Self-Assembly of Patterned Nanoparticles on Cellular Membranes: Effect of Charge Distribution

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Spatial arrangements of spherical nanoparticles on lipid vesicles

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

Stability of membrane-induced self-assemblies of spherical nanoparticles

The self-assembly of spherical nanoparticles, resulting from their adhesion on tensionless lipid membranes, is investigated through molecular dynamics simulations of a coarse-grained implicit-solvent model. Our simulations indicate that, with increasing adhesion strength, while reshaping the membrane, the nanoparticles aggregate into a sequence of self-assemblies corresponding to in-plane chains, two-row tubular (bitube) chains, annular (ring) chains, and single-row tubular (tube) chains. Annealing scans, with respect to adhesion strength, show that the transitions between the various phases are highly first-order with significant hystereses. Free energy calculations indicate that the gas and single-row tubular chains are stable over wide ranges of adhesion strength. In contrast, the in-plane chains are only stable for small aggregates of NPs, and the bitube and ring chains are long-lived metastable states over a wide range of adhesion strength.

Dynamic simulations of many-body electrostatic self-assembly

Two experimental studies relating to electrostatic self-assembly have been the subject of dynamic computer simulations, where the consequences of changing the charge and the dielectric constant of the materials concerned have been explored. One series of calculations relates to experiments on the assembly of polymer particles that have been subjected to tribocharging and the simulations successfully reproduce many of the observed patterns of behaviour. A second study explores events observed following collisions between single particles and small clusters composed of charged particles derived from a metal oxide composite. As before, observations recorded during the course of the experiments are reproduced by the calculations. One study in particular reveals how particle polarizability can influence the assembly process.This article is part of the theme issue 'Modern theoretical chemistry'.

Hydrophilic nanoparticles stabilising mesophase curvature at low concentration but disrupting mesophase order at higher concentrations

Using high pressure small angle X-ray scattering (HP-SAXS), we have studied monoolein (MO) mesophases at 18 wt% hydration in the presence of 10 nm silica nanoparticles (NPs) at NP-lipid number ratios (ν) of 1 × 10(-6), 1 × 10(-5) and 1 × 10(-4) over the pressure range 1-2700 bar and temperature range 20-60 °C. In the absence of the silica NPs, the pressure-temperature (p-T) phase diagram of monoolein exhibited inverse bicontinuous cubic gyroid (Q), lamellar alpha (Lα), and lamellar crystalline (Lc) phases. The addition of the NPs significantly altered the p-T phase diagram, changing the pressure (p) and the temperature (T) at which the transitions between these mesophases occurred. In particular, a strong NP concentration effect on the mesophase behaviour was observed. At low NP concentration, the p-T region pervaded by the Q phase and the Lα-Q mixture increased, and we attribute this behaviour to the NPs forming clusters at the mesophase domain boundaries, encouraging transition to the mesophase with a higher curvature. At high NP concentrations, the Q phase was no longer observed in the p-T phase diagram. Instead, it was dominated by the lamellar (L) phases until the transition to a fluid isotropic (FI) phase at 60 °C at low pressure. We speculate that NPs formed aggregates with a "chain of pearls" structure at the mesophase domain boundaries, hindering transitions to the mesophases with higher curvatures. These observations were supported by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). Our results have implications to nanocomposite materials and nanoparticle cellular entry where the interactions between NPs and organised lipid structures are an important consideration.

How hydrophobic nanoparticles aggregate in the interior of membranes: A computer simulation

Lipid-based dispersion of hydrophobic nanoparticles (NPs) not only gives fundamental insight into how nanomaterials distribute in live cells and organisms, but also provides a quite general route to designing nanocarrier agents in triggered drug delivery and medical imaging. It is not clearly understood how hydrophobic NPs arrange in the interior of a membrane. In this paper, with computer simulation techniques, we demonstrate that hydrophobic NPs having a diameter compared to the hydrophobic thickness of the membrane are capable of clustering in the hydrophobic interior of a cell membrane. Except from the isotropic aggregation, an unexpected linear arrangement of spherical NPs, which is still not found from experiments, is identified here. The free-energy costs associated with linear and isotropic aggregations are computed explicitly to interpret aggregation behavior and the obtained phase diagrams give us a comprehensive understanding of where linear aggregation is expected. In this work we also shows that NP size and membrane tension play key roles in determining the NP aggregate, while the effects of NP concentration and membrane curvature seem to be relatively weak.

A spontaneous penetration mechanism of patterned nanoparticles across a biomembrane

Recent experimental studies have shown the ability of tailoring the nanoparticle (NP)-cell interaction via the engineering of NP surfaces. Although the considerable progress has been made in design of patterned NPs for drug delivery, the effect of surface pattern on the NP-cell interaction is not fully understood yet. In this work, we used a dissipative particle dynamics method to systematically investigate the effects of NP surface pattern on its penetration across a membrane. For stripy NPs or patchy NPs having a large stripe width or patch size, an "insertion-rotation" penetration mechanism is found. Results indicate that stripy NPs and patchy NPs coated with narrow stripes or small patches can directly penetrate the cell membrane with a less constrained rotation. By considering the spontaneous penetration of many NPs into a vesicle, we found that NP aggregation would lead to the shape change of the vesicle, and therefore cause the leakage of encapsulated solvent or membrane rupture, implying the possible cytotoxicity. In short, this work gives a fundamental understanding for the penetration mechanism of the ligand patterned NPs, which provides useful reference for the design of NPs for controllable cell penetrability and targeted delivery of drugs.