new vehicles and therapeutic agents in intercellular communication. During internal circulation, if EVs are not effectively taken up by recipient cells, they will be cleared as "cellular waste" and unable to deliver therapeutic components. It can be seen that cells uptake EVs are the prerequisite premise for sharing intercellular biological information. However, natural EVs have a low rate of absorption by their recipient cells, off-target delivery, and rapid clearance from circulation, which seriously reduces the utilization rate. Affecting the uptake rate of EVs through engineering technologies is essential for therapeutic applications. Engineering strategies for customizing EV uptake can potentially overcome these limitations and enable desirable therapeutic uses of EVs. In this review, the mechanism and influencing factors of natural EV uptake will be described in detail. Targeting each EV uptake mechanism, the strategies of engineered EVs and their application in diseases will be emphatically discussed. Finally, the future challenges and perspectives of engineered EVs are presented multidimensionally.

Nanoparticle-induced biomembrane fusion: unraveling the effect of core size on stalk formation

Membrane fusion in vitro is a strategy to load model or cell-derived vesicles with proteins, drugs, and genetic materials for theranostic applications. It is thus crucial to develop strategies to control the fusion process, also through synthetic fusogenic agents. Ligand-protected, membrane-penetrating gold nanoparticles (Au NPs) can facilitate membrane fusion, but the molecular mechanisms remain unresolved. Here, we tackle NP-induced stalk formation using a coarse-grained molecular dynamics approach and enhanced sampling techniques. We show that smaller (2 nm in diameter) NPs lead to a lower free energy barrier and higher stalk stability than larger NPs (4 nm). We demonstrate that this difference is due to a different ligand conformational freedom, which in turn depends on the Au core curvature. Our study provides precious insights into the mechanisms underlying NP-mediated membrane fusion, while our computational approach is general and applicable to studying stalk formation caused by other fusogenic agents.

The role of size, charge, and cholesterol of cell membrane models in interactions with graphene oxide

The growing in manufacturing and applications of graphene oxide (GO), a two-dimensional nanomaterial, highlights the need for a better understanding of its environmental impact and toxicity. This work investigates the interaction of GO with cell membrane models as an indication for GO's potential harmfulness. A wide range of biologically-relevant membrane parameters (size, charge and, cholesterol content) and simple optical techniques were used to evaluate the outcome of interactions of vesicular cell membrane models with GO. Loss of membrane integrity was found to be positively correlated with electrostatic attraction and negatively correlated with cholesterol content. The size of vesicle-GO aggregates increased as a function of initial vesicle size, while cholesterol content was found to have a negligible effect on aggregation. Interestingly, charged vesicles reduced vesicle-GO aggregate size either by electrostatic repulsion of negatively charge vesicles or by GO folding following attachment of positively charge vesicles. Overall, by examining how key biologically-relevant parameters of membrane models affect interactions with GO, we have augmented the understanding of the potential threats of GO towards biological cell and to the environment.

Effect of Shape on the Entering of Graphene Quantum Dots into a Membrane: A Molecular Dynamics Simulation

Graphene quantum dots (GQDs), a new quasi-zero-dimensional nanomaterial, have the advantages of a smaller transverse size, better biocompatibility, and lower toxicity. They have potential applications in biosensors, drug delivery, and biological imaging. Therefore, it is particularly important to understand the transport mechanism of the GQDs on the cell membrane. In particular, the effect of the GQD shapes on the translocation mechanism should be well understood. In this study, the permeation process of the GQDs with different shapes through a 1-palmitoyl-2-oleoylphosphatidylcholine membrane was studied using molecular dynamics. The results show that all small-sized GQDs with different shapes translocated through the lipid membrane at a nanosecond timescale. The GQDs tend to remain on the surface of the cell membrane; then, the corners of the GQDs spontaneously enter the cell membrane; and, finally, the entire GQDs enter the cell membrane and tend to stabilize in the middle of the cell membrane. Moreover, the GQDs do not induce notable damage to the cell membrane, indicating that they are less toxic to cells and can be used as a potential biomedical material.

Investigation on drug entrapment location in liposomes and transfersomes based on molecular dynamics simulation

In this study, liposome and transfersome were successfully constructed using molecular dynamics simulation. Three drugs with different polarity, including 5-fluorouracil, ligustrazine, and osthole, were selected as model drugs to study the distribution of drugs in lipid vesicles by calculating the radial distribution function and the potential of mean force. The solubility parameters between drugs and different regions in lipid vesicles were calculated to characterize the compatibility of drugs in different regions in lipid vesicles, which provided the basis for the conclusion of this paper. It showed that the radial distribution function and the potential of mean force were consistent in the characterization of drug distribution in vesicles, and the drug distribution in vesicles was closely related to the compatibility between drugs and vesicles. Therefore, the radial distribution function and the potential of mean force can be used to characterize the distribution of drugs in vesicles, and molecular simulation technology has a great potential in studying the characteristics of vesicles. Graphical abstract.

