An unusual pathway for the membrane wrapping of rodlike nanoparticles and the orientation- and membrane wrapping-dependent nanoparticle interaction

Probing wrapping dynamics of spherical nanoparticles by 3D vesicles using force-based simulations

Nanoparticles present in various environments can interact with living organisms, potentially leading to deleterious effects. Understanding how these nanoparticles interact with cell membranes is crucial for rational assessment of their impact on diverse biological processes. While previous research has explored particle-membrane interactions, the dynamic processes of particle wrapping by fluid vesicles remain incompletely understood. In this study, we introduce a force-based, continuum-scale model utilizing triangulated mesh representation and discrete differential geometry to investigate particle-vesicle interaction dynamics. Our model captures the transformation of vesicle shape and nanoparticle wrapping by calculating the forces arising from membrane bending energy and particle adhesion energy. Inspired by cell phagocytosis of large particles, we focus on establishing a quantitative understanding of large-scale vesicle deformation induced by the interaction with particles of comparable sizes. We first examine the interactions between spherical vesicles and individual nanospheres, both externally and internally, and quantify energy landscapes across different wrapping fractions of the nanoparticles. Furthermore, we explore multiple particle interactions with biologically relevant fluid vesicles with nonspherical shapes. Our study reveals that initial particle positions and interaction sequences are critical in determining the final equilibrium shapes of the vesicle-particle complexes in these interactions. These findings emphasize the importance of nanoparticle positioning and wrapping fractions in the dynamics of particle-vesicle interactions, providing crucial insights for future research in the field.

Converting Nanotoxicity Data to Information Using Artificial Intelligence and Simulation

Decades of nanotoxicology research have generated extensive and diverse data sets. However, data is not equal to information. The question is how to extract critical information buried in vast data streams. Here we show that artificial intelligence (AI) and molecular simulation play key roles in transforming nanotoxicity data into critical information, i.e., constructing the quantitative nanostructure (physicochemical properties)-toxicity relationships, and elucidating the toxicity-related molecular mechanisms. For AI and molecular simulation to realize their full impacts in this mission, several obstacles must be overcome. These include the paucity of high-quality nanomaterials (NMs) and standardized nanotoxicity data, the lack of model-friendly databases, the scarcity of specific and universal nanodescriptors, and the inability to simulate NMs at realistic spatial and temporal scales. This review provides a comprehensive and representative, but not exhaustive, summary of the current capability gaps and tools required to fill these formidable gaps. Specifically, we discuss the applications of AI and molecular simulation, which can address the large-scale data challenge for nanotoxicology research. The need for model-friendly nanotoxicity databases, powerful nanodescriptors, new modeling approaches, molecular mechanism analysis, and design of the next-generation NMs are also critically discussed. Finally, we provide a perspective on future trends and challenges.

On the interface between biomaterials and two-dimensional materials for biomedical applications

Two-dimensional (2D) materials have garnered significant attention due to their ultrathin 2D structures with a high degree of anisotropy and functionality. Reliable manipulation of interfaces between 2D materials and biomaterials is a new frontier for biomedical nanoscience and combining biomaterials with 2D materials offers a promising way to fabricate innovative 2D biomaterials composites with distinct functionality for biomedical applications. Here, we focus exclusively on a summary of the current work in the interface investigation of 2D biomaterials. Specifically, we highlight extraordinary features that make 2D materials so desirable, as well as the molecular level interactions between 2D materials and biomaterials that have been studied thus far. Furthermore, the approaches for investigating the interface characteristics of 2D biomaterials are presented and described in depth. To capture the emerging trend in mass manufacturing of 2D materials, we review the research progress on biomaterial-assisted exfoliation. Finally, we present a critical assessment of newly developed 2D biomaterials in biomedical applications.

Mesoscopic Simulation for the Effect of Cross-Linking Reactions on the Drug Diffusion Properties in Microneedles

The drug diffusion issue in microneedles is the focus of its medical application. It will not only affect the distribution of drugs in the needle body but will also have an impact on the drug release performance of the microneedle. The utilization of cross-linked polymer materials to obtain the drug diffusion control has been experimentally verified as a feasible method. However, the mechanism research on the molecular level is still incomplete. In this study, the dissipative particle dynamics (DPD) simulation has been applied to study the effect of the cross-linking reaction on drug diffusion in hyaluronic acid microneedles. We have discovered that when the cross-linking degree reaches 90%, the diffusion coefficient of the drug is 6.45 times lower than that of the uncross-linked system. The main reason for the decline in drug diffusion ability is that the cross-linking reaction varies the conformation of the polymer. The amplification in the cross-linking degree makes the polymer coils more compact and approach each other, finally forming a continuously distributed cross-linked network, which reduces its degradation rate in the body. Simultaneously, these cross-linked networks can also hinder the interaction of soluble drugs with water, thereby preventing the premature release of drugs. The simulation results are consistent with the data collected in the previous microneedle experiment. This work will be an extension of DPD simulation in the application of biological materials.

