Nanoparticle-induced permeability of lipid membranes

Gold nanoparticle adsorption alters the cell stiffness and cell wall bio-chemical landscape of Candida albicans fungal cells

HYPOTHESIS

Nanomaterials have been extensively investigated for a wide range of biomedical applications, including as antimicrobial agents, drug delivery vehicles, and diagnostic devices. The commonality between these biomedical applications is the necessity for the nanoparticle to interact with or pass through the cellular wall and membrane. Cell-nanomaterial interactions/uptake can occur in various ways, including adhering to the cell wall, forming aggregates on the surface, becoming absorbed within the cell wall itself, or transversing into the cell cytoplasm. These interactions are common to mammalian cells, bacteria, and yeast cells. This variety of interactions can cause changes to the integrity of the cell wall and the cell overall, but the precise mechanisms underpinning such interactions remain poorly understood. Here, we investigate the interaction between commonly investigated gold nanoparticles (AuNPs) and the cell wall/membrane of a model fungal cell to explore the general effects of interaction and uptake.

EXPERIMENTS

The interactions between 100 nm citrate-capped AuNPs and the cell wall of Candida albicans fungal cells were studied using a range of advanced microscopy techniques, including atomic force microscopy, confocal laser scanning microscopy, scanning electron microscopy, transmission electron microscopy, and synchrotron-FTIR micro-spectroscopy.

FINDINGS

In most cases, particles adhered on the cell surface, although instances of particles being up-taken into the cell cytoplasm and localised within the cell wall and membrane were also observed. There was a measurable increase in the stiffness of the fungal cell after AuNPs were introduced. Analysis of the synchrotron-FTIR data showed significant changes in spectral features associated with phospholipids and proteins after exposure to AuNPs.

Magnetothermal spider silk-based scaffolds for cartilage regeneration

Developing biocompatible, magnetically controlled polymers is a multifunctional solution to many surgical complications. By combining nanoparticle technology with the latest advancements in polymer materials science, we created a multicomponent hybrid system comprised of a robust native spider silk-based matrix; a Mn0.9Zn0.1Fe2O4 nanoparticles coating to provide a controlled thermal trigger for drug release; and liposomes, which act as drug carriers. Fluorescent microscope images show that the dye loaded into the liposomes is released when the system is exposed to an alternating magnetic field due to heating of ferromagnetic nanoparticles, which had a low Curie temperature (40-46°С). The silk matrix also demonstrated outstanding biocompatibility, creating a favorable environment for human postnatal fibroblast cell adhesion, and paving the way for their directed growth. This paper describes a complex approach to cartilage regeneration by developing a spider silk-based scaffold with anatomical mechanical properties for controlled drug delivery in a multifunctional autologous matrix-induced chondrogenesis.

Field application of nanoliposomes delivered quercetin by inhibiting specific hsp70 gene expression against plant virus disease

BACKGROUND

The annual economic loss caused by plant viruses exceeds 10 billion dollars due to the lack of ideal control measures. Quercetin is a flavonol compound that exerts a control effect on plant virus diseases, but its poor solubility and stability limit the control efficiency. Fortunately, the development of nanopesticides has led to new ideas.

RESULTS

In this study, 117 nm quercetin nanoliposomes with excellent stability were prepared from biomaterials, and few surfactants and stabilizers were added to optimize the formula. Nbhsp70er-1 and Nbhsp70c-A were found to be the target genes of quercetin, through abiotic and biotic stress, and the nanoliposomes improved the inhibitory effect at the gene and protein levels by 33.6 and 42%, respectively. Finally, the results of field experiment showed that the control efficiency was 38% higher than that of the conventional quercetin formulation and higher than those of other antiviral agents.

CONCLUSION

This research innovatively reports the combination of biological antiviral agents and nanotechnology to control plant virus diseases, and it significantly improved the control efficiency and reduced the use of traditional chemical pesticides.

Association Mechanism of Peptide-Coated Metal Nanoparticles with Model Membranes: A Coarse-Grained Study

Functionalized metal nanoparticles (NPs) hold great promise as innovative tools in nanomedicine. However, one of the main challenges is how to optimize their association with the cell membrane, which is critical for their effective delivery. Recent findings show high cellular uptake rates for NPs coated with the polycationic cell-penetrating peptide gH625-644 (gH), although the underlying internalization mechanism is poorly understood. Here, we use extended coarse-grained simulations and free energy calculations to study systems that simultaneously include metal NPs, peptides, lipids, and sterols. In particular, we investigate the first encounter between multicomponent model membranes and 2.5 nm metal NPs coated with gH (gHNPs), based on the evidence from scanning transmission electron microscopy. By comparing multiple membrane and (membranotropic) NP models, we found that gHNP internalization occurs by forming an intermediate state characterized by specific stabilizing interactions formed by peptide-coated nanoparticles with multicomponent model membranes. This association mechanism is mainly characterized by interactions of gH with the extracellular solvent and the polar membrane surface. At the same time, the NP core interacts with the transmembrane (cholesterol-rich) fatty phase.

Protein corona modulates interaction of spiky nanoparticles with lipid bilayers

The impact of protein corona on the interactions of nanoparticles (NPs) with cells remains an open question. This question is particularly relevant to NPs which sizes, ranging from tens to hundreds nanometers, are comparable to the sizes of most abundant proteins in plasma. Protein sizes match with typical thickness of various coatings and ligands layers, usually present at the surfaces of larger NPs. Such size match may affect the properties and the designed function of NPs. We offer a direct demonstration of how protein corona can dramatically change the interaction mode between NPs and lipid bilayers. To this end, we choose the most extreme case of NP surface modification: nanostructures in the form of rigid spikes of 10-20 nm length at the surface of gold nanoparticles. In the absence of proteins we observe the formation of reversible pores when spiky NPs adsorb on lipid bilayers. In contrast, the presence of bovine serum albumin (BSA) proteins adsorbed at the surface of spiked NPs, effectively reduces the length of spikes exposed to the interaction with lipid bilayers. Thus, protein corona changes qualitatively the dynamics of pore formation, which is completely suppressed at high protein concentrations. These results suggest that protein corona can not only be critical for interaction of NPs with membranes, it may change their mode of interaction, thus offsetting the role of surface chemistry and ligands.

Defects and defect engineering in Soft Matter

Soft matter covers a wide range of materials based on linear or branched polymers, gels and rubbers, amphiphilic (macro)molecules, colloids, and self-assembled structures. These materials have applications in various industries, all highly important for our daily life, and they control all biological functions; therefore, controlling and tailoring their properties is crucial. One way to approach this target is defect engineering, which aims to control defects in the material's structure, and/or to purposely add defects into it to trigger specific functions. While this approach has been a striking success story in crystalline inorganic hard matter, both for mechanical and electronic properties, and has also been applied to organic hard materials, defect engineering is rarely used in soft matter design. In this review, we present a survey on investigations on defects and/or defect engineering in nine classes of soft matter composed of liquid crystals, colloids, linear polymers with moderate degree of branching, hyperbranched polymers and dendrimers, conjugated polymers, polymeric networks, self-assembled amphiphiles and proteins, block copolymers and supramolecular polymers. This overview proposes a promising role of this approach for tuning the properties of soft matter.

