How does a polymer chain pass through a cylindrical pore under an elongational flow field?

Na+-Mg2+ ion effects on conformation and translocation dynamics of single-stranded RNA: Cooperation and competition

The nanopore-based translocation of a single-stranded RNA (ssRNA) in mixed salt solution has garnered increasing interest for its biological and technological significance. However, it is challenging to comprehensively understand the effects of the mixed ion species on the translocation dynamics due to their cooperation and competition, which can be directly reflected by the ion screening and neutralizing effects, respectively. In this study, Langevin dynamics simulation is employed to investigate the properties of ssRNA conformation and translocation in mixed Na+-Mg2+ ion environments. Simulation results reveal that the ion screening effect dominates the change in the ssRNA conformational size, the ion neutralizing effect controls the capture rate of the ssRNA by the nanopore, and both of them take charge of the different changes in translocation time of the ssRNA under various mixed ion environments. Under high Na+ ion concentration, as Mg2+ concentration increases, the ion neutralizing effect strengthens, weakening the driving force inside the nanopore, leading to longer translocation time. Conversely, at low Na+ concentration, an increase in Mg2+ concentration enhances the ion screening effect, aiding in faster translocation. Furthermore, these simulation results will be explained by quantitative analysis, advancing a deeper understanding of the complicated effects of the mixed Na+-Mg2+ ions.

Cartilage-Inspired Hydrogel with Mechanical Adaptability, Controllable Lubrication, and Inflammation Regulation Abilities

Cartilage is a key component in joints because of its load-bearing and lubricating abilities. However, osteoarthritis often leads to afunction of load-bearing/lubrication and occurrence of inflammation with overexpressed reactive oxygen species (ROS) and nitric oxide (NO). To address these issues, we fabricated a novel polyanionic hydrogel with abundant carboxylates/sulfonates ("CS" hydrogel), inspired by normal cartilage rich in anionic hyaluronate/sulfonate glycosaminoglycan/lubricin, and crosslinked it tightly by Fe3+ ("CS-Fe" hydrogel). The "CS-Fe" hydrogel displayed mechanical adaptability and shear resistance. A low coefficient of friction (∼0.02) appeared when a loose hydrogel layer was generated because of the photoreduction of Fe3+ to Fe2+ by UV irradiation. This biocompatible "CS-Fe" hydrogel suppressed the overexpressed hydroxyl radical (·OH) and NO in macrophages and protected chondrocytes/fibroblasts from aggressive inflammation. Moreover, the layered "CS-Fe" hydrogel avoided cell death of chondrocytes in sliding tests. The results demonstrate that this cartilage-inspired hydrogel is a promising candidate material in cartilage tissue engineering to especially address inflammation.

Dynamics of long hyaluronic acid chains through conical nanochannels for characterizing enzyme reactions in confined spaces

This research reports the transport behaviors of long flexible polymers (hyaluronic acid) through long conical track-etched nanochannels with and without grafted enzymes. The impacts of the channel diameter and the polymer regimes in solution (dilute and semi-dilute) have been investigated. Without enzymes, the experimental results can be well explained by the analytical models of the scaling law of de Gennes. Then, the corresponding enzymes (hyaluronidase) were grafted inside the channel. When enzymes are located at the base side, polymers get degraded at the entrance and the degraded products are detected. When enzymes are grafted at the tip side, the extension of translocation duration due to the binding of substrate-enzyme is observed. This is for the first time that the enzymatic degradation reactions are characterized in situ at the single molecule level by nanopore technology.

Separation of Caustic Nano-Emulsions and Macromolecular Conformations with Nanofibrous Membranes of Marine Chitin

Sustainable development of nanotechnology is challenged by nanoscale pollutants and oily water. Biobased nanoporous membranes, though serving as one of the most eco-friendly separation technologies, cannot be applied widely because of their broad pore distributions, poor solvent resistance, and structural instability. In order to avoid possible leakage of nanoscale objects in caustic and organic solvents, herein, we endeavored to exfoliate chitin nanofibrils with identical chemical and crystalline structures to pristine chitin in portunid carapace and further produce nanoporous and mesoporous membranes with super structural stability, endurance, permeation flux and rejection. The final membranes had minimal ionization, controllable thickness, and tunable and narrow distribution of pore size, being able to separate nano-emulsions, nanoparticles, and rigid macromolecules in caustic aqueous solutions and organic solvents. Thus, these scalable, low-cost, and sustainable membranes may promise applications as diverse as in separating and concentrating nanoparticles in nanotechnology, oil/water separation in wastewater treatment, and molecular sieving in biomedicine and material science.

Effects of tensile strain on the peculiarities of PEO penetration into the nanoporous structure of PET deformed via the crazing mechanism

Solvent crazing involves the development of a highly dispersed fibrillar-porous structure with dimensions of pores and craze fibrils of about 2-20 nm, and crazing by itself can be treated as a universal method for the development of nanoscale porosity. The penetration and release of poly(ethylene oxide) macromolecules into and from the crazes during the development of the nanoporous structure of poly(ethylene terephthalate) have been studied. In particular, PET has been deformed in dilute or semidilute (unentangled as well as entangled) solutions of PEO (a Mw of 4 and 40 kDa) via the mechanism of solvent crazing. Hydrodynamic coil radii Rh, blob sizes ξ, and concentration ranges (crossover and entanglement concentrations) have been determined for the PEO solutions. The evolution of the craze structure (change in porosity W and pore diameters d) has been described as a function of the tensile strain of PET during its drawing in an adsorption-active medium and in the PEO solutions. PEO has been shown to penetrate into the nanoporous structure of the crazes under the conditions corresponding to Rh≤d and ξ < d. It has been shown that coagulation processes in the structure of crazed PET, PEO adsorption at the highly developed surface of PET, and the mechanism of PEO transport in the nanopores are equally important factors affecting the direction of the macromolecule mass transfer in the nanopores (penetration or release) and PEO content variation as a function of PET tensile strain.