Membrane-curvature-mediated co-endocytosis of bystander and functional nanoparticles

Efficient cellular uptake of nanoparticles (NPs) is necessary for the development of nanomedicine in biomedical applications. Recently, the coadministration of functionalized NPs (FNPs) was shown to stimulate the cellular uptake of nonfunctionalized NPs (termed bystander NPs, BNPs), which presents a new strategy to achieve synergistic delivery. However, a mechanistic understanding of the underlying mechanism is still lacking. In this work, the bystander uptake effect was investigated at the cell membrane level by combining the coarse-grained molecular dynamics, potential of mean force calculation and theoretical energy analysis methods. The membrane internalization efficiency of BNPs was enhanced by co-administered FNPs, and such activity depends on the affinity of both NPs to the membrane and the resultant membrane deformation. The membrane-curvature-mediated attraction and aggregation of NPs facilitated the membrane uptake of BNPs. Furthermore, quantitative suggestions were given to modulate the BNP internalization through controlling the FNP properties such as size, concentration and surface-ligand density. Our results provide insight into the molecular mechanism of the bystander uptake effect, and offer a practical guide to regulate the cellular internalization of NPs for targeted and efficient delivery to cells.

Boron nitride nanosheets elicit significant hemolytic activity via destruction of red blood cell membranes

Boron nitride (BN) nanosheets have emerged as promising nanomaterials in a wide range of biomedical applications. Despite extensive studies on these bio-nano interfacial systems, the underlying molecular mechanisms remain elusive. In this study, we used hemolysis assays and morphology observations to demonstrate for the first time that BN nanosheets can cause damages to the red-blood-cell membranes, leading to significant hemolysis. Further molecular dynamics simulations revealed that BN nanosheets can penetrate into the cell membrane and also extract considerable amount of phospholipid molecules directly from the lipid bilayer. The potential of mean force calculations then showed that their penetration effect was thermodynamically favorable due to the strong attractive van der Waals interactions between BN nanosheets and phospholipids. Overall, these findings provided valuable insights into the interaction of BN nanosheets with cell membranes at the atomic level, which can help future de novo design of BN-based nanodevices with better biocompatibility.

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.

Thermodynamic analysis of multivalent binding of functionalized nanoparticles to membrane surface reveals the importance of membrane entropy and nanoparticle entropy in adhesion of flexible nanoparticles

We present a quantitative model for multivalent binding of ligand-coated flexible polymeric nanoparticles (NPs) to a flexible membrane expressing receptors. The model is developed using a multiscale computational framework by coupling a continuum field model for the cell membrane with a coarse-grained model for the polymeric NPs. The NP is modeled as a self-avoiding bead-spring polymer chain, and the cell membrane is modeled as a triangulated surface using the dynamically triangulated Monte Carlo method. The nanoparticle binding affinity to a cell surface is mainly determined by the delicate balance between the enthalpic gain due to the multivalent ligand-receptor binding and the entropic penalties of various components including receptor translation, membrane undulation, and NP conformation. We have developed new methods to compute the free energy of binding, which includes these enthalpy and entropy terms. We show that the multivalent interactions between the flexible NP and the cell surface are subject to entropy-enthalpy compensation. Three different entropy contributions, namely, those due to receptor-ligand translation, NP flexibility, and membrane undulations, are all significant, although the first of these terms is the most dominant. However, both NP flexibility and membrane undulations dictate the receptor-ligand translational entropy making the entropy compensation context-specific, i.e., dependent on whether the NP is rigid or flexible, and on the state of the membrane given by the value of membrane tension or its excess area.