Intracellular Distribution of Lipids and Encapsulated Model Drugs from Cationic Liposomes with Different Uptake Pathways

AIM

The uptake pathway of liposomes into cells is mainly via endocytosis or membrane fusion; however, the relationship between the uptake pathway and the intracellular pharmacokinetics of the liposome components remains unclear. This study aimed at revealing the relationship by using cationic liposomes having similar physical properties and different uptake pathways.

MATERIALS AND METHODS

We prepared cationic liposomes composed of amino acid-type lipids, K3C14 and K3C16, which have different uptake pathways by a hydration method, and fluorescently modified them by encapsulating FITC-dextran and surface conjugation with Alexa Fluor® 488 (AF488). Then, we investigated their intracellular distribution in HeLa cells over time.

RESULTS

The liposomes had similar physical properties and did not cause significant cell mortality after treatment for 180 min. The delivery rate and efficiency of encapsulated FITC-dextran with the fusogenic K3C16 liposomes were 3 and 1.6 times higher, respectively, than with the endocytic K3C14 liposomes. FITC-dextran molecules delivered with K3C16 liposomes were observed throughout the cytosolic space after 10 min, while those delivered with K3C14 liposomes were mainly observed as foci and took 60 min to diffuse into the cytosolic space. K3C14 lipids modified with AF488 were distributed mostly in the cytosolic space. In contrast, fluorescently labeled K3C16 lipids were colocalized with the plasma membrane of 50% of the HeLa cells after 10 min and were gradually internalized intracellularly.

CONCLUSION

Fusogenic K3C16 liposomes internalized into HeLa cells faster than endocytic K3C14 liposomes, and their components differently distributed in the cells.

Partition and Solubilization of Phospholipid Vesicles by Noncovalently Constructed Oligomeric-like Surfactants

This work has investigated the interaction of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles with oligomeric surfactants noncovalently formed by sodium dodecyl sulfate (SDS) and a series of polyamines, 1,3-diaminopropane (PDA), triamine, spermidine, and spermine. The partition coefficients (P) of these surfactants between lipid bilayers and the aqueous phase are measured by isothermal titration microcalorimetry (ITC), showing that the P value increases and the Gibbs free energy of the partition becomes more negative with increasing oligomerization degree of the surfactants. This changing trend is similar to that of synthetic oligomeric surfactants regardless of the charge properties, suggesting that the polyamine and SDS molecules interact with the DOPC bilayer simultaneously. Meanwhile, the DOPC solubilization by these surfactants is evaluated by the effective surfactant-to-lipid molar ratios for the onset (R_e^sat) and end (R_e^sol) of the solubilization process, which are determined from the phase boundaries obtained by ITC, turbidity, and dynamic light scattering measurements. With the increment of oligomerization degree, the R_e^sat and R_e^sol values increase anomalously and are much larger than those of the synthetic surfactants with the same oligomerization degree, suggesting that noncovalently constructed oligomeric surfactants exhibit lower solubilization ability to phospholipid vesicles than the corresponding covalent oligomeric surfactants. Therefore, the noncovalently constructed oligomeric-like surfactants facilitate strong partition but weak solubilization to phospholipid vesicles, which may provide a useful strategy to mildly adjust the permeation and fluidity of phospholipid vesicles with solubilization delay.

Cholesterol-like Condensing Effect of Perfluoroalkyl Substances on a Phospholipid Bilayer

To understand the potential cytotoxicity of perfluoroalkyl substances (PFAS), we study their interactions with a model phospholipid bilayer membrane using molecular dynamics (MD) simulations. Four typical PFAS molecules are investigated, including perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and perfluorohexane sulfonate (PFHxS). All of these PFAS molecules are found to spontaneously penetrate the lipid bilayer within a short simulation time (a few nanoseconds). During the penetration process, further free-energy analysis reveals that a PFAS molecule encounters an energy barrier at the bilayer/water interface. To overcome this free-energy barrier, the PFAS molecule flips itself at the interface. We further investigate the influence of embedded PFAS molecules on the membrane properties. All of the embedded PFAS molecules are found to produce a cholesterol-like condensing effect on the lipid bilayer, which includes increases of the order parameters of lipid tails and the thickness of the lipid bilayer and a decrease of area per lipid. Moreover, the PFAS molecules are found to form hydrogen bonds with oxygen atoms at three different positions of a lipid molecule. Our work reveals the penetration pathway of PFAS molecules entering into a lipid bilayer. In addition, the cholesterol-like condensing effect induced by embedded PFAS molecules on model membranes is systematically investigated and discussed. Our simulations can help understand the physical mechanisms of PFAS cytotoxicity.

New insights of the bacterial response to exposure of differently sized silver nanomaterials

The release of silver nanomaterials (AgNMs) from extensive use poses potential risks to human health and ecological environments. Although previous studies have reported the negative effects of AgNMs on various microorganisms, little is known about the response of bacteria under the exposure of AgNMs at the cellular level. Here, we report the multiple responses of Pseudomonas aeruginosa PAO1 (PAO1) under the exposure of two types of AgNMs, including spherical silver nanoparticles (AgNPs) and fibrous silver nanorods (AgNRs), by physiological experiments, microscopy, synchrotron-based X-ray Absorption Spectroscopy (XAS), flow cytometry and genome-wide RNA sequencing. Our results demonstrated that the exposure to both types of AgNMs could inhibit the growth of PAO1, accompanied by the overproduction of oxidative stress and inducing cell membrane damage. Transmission electron microscopy revealed the roughened cell membrane under both AgNMs treatment. In addition, both AgNMs repressed the expression of quorum sensing and metal efflux-related genes in PAO1, but stimulated denitrification, glycerol and amino acid metabolisms, SOS response and pyocin overproduction of PAO1. Compared to AgNRs, AgNPs exposure showed a much lower threshold concentration to trigger the inhibitory effect and induced greater transcriptional responses of PAO1. This study suggested that AgNMs could cause multiple effects on the proliferation, metabolism, virulence and pathogenesis of PAO1, which might further affect the corresponding environmental microbial communities. Overall, our findings offer insights into the interactions between AgNMs and bacteria at the molecular level.

