Experiments show that elastic constants of lipid bilayers vary greatly during the liquid-to-gel phase transition. This fact forms the cornerstone of the Heimburg–Jackson model of soliton propagation ...along membranes of axons, in which the action potential is accompanied by a traveling phase transition. However, the dispersion term, which is crucial for the existence of solitons, is added to the Heimburg–Jackson model ad hoc and set to fit experimental observations. In the present paper, we aim to consolidate this view with continuous membrane mechanics. Using literature data, we show that the compression modulus of a DPPC membrane is smaller by approximately an order of magnitude during phase transition. With a series expansion of the compression modulus, we write the action of a membrane and solve the corresponding wave equation analytically using an Exp-function method. We confirm that membrane solitons with speeds around 200 m/s are possible with amplitudes inversely proportional to their speed. We conclude that dispersion necessary for existence of solitons is directly related to a membrane’s bending properties, offering a possible explanation for
h
. Our findings are in general agreement with existing literature and give insight into a general mechanism of wave propagation in membranes close to transition.
Graphical abstract
It is well known that positions of topological defects (TDs) in liquid crystals can be manipulated experimentally by locally distorting the liquid crystalline (LC) order, as for example by melting ...induced by optical tweezers. In this work, we study numerically the nematic ordering profiles and the corresponding topological defect configurations in thin nematic liquid crystalline shells controlled by imposed local distortion of LC order. We demonstrate that within curved LC films such manipulations could be strongly affected by local Gaussian curvature if it exhibits strong spatial variations. We use mesoscopic approach in which the shell geometry and LC orientational order are described by curvature of the surface and nematic order parameter tensor. For illustration purposes, we consider LC shells exhibiting spherical topology. We show that on increasing prolateness of shells, which imposes spatially inhomogeneous Gaussian curvature, TDs are relatively strongly “glued” to a local Gaussian curvature.
Graphical abstract
The preparation of autologous platelet and extracellular vesicle-rich plasma (PVRP) has been explored in many medical fields with the aim to benefit from its healing potential. In parallel, efforts ...are being invested to understand the function and dynamics of PVRP that is complex in its composition and interactions. Some clinical evidence reveals beneficial effects of PVRP, while some report that there were no effects. To optimize the preparation methods, functions and mechanisms of PVRP, its constituents should be better understood. With the intention to promote further studies of autologous therapeutic PVRP, we performed a review on some topics regarding PVRP composition, harvesting, assessment and preservation, and also on clinical experience following PVRP application in humans and animals. Besides the acknowledged actions of platelets, leukocytes and different molecules, we focus on extracellular vesicles that were found abundant in PVRP.
This book is a survey on the theoretical as well as experimental results on nanostructures in biological systems. It shows how a unifying approach starting from single-particle energy, deriving free ...energy of the system and determining the equilibrium by minimizing the free energy, can be applied to describe electrical and elastic phenomena. It hel
Crystallization alters the characteristics of TiO2 nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is ...preferred over amorphous TiO2. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO2 surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed.
Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface ...curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro‐organisms and the emergence of curvature across length scales is addressed with examples demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by‐product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co‐determines these processes.
Curvature as a local descriptor for shape has been revealed to play a fundamental role in the development of biological systems. Advanced 3D characterization methods allow its quantification across time and length scales indicating that cells and tissue growth can cause emergence of curved surfaces but in turn curvature also acts as a trigger for specific biological processes.
Like-charged macroions in aqueous electrolyte solution can attract each other because of the presence of inter- and/or intramolecular correlations. Poisson−Boltzmann theory is able to predict ...attractive interactions if the spatially extended structure (which reflects the presence of intramolecular correlations) of the mobile ions in the electrolyte is accounted for. We demonstrate this for the case of divalent, mobile ions where each ion consists of two individual charges separated by a fixed distance. Variational theory applied to this symmetric 2:2 electrolyte of rodlike ions leads to an integro-differential equation, valid for arbitrary rod length. Numerical solutions reveal the existence of a critical rod length above which electrostatic attraction starts to emerge. This electrostatic attraction is distinct from nonelectrostatic depletion forces. Analysis of the orientational distribution functions suggests a bridging mechanism of the rodlike ions to hold the two macroions together. For sufficiently large rod length, we also observe “overcharging”, that is, an over-compensation of the macroion charges by the diffuse layer of mobile rodlike ions. Our results emphasize the importance of the often rodlike internal structure that condensing agents such as polyamines, peptides, or polymer segments exhibit. The results were compared with Monte Carlo simulations.
PDF
