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

Conformational control of antimicrobial peptide amphiphilicity: consequences for boosting membrane interactions and antimicrobial effects of photocatalytic TiO2 nanoparticles

This study reports on the effects of conformationally controlled amphiphilicity of antimicrobial peptides (AMPs) on their ability to coat TiO2 nanoparticles (NPs) and boost the photocatalytic antimicrobial effects of such NPs. For this, TiO2 NPs were combined with AMP EFK17 (EFKRIVQRIKDFLRNLV), displaying a disordered conformation in aqueous solution but helix formation on interaction with bacterial membranes. The membrane-bound helix is amphiphilic, with all polar and charged amino acid residues located at one side and all non-polar and hydrophobic residues on the other. In contrast, the d-enantiomer variant EFK17-d (E(dF)KR(dI)VQR(dI)KD(dF)LRNLV) is unable to form the amphiphilic helix on bacterial membrane interaction, whereas the W-residues in EFK17-W (EWKRWVQRWKDFLRNLV) boost hydrophobic interactions of the amphiphilic helix. Circular dichroism results showed the effects displayed for the free peptide, to also be present for peptide-coated TiO2 NPs, causing peptide binding to decrease in the order EFK17-W > EFK17 > EFK17-d. Notably, the formation of reactive oxygen species (ROS) by the TiO2 NPs was essentially unaffected by the presence of peptide coating, for all the peptides investigated, and the coatings stabilized over hours of UV exposure. Photocatalytic membrane degradation from TiO2 NPs coated with EFK17-W and EFK17 was promoted for bacteria-like model bilayers containing anionic phosphatidylglycerol but suppressed in mammalian-like bilayers formed by zwitterionic phosphatidylcholine and cholesterol. Structural aspects of these effects were further investigated by neutron reflectometry with clear variations observed between the bacteria- and mammalian-like model bilayers for the three peptides. Mirroring these results in bacteria-like model membranes, combining TiO2 NPs with EFK17-W and EFK17, but not with non-adsorbing EFK17-d, resulted in boosted antimicrobial effects of the resulting cationic composite NPs already in darkness, effects enhanced further on UV illumination.

Magnetically controlled insertion of magnetic nanoparticles into membrane model

Polysaccharide-coated magnetic nanoparticles (MNPs) have been reported to show potential applications in many biomedical fields. In this report, we have studied the interactions between magnetite (Fe3O4) MNPs functionalized with polysaccharides (diethylamino-ethyl dextran, DEAE-D or chitosan, CHI) with different membranes models by Langmuir isotherms, incorporation experiments, and brewster angle microscopy (BAM). In this report, zwitterionic 1,2-distearoyl-sn-glycerol-3-phosphoethanolamine (DSPE) and anionic 1,2-distearoyl-sn-glycerol-3-phosphate (DSPA) phospholipid, were used to form membrane models. Incorporation experiments (π-t) as well as the compression isotherms demonstrate positive interactions between MNPs and DSPE or DSPA monolayers. The study assessed the impact of varying initial surface pressure on a preformed phospholipid monolayer to determine the maximum insertion pressure (MIP) and synergy. Our findings indicate that the primary driving force of the coated MNPs incorporation into the monolayer predominantly stems from electrostatic interaction. The drop in the subphase pH from 6.0 to 4.0 led to an enhancement of the MIP value for DSPA phospholipid monolayer. On the other hand, for DSPE, the drop in the pH does not affect the MIP values. Besides, the presence of a magnetic field induces an enhancement of the insertion process of the MNPs into DSPA preformed monolayer, demonstrating that a previous interaction between MNPs and phospholipid preformed monolayer needs to take place to enhance the incorporation process. This work opens novel perspectives for the research of the influence of magnetic fields on the incorporation of MNPs into model membranes.