Membrane fusogenic lysine type lipid assemblies possess enhanced NLRP3 inflammasome activation potency

Lysine (K) type cationic lipid with a propyl spacer and ditetradecyl hydrophobic moieties composing liposomes, K3C14, previously studied for gene delivery, were reported to activate the NLRP3 inflammasomes in human macrophages via the conventional phagolysosomal pathway. In this study, K3C16, a propyl spacer bearing lysine type lipids with dihexadecyl moieties (an extension of two hydrocarbon tail length) were compared with K3C14 as liposomes. Such a small change in tail length did not alter the physical properties such as size distribution, zeta potential and polydispersity index (PDI). The NLRP3 activation potency of K3C16 was shown to be 1.5-fold higher. Yet, the toxicity was minimal, whereas K3C14 has shown to cause significant cell death after 24 h incubation. Even in the presence of endocytosis inhibitors, cytochalasin D or dynasore, K3C16 continued to activate the NLRP3 inflammasomes and to induce IL-1β release. To our surprise, K3C16 liposomes were confirmed to fuse with the plasma membrane of human macrophages and CHO-K1 cells. It is demonstrated that the change in hydrophobic tail length by two hydrocarbons drastically changed a cellular entry route and potency in activating the NLRP3 inflammasomes.

Concepts of nanoparticle cellular uptake, intracellular trafficking, and kinetics in nanomedicine

Nanoparticle-based therapeutics and diagnostics are commonly referred to as nanomedicine and may significantly impact the future of healthcare. However, the clinical translation of these technologies is challenging. One of these challenges is the efficient delivery of nanoparticles to specific cell populations and subcellular targets in the body to elicit desired biological and therapeutic responses. It is critical for researchers to understand the fundamental concepts of how nanoparticles interact with biological systems to predict and control in vivo nanoparticle transport for improved clinical benefit. In this overview article, we review and discuss cellular internalization pathways, summarize the field`s understanding of how nanoparticle physicochemical properties affect cellular interactions, and explore and discuss intracellular nanoparticle trafficking and kinetics. Our overview may provide a valuable resource for researchers and may inspire new studies to expand our current understanding of nanotechnology-biology interactions at cellular and subcellular levels with the goal to improve clinical translation of nanomedicines.

Curvature-driven adsorption of cationic nanoparticles to phase boundaries in multicomponent lipid bilayers

Understanding the interactions between surface-functionalized gold nanoparticles (NPs) and lipid bilayers is necessary to guide the design of NPs for biomedical applications. Recent experiments found that cationic NPs adsorb more strongly to phase-separated multicomponent lipid bilayers than single-component liquid-disordered bilayers, suggesting that phase separation affects NP-bilayer interactions. In this work, we use coarse-grained molecular dynamics simulations to investigate the effect of lipid phase behavior on the adsorption of small cationic NPs. We first determined the free energy change for adsorbing a NP to one-phase liquid-disordered and one-phase liquid-ordered bilayers. The simulations indicate that NP adsorption depends on a competition between favorable NP-lipid interactions and the unfavorable curvature deformation of the bilayer, resulting in stronger interactions with the liquid-disordered bilayer due to its lower bending modulus. We then measured the free energy change associated with moving a NP across the surface of a phase-separated bilayer and identified a free energy minimum at the phase boundary. The free energy minimum is attributed to the thickness gradient between the two phases that enables favorable NP-lipid interactions without necessitating large curvature deformations. The simulation results thus indicate that the intrinsic curvature present at phase boundaries drives preferential interactions with surface-adsorbed NPs, providing new insight into the forces that drive NP behavior at multicomponent, phase-separated lipid bilayers.

Energy landscape for the insertion of amphiphilic nanoparticles into lipid membranes: A computational study

Amphiphilic, monolayer-protected gold nanoparticles (NPs) have been shown to enter cells via a non-endocytic, non-disruptive pathway that could be valuable for biomedical applications. The same NPs were also found to insert into a series of model cell membranes as a precursor to cellular uptake, but the insertion mechanism remains unclear. Previous simulations have demonstrated that an amphiphilic NP can insert into a single leaflet of a planar lipid bilayer, but in this configuration all charged end groups are localized to one side of the bilayer and it is unknown if further insertion is thermodynamically favorable. Here, we use atomistic molecular dynamics simulations to show that an amphiphilic NP can reach the bilayer midplane non-disruptively if charged ligands iteratively "flip" across the bilayer. Ligand flipping is a favorable process that relaxes bilayer curvature, decreases the nonpolar solvent-accessible surface area of the NP monolayer, and increases attractive ligand-lipid electrostatic interactions. Analysis of end group hydration further indicates that iterative ligand flipping can occur on experimentally relevant timescales. Supported by these results, we present a complete energy landscape for the non-disruptive insertion of amphiphilic NPs into lipid bilayers. These findings will help guide the design of NPs to enhance bilayer insertion and non-endocytic cellular uptake, and also provide physical insight into a possible pathway for the translocation of charged biomacromolecules.

Rational Design Principles for the Transport and Subcellular Distribution of Nanomaterials into Plant Protoplasts

The ability to control the subcellular localization of nanoparticles within living plants offers unique advantages for targeted biomolecule delivery and enables important applications in plant bioengineering. However, the mechanism of nanoparticle transport past plant biological membranes is poorly understood. Here, a mechanistic study of nanoparticle cellular uptake into plant protoplasts is presented. An experimentally validated mathematical model of lipid exchange envelope penetration mechanism for protoplasts, which predicts that the subcellular distribution of nanoparticles in plant cells is dictated by the particle size and the magnitude of the zeta potential, is advanced. The mechanism is completely generic, describing nanoparticles ranging from quantum dots, gold and silica nanoparticles, nanoceria, and single-walled carbon nanotubes (SWNTs). In addition, the use of imaging flow cytometry to investigate the influence of protoplasts' morphological characteristics on nanoparticle uptake efficiency is demonstrated. Using DNA-wrapped SWNTs as model nanoparticles, it is found that glycerolipids, the predominant lipids in chloroplast membranes, exhibit stronger lipid-nanoparticle interaction than phospholipids, the major constituent in protoplast membrane. This work can guide the rational design of nanoparticles for targeted delivery into specific compartments within plant cells without the use of chemical or mechanical aid, potentially enabling various plant engineering applications.

Nanoparticles Self-Assembly within Lipid Bilayers

Coarse-grained molecular dynamics simulations are used to model the self-assembly of small hydrophobic nanoparticles (NPs) within the interior of lipid bilayers. The simulation results reveal the conditions under which NPs form clusters and lattices within lipid bilayers of planar and spherical shapes, depending on the NP-lipid coupling strengths. The formation of nanopores within spherical bilayers with self-assembled planar NPs is also described. These observations can provide guidance in the preparation of functional bio-inorganic systems.

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.

