Real mesogenic (liquid–crystal exhibiting) molecules often possess a flexible alkyl chain(s) in addition to a rigid and anisotropic core, which most abstract theories of liquid crystals treat as an essential feature. This short account describes the thermodynamic analyses of the state of chains in real liquid crystals and the derived conclusions concerning their active and decisive role and aggregation structures from the analyses’ results. Encountered is a startling resemblance of layered thermotropic liquid crystals and surfactant bilayer membranes.
Amphiphilic molecules, such as phospholipids and surfactants, self–assemble in water to form various aggregation structures such as bilayers. However, it is not understood whether hydration states of the molecules have roles in the self–assembly behavior or water is just a solvent. In the present study, we observed the hydration state of phospholipid bilayers using the terahertz spectroscopy, with which even weakly bound water is included as a hydration water. We found the long–range hydration states strongly depend on the chemical structures of the headgroups, and the change in the self–assembly structures from a bilayer is affected by the long–range hydration states. It can be said that water have crucial roles for the self–assembly of soft matters and bio molecules.
We have so far investigated the phase behavior of various kinds of sterol-containing binary bilayer membranes of phospholipids with different chemical structures by means of differential scanning calorimetry (DSC) and fluorescence spectroscopy using 6-propionyl-2-(N,N-dimethylamino)naphthalene (Prodan) as a probe, and constructed temperature- composition phase diagrams for those binary bilayers to clarify the effects of the sterols on the lateral organization of phospholipid molecules within the binary bilayer membrane. This review describes the compositiondependent phase behavior of different kinds of sterol-containing binary bilayer membranes by introducing our new concept based on the so-called superlattice view to explain how the sterol effects is varied with the variation in the chemical structure of the constituent phospholipids or sterols. In the last place, we briefly mention our recent attempt to examine whether cholesterol-containing binary model membrane will function as if it were the real cell membrane in terms of the binding ability of a cholesterol-dependent cytolytic toxin suilysin (SLY).
Sphingomyelin (SM)–rich membrane domains, called lipid rafts, have been stimulating multi–disciplinary interests because they form signaling platforms. However, structure and physical property of lipid rafts are not sufficiently understood owing to two critical reasons. 1) Appropriate probes, which show similar behavior of raft lipids, have been lacking. 2) The size of lipid rafts is much smaller than the optical resolution and, thus, conventional light microscopy hardly visualizes lipid rafts. Recently, we developed fluorescent SM probes, which show the similar partition and dynamic behavior of native SMs. These probes disclosed transient assembly of putative raft–constituents such as SM, cholesterol and a glycophosphatidylinositol–anchored protein, in live cell membranes. Moreover, we examined distribution of two different types of SMs and found that a small structural difference of these SMs markedly affects their cluster formability.
Biomedical engineering is an integration of engineering and medicine to understand and treat biological, medical, and healthcare problems. The biomedical engineering techniques inherently involve various non–equilibrium phenomena in biological systems, and it is essential to understand the phenomenon for the safe, reliable, and effective use of them. Non–equilibrium molecular dynamics simulation is a potential tool to understand non–equilibrium phenomena at the molecular scale. In this review, we introduce the basis of molecular dynamics simulations of the lipid bilayer and the potential applications to the development of ultrasound and liposomal drug delivery systems based mainly on our previous studies.
Membranes are being used to solve problems related to ecosystems such as medical care and the environment. In this case, not only the mechanical properties and processing properties required for the membrane materials but also the surface properties strongly affect the whole performance of the membrane. In particular, when the biomolecules and cells act on the membrane surface, their characteristics are greatly changed by the surface properties of the membrane materials. To make development a high–performance membrane that takes advantage of biological characteristics, it is important to suppress biological reactions on the surface and prevent nonspecific adsorption of biomolecules. Living cells regulate various biological responses at the cell membrane surface. Here, it is introduced the bioinspired design concept based on the cell membrane surfaces. Also, some membranes installed this surface are summarized.
Sensory functions including vision are necessary to maintain the quality of life, but those functions deteriorate due to diseases and aging. Because approximately 80% of all sensory input is received via the eyes, countermeasures against emerging visual dysfunctions should be developed, especially in super-aging countries such as Japan. Retinal degenerative diseases are a leading cause of irreversible blindness and visual impairment, affecting millions of people worldwide. Although intravitreal injection can directly deliver drugs to the posterior segment of the eye, it is invasive and associated with serious side effects. The design of drug delivery systems targeting the posterior segment of the eye in a less invasive manner has still been challenging because of various anatomical and physiological barriers. Herein, the transscleral drug delivery system and the subretinal cell delivery system we have been developing are introduced.
Biomaterials have been widely investigated as a tool to be applied for regenerative medicine. In the past three decades, it has been demonstrated that three–dimensional porous scaffolds with cells as well as biodegradable drug delivery vehicles with a growth factor could enhance regeneration of tissues, such as skin, bone, cartilage, blood vessel, nerve, in clinical treatments. On the contrary, recent advancement in stem cell biology enables us to utilize stem cells for developing regenerative medicine and drug researches, and these developments need new biomaterials to control cell proliferation, differentiation, and tissue construction. In this article, recent challenges in biomaterials– based regenerative medicine will be discussed.
Membrane bioreactor (MBR), a kind of activated sludge process, is an advanced wastewater treatment technology that uses UF/MF membranes for solid–liquid separation instead of the final settling tank. MBR has a small footprint compared to the conventional activated sludge process, and it also produces high–quality treated water that can be reused. On the other hand, in order to promote the spread of MBR, it is important to solve the problem of high energy consumption. We developed a high packing–density membrane module using a small diameter PVDF hollow fiber membrane to achieve 0.4 kWh/m3 or less of energy consumption per treated water volume in the entire MBR system. As a result, the total energy consumption was estimated to be 0.347 kWh/m3, and it was expected to reach approximately 0.24 kWh/m3 due to the efficiency of equipment. In addition, the daily flow rate fluctuation test assuming a large–scale sewage treatment plant and the 24–hour peak flow test assuming a rainwater inflow were carried out, and both were operated stably.