Curvature-mediated cooperative wrapping of multiple nanoparticles at the same and opposite membrane sides

Cell membrane interactions with nanoparticles (NPs) are essential to cellular functioning and mostly accompanied by membrane curvature generation and sensing. Multiple NPs inducing curvature from one side of a membrane are believed to be wrapped cooperatively by the membrane through curvature-mediated interactions. However, little is known about another biologically ubiquitous and important case, i.e., NPs binding to opposite membrane sides induce a curved bend of different directions. Combining coarse-grained molecular dynamics and theoretical analysis, here we systematically investigate the cooperative effect in the wrapping of multiple adhesive NPs at the same and opposite membrane sides and demonstrate the importance of the magnitude and direction of the membrane bend in regulating curvature-mediated NP interactions. Effects of the NP size, size difference, initial distance, number, and strength of adhesion with the membrane on the wrapping cooperativity and wrapping states are analyzed. For NPs binding to the same membrane side, rich membrane wrapping and NP aggregation states are observed, and the curvature-mediated interactions could be either attractive or repulsive, depending on the initial NP distance and the competition between the membrane bending, NP binding and membrane protrusion. In sharp contrast, the interaction between two NPs binding to opposite membrane sides is always attractive and the cooperative wrapping of NPs is promoted, as the curved membrane regions induced by the NPs are shared in a manner that the NP-membrane contact is increased and the energy cost of membrane bending is reduced. Owing to the ubiquity and heterogeneity of membrane shaping proteins in biology, our results enrich the cutting-edge knowledge on the curvature-mediated interaction of NPs for better and profound understanding on high-order cooperative assemblies of NPs or proteins in numerous biological processes.

Membrane Wrapping Pathway of Injectable Hydrogels: From Vertical Capillary Adhesion to Lateral Compressed Wrapping

Membrane wrapping pathway of injectable hydrogels (IHs) plays a vital role in the nanocarrier effectiveness and biomedical safety. Although considerable progress in understanding this complicated process has been made, the mechanism behind this process has remained elusive. Herein, with the help of large-scale dissipative particle dynamics simulations, we explore the molecular mechanism of membrane wrapping by systematically examining the IH architectures and hydrogel-lipid binding strengths. To the best of our knowledge, this is the first report on the membrane wrapping pathway on which IHs transform from vertical capillary adhesion to lateral compressed wrapping. This transformation results from the elastocapillary deformation of networked gels and nanoscale confinement of the bilayer membrane, and it takes long time for the IHs to be fully wrapped owing to the high energy barriers and wrapping-induced shape deformation. Collapsed morphologies and small compressed angles are identified in the IH capsules with a thick shell or strong binding strength to lipids. In addition, the IHs binding intensively to the membrane exhibit special nanoscale mixing and favorable deformability during the wrapping process. Our study provides a detailed mechanistic understanding of the influence of architecture and binding strength on the IH membrane wrapping efficiency. This work may serve as rational guidance for the design and fabrication of IH-based drug carriers and tissue engineering.

Design of Small Nanoparticles Decorated with Amphiphilic Ligands: Self-Preservation Effect and Translocation into a Plasma Membrane

Design of nanoparticles (NPs) for biomedical applications requires a thorough understanding of cascades of nano-bio interactions at different interfaces. Here, we take into account the cascading effect of NP functionalization on interactions with target cell membranes by determining coatings of biomolecules in biological media. Cell culture experiments show that NPs with more hydrophobic surfaces are heavily ingested by cells in both the A549 and HEK293 cell lines. However, before reaching the target cell, both the identity and amount of recruited biomolecules can be influenced by the pristine NPs' hydrophobicity. Dissipative particle dynamics (DPD) simulations show that hydrophobic NPs acquire coatings of more biomolecules, which may conceal the properties of the as-engineered NPs and impact the targeting specificity. Based on these results, we propose an amphiphilic ligand coating on NPs. DPD simulations reveal the design principle, following which the amphiphilic ligands first curl in solvent to reduce the surface hydrophobicity, thus suppressing the assemblage of biomolecules. Upon attaching to the membrane, the curled ligands extend and rearrange to gain contacts with lipid tails, thus dragging NPs into the membrane for translocation. Three NP-membrane interaction states are identified that are found to depend on the NP size and membrane surface tension. These results can provide useful guidelines to fabricate ligand-coated NPs for practical use in targeted drug delivery, and motivate further studies of nano-bio-interactions with more consideration of cascading effects.

Why are nanoparticles trapped at cell junctions when the cell density is high?

Research on nanoparticle (NP)-cell interactions has been extensively carried out in dilute cell cultures, where NPs are heavily internalized by cells. However, it is not known whether the findings from cell culture studies are still true in tissues where cells are tightly packed. Here, we show experimentally and theoretically that when cells are tightly packed, cellular uptake is strongly hindered. When simultaneously encountering two adjacent cells as is often the case in tissues, adhesion, bending and protrusion of at least two membranes from these cells generate complicated energy contributions that cause trapping of NPs at cell junctions with impeded uptake.