Partner-facilitating transmembrane penetration of nanoparticles: a biological test in silico

Transmembrane penetration of nanoparticles (NPs) promises an effective pathway for cargo delivery into cells, and offers the possibility of organelle-specific targeting for biomedical applications. However, a full understanding of the underlying NP-membrane interaction mechanism is still lacking. In this work, the membrane penetration behavior of NPs is statistically analyzed based on the simulations of over 2.2 ms, which are performed with dissipative particle dynamics (DPD). Influences from multiple factors including the NP concentration, shape and surface chemistry are taken into account. It is interesting to find that, the introduction of a partner NP would greatly facilitate the transmembrane penetration of a host spherical NP. This is probably due to the membrane-mediated cooperation between the NPs. Moreover, the proper selection of a partner NP with specific surface chemistry is of great significance. For example, the best partner for a hydrophilic NP to achieve transmembrane penetration is a Janus-like one, in comparison with the hydrophilic, hydrophobic or randomly surface-decorated NPs. Furthermore, such a partner-facilitating effect in NP translocation also works for a shaped NP although less pronounced. Our results are helpful for a better understanding of the complicated nano-bio interactions, and offer a practical guide to the NP-based drug delivery strategy with high efficiency.

Rupture of Lipid Membranes Induced by Amphiphilic Janus Nanoparticles

The surface coatings of nanoparticles determine their interaction with biomembranes, but studies have been limited almost exclusively to nanoparticles with a uniform surface chemistry. Although nanoparticles are increasingly made with complex surface chemistries to achieve multifunctionalities, our understanding of how a heterogeneous surface coating affects particle-biomembrane interaction has been lagging far behind. Here we report an investigation of this question in an experimental system consisting of amphiphilic "two-faced" Janus nanoparticles and supported lipid membranes. We show that amphiphilic Janus nanoparticles at picomolar concentrations induce defects in zwitterionic lipid bilayers. In addition to revealing the various effects of hydrophobicity and charge in particle-bilayer interactions, we demonstrate that the Janus geometry-the spatial segregation of hydrophobicity and charges on particle surface-causes nanoparticles to bind more strongly to bilayers and induce defects more effectively than particles with uniformly mixed surface functionalities. We combine experiments with computational simulation to further elucidate how amphiphilic Janus nanoparticles extract lipids to rupture intact lipid bilayers. This study provides direct evidence that the spatial arrangement of surface functionalities on a nanoparticle, rather than just its overall surface chemistry, plays a crucial role in determining how it interacts with biological membranes.

Translocation of Bioactive Molecules through Carbon Nanotubes Embedded in the Lipid Membrane

One of the major challenges of nanomedicine and gene therapy is the effective translocation of drugs and genes across cell membranes. In this study, we describe a systematic procedure that could be useful for efficient drug and gene delivery into the cell. Using fully atomistic molecular dynamics (MD) simulations, we show that molecules of various shapes, sizes, and chemistries can be spontaneously encapsulated in a single-walled carbon nanotube (SWCNT) embedded in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer, as we have exemplified with dendrimers, asiRNA, ssDNA, and ubiquitin protein. We compute the free energy gain by the molecules upon their entry inside the SWCNT channel to quantify the stability of these molecules inside the channel as well as to understand the spontaneity of the process. The free energy profiles suggest that all molecules can enter the channel without facing any energy barrier but experience a strong energy barrier (≫k_BT) to translocate across the channel. We propose a theoretical model for the estimation of encapsulation and translocation times of the molecules. Whereas the model predicts the encapsulation time to be of the order of few nanoseconds, which match reasonably well with those obtained from the simulations, it predicts the translocation time to be astronomically large for each molecule considered in this study. This eliminates the possibility of passive diffusion of the molecules through the CNT-nanopore spanning across the membrane. To counter this, we put forward a mechanical method of ejecting the encapsulated molecules by pushing them with other free-floating SWCNTs of diameter smaller than the pore diameter. The feasibility of the proposed method is also demonstrated by performing MD simulations. The generic strategy described here should work for other molecules as well and hence could be potentially useful for drug- and gene-delivery applications.

Passive membrane penetration by ZnO nanoparticles is driven by the interplay of electrostatic and phase boundary conditions

The internalization of nanoparticles through the biological membrane is of immense importance for biomedical applications. A fundamental understanding of the lipid specificity and the role of the membrane biochemical and physical forces at play in modulating penetration are lacking. The current understanding of nanoparticle-membrane interaction is drawn mostly from computational studies and lacks sufficient experimental evidence. Herein, using confocal fluorescence imaging and potentiometric dye-based fluorimetry, we first investigated the interaction of ZnONP in both multi-component and individual lipid membranes using cell-like giant unilamellar vesicles to dissect the lipid specificity; also, we investigated the changes in membrane order, anisotropy and hydrophobicity. ZnONP was found to interact with phosphatidylinositol and phosphatidylcholine head-group-containing lipids specifically. We further investigated the interaction of ZnONP with three physiologically relevant membrane conditions varying in composition and dipole potential. We found that ZnONP interaction leads to a photoinduced enhancement of the partial-to-complete phase separation depending upon the membrane composition and cholesterol content. Interestingly, while the lipid order of a partially-phase-separated membrane remained unchanged upon ZnONP crowding, a fully-phase-separated membrane showed an increase in the lipid order. Strikingly, ZnONP crowding induced a contrasting effect on the fluorescence anisotropy of the membrane upon binding to the two membrane conditions, in line with the measured diffusion coefficient. ZnONP seems to preferentially penetrate through the liquid disordered areas of the membrane and the boundaries of the phase-separated regions driven by the interplay between the electrostatics and phase boundary conditions, which are collectively dictated by the composition and ZnONP-induced lipid reorganization. The results may lead to a greater understanding of the interplay of membrane parameters and ZnONP interaction in driving passive penetration.

Understanding the Capsanthin Tails in Regulating the Hydrophilic-Lipophilic Balance of Carbon Dots for a Rapid Crossing Cell Membrane

Here we use natural Chinese paprika to prepare a new kind of amphiphilic carbon dot (A-Dot) that exhibits bright, multicolored fluorescence and contains hydrophilic groups as well as lipophilic capsanthin tails on the surface. It is found that the capsanthin tails in a phospholipid-like structure can promote cell internalization of the A-Dots via crossing cell membranes rapidly in an energy-independent fashion. Compared to highly hydrophilic carbon dots (H-Dots), a control sample prepared from the microwave thermolysis of citric acid and ethylenediamine, our synthesized A-Dots can be taken up by CHO, HeLa, and HFF cells more easily. More importantly, we develop a method to calibrate the hydrophilic-lipophilic balance (HLB) values of various kinds of carbon dots (C-Dots). HLB values of A-Dots and H-Dots are determined to be 6.4 and 18.4, respectively. Moreover, we discover that the cellular uptake efficiency of C-Dots is closely related to their HLBs, and the C-Dots with an HLB value of around 6.4 cross the cell membrane easier and faster. As we regulate the HLB value of the A-Dots from 6.4 to 15.3 by removing the capsanthin tails from their surfaces via alkali refluxing, it is found that the refluxed A-Dots can hardly cross HeLa cell membranes. Our work is an essential step toward understanding the importance of regulating the HLB values as well as the surface polarity of the C-Dots for their practical use in bioimaging and also provides a simple but effective way to judge whether the C-Dots in hand are appropriate for cell imaging.