Influence of the Type of Biocompatible Polymer in the Shell of Magnetite Nanoparticles on Their Interaction with DPPC in Two-Component Langmuir Monolayers

Magnetite nanoparticles (MNPs) are attractive nanomaterials for applications in magnetic resonance imaging, targeted drug delivery, and anticancer therapy due to their unique properties such as nontoxicity, wide chemical affinity, and intrinsic superparamagnetism. Their functionalization with polymers such as chitosan or poly(vinyl alcohol) (PVA) can not only improve their biocompatibility and biodegradability but it also plays an important role in their interactions with biological cells. In this work, the effect of the functionalization of MNPs with chitosan, PVA, and their blend on model cell membranes formed from 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) using a Langmuir technique was studied. The studies performed showed that the type of biocompatible polymer in the MNP shell plays a crucial role in the effectiveness of its adsorption process into the model cell membrane. Modification of MNPs with chitosan facilitates significantly more effective adsorption than coating them with PVA or with a chitosan and PVA blend. The presence of all the investigated MNPs in the DPPC monolayer at low concentrations does not affect its thermodynamic state, fluidity, or morphology, which is promising in terms of their biocompatibility. On the other hand, their high concentration (molar fraction above ≈0.05) exerts a disruptive effect on the model cell membrane and results in their aggregation, leading probably to the loss of their superparamagnetic properties essential for nanomedicine.

Mechanistic Pathway of Lipid Phase-Dependent Lipid Corona Formation on Phenylalanine-Functionalized Gold Nanoparticles: A Combined Experimental and Molecular Dynamics Simulation Study

In recent years, the underlying mechanism of formation of the lipid corona and its stability have begun to garner interest in the nanoscience community. However, until now, very little is known about the role of different properties of nanoparticles (NPs) (surface charge density, hydrophobicity, and size) in lipid corona formation. Apart from the physicochemical properties of NPs, the different properties of lipids remain elusive in lipid corona formation. In the present contribution, we have investigated the interaction of phenylalanine-functionalized gold NPs (Au-Phe NPs) with different zwitterionic lipid vesicles of different phase states (sol-gel and liquid crystalline at room temperature) as a function of lipid concentration. The main objective of the present work is to understand how the lipid phase affects lipid corona formation and lipid-induced aggregation in various media. Our results establish that the lipid phase state, area per lipid head group, and the buffer medium play important roles in lipid-induced aggregation. The lipid corona occurs for NPs at high lipid concentration, irrespective of the phase states and area per lipid head group of the lipid bilayer. Notably, the lipid corona also forms at a low concentration of lipid vesicles in the liquid crystalline phase (1,2-dioleoyl-sn-glycero-3-phosphocholine). The corona formation brings in remarkable stability to NPs against freeze-thaw cycles. Based on the stability, for the first time, we classify lipid corona as "hard lipid corona" and "soft lipid corona". This distinct classification will help to develop suitable nanomaterials for various biomedical applications.

Photocatalytic nanoparticles - From membrane interactions to antimicrobial and antiviral effects

As a result of increasing resistance among pathogens against antibiotics and anti-viral therapeutics, nanomaterials are attracting current interest as antimicrobial agents. Such materials offer triggered functionalities to combat challenging infections, based on either direct membrane action, effects of released ions, thermal shock induced by either light or magnetic fields, or oxidative photocatalysis. In the present overview, we focus on photocatalytic antimicrobial effects, in which light exposure triggers generation of reactive oxygen species. These, in turn, cause oxidative damage to key components in bacteria and viruses, including lipid membranes, lipopolysaccharides, proteins, and DNA/RNA. While an increasing body of studies demonstrate that potent antimicrobial effects can be achieved by photocatalytic nanomaterials, understanding of the mechanistic foundation underlying such effects is still in its infancy. Addressing this, we here provide an overview of the current understanding of the interaction of photocatalytic nanomaterials with pathogen membranes and membrane components, and how this translates into antibacterial and antiviral effects.