Remote Induction of Cell Autophagy by 2D MoS2 Nanosheets via Perturbing Cell Surface Receptors and mTOR Pathway from Outside of Cells

The ability of nanoparticles to induce adverse consequences in human cells relies on their physical shapes. In this aspect, how two-dimensional nanoparticles differ from three-dimensional nanoparticles is not well-known. To elucidate this difference, combined experimental and theoretical approaches are employed to compare MoS₂ nanosheets with 5-layer and 40-layer thicknesses for their cellular effects and the associated molecular events. At a concentration as defined by the nanosheet surface areas (10 cm²/mL), 40-layer nanosheets are internalized by cells, whereas 5-layer nanosheets mostly bind to the cell surface without internalization. Although they alter different autophagy-related genes, a common mechanism is that they both perturb cell surface protein amyloid precursor proteins and activate the mTOR signaling pathway. Our findings prove that the perturbation of cellular function without nanoparticle internalization has significant nanomedicinal and nanotoxicological significances.

4/6-Herto-arm and 4/6-mikto-arm star-shaped block polymeric drug-loaded micelles and their pH-responsive controlled release properties: a dissipative particle dynamics simulation

Star-shaped polymers have received significant attention and have been widely developed for prospective applications in drug delivery owing to their topological structure and unique physiochemical characteristics.

Steered molecular dynamics simulations reveal a self-protecting configuration of nanoparticles during membrane penetration

Cell entry of polynucleotide-based therapeutic agents can be facilitated by nanoparticle (NP) mediated delivery. In this work, using steered molecular dynamics simulations, we simulated the membrane penetration process of a NP formed by 2 short interfering RNA (siRNA) and 6 polyethylenimine (PEI) molecules. To the best of our knowledge, this is the first set of simulations that explore the direct penetration of an siRNA/PEI NP through a membrane at an all-atom scale. Three types of PEI molecules were used for NP formation: a native PEI, a PEI modified with caprylic acids and a PEI modified with linoleic acids. We found that hydrogen bond formation between the PEIs and the membrane did not lead to instability of the siRNA/PEI NPs during the internalization process. Instead, our results suggested adoption of a "self-protecting" configuration by the siRNA/PEI NP during membrane penetration, where the siRNA/PEI NP becomes more compact and siRNAs become aligned, leading to more stable configurations while detaching from the membrane. The siRNA/PEI NP modified with linoleic acid showed the smallest structural change due to its strong intra-particle lipid associations and the resulting rigidity, while NP modified with caprylic acid showed the largest structural changes. Our observations provide unique insight into the structural changes of siRNA/PEI NPs when crossing the cell membrane, which can be important for the design of new NP carriers for nucleic acid delivery.

Receptor-Mediated Endocytosis of Nanoparticles: Roles of Shapes, Orientations, and Rotations of Nanoparticles

A complete understanding of the interactions between nanoparticles (NPs) and the cell membrane is essential for the potential biomedical applications of NPs. The rotation of the NP during the cellular wrapping process is of great biological significance and has been widely observed in experiments and simulations. However, the underlying mechanisms of the rotation and their potential influences on the wrapping behavior are far from being fully understood. Here, by coupling the rotation of the NP with the diffusion of the receptors, we set up a model to theoretically investigate the wrapping pathway and the internalization rate of the rotatable NP in the receptor-mediated endocytosis. Based on this model, it is found that the endocytosis proceeds through the symmetric-asymmetric or asymmetric-symmetric-asymmetric wrapping pathway due to the bending and membrane tension competition induced rotation of NP. In addition, we show that the wrapping rate in the direction that the wrapping proceeds can be largely accelerated by the rotation. Moreover, the time to fully wrap the NP depends not only on the size and shape of the NP but also on its rotation and initial orientation. These results reveal the roles of the shape, rotation, and initial orientation of the NP on the receptor-mediated endocytosis and may provide guidelines for the design of NP-based drug delivery systems.