Nanoparticles of Various Degrees of Hydrophobicity Interacting with Lipid Membranes

Using coarse-grained molecular dynamics simulations, we study the passive translocation of nanoparticles with a size of about 1 nm and with tunable degrees of hydrophobicity through lipid bilayer membranes. We observe a window of translocation with a sharp maximum for nanoparticles having a hydrophobicity in between hydrophilic and hydrophobic. Passive translocation can be identified as diffusive motion of individual particles in a free energy landscape. By combining direct sampling with umbrella-sampling techniques we calculate the free energy landscape for nanoparticles covering a wide range of hydrophobicities. We show that the directly observed translocation rate of the nanoparticles can be mapped to the mean-escape-rate through the calculated free energy landscape, and the maximum of translocation can be related with the maximally flat free energy landscape. The limiting factor for the translocation rate of nanoparticles having an optimal hydrophobicity can be related with a trapping of the particles in the surface region of the membrane. Here, hydrophobic contacts can be formed but the free energy effort of insertion into the brush-like tail regions can still be avoided. The latter forms a remaining barrier of a few k_BT and can be spontaneously surmounted. We further investigate cooperative effects of a larger number of nanoparticles and their impact on the membrane properties such as solvent permeability, area per lipid, and the orientation order of the tails. By calculating the partition of nanoparticles at the phase boundary between water and oil, we map the microscopic parameter of nanoparticle hydrophobicity to an experimentally accessibly partition coefficient. Our studies reveal a generic mechanism for spherical nanoparticles to overcome biological membrane-barriers without the need of biologically activated processes.

The effect of a high frequency electromagnetic field in the microwave range on red blood cells

The effect of red blood cells (RBC) exposed to an 18 GHz electromagnetic field (EMF) was studied. The results of this study demonstrated for the first time that exposure of RBCs to 18 GHz EMF has the capacity to induce nanospheres uptake in RBCs. The uptake of nanospheres (loading efficiency 96% and 46% for 23.5 and 46.3 nm nanospheres respectively), their presence and locality were confirmed using three independent techniques, namely scanning electron microscopy, confocal laser scanning microscopy and transmission electron microscopy. It appeared that 23.5 nm nanospheres were translocated through the membrane into the cytosol, while the 46.3 nm-nanospheres were mostly translocated through the phospholipid-cholesterol bilayer, with only some of these nanospheres passing the 2D cytoskeleton network. The nanospheres uptake increased by up to 12% with increasing temperature from 33 to 37 °C. The TEM analysis revealed that the nanospheres were engulfed by the cell membrane itself, and then translocated into the cytosol. It is believed that EMF-induced rotating water dipoles caused disturbance of the membrane, initiating its deformation and result in an enhanced degree of membrane trafficking via a quasi-exocytosis process.

Thermal Tunneling of Homopolymers through Amphiphilic Membranes

We propose a theory to predict the passive translocation of flexible polymers through amphiphilic membranes. By using a generic model for the potential felt by a monomer across the membrane we calculate the free energy profile for homopolymers as a function of their hydrophobicity. Our model explains the translocation window and the translocation rates as a function of chain hydrophobicity in quantitative agreement with simulation results. The potential model leads to a new adsorption transition where chains switch from a one-sided bound adsorbed state into a bridging state through the membrane core by increasing the hydrophobicity beyond a critical value. We demonstrate that the hydrophobicity leading to the fastest translocation coincides with the solution for the critical point of adsorption in the limit of long chains.

Proton-sensing transistor systems for detecting ion leakage from plasma membranes under chemical stimuli

The membrane integrity of live cells is routinely evaluated for cytotoxicity induced by chemical or physical stimuli. Recent progress in bioengineering means that high-quality toxicity validation is required. Here, we report a pH-sensitive transistor system developed for the continuous monitoring of ion leakage from cell membranes upon challenge by toxic compounds. Temporal changes in pH were generated with high reproducibility via periodic flushing of HepG2 cells on a gate insulator of a proton-sensitive field-effect transistor with isotonic buffer solutions with/without NH₄Cl. The pH transients at the point of NH₄Cl addition/withdrawal originated from the free permeation of NH₃ across the semi-permeable plasma membranes, and the proton sponge effect produced by the ammonia equilibrium. Irreversible attenuation of the pH transient was observed when the cells were subjected to a membrane-toxic reagent. Experiments and simulations proved that the decrease in the pH transient was proportional to the area of the ion-permeable pores on the damaged plasma membranes. The pH signal was correlated with the degree of hemolysis produced by the model reagents. The pH assay was sensitive to the formation of molecularly sized pores that were otherwise not measurable via detection of the leakage of hemoglobin, because the hydrodynamic radius of hemoglobin was greater than 3.1nm in the hemolysis assay. The pH transient was not disturbed by inherent ion-transporter activity. The ISFET assay was applied to a wide variety of cell types. The system presented here is fast, sensitive, practical and scalable, and will be useful for validating cytotoxins and nanomaterials.

STATEMENT OF SIGNIFICANCE

The plasma membrane toxicity and hemolysis are widely and routinely evaluated in biomaterials science and biomedical engineering. Despite the recent development of a variety of methods/materials for efficient gene/drug delivery systems to the cytosol, the methodologies for safety validation remain unchanged in many years while leaving some major issues such as sensitivity, accuracy, and fast response. The paper describes a new way of measuring the plasma membrane leakage in real time upon challenge by toxic reagents using a solid-state transistor that is sensitive to proton as the smallest indicator. Our system was reliable and was correlated to the results from hemolysis assay with advanced features in sensitivity, fast response, and wide applicability to chemical species. The downsizing and integration features of semiconductor fabrication technologies may realize cytotoxicity assays at the single-cell level in multi-parallel.

Counterintuitive cooperative endocytosis of like-charged nanoparticles in cellular internalization: computer simulation and experiment

The nanoparticles (NPs) functionalized with charged ligands are of particular significance due to their potential drug/gene delivery and biomedical applications. However, the molecular mechanism of endocytosis of the charged NPs by cells, especially the effect of the NP-NP and NP-biomembrane interactions on the internalization pathways is still poorly understood. In this work, we systematically investigate the internalization behaviors of the positively charged NPs by combining experiment technology and dissipative particle dynamics (DPD) simulation. We experimentally find an interesting but highly counterintuitive phenomenon, i.e. the multiple positively charged NPs prefer to enter cells cooperatively although the like-charged NPs have obvious electrostatic repulsion. Furthermore, we adopt the DPD simulation to confirm the experimental findings, and reveal that the mechanism of the cooperative endocytosis between like-charged NPs is definitely caused by the interplay of particle size, the charged ligand density on particle surface and local concentration of NPs. Importantly, we not only observe the normal cooperative endocytosis of like-charged NPs in cell biomembrane like neutral NP case, but also predict the 'bud' cooperative endocytosis of like-charged NPs which is absence in the neutral NP case. The results indicate that electrostatic repulsion between the positively charged nanoparticles plays an important role in the 'bud' cooperative endocytosis of like-charged NPs.