Probing of Interactions of Magnetite Nanoparticles Coated with Native and Aminated Starch with a DPPC Model Membrane

Understanding the mechanism of interactions between magnetite nanoparticles and phospholipids that form cellular membranes at the molecular level is of crucial importance for their safe and effective application in medicine (e.g. magnetic resonance imaging, targeted drug delivery, and hyperthermia-based anticancer therapy). In these interactions, their surface coating plays a crucial role because even a small modification to its structure can cause significant changes to the behaviour of the magnetite nanoparticles that come in contact with a biomembrane. In this work, the influence of the magnetite nanoparticles functionalized with native and aminated starch on the thermodynamics, morphology, and dilatational elasticity of the model cell membranes was studied. The model cell membranes constituted the Langmuir monolayers formed at the air-water interface of dipalmitoylphosphatidylcholine (DPPC). The surface of the aminated starch-coated nanoparticles was enriched in highly reactive amino groups, which allowed more effective binding of drugs and biomolecules suitable for specific nano-bio applications. The studies indicated that the presence of these groups also reduced to some extent the disruptive effect of the magnetite nanoparticles on the model membranes and improved their adsorption.

Effect of Aminated Chitosan-Coated Fe3O4 Nanoparticles with Applicational Potential in Nanomedicine on DPPG, DSPC, and POPC Langmuir Monolayers as Cell Membrane Models

An adsorption process of magnetite nanoparticles functionalized with aminated chitosan (Fe₃O₄-AChit) showing application potential in nanomedicine into cell membrane models was studied. The cell membrane models were formed using a Langmuir technique from three selected phospholipids with different polar head-groups as well as length and carbon saturation of alkyl chains. The research presented in this work reveals the existence of membrane model composition-dependent regulation of phospholipid-nanoparticle interactions. The influence of the positively charged Fe₃O₄-AChit nanoparticles on a Langmuir film stability, phase state, and textures is much greater in the case of these formed by negatively charged 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) than those created by zwitterionic 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC). The adsorption kinetics recorded during penetration experiments show that this effect is caused by the strongest adsorption of the investigated nanoparticles into the DPPG monolayer driven very likely by the electrostatic attraction. The differences in the adsorption strength of the Fe₃O₄-AChit nanoparticles into the Langmuir films formed by the phosphatidylcholines were also observed. The nanoparticles adsorbed more easily into more loosely packed POPC monolayer.

Anionic nanoparticle-induced perturbation to phospholipid membranes affects ion channel function

Understanding the mechanisms of nanoparticle interaction with cell membranes is essential for designing materials for applications such as bioimaging and drug delivery, as well as for assessing engineered nanomaterial safety. Much attention has focused on nanoparticles that bind strongly to biological membranes or induce membrane damage, leading to adverse impacts on cells. More subtle effects on membrane function mediated via changes in biophysical properties of the phospholipid bilayer have received little study. Here, we combine electrophysiology measurements, infrared spectroscopy, and molecular dynamics simulations to obtain insight into a mode of nanoparticle-mediated modulation of membrane protein function that was previously only hinted at in prior work. Electrophysiology measurements on gramicidin A (gA) ion channels embedded in planar suspended lipid bilayers demonstrate that anionic gold nanoparticles (AuNPs) reduce channel activity and extend channel lifetimes without disrupting membrane integrity, in a manner consistent with changes in membrane mechanical properties. Vibrational spectroscopy indicates that AuNP interaction with the bilayer does not perturb the conformation of membrane-embedded gA. Molecular dynamics simulations reinforce the experimental findings, showing that anionic AuNPs do not directly interact with embedded gA channels but perturb the local properties of lipid bilayers. Our results are most consistent with a mechanism in which anionic AuNPs disrupt ion channel function in an indirect manner by altering the mechanical properties of the surrounding bilayer. Alteration of membrane mechanical properties represents a potentially important mechanism by which nanoparticles induce biological effects, as the function of many embedded membrane proteins depends on phospholipid bilayer biophysical properties.