Molecular mechanisms underlying the role of the puckered surface in the biocompatibility of black phosphorus

As a newly emerging two-dimensional material, black phosphorus (BP) has received broad attention in the field of biomedical applications. Prior to its clinical application, its cytotoxicity to cells should be carefully evaluated; however, this field is still in its infancy. Motivated by this, we performed molecular dynamics (MD) simulations to systematically investigate the potential mechanisms of the cytotoxicity of BP to the lipid membrane, including lipid extraction, penetration into the membrane, and the impacts of BP on the physical properties of the membrane. Surprisingly, we observed that BP could not extract lipid molecules from the membrane. The thermodynamic analyses suggested that the puckered surface structure could weaken the interactions between BP and lipid molecules, thus inhibiting the lipid extraction. Additionally, through simulating the spontaneous interaction modes between BP and the lipid membrane, we found that the "passivated" edges of BP prohibited it from penetrating into the membrane. As a result, BP could only spontaneously lie parallel on the surface of the membrane, in which manner BP exerted little influence on the properties of the lipid membrane. To comprehensively appraise the cytotoxicity, we even artificially inserted BP into the membrane and compared the effects of BP and graphene on the properties of the membrane. Simulation results showed that the influences of the inserted BP on the lipid properties were much milder than those of graphene. Overall, the present work suggests that BP possesses distinctive biocompatibility benefiting from its puckered surface structure. This work provides a better understanding of the interactions between BP and the membrane, which may offer some useful suggestions for exploring strategies to improve the biocompatibility of nanomaterials.

Liposome Fusion Mediated by Hydrophobic Magnetic Nanoparticles Stabilized with Oleic Acid and Modulated by an External Magnetic Field

Membrane fusion is considered relevant in countless scientific areas and biotechnological processes, ranging from vital life events to biomedicine, pharmaceuticals, and materials engineering, among others. In this study, we employed hydrophobic oleic acid (OA)-coated magnetite (Fe₃O₄) nanoparticles (MNP-OA) as a platform to induce the fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine liposomes [large unilamellar vesicles (LUVs)] in a colloidal dispersion. This fusion was monitored through dynamic light scattering, turbidimetry, and fluorescence assay using the well-known Tb/dipicolinic acid (DPA) complex formation assay. MNP-OA have shown to be able to induce fusion with the mixing of liposomal inner content with direct dependence on the nanoparticle concentration added to the LUVs. Moreover, changes in the permeability of the liposome bilayer, upon the addition of MNP-OA to liposomes, were evaluated by studying the leakage of carboxyfluorescein and of the co-encapsulated Tb/DPA complex. These assays allowed us to determine that MNP-OA did not significantly modify liposome permeability during the fusion process. Transmission electron microscopy and confocal microscopy revealed that MNP-OA remained embedded in the lipid bilayer without producing membrane rupture, liposome deformation, or destruction. In addition, we evaluated the effect of applying a low-intensity magnetic field to the LUVs/MNP-OA system and observed that the nanoparticles considerably increased their fusogenic activity under this external stimulus, as well as they are capable of responding to low magnetic fields of around 0.45 mT. These results revealed the potential of hydrophobic magnetic nanoparticles, stabilized with OA, to act as a fusogen, thus representing a valuable tool for biotechnological applications.

Interaction of Graphene Nanoparticles and Lipid Membranes Displaying Different Liquid Orderings: A Molecular Dynamics Study

Understanding the effects of graphene-based nanomaterials on lipid membranes is fundamental to determine their environmental impact and the efficiency of their biomedical use. By means of molecular dynamics simulations of simple model lipid bilayers, we analyze in detail the different interaction modes. We have studied bilayers consisting of lipid species (including cholesterol) which display different internal liquid orderings. Nanometric graphene layers can be transiently adsorbed onto the lipid membrane and/or inserted in its hydrophobic region. Once inserted, graphene nanometric flakes display a diffusive dynamics in the membrane plane, they adopt diverse orientations depending on their size and oxidation degree, and they show a particular aversion to be placed close to cholesterol molecules in the membrane. Addition of graphene to phase-segregated ternary membranes is also investigated in the context of the lipid raft model for the lipid organization of biological membranes. Our simulation results show that graphene layers can be inserted indistinctly in the ordered and disordered regions. Once inserted, nanometric flakes migrate to disordered and cholesterol-poor lipid phases.

Influence of Single-Stranded DNA Coatings on the Interaction between Graphene Nanoflakes and Lipid Bilayers

Using molecular dynamics simulations, it is demonstrated that a partial coating of single-stranded DNA (ssDNA) reduces the penetration depth of a graphene nanoflake (GNF) into a phospholipid bilayer by attenuating the hydrophobic force that drives the penetration. As the GNF penetrates the bilayer, the ssDNA remains adsorbed to the GNF outside of the bilayer where it shields the graphene from the surrounding water. The penetration depth is found to be controlled by the amount of ssDNA coating the GNF, with a sparser coating resulting in a deeper penetration since the ssDNA shields less of the GNF surface. As the coating density is increased, the likelihood of the GNF entering the bilayer is reduced where it instead tends to lie flat on the bilayer surface with the sugar phosphate backbone of ssDNA interacting with the hydrophilic lipid head groups. While no bilayer disruption is observed for a partially inserted ssDNA-coated GNF, a larger, bare, partially inserted GNF is found to preferentially extract phospholipids from the bilayer, offering further evidence of lipid extraction as a main cytotoxicity mechanism of GNFs. Therefore, a coating of ssDNA may reduce the cytotoxicity of GNFs by shielding the unfavorable graphene-water interaction, thus preventing graphene penetration and lipid extraction.