Interaction Pathways between Plasma Membrane and Block Copolymer Micelles

In this work, the interactions between block copolymer micelles (BCMs) and plasma membranes were investigated by performing coarse-grained molecular dynamics (CGMD) simulations. Different binding strengths between the BCMs and the membranes were tested, and four interaction pathways were discovered: attachment, semiendocytosis, endocytosis, and fusion. Endocytosis was the most efficient way for the BCMs to be taken up, and fusion could lead to cytotoxicity. Unlike rigid particles, deformation of the BCMs strongly affected the interaction pathways. We examined the effects of changing the aggregation number of the BCMs (N_agg), the chain length of the polymer (N_b), and the chain stiffness of the hydrophobic block (k_a), and we learned that smaller N_agg and lower N_b could lead to weaker cellular uptake capacities, whereas larger N_agg and higher N_b gave rise to higher cytotoxicities. Moreover, a weaker chain stiffness of the hydrophobic block could be more favorable for obtaining BCMs with higher internalization efficacies and lower cytotoxicities. The results of these simulations could aid in the design of BCMs with desirable cellular internalization capacities and lower cytotoxicities. Such BCMs could be useful in drug-delivery systems.

Self-assembly of anionic, ligand-coated nanoparticles in lipid membranes

Ligand-functionalized nanoparticles (NPs) are a promising platform for imaging and drug delivery applications. A number of recent molecular simulation and theoretical studies explored how these NPs interact with model lipid membranes. However, interactions between ligand-coated NPs leading to possible cooperative effects and association have not been investigated. In this coarse-grained molecular dynamics study, we focus on a specific case of several anionic, ligand-coated NPs embedded in a lipid membrane. Several new effects are observed. Specifically, in the presence of cholesterol in the membrane, NPs tend to form linear clusters, or chains. Analysis of the driving forces for this association reveals an important role of the recently discovered orderphobic effect, although we acknowledge that a combination of factors must be at play. At the same time, we argue that the specific linear shape of the clusters is a result of a subtle balance between the forces that stabilize a NP in the membrane and the forces that drive the NP-NP association processes. These effects, observed for the first time in the NP-membrane systems, have also direct correspondence to similar effects in protein-membrane systems and these links between the two realms should be explored further.

Molecular Understanding of the Penetration of Functionalized Gold Nanoparticles into Asymmetric Membranes

In this work, the interactions between surface-functionalized gold nanoparticles (AuNPs) and asymmetric membranes and the associated cytotoxicity were explored by coarse-grained molecular dynamics simulations. Simulation results show that the surface chemistry of AuNPs and the asymmetry of lipid membranes play significant roles. AuNPs with different signs of charges spontaneously adhere to the membrane surface or penetrate the membrane core. Also, the asymmetric distribution of charged lipids in membranes can facilitate the penetration of cationic AuNPs. Increasing the surface charge density (SCD) of AuNPs can not only improve the penetration efficiency but also lead to more disruption of the membrane structure. Moreover, the flip-flop of charged lipids in the inner leaflet can be observed during the translocation of AuNPs with a high SCD. The breakdown of membrane asymmetry may hinder the cellular internalization of AuNPs in a direct penetration mechanism. More importantly, we demonstrate that the hydrophobic contact between protruding solvent-exposed lipid tails and the hydrophobic moieties of ligands can mediate the insertion of AuNPs with a low SCD into cell membranes, which will exhibit less cytotoxicity in most in vivo applications. This may open a new exciting avenue to developing nanocarriers with a higher translocation efficiency and a lower toxicity simultaneously for biomedical applications.

Elucidating the mechanisms of nanodiamond-promoted structural disruption of crystallised lipid

The removal or structural disruption of crystallised lipid is a pivotal but energy-intensive step in a wide range of industrial and biological processes. Strategies to disrupt the structure of crystallised lipid in aqueous solution at lower temperatures are much needed, where nanoparticle-based strategies show enormous promise. Using the aqueous tristearin bilayer as a model for crystallised lipid, we demonstrate that the synergistic use of surfactant and detonation nanodiamonds can depress the onset temperature at which disruption of the crystallised lipid structure occurs. Our simulations reveal the molecular-scale mechanisms by which this disruption takes place, indicating that the nanodiamonds serve a dual purpose. First, the nanodiamonds are predicted to facilitate delivery of surfactant to the lipid/water interface, and second, nanodiamond adsorption acts to roughen the lipid/water interface, enhancing ingress of surfactant into the bilayer. We find the balance of the hydrophobic surface area of the nanodiamond and the nanodiamond surface charge density to be a key determinant of the effectiveness of using nanodiamonds to facilitate lipid disruption. For the nanodiamond size considered here, we identify a moderate surface charge density, that ensures the nanodiamonds are neither too hydrophobic nor too hydrophilic, to be optimal.

Interactions of Lipidic Cubic Phase Nanoparticles with Lipid Membranes

The interactions of liquid-crystalline monoolein (GMO) cubic phase nanoparticles with various model lipid membranes spread at the air-solution interface by the Langmuir technique were investigated. Cubosomes have attracted attention as potential biocompatible drug delivery systems, and thus understanding their mode of interaction with membranes is of special interest. Cubosomes spreading at the air-water interface as well as interactions with a monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) compressed to different surface pressures were studied by monitoring surface pressure-time dependencies at constant area. Progressive incorporation of the nanoparticles was shown to lead to mixed monolayer formation. The concentration of cubosomes influenced the mechanism of incorporation, as well as the fluidity and permeability of the resulting lipid membranes. Brewster angle microscopy images reflected the dependence of the monolayer structure on the cubosomes presence in the subphase. A parameter Csat was introduced to indicate the point of saturation of the lipid membrane with the cubosomal material. This parameter was found to depend on the surface pressure showing that the cubosomes disintegrate in prolonged contact with the membrane, filling available voids in the lipid membrane. At highest surface pressures when the layer is most compact, the penetration of cubosomal material is not possible and only some exchange with the membrane lipid becomes the route of including GMO into the layer. Finally, comparative studies of the interactions between lipids with various headgroup charges with cubosomes suggest that at high surface pressure an exchange of lipid component between the monolayer and the cubosome in its intact form may occur.

