Minireview: Laser-Induced Formation of Microbubbles-Biomedical Implications

Thermophysical Properties of Liquids in Not Fully Stable States—From the First Steps to the Current Trends

The present article marks the 95th anniversary of the birth of Vladimir P. Skripov, author of the classic study of superheated and supercooled liquids. It presents a discussion based on the early work carried out by Skripov and his research team in Ekaterinburg during the 1950s and 1960s. Due to their pioneering nature, these works laid the foundation for the study of metastable liquid states. For various reasons, although they remain relevant to this day, these groundbreaking works remain unknown to most non-Russian-speaking readers. As well as elucidating the behavior of the heat capacity of a solution in the liquid–liquid critical region, the presented research also concerns the characteristic features of light scattering and free-convective heat transfer in the liquid–vapor critical region of a one-component system, discussing two options for the position of the superheated liquid spinodal on the phase diagram of water, including the area of supercooled states and negative pressures. The issues involved in the discussion are united by the fluctuating nature of such phenomena. Indeed, the very possibility of their experimental study is due to a significant increase in the scale of fluctuations of the corresponding quantities when approaching the critical point or spinodal. The ongoing development of the approaches proposed in these papers for solving contemporary problems in the thermophysics of superheated liquids is discussed.

Impact of Shock-Induced Cavitation Bubble Collapse on the Damage of Cell Membranes with Different Lipid Peroxidation Levels

Although the interaction mechanism between shock waves and cells is critical for advancing the medical applications of shock waves, we still have little understanding about it. This work aims to study the response of diseased cells subjected to lipid peroxidation to the nanojet from shock wave-induced bubble collapse by using the coarse-grained molecular dynamics simulation. Factors considered in the simulations include the shock velocity (up), movement time of piston (τp), bubble size (R), and peroxidation level of membranes. Here, we mainly focus on the role of peroxidation levels, that is, the degree (%) and the distribution of oxidized lipids in membranes. The results indicate that the shock damage threshold (up at which the pore in membranes is formed) of peroxidation membranes is less than that of normal membranes and decreases with the peroxidation degree. Importantly, the distribution of oxidized lipids has more effect on the damage threshold than the peroxidation degree. The threshold of membrane with 33% localized oxidized lipids is lower than that of membrane with 50% average oxidized lipids. The results can be explained by the stretching modulus (κs) and bending modulus (κb) of cell membranes. For example, the κb value (4.3 × 10-20 J) of 100% peroxidation membrane is about half of that (8.4 × 10-20 J) of a membrane without peroxidation. A lower modulus means high deformation under the same impact. Further analysis shows that peroxidation introduces a polar hydrophobic group to the tail of phospholipids that increases the hydrophilicity of tails and warps the tail of phospholipids toward the membrane-water interface, resulting in looser accumulation. This can be confirmed by the increased average phospholipid area with peroxidation levels. Indeed, most of the pores formed during the shock can heal. However, the permeation of water molecules across the healing membrane still increased. All these membrane-level information obtained from this study will be useful for improving the biomedical applications of shock waves.

Don't Forget Langmuir-Blodgett Films 2020: Interfacial Nanoarchitectonics with Molecules, Materials, and Living Objects

Designing interfacial structures with nanoscale (or molecular) components is one of the important tasks in the nanoarchitectonics concept. In particular, the Langmuir-Blodgett (LB) method can become a promising and powerful strategy in interfacial nanoarchitectonics. From this viewpoint, the status of LB films in 2020 will be discussed in this feature article. After one section on the basics of interfacial nanoarchitectonics with the LB technique, various recent research examples of LB films are introduced according to classifications of (i) growing research, (ii) emerging research, and (iii) future research. In recent LB research, various materials other than traditional lipids and typical amphiphiles can be used as film components of the LB techniques. Two-dimensional materials, supramolecular structures such as metal organic frameworks, and biomaterials such as DNA origami pieces are capable of working as functional components in the LB assemblies. Possible working areas of the LB methods would cover emerging demands, including energy, environmental, and biomedical applications with a wide range of functional materials. In addition, forefront research such as molecular manipulation and cell fate control is conducted in LB-related interfacial science. The LB technique is a traditional and well-develop methodology for molecular films with a ca. 100 year history. However, there is plenty of room at the interfaces, as shown in LB research examples described in this feature article. It is hoped that the continuous development of the science and technology of the LB method make this technique an unforgettable methodology.

Investigating the Role of Lipid Transfer in Microbubble-Mediated Drug Delivery

Sonoporation, the permeabilization of cell membranes following exposure to microbubbles and ultrasound, has considerable potential for therapeutic delivery. To date, engineering of microbubbles for these applications has focused primarily upon optimizing microbubble size and stability, or attachment of targeting species and/or drug molecules. In this work, it is demonstrated that the microbubble coating can also be tailored to directly influence cell permeabilization. Specifically, lipid exchange mechanisms between phospholipid microbubbles and cells can be exploited to significantly increase sonoporation efficiency in vitro. A theoretical analysis of the energy required for pore formation was carried out. From this, it was hypothesized that sonoporation could be promoted by the transfer of lipid molecules with appropriate carbon chain length and/or shape (cylindrical or conical). Spectral imaging with a hydration-sensitive membrane probe (C-Laurdan) was used to measure changes in the membrane lipid order of A-549 cancer cells following exposure to suspensions of different phospholipids. Two candidate lipids were identified, a short-chain-length phospholipid (1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC)) and a medium-chain-length lysolipid (1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (16:0 lyso-PC)). Microbubbles were prepared with matched concentrations, size distributions, and acoustic responses. Confocal microscopy was used to measure cell uptake of a model drug (propidium iodide) with and without ultrasound exposure (1 MHz, 250 kPa peak negative pressure, 1 kHz pulse repetition frequency, 10% duty cycle, 15 s exposure). Despite significantly decreasing the cell membrane lipid order, DLPC did not increase sonoporation. Microbubbles containing 16:0 lyso-PC, however, produced a ∼5-fold increase in sonoporation compared to control microbubbles. Importantly, the lyso-PC molecules were incorporated into the microbubble coating and did not affect cell permeability prior to ultrasound exposure. These findings indicate that microbubbles can be engineered to exploit lipid exchange between microbubble shells and cell membranes to enhance drug delivery, a new optimization route that may lead to enhanced therapeutic efficacy of ultrasound-mediated treatments.