Controlling the Interaction of Nanoparticles with Cell Membranes by the Polymeric Tether

Endocytosis efficiency and targeting ability by the cooperation of nanoparticles

Cooperative wrapping of nanoparticles (NPs) with small sizes is an important pathway for the uptake of NPs by cell membranes. However, the cooperative wrapping efficiency and the effects of NPs' rigidity remain ambiguous. With the aid of computer simulations, we show that the complete wrapping mechanism of cooperative endocytosis is that the aggregation of NPs leads to greater wrapping forces than the single NP case, which triggers the increase of the wrapping degree and in turn further increases the wrapping forces until they are finally fully taken up. The effects of the NP size, initial distance, interaction strength, arrangement and stiffness on cooperative endocytosis were systematically studied. The cooperative wrapping efficiency increases as the NP radius increases. Hexagonal close packed NPs have the highest internalization efficiency. When the interactions are strong, softer NPs exhibit higher endocytosis efficiency. We further propose two strategies by combining NPs with different wrapping properties for targeting applications. By combining two NPs decorated with different types of ligands, the combination NPs can only be fully endocytosed by the cell membrane with two cognate types of receptors and adhere to the normal cell membrane with only one type of receptor. We also design composite NPs using a large NP non-covalently decorated with several small NPs. By harnessing the competition between the ligand-receptor interactions and the excluded volume interactions between the small NPs and the lipid membrane, the composite NPs have targeting ability towards the cancer cell membrane. The design concept of combining NPs with different wrapping properties for drug targeting applications may be very promising in biomedicine.

1,4-Benzenedithiol-Bridged Nanogap-Based Individual Particle Surface-Enhanced Raman Spectroscopy Mechanical Probe for Revealing the Endocytic Force

1,4-Benzenedithiol (BDT)-bridged core-satellite assemblies, as surface-enhanced Raman spectroscopy (SERS) mechanical probes, can be employed for real-time monitoring of the dynamics of endocytic forces and the accompanying trajectory of nanoparticles during the endocytosis process. These mechanical probes exhibit good responses in terms of SERS intensity ratios while undergoing mechanical pressure. Force tracing and the accompanying trajectory of nanoparticles are resolved accurately to render the endocytosis process in live cells. Density functional theory simulation results further proved the sensing scheme due to the electrons transforming between BDT and gold nanoparticles. Furthermore, this SERS mechanical probe is a valid method to visualize endocytic forces at multiple locations and establish a direct criterion to discriminate between cancer cells and normal cells.

Molecular Simulation Studies on the Interactions of Bilirubin at Different States with a Lipid Bilayer

The unconjugated bilirubin (BR) may penetrate through the cell membrane and cause a severe cytotoxicity. However, the molecular mechanism underlying the penetration of BR into the cell membrane is still largely unknown. In this work, we systematically investigate the interaction of BR and a lipid bilayer under different conditions by using all-atom molecular dynamics simulations. It is found that BR at the Z,Z conformation can easily enter into the interior of the lipid bilayer due to its hydrophobicity. However, when BR transforms from the Z,Z conformation to the E,E conformation (after the blue-light emission), its penetration ability is greatly reduced (especially at its ionized state). This study may offer useful physical insights into the effect of phototherapy on the penetration behavior and the cytotoxicity of the unconjugated BR.

Stability and Diffusion Properties of Insulin in Dissolvable Microneedles: A Multiscale Simulation Study

Microneedle (MN) technology has been proven to be promising to become an effective drug delivery route of insulin for diabetes treatment, with the advantages of high delivery efficiency, convenient management, and minimal risk of infection. However, efforts are still required to verify the insulin activity in MNs for further clinical application. Moreover, it is also essential to study the diffusion properties of insulin to understand the ability of various MN materials to control insulin release. Herein, we have combined all-atom molecular dynamics simulation and coarse-grained dissipative particle dynamics to systematically study insulin's structural stability and diffusion coefficient in polyvinyl alcohol and hyaluronic acid solutions. The all-atom simulation reveals the dissimilarities in the interaction mode between insulin and the two polymers. It also points out that the presence of the two polymers would not irreversibly impact the secondary structure of insulin, thereby ensuring regular insulin expression in vivo. Mesoscopic simulation results manifest that the diffusion coefficient of insulin in hyaluronic acid (HA) solution is greater than that of the polyvinyl alcohol (PVA) system. Meanwhile, through the study of insulin centroid trajectory, we have claimed two different diffusion mechanisms of insulin in polymer solution: The movement of insulin in the HA and water solution follows the Brownian motion rule. In comparison, the hopping effect of insulin has been observed in the PVA solution due to poor intermolecular affinity as well as lower polymer water solubility. By summarizing different diffusion mechanisms, this study can provide theoretical guidance for preparing insulin-loaded dissolvable MNs.

Effect of Cell Labeling on the Function of Human Pluripotent Stem Cell-Derived Cardiomyocytes

Cell labeling technologies are required to monitor the fate of transplanted cells in vivo and to select target cells for the observation of certain changes in vitro. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been transplanted for the treatment of heart injuries or used in vitro for preclinical cardiac safety assessments. Cardiomyocyte (CM) labeling has been used in these processes to facilitate target cell monitoring. However, the functional effect of the labeling agent on hiPSC-CMs has not been studied. Therefore, we investigated the effects of labeling agents on CM cellular functions. 3'-Dioctadecyloxacarbocyanine perchlorate (DiO), quantum dots (QDs), and a DNA plasmid expressing EGFP using Lipo2K were used to label hiPSC-CMs. We conclude that the hiPSC-CM labeling with DiO and QDs does not induce arrhythmogenic effects but rather improves the mRNA expression of cardiac ion channels and Ca^2＋ influx by L-type Ca^2＋ channels. Thus, DiO and QD labeling agents may be useful tools to monitor transplanted CMs, and further in vivo influences of the labeling agents should be investigated in the future.