Conformations and membrane-driven self-organization of rodlike fd virus particles on freestanding lipid membranes

Membrane-mediated interactions and aggregation of colloidal particles adsorbed to responsive elastic membranes are challenging problems relevant for understanding the microscopic organization and dynamics of biological membranes. We experimentally study the behavior of rodlike semiflexible fd virus particles electrostatically adsorbed to freestanding cationic lipid membranes and find that their behavior can be controlled by tuning the membrane charge and ionic strength of the surrounding medium. Three distinct interaction regimes of rodlike virus particles with responsive elastic membranes can be observed. (i) A weakly charged freestanding cationic lipid bilayer in a low ionic strength medium represents a gentle quasi-2D substrate preserving the integrity, structure, and mechanical properties of the membrane-bound semiflexible fd virus, which under these conditions is characterized by a monomer length of 884 ± 4 nm and a persistence length of 2.5 ± 0.2 μm, in perfect agreement with its properties in bulk media. (ii) An increase in the membrane charge leads to the membrane-driven collapse of fd virus particles on freestanding lipid bilayers and lipid nanotubes into compact globules. (iii) When the membrane charge is low, and the mutual electrostatic repulsion of membrane-bound virus particles is screened to a considerable degree, membrane-driven self-organization of membrane-bound fd virus particles into long linear tip-to-tip aggregates showing dynamic self-assembly/disassembly and quasi-semiflexible behavior takes place. These observations are in perfect agreement with the results of recent theoretical and simulation studies predicting that membrane-mediated interactions can control the behavior of colloidal particles adsorbed on responsive elastic membranes.

Design strategy of surface decoration for efficient delivery of nanoparticles by computer simulation

Understanding the role of surface decoration of nanoparticles in protein adsorption and cellular uptake is of great importance in biomedicine. Here, by using dissipative particle dynamics simulations, we take two typical coating polymers (i.e., hydrophilic and zwitterionic polymers) as an example, and systematically investigate their effect on cellular delivery of hydrophobic and charged nanoparticles (in the presence of serum protein). Our results show that though two types of polymers are charge-neutral and can both reduce the protein adsorption, there exist some differences between their ability of protein resistance, especially in the case of positively charged nanoparticles. Besides, it is found that the coating polymers may also greatly decrease the cellular uptake efficiency of nanoparticles. Nevertheless, and importantly, since the zwitterionic polymers may become positively charged under low pH environments, the nanoparticle can attach onto cell membrane more firmly than that coated with hydrophilic polymers, which can further enhance the active targeting of nanoparticles. Finally, we also provide the design maps for surface decoration to achieve efficient cellular delivery. These results can help better understand how to keep the balance between protein resistance and cell targeting, which may give some useful guidelines on optimal design of future nanomaterials in drug delivery.

How tubular aggregates interact with biomembranes: wrapping, fusion and pearling

How soft tubular aggregates interact with biomembranes is crucial for understanding the formation of membrane tubes connecting two eukaryotic cells, which are initially created from one cell and then connect with the other.

Wrapping of nanoparticles by the cell membrane: the role of interactions between the nanoparticles

A fundamental understanding of the interactions between nanoparticles (NPs) and the cell membrane is essential to improve the performance of the NP-based biomedical applications and assess the potential toxicity of NPs. Despite the great progress in understanding the interaction between individual NP and the membrane, little is known about the interaction between multiple NPs and the membrane. In this work, we investigate the wrapping of two parallel elongated NPs by the membrane, taking the NP-NP electrostatic interaction and van der Waals (vdW) interaction into consideration. Three types of NPs, namely the rigid NPs with circular and elliptic cross-sections and the deformable NPs, are systematically investigated. The results show that the electrostatic interaction would enhance the tendency of the independent wrapping and inhibit the rotation of the elongated and equally charged NPs with elliptic cross-sections. Under the vdW interaction, the competition of the NP-NP adhesion and the membrane elastic energies with the NP-membrane adhesion energy leads the NPs to be wrapped cooperatively or independently. For the system with elongated NPs with elliptic cross-sections, the NPs are more likely to be wrapped independently as the shapes become more anisotropic and the NPs would rotate to contact each other with the flat sides in the cooperative wrapping configuration. Moreover, the soft NPs are more likely to be wrapped cooperatively compared with the stiff NPs. These results may provide guidelines to control the internalization pathway of NPs and improve the efficiency of NP-based drug delivery systems.

Molecular modeling of membrane responses to the adsorption of rotating nanoparticles: promoted cell uptake and mechanical membrane rupture

Recently, a unique dynamic magnetic field was developed to induce the rotational movement of superparamagnetic iron oxide nanoparticles. This technique has been applied to remotely control both cellular internalization and apoptosis. Therefore, a thorough understanding of how a lipid membrane responds to the introduction of rotating NPs is quite important to promote the applications of this technique in a variety of biomedical area. Here, we performed Dissipative Particle Dynamics (DPD) simulations to systematically investigate the interaction mechanism between lipid membranes and rotating NPs. Two kinds of membrane responses are observed. One is the promoted cell uptake and the other is the mechanical membrane rupture. The promoting effect of NP rotation on the cell uptake is ascribed to the enhanced membrane monolayer protrusion, which can wrap the NP from the top side. Meanwhile, the rotating NP exerts a shearing force on the membrane. Accordingly, the membrane undergoes a local distortion around the NP. If the shearing force exceeds a critical value, the local membrane distortion develops into a mechanical rupture. A number of factors, like NP size, NP shape, ligand density and rotation speed, are critical in both of the above membrane responses.

