Energy and Speed Landscapes of the Membrane Internalization Behavior of Soft Nanoparticles.

The cellular endocytosis of nanoparticles (NPs) is a fundamental biological process with significant potential in biomedical applications. However, a comprehensive understanding of the mechanistic aspects of endocytosis and the impact of particle properties on this process remains elusive. In this study, we investigated the membrane-wrapping behavior of soft NPs (SNPs) with varying rigidities using theoretical calculations. Our findings reveal that the membrane-wrapping process of SNPs involves a complex energy change including the possible existence of an energy barrier; moreover, it is found that the location and height of this barrier strongly depend on the mechanistic properties of the NPs and membranes. Additionally, by considering force balance in the membrane-wrapping process, we calculated the speed at which NP is internalized by the membrane, showing a nonmonotonic dependence on particle rigidity and/or wrapping degree. These phenomena can be attributed to competition between different energy components associated with NP-membrane binding, membrane tension, and deformations occurring during SNP-membrane interaction processes. Our results contribute to a deeper understanding of cellular-level endocytosis mechanisms and offer potential applications for soft NPs in biomedicine.

Asymmetric disturbance and permeabilization of bilayer membranes by 3-nm carbon dots.

Small-sized fluorescent carbon dots (CDs) are gaining increasing attention in the field of biomedical applications. The environmental and biological compatibility of positively charged CDs has been extensively investigated; however, the potential cytotoxicity caused by negatively and particularly neutrally charged small CDs has been significantly overlooked. In this study, we conducted a comprehensive investigation into the cellular membrane disruption effect of weakly negatively charged 3-nm CDs using a combination of various biophysical techniques. Our findings demonstrate that even at a low concentration of 0.5 µg mL-1, these CDs induce significant perturbations on the cellular membrane, resulting in increased membrane permeability due to asymmetric disruption of the bilayer structure. Furthermore, CDs exhibit distinct mechanisms at different concentrations, including prompt insertion into the bilayer at low concentrations (<20 µg mL-1) and a synergistic effect after a threshold time at high concentrations (e.g., 25-200 µg mL-1). Moreover, these CDs possess specific antibacterial properties against Acinetobacter baumannii (with a minimum inhibitory concentration of 50 µg mL-1) while showing minimal hemolytic or cytotoxic effects on mammalian cells. This study provides comprehensive insights into the biophysical aspects of cellular membrane toxicity caused by small weakly negatively charged CDs and contributes to assessing their potential biomedical applications.

Thermal-controlled cellular uptake of "hot" nanoparticles.

Nanoparticles (NPs) have shown immense potential in the field of biomedical applications, particularly in NP-based photothermal therapy, which offers a remote-controlled approach to achieve precise temperature control for site-specific heating and sub-cellular tumor treatment. However, the molecular mechanisms underlying related cellular activities, such as the cellular uptake behavior of irradiated NPs in photothermal effects, remain elusive. In this study, we conducted a thorough investigation of the interaction between an irradiated NP with elevated temperature (ranging from 270 to 360 K) and a model bilayer membrane composed of DPPC or DOPC using nonequilibrium coarse-grained molecular dynamics simulations with the implicit-solvent Dry Martini force field. We observe that the interaction between a "hot" NP and a membrane is thermally regulated. In addition, the wrapping of membranes around NPs exhibits a strong dependence on the temperature of the irradiated NP, demonstrating a step-like change in behavior. This membrane wrapping effect is attributed to the heat conduction between NPs and membrane lipids, which occurs almost simultaneously with the membrane deformation and wrapping of NPs during the NP-membrane interaction process. Especially, during the process of heat conduction, a gel-to-fluid phase transition of the membrane may occur, which plays a crucial role in determining the deformation behavior of the membrane. Moreover, it is found that the membrane lipids in the two leaflets exhibit obvious and asymmetric molecular-level responses to heat flux, characterized by significant changes in packing states (e.g., the order parameter of lipid tails and area per lipid) and possible interdigitation between lipids. Furthermore, the thermal-controlled wrapping effect is tightly linked to the properties of NPs (e.g., size, NP-lipid affinity) and lipid species. Our findings are valuable for comprehending the thermal-regulated cellular internalization of NPs and offer insights into devising strategies to precisely modulate NP endocytosis by exploiting the interplay between heating and NP properties.