Nanoparticles and organized lipid assemblies: from interaction to design of hybrid soft devices

This contribution reviews the state of art on hybrid soft matter assemblies composed of inorganic nanoparticles (NP) and lamellar or non-lamellar lipid bilayers. After a short outline of the relevant energetic contributions, we address the interaction of NPs with synthetic lamellar bilayers, meant as cell membrane mimics. We then review the design of hybrid nanostructured materials composed of lipid bilayers and some classes of inorganic NPs, with particular emphasis on the effects on the amphiphilic phase diagram and on the additional properties contributed by the NPs. Then, we present the latest developments on the use of lipid bilayers as coating agents for inorganic NPs. Finally, we remark on the main achievements of the last years and our vision for the development of the field.

Polymer Coating and Lipid Phases Regulate Semiconductor Nanorods' Interaction with Neuronal Membranes: A Modeling Approach

The interplay between nanoparticles (NPs) and cell membranes is extremely important with regard to using NPs in biology applications. With the aim of unraveling the dominating factors on the molecular scale, we have studied the interaction between polymer-coated semiconductor nanorods (NRs) made of cadmium selenium/cadmium sulfur and model lipid membranes. The zeta potential (ζ) of the NRs was tuned from having a negative value (-24 mV) to having a positive one (+11 mV) by changing the amine content in the polymer coating. Supported lipid bilayers (SLBs) and lipid monolayers (LMs) were used as model membranes. Lipid mixtures containing anionic or cationic lipids were employed in order to change the membrane ζ from -77 to +49 mV; lipids with saturated hydrophobic chains were used to create phase-separated gel domains. NR adsorption to the SLBs was monitored by quartz crystal microbalance with dissipation monitoring; interactions with LMs with the same lipid composition were measured by surface pressure-area isotherms. The results showed that the NRs only interact with the model membrane if the mutual Δζ is higher than 70 mV; at the air-water interface, positively charged NRs remove lipids from the anionic lipid mixtures, and the negative ones penetrate the space between the polar heads in the cationic mixtures. However, the presence of gel domains in the membrane inhibits this interaction. The results of the Derjaguin-Landau-Verwey-Overbeek model frame indicate that the interaction occurs not only due to electrostatic and van der Waals forces, but also due to steric and/or hydration forces.

Surface Activity of Poly(ethylene glycol)-Coated Silver Nanoparticles in the Presence of a Lipid Monolayer

We have investigated the surface activity of poly(ethylene glycol) (PEG)-coated silver nanoparticles (Ag-PEG) in the presence or absence of lipid monolayers comprised of monounsaturated dioleoylphosphocholine and dioleoylphosphoglycerol (DOPC/DOPG; 1:1 mol ratio). Dynamic measurements of surface pressure demonstrated that Ag-PEG were surface-active at the air/water interface. Surface excess concentrations suggested that at high Ag-PEG subphase concentrations, Ag-PEG assembled as densely packed monolayers in the presence and absence of a lipid monolayer. The presence of a lipid monolayer led to only a slight decrease in the excess surface concentration of Ag-PEG. Surface pressure-area isotherms showed that in the absence of lipids Ag-PEG increased the surface pressure up to 45 mN m^-1 upon compression before the Ag-PEG surface layer collapsed. Our results suggest that surface activity of Ag-PEG was due to hydrophobic interactions imparted by a combination of the amphiphilic polymer coating and the hydrophobic dodecanethiol ligands bound to the Ag-PEG surface. With lipid present, Ag-PEG + lipid surface pressure-area (π-A) isotherms reflected Ag-PEG incorporation within the lipid monolayers. At high Ag-PEG concentrations, the π-A isotherms of the Ag-PEG + lipid films closely resembled that of Ag-PEG alone with a minimal contribution from the lipids present. Analysis of the subphase silver (Ag) and phosphorus (P) concentrations revealed that most of the adsorbed material remained at the air/lipid/water interface and was not forced into the aqueous subphase upon compression, confirming the presence of a composite Ag-PEG + lipid film. While interactions between "water-soluble" nanoparticles and lipids are often considered to be dominated by electrostatic interactions, these results provide further evidence that the amphiphilic character of a nanoparticle coating can also play a significant role.

Membrane interactions and antimicrobial effects of inorganic nanoparticles

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