Discovery of “punch-through” or membrane electrical breakdown and electroporation

Impact of Lipid Peroxidation on the Response of Cell Membranes to High-Speed Equibiaxial Stretching: A Computational Study

The difference between diseased and healthy cellular membranes in response to mechanical stresses is crucial for biology, as well as in the development of medical devices. However, the biomolecular mechanisms by which mechanical stresses interact with diseased cellular components remain largely unknown. In this work, we focus on the response of diseased cellular membranes with lipid peroxidation to high-speed tensile loadings. We find that the critical areal strain (ξ_c, when the pore forms) is highly sensitive to lipid peroxidation. For example, ξ_c of a fully oxidized bilayer is only 64 and 69% of the nonoxidized one at the stretching speed of 0.1 and 0.6 m/s, respectively. ξ_c decreases with the increase in the oxidized lipid ratio, regardless of the speeds. Also, the critical rupture tension of membranes exhibits a similar change. It is obvious that the oxidized membranes are more easily damaged than normal ones by high-speed stretching, which coincides with experimental findings. The reason is that peroxidation introduces a polar group to the tail of lipids, increases the hydrophilicity of tails, and warps the tails to the membrane-water interface, which causes loose accumulation and disorder of lipid tails. This can be deduced from the variation in the area per lipid and order parameter. In addition, the lowering stretching modulus and line tension of membranes (i.e., softening) after lipid peroxidation is also a significant factor. We reveal the difference between the peroxidized (diseased) and normal membrane in response to high-speed stretching, give the ξ_c value in the pore formation of membranes and analyze the influence of the stretching speed, peroxidation ratio, and molecular structure of phospholipids. We hope that the molecular-level information will be useful for the development of biological and medical devices in the future.

Ionic Current Rectification of Porous Anodic Aluminum Oxide (AAO) with a Barrier Oxide Layer

Synthetic nanofluidic diodes with highly nonlinear current-voltage characteristics are currently of particular interest because of their potential applications in biosensing, separation, energy harvesting, and nanofluidic electronics. We report the ionic current rectification (ICR) characteristics of a porous anodic aluminum oxide membrane, whose one end of the nanochannels is closed by a barrier oxide layer. The membrane exhibits intriguing pH-dependent ion transport characteristics, which cannot be explained by the conventional surface charge governed ionic transport mechanism. We reveal experimentally and theoretically that the space charge density gradient present across the 40-nm-thick barrier oxide is mainly responsible for the evolution of ICR. Based on our findings, we demonstrate the formation of a single 5-8-nm-sized pore in each hexagonal cell of the barrier oxide. The present work would provide valuable information for the design and fabrication of future ultrathin nanofluidic devices without being limited by the engineering of the nanochannel geometry or surface charge.

Irreversible electropermeabilization of the human pathogen Candida albicans: an in-vitro experimental study

Pathogenic fungi cause many life-threatening infections, especially among individuals with immune system dysfunction. The antifungal drugs commonly used to suppress fungal pathogens can result in long-lasting and toxic therapy. In this work, irreversible electropermeabilization was used to investigate the dynamics of the decrease in Candida albicans colony vitality after application of a pulsed electric field (PEF) and use of antifungal drugs. The fungi were subjected to single 250-µs to 2-ms (0.5-2.5 kV/cm) pulses or repeated short 5-µs pulses, and efficacy was compared. It was shown that electropermeabilization combined with antifungal agents results in rapid and more effective treatment, eliminating more than 90% of C. albicans colony-forming units in a single procedure, which is advantageous in biomedicine. It was also observed that, because of application of PEF and use of the antifungal agents, the Candida cells form cell aggregates and average live cell size is reduced by as much as 53%.