Physicochemical Properties and Route of Systemic Delivery Control the In Vivo Dynamics and Breakdown of Radiolabeled Gold Nanostars.

The in vivo dynamics of nanoparticles requires a mechanistic understanding of multiple factors. Here, for the first time, the surprising breakdown of functionalized gold nanostars (F-AuNSs) conjugated with antibodies and 64 Cu radiolabels in vivo and in artificial lysosomal fluid ex vivo, is shown. The short-term biodistribution of F-AuNSs is driven by the route of systemic delivery (intravenous vs intraperitoneal) and long-term fate is controlled by the tissue type in vivo. In vitro studies including endocytosis pathways, intracellular trafficking, and opsonization, are combined with in vivo studies integrating a milieu of spectroscopy and microcopy techniques that show F-AuNSs dynamics is driven by their physicochemical properties and route of delivery. F-AuNSs break down into sub-20 nm broken nanoparticles as early as 7 days postinjection. Martini coarse-grained simulations are performed to support the in vivo findings. Simulations suggest that shape, size, and charge of the broken nanoparticles, and composition of the lipid membrane depicting various tissues govern the interaction of the nanoparticles with the membrane, and the rate of translocation across the membrane to ultimately enable tissue clearance. The fundamental study addresses critical gaps in the knowledge regarding the fate of nanoparticles in vivo that remain a bottleneck in their clinical translation.

Membrane-Specific Binding of 4 nm Lipid Nanoparticles Mediated by an Entropy-Driven Interaction Mechanism.

Lipid nanoparticles (LNPs) are a leading biomimetic drug delivery platform due to their distinctive advantages and highly tunable formulations. A mechanistic understanding of the interaction between LNPs and cell membranes is essential for developing the cell-targeted carriers for precision medicine. Here the interactions between sub 10 nm cationic LNPs (cLNPs; e.g., 4 nm in size) and varying model cell membranes are systematically investigated using molecular dynamics simulations. We find that the membrane-binding behavior of cLNPs is governed by a two-step mechanism that is initiated by direct contact followed by a more crucial lipid exchange (dissociation of cLNP's coating lipids and subsequent flip and intercalation into the membrane). Importantly, our simulations demonstrate that the membrane binding of cLNPs is an entropy-driven process, which thus enables cLNPs to differentiate between membranes having different lipid compositions (e.g., the outer and inner membranes of bacteria vs the red blood cell membranes). Accordingly, the possible strategies to drive the membrane-targeting behaviors of cLNPs, which mainly depend on the entropy change in the complicated entropy-enthalpy competition of the cLNP-membrane interaction process, are investigated. Our work unveils the molecular mechanism underlying the membrane selectivity of cLNPs and provides useful hints to develop cLNPs as membrane-targeting agents for precision medicine.

Atomistic Simulations on Interactions between Amphiphilic Janus Nanoparticles and Lipid Bilayers: Effects of Lipid Ordering and Leaflet Asymmetry.

Amphiphilic Janus nanoparticles, which are hydrophilic on one-half of the particle surface and hydrophobic on the other half, are ideal carrier candidates for drug delivery due to their unique physicochemical properties. In this study, we investigate the interactions between amphiphilic Janus nanoparticles coated with hydrophilic and hydrophobic ligands on each half of the surface of the nanoparticle and lipid bilayers with either symmetric or asymmetric leaflet structure and in different phases using atomistic molecular dynamics simulations. The results show that the Janus nanoparticle can easily insert into the liquid-disordered lipid bilayer and asymmetric lipid bilayers with the hydrophobic ligands inserted into the liquid-ordered leaflet. However, the nanoparticle barely inserts into the symmetric liquid-ordered lipid bilayer and tends to be adsorbed onto the surface of the liquid-ordered bilayers with the hydrophilic ligands contacting the surface of the bilayer. The insertion of the nanoparticle is mainly dominated by the hydrophobicity of the ligands, the lipid ordering, and the curvature of the bilayer. Rotation of the nanoparticle only occurs during the initial adsorption process of the nanoparticle onto the surface of the lipid bilayers. This work provides new insight into understanding the interactions of amphiphilic Janus nanoparticles with model biological membranes at the atomistic scale and the application of Janus nanoparticles for drug delivery.