Size-dependent partitioning of nano/microparticles mediated by membrane lateral heterogeneity.

It is important that we understand the physical, chemical, and biological mechanisms that govern the interaction between nanoparticles (NPs) and heterogeneous cellular surfaces because of the possible cytotoxicity of engineered nanomaterials. In this study, we investigated the lateral localization of nano/microparticles within a biomimetic heterogeneous membrane interface using cell-sized two-phase liposomes. We found that lateral heterogeneity in the membrane mediates the partitioning of nano/microparticles in a size-dependent manner: small particles with a diameter of ≤200 nm were localized in an ordered phase, whereas large particles preferred a fluidic disordered phase. This partitioning behavior was verified by temperature-controlled membrane miscibility transition and laser-trapping of associated particles. In terms of the membrane elastic energy, we present a physical model that explains this localization preference of nano/microparticles. The calculated threshold diameter of particles that separates the particle-partitioning phase was 260 nm, which is in close agreement with our observation (200 nm). These findings may lead to a better understanding of the basic mechanisms that underlie the association of nanomaterials within a cell surface.

Membrane disk and sphere: controllable mesoscopic structures for the capture and release of a targeted object.

Design of molecules for self-assembled mesoscopic structures with specific functions is an important and interesting challenge that spans across disciplines such as nanosciences. A closed lipid membrane is a good example of a self-assembled mesostructure. In this study, we developed controllable membrane formation by making a subtle change at the molecular level. We utilized a synthetic photosensitive amphiphile (KAON12) to achieve the photobased molecular manipulation of the opening and closing of membranes through reversible transitions between sphere and disk structures. We found that the mechanism is based on the photoswitching of the membrane line tension, as deduced from the fluctuation of the membrane edge, through the action of KAON12. Furthermore, we demonstrated the controllable capture and release of colloidal particles into and from a membrane sphere. The observation of Brownian motion of the particle confirmed colloidal encapsulation. This successful photomanipulation of mesoscopic membrane structures in a noncontact and reversible manner should lead to a better understanding of the mechanism of membrane self-organization and may see wider application, such as in microreactors and drug-delivery systems.

Reversible control of exo- and endo-budding transitions in a photosensitive lipid membrane.

We have developed a method for the photomanipulation of lipid membrane morphology in which the shape of a vesicle can be switched by light through the use of a synthetic photosensitive amphiphile containing an azobenzene unit (KAON12). We prepared cell-sized liposomes from KAON12 and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and conducted real-time observations of vesicular transformation in the photosensitive liposome by phase-contrast microscopy. Budding transitions-either budding toward the centre of the liposome (endo-bud) or budding out of the liposome (exo-bud)-could be controlled by light. We discuss the mechanism of this transformation in terms of the change in the effective membrane surface area due to photoisomerization of the constituent molecules.

Staphylococcus cohnii as a cause of multiple brain abscesses in Weber-Christian disease.

We report a patient with multiple brain abscesses due to Staphylococcus cohnii. While these brain abscesses markedly responded to the antibiotics, this patient was subsequently suffered from subcutaneous inflammatory nodules in the adipose tissue, which diagnosed him as having Weber-Christian disease (WCD). This is the first report that subcutaneous inflammatory nodules in the adipose tissue, which lead the diagnosis of WCD, followed multiple brain abscesses. To our knowledge, S. cohnii has not yet been reported to cause multiple brain abscesses in humans. Although the etiology of WCD is unknown, an immune mechanism has been implicated in the pathogenesis. Therefore, we should notice that patients with WCD could be immunocompromised hosts with a higher risk to suffer from severe opportunistic infections.