Molecular modeling of interaction between lipid monolayer and graphene nanosheets: implications for pulmonary nanotoxicity and pulmonary drug delivery

Understanding how nanoparticles interact with the pulmonary surfactant monolayer (PSM) is of great importance for safe applications in biomedicine and for evaluation of both health and environment impacts.

Drug release from pH-sensitive polymeric micelles with different drug distributions: insight from coarse-grained simulations

How to control the release of drugs from pH-sensitive polymeric micelles is an issue of common concern, which is important to the effectiveness of the micelles. The components and properties of polymers can notably influence the drug distributions inside micelles which is a key factor that affects the drug release from the micelles. In this work, the dissipative particle dynamics simulation method is first used to study the structural transformation of micelles during the protonation process and the drug release process from micelles with different drug distributions. And then the effects of polymer structures, including different lengths of hydrophilic blocks, pH-sensitive blocks and hydrophobic blocks, on drug release are also studied. In the end, several corresponding design principles of pH-sensitive polymers for drug delivery are proposed according to the simulation results. This work is in favor of establishing qualitative rules for the design and optimization of congener polymers for desired drug delivery, which is of great significance to provide a potential approach for the development of new multiblock pH-sensitive polymeric micelles.

In vitro interaction of colloidal nanoparticles with mammalian cells: What have we learned thus far?

The interfacing of colloidal nanoparticles with mammalian cells is now well into its second decade. In this review our goal is to highlight the more generally accepted concepts that we have gleaned from nearly twenty years of research. While details of these complex interactions strongly depend, amongst others, upon the specific properties of the nanoparticles used, the cell type, and their environmental conditions, a number of fundamental principles exist, which are outlined in this review.

Interaction of nanoparticles with lipid membranes: a multiscale perspective

Freestanding lipid bilayers were challenged with 15 nm Au nanospheres either coated by a citrate layer or passivated by a protein corona. The effect of Au nanospheres on the bilayer morphology, permeability and fluidity presents strong differences or similarities, depending on the observation length scale, from the colloidal to the molecular domains. These findings suggest that the interaction between nanoparticles and lipid membranes should be conveniently treated as a multiscale phenomenon.

Wrapping of nanoparticles by membranes

How nanoparticles interact with biomembranes is central for understanding their bioactivity. Biomembranes wrap around nanoparticles if the adhesive interaction between the nanoparticles and membranes is sufficiently strong to compensate for the cost of membrane bending. In this article, we review recent results from theory and simulations that provide new insights on the interplay of bending and adhesion energies during the wrapping of nanoparticles by membranes. These results indicate that the interplay of bending and adhesion during wrapping is strongly affected by the interaction range of the particle-membrane adhesion potential, by the shape of the nanoparticles, and by shape changes of membrane vesicles during wrapping. The interaction range of the particle-membrane adhesion potential is crucial both for the wrapping process of single nanoparticles and the cooperative wrapping of nanoparticles by membrane tubules.

Membrane monolayer protrusion mediates a new nanoparticle wrapping pathway

Understanding how nanoparticles (NPs) interact with the lipid membrane is of importance for their potential applications in biomedicine and cytotoxic effects. In this paper, with the aid of computer simulation techniques, we report that NPs can be wrapped by lipid membranes in a pathway different from the conventional endocytic pathway. Our simulation results show that under the conditions of strong NP-membrane adhesion and low membrane tension, NPs can be wrapped by membranes with a pathway regulated by membrane monolayer protrusion. We also find that in the monolayer protrusion mediated wrapping pathway NPs are first trapped in the membrane and the subsequent NP internalization can be achieved by several means, including decreasing the membrane tension, breaking the membrane symmetry between upper and lower leaflets, and exerting an external force on the NPs. The findings from our simulations are well supported by the free energy analysis.

Molecular modeling of membrane tube pearling and the effect of nanoparticle adsorption

DPD simulations suggest that the membrane tube pearling can be regulated by the inner water pressure and NP adsorption.