Effect of anionic and cationic polyamidoamine (PAMAM) dendrimers on a model lipid membrane

In spite of the growing variety of biological applications of dendrimer-based nanocarriers, a major problem of their potential applications in bio-medicine is related to the disruption of lipid bilayers and the cytotoxicity caused by the aggregation processes involved onto cellular membranes. With the aim to study model dendrimer-biomembrane interaction, the self-assembly processes of a mixture of charged polyamidoamine (PAMAM) dendrimers and dipalmitoylphosphatidylcholine (DPPC) lipids were investigated by means of Zeta potential analysis, Raman and x-ray scattering. Zwitterionic DPPC liposomes showed substantially different behaviors during their interaction with negatively charged (generation G=2.5) sodium carboxylate terminated (COO^- Na⁺) dendrimers or positively charged (generation G=3.0) amino terminated (-NH₂) dendrimers. More specifically the obtained results evidence the sensitive interactions between dendrimer terminals and lipid molecules at the surface of the liposome, with an enhancement of the liposome surface zeta potential, as well as in the hydrophobic region of the bilayers, where dendrimer penetration produce a perturbation of the hydrophobic alkyl chains of the bilayers. Analysis of the SAXS structure factor with a suitable model for the inter-dendrimers electrostatic potential allows an estimation of an effective charge of 15 ǀeǀ for G=2.5 and 7.6 ǀeǀ for G=3.0 PAMAM dendrimers. Only a fraction (about 1/7) of this charge contributes to the linear increase of liposome zeta-potential with increasing PAMAM/DPPC molar fraction. The findings of our investigation may be applied to rationalize the effect of the nanoparticles electrostatic interaction in solution environments for the design of new drug carriers combining dendrimeric and liposomal technology.

The Bioeffects Resulting from Prokaryotic Cells and Yeast Being Exposed to an 18 GHz Electromagnetic Field

The mechanisms by which various biological effects are triggered by exposure to an electromagnetic field are not fully understood and have been the subject of debate. Here, the effects of exposing typical representatives of the major microbial taxa to an 18 GHz microwave electromagnetic field (EMF)were studied. It appeared that the EMF exposure induced cell permeabilisation in all of the bacteria and yeast studied, while the cells remained viable (94% throughout the exposure), independent of the differences in cell membrane fatty acid and phospholipid composition. The resulting cell permeabilisation was confirmed by detection of the uptake of propidium iodine and 23 nm fluorescent silica nanospheres using transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Upon EMF exposure, the bacterial cell membranes are believed to become permeable through quasi-endocytosis processes. The dosimetry analysis revealed that the EMF threshold level required to induce the uptake of the large (46 nm) nanopsheres was between three and six EMF doses, with a specific absorption rate (SAR) of 3 kW/kg and 5 kW/kg per exposure, respectively, depending on the bacterial taxa being studied. It is suggested that the taxonomic affiliation and lipid composition (e.g. the presence of phosphatidyl-glycerol and/or pentadecanoic fatty acid) may affect the extent of uptake of the large nanospheres (46 nm). Multiple 18 GHz EMF exposures over a one-hour period induced periodic anomalous increases in the cell growth behavior of two Staphylococcus aureus strains, namely ATCC 25923 and CIP 65.8^T.

Soft Interaction in Liposome Nanocarriers for Therapeutic Drug Delivery

The development of smart nanocarriers for the delivery of therapeutic drugs has experienced considerable expansion in recent decades, with the development of new medicines devoted to cancer treatment. In this respect a wide range of strategies can be developed by employing liposome nanocarriers with desired physico-chemical properties that, by exploiting a combination of a number of suitable soft interactions, can facilitate the transit through the biological barriers from the point of administration up to the site of drug action. As a result, the materials engineer has generated through the bottom up approach a variety of supramolecular nanocarriers for the encapsulation and controlled delivery of therapeutics which have revealed beneficial developments for stabilizing drug compounds, overcoming impediments to cellular and tissue uptake, and improving biodistribution of therapeutic compounds to target sites. Herein we present recent advances in liposome drug delivery by analyzing the main structural features of liposome nanocarriers which strongly influence their interaction in solution. More specifically, we will focus on the analysis of the relevant soft interactions involved in drug delivery processes which are responsible of main behaviour of soft nanocarriers in complex physiological fluids. Investigation of the interaction between liposomes at the molecular level can be considered an important platform for the modeling of the molecular recognition processes occurring between cells. Some relevant strategies to overcome the biological barriers during the drug delivery of the nanocarriers are presented which outline the main structure-properties relationships as well as their advantages (and drawbacks) in therapeutic and biomedical applications.

Structural characterization in mixed lipid membrane systems by neutron and X-ray scattering

Lipids membranes, the primary component of the living cell, involve collective behaviour of numerous interacting molecules. The rich morphology and complex phase diagram of the lipid systems require different strategies in describing bio-membranes in order to capture the essential properties of self-assembly processes as well as the underling molecular collective phenomena involved in biological functions. Among the experimental methods used, the scattering techniques such as small angle neutrons and X-rays scattering (SANS and SAXS) are probably the most important experimental approaches for the structural investigation of bio-membranes and mixed lipids complex systems. In this tutorial review we describe the main approaches employed in the investigation of lipid bio-membranes by means of the neutron and x-ray scattering techniques. While introducing the main structural properties of lipid bio-membranes we highlight the important role of lipid components in different biological functions of living organisms. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

The relevance of membrane models to understand nanoparticles-cell membrane interactions

Over the past two decades, numerous types of nanoparticles (NPs) have been developed for medical applications; however only a few nanomedicines are actually available on the market. One reason is the lack of understanding and data concerning the NP fate and their behavior upon contact with biological media and cell membranes. Biomimetic membrane models are interesting tools to approach and understand NPs-cell membrane interactions. The use of these models permits one to control physical and chemical parameters and to rapidly compare membrane types and the influence of different media conditions. The interactions between NPs and cell membranes can be qualified and quantified using analytical and modeling methods. In this review, the major studies concerning NPs-cell membrane models and associated methods are described. The advantages and drawbacks for each method are compared for the different models. The key mechanisms of interactions between NPs and cell membranes are revealed using cell membrane models and are interrogated in comparison with the NP behavior in cellulo or in vivo. Investigating the interactions between NPs and cell membrane models is now proposed as an intermediate step between physicochemical characterization of NPs and biological assays.

A flow cytometric approach to study the mechanism of gene delivery to cells by gemini-lipid nanoparticles: an implication for cell membrane nanoporation

BACKGROUND

Gemini-lipid nanoparticles have been received major attention recently as non-viral delivery systems due to their successful non-invasive gene delivery through tough barriers such as eye and skin. The aim of this study was to evaluate non-viral gene delivery by a series of dicationic gemini surfactant-phospholipid nanoparticles (GL-NPs) and to explore their mechanism of interaction with cellular membranes of murine PAM212 epidermal keratinocytes.

METHODS

NPs containing pCMV-tdTomato plasmid encoding red fluorescent protein (RFP) were prepared using 12 different gemini surfactants (m-s-m, with m = 12, 16 and 18C alkyl tail and s = 3 and 7C polymethylene spacer group and 7C substituted spacers with 7NH and 7NCH3) and dioleoylphosphatidylethanolamine helper lipid. RFP gene expression and cell viability status were evaluated using flow cytometry. MitoTracker Deep Red mitochondrial stain and the cell impermeable Sytox red nuclear stain were used as indicators of cell viability and cell membrane integrity, respectively.

RESULTS

No significant viability loss was detected in cells transfected with 18-3-18, 18-7-18, 18-7NH-18, and 18-7NCH3-18 NPs, whereas a significant reduction of viability was detected in cells treated with 12-3-12, 12-7-12, 12-7NH-12, 16-7NH-16, or 16-7NCH3-16 GL-NPs. Compared to Lipofectamine Plus, 18-3-18 GL-NPs showed higher transfection efficiency and comparable viability profile by evaluation using MitoTracker Deep Red in PAM212 cells. Flow cytometric analysis of PAM212 cells stained with Sytox red revealed two cell populations with low and high fluorescent intensity, representing cells with partially-porated and highly-porated membranes, respectively. Additional combined staining with MitoTracker and ethidium homodimer showed that that 18-3-18 GL-NPs disturbed cell membrane integrity, while cells were still alive and had mitochondrial activity.

CONCLUSION

Taken together, this study demonstrated that 18-3-18 GL-NPs have higher transfection efficiency and comparable viability profile to the commercial Lipofectamine Plus, and the interaction of 18-3-18 GL-NPs with PAM212 cell membranes involves a permeability increase, possibly through the formation of nanoscale pores, which could explain efficient gene delivery. This novel nanoconstruct appears to be a promising delivery system for further skin gene therapy studies in vivo.

CO2 bubbling-based 'Nanobomb' System for Targetedly Suppressing Panc-1 Pancreatic Tumor via Low Intensity Ultrasound-activated Inertial Cavitation

Noninvasive and targeted physical treatment is still desirable especially for those cancerous patients. Herein, we develop a new physical treatment protocol by employing CO₂ bubbling-based 'nanobomb' system consisting of low-intensity ultrasound (1.0 W/cm²) and a well-constructed pH/temperature dual-responsive CO₂ release system. Depending on the temperature elevation caused by exogenous low-intensity therapeutic ultrasound irradiation and the low pH caused by the endogenous acidic-environment around/within tumor, dual-responsive CO₂ release system can quickly release CO₂ bubbles, and afterwards, the generated CO₂ bubbles waves will timely explode before dissolution due to triggering by therapeutic ultrasound waves. Related bio-effects (e.g., cavitation, mechanical, shock waves, etc) caused by CO₂ bubbles' explosion effectively induce instant necrosis of panc-1 cells and blood vessel destruction within panc-1 tumor, and consequently inhibit the growth of panc-1 solid tumor, simultaneously minimizing the side effects to normal organs. This new physiotherapy employing CO₂ bubbling-based 'nanobomb' system promises significant potentials in targetedly suppressing tumors, especially for those highly deadly cancers.

Cooperative transmembrane penetration of nanoparticles

Physical penetration of lipid bilayer membranes presents an alternative pathway for cellular delivery of nanoparticles (NPs) besides endocytosis. NPs delivered through this pathway could reach the cytoplasm, thereby opening the possibility of organelle-specific targeting. Herein we perform dissipative particle dynamics simulations to elucidate the transmembrane penetration mechanisms of multiple NPs. Our simulations demonstrate that NPs' translocation proceeds in a cooperative manner, where the interplay of the quantity and surface chemistry of the NPs regulates the translocation efficiency. For NPs with hydrophilic surfaces, the increase of particle quantity facilitates penetration, while for NPs with partly or totally hydrophobic surfaces, the opposite highly possibly holds. Moreover, a set of interesting cooperative ways, such as aggregation, aggregation-dispersion, and aggregation-dispersion-reaggregation of the NPs, are observed during the penetration process. We find that the penetration behaviors of multiple NPs are mostly dominated by the changes of the NP-membrane force components in the membrane plane direction, in addition to that in the penetration direction, suggesting a different interaction mechanism between the multiple NPs and the membrane compared with the one-NP case. These results provide a fundamental understanding in the underlying mechanisms of cooperative penetration of NPs, and shed light on the NP-based drug and gene delivery.

Aberrant cytokinesis and cell fusion result in multinucleation in HepG2 cells exposed to silica nanoparticles

The multinucleation effect of silica nanoparticles (SiNPs) had been determined in our previous studies, but the relative mechanisms of multinucleation and how the multinucleated cells are generated were still not clear. This extensional study was conducted to investigate the mechanisms underlying the formation of multinucleated cells after SiNPs exposure. We first investigated cellular multinucleation, then performed time-lapse confocal imaging to certify whether the multinucleated cells resulted from cell fusion or abnormal cell division. Our results confirmed for the first time that there are three patterns contributing to the SiNPs-induced multinucleation in HepG2 cells: cell fusion, karyokinesis without cytokinesis, and cytokinesis followed by fusion. The chromosomal passenger complex (CPC) deficiency and cell cycle arrest in G1/S and G2/M checkpoints may be responsible for the cell aberrant cytokinesis. The activated MAPK/ERK1/2 signaling and decreased mitosis related proteins might be the underlying mechanism of cell cycle arrest and thus multinucleation. In summary, we confirmed the hypothesis that aberrant cytokinesis and cell fusion resulted in multinucleation in HepG2 cells after SiNPs exposure. Since cell fusion and multinucleation were involved in genetic instability and tumor development, this study suggests the potential ability of SiNPs to induce cellular genetic instability. These findings raise concerns with regard to human health hazards and environmental risks with SiNPs exposure.

A semi-empirical model for transport of inorganic nanoparticles across a lipid bilayer: implications for uptake by living cells

Due to increasing application, release of nanoparticles (NPs) and nanomaterials into the environment becomes likely. Knowledge about NP uptake in organisms is crucial for risk assessment including estimations on the behavior of NPs based on their physicochemical properties. In the present study, the authors have applied current scientific knowledge to construct a mathematical model, which estimates the transport of NPs through a model biological membrane. The semi-empirical model developed showed all parameters studied to substantially affect the agglomeration of the NPs in suspension, thereby also affecting passive transport. The authors quantified the effects of pH, ionic strength, organic matter concentration of medium, and NP size of several inorganic NPs on the permeation through the lipid membrane. Model outcomes and experimental results described in literature were strongly correlated for several metal oxide NPs. With caution, the model may be used to explain some of the existing variance in nano-uptake and toxicity experiments.

Experimental modulation and computational model of nano-hydrophobicity

We demonstrate that nano-hydrophobicity, which governs the biological aggressiveness of nanoparticles, is determined by the outermost regions of surface ligands. We have also successfully modulated nano-hydrophobicity using systematic surface ligand modifications and built the first computational model of nano-hydrophobicity.