Antireflection in Green Lacewing Wings with Random Height Surface Protrusions.

Wings of insects exhibit many functions apart from flying. In particular, their antireflection function is important for insects to avoid detection by their enemies. This function can be applied to antireflection biomimetic films in engineering fields. For such applications, confirming the antireflection mechanisms of insect wings is important. Herein, we used electron microscopy to compare the surfaces of green lacewing wings with and without a surface wax structure and recorded the transmittance spectra to clarify the surface structural and optical properties of insect wings. The spectral transmittance was higher for wings with a surface wax structure than for wings without a wax layer in the light wavelength regime from 500 to 750 nm. We constructed a concise model of the green lacewing wing with flake-like surface structure with a graded effective refractive index corresponding to the wing samples with a surface wax layer; we also constructed a simple thin-film model corresponding to the wing samples without a wax layer. The graded refractive indices were calculated using the effective medium theory, and the transmittance spectra of such models were then calculated using the transfer-matrix method. It was observed that the calculated spectra are in good agreement with the experimental results. In addition, wing samples without a surface structure induce thin-film interference. These results suggest that a wax structure can reduce the reflectance and increase the transmittance enabling the green lacewings to avoid detection by their enemies. These findings may lead to further advances in both the biomimetic field and fundamental research fields.

Confinement Effects on Polymer Dynamics: Thermo-Responsive Behaviours of Hydroxypropyl Cellulose Polymers in Phospholipid-Coated Droplets (Water-in-Oil Emulsion).

In order to construct the artificial cells and to understand the physicochemical properties of living cells, it is important to clarify the cell-sized confinement effect on the behaviours of bio-inspired polymers. We report the dynamic behaviours of aqueous hydroxypropyl cellulose (HPC) solution coated with phospholipids in oil (water-in-oil droplets, W/O droplets), accompanied by an increase in the temperature. We directly observed the beginning of phase separation of HPC solution using a fluorescence microscope and confirmed the dependence of such phenomena on droplet size. The results indicate that the start time of phase separation is decreased with an increase in droplet size. The experimental results suggest that the confinement situation accelerates the phase separation of aqueous HPC solutions.

Real-time observation of liposome bursting induced by acetonitrile.

We show the bursting process of dioleoylphosphatidylcholine (DOPC) liposomes in response to the addition of acetonitrile, a small toxic molecule widely used in the fields of chemistry and industry. The percentage of destroyed liposomes is reduced upon decreasing the acetonitrile fraction in the aqueous solution and vesicle bursting is not observed at volume ratios of 4:6 and below. This indicates that a high fraction of acetonitrile causes the bursting of liposomes, and it is proposed that this occurs through insertion of the molecules into outer leaflet of the lipid bilayer. The elapsed time between initial addition of acetonitrile and liposome bursting at each vesicle is also measured and demonstrated to be dependent on the volume fraction of acetonitrile and the vesicle size.

Deformation of lipid membranes containing photoresponsive molecules in response to ultraviolet light.

Recently, membrane deformation using photoresponsive molecules has been extensively studied toward controlling their shapes because light can supply energy without contacting the vesicles. In this study, photoresponsive pseudogem-bis(diphenylimidazole) [2.2]paracyclophane (pseudogem-bisDPI[2.2]PC) molecules were doped into dioleoylphosphatidylcholine (DOPC) membranes, and the deformation of the DOPC/pseudogem-bisDPI[2.2]PC vesicles was observed under ultraviolet (UV)-light irradiation. It was also found that the volume-to-surface area ratio of spherical vesicles was changed by UV irradiation. Further, we performed high performance liquid chromatography (HPLC) analysis of membrane components in order to clarify the absence of irreversible chemical reactions and UV-irradiation experiments under an osmotic pressure in order to investigate the volume change of the vesicles. Then, we calculated the time-correlation function of membrane fluctuation. Change in the relaxation time of the time-correlation function indicated that the photoisomerization of pseudogem-bisDPI[2.2]PC might decrease the membrane fluidity. We consider that decreasing fluidity is induced by physical entanglement between photochromic compounds and lipids. This technique of membrane deformation may be expected to be applied to various situations such as drug delivery systems (DDS).

Isobars, the coexistence curve, and the critical exponent ß of N-isopropylacrylamide gels obtained using a simple experimental method.

We have obtained "iso-osmobars," which refer to lines with constant osmotic pressures, and coexistence curve of the volume phase transition of N-isopropylacrylamide gel using a very simple method: hanging gels above NaCl solution having a given concentration in a sealed container that was placed in a temperature controlled bath. Since the chemical potential of the water molecules in the gel is equal to that of the water molecules in the NaCl solution, the osmotic pressure of the gel became the same value with that of the NaCl solution. Thus, air that separated the gel and the NaCl solution played a role of infinitely flexible semipermeable membrane. We have succeeded to obtain the coexistence curve and related critical exponent ß from the series of the iso-osmobars of the gel. The value of ß we obtained was 0.38(1.5).

Volume phase transition of N-isopropylacrylamide gels crosslinked by a crosslinker with six hands.

Crosslinkers play an essential role in determining the physical properties of gels. We synthesized a new type of crosslinker with three vinyl groups [trisacrylaminomethan (TRI), which joins six polymer chains per single molecule]. We found that N-isopropylacrylamide (NIPA) gels crosslinked with the new crosslinker gel at a much lower fraction of crosslinker than the gel crosslinked with popular N,N'-methylenebisacrylamide (BIS). We also found that the NIPA gels with TRI crosslinker displayed larger discrete volume changes at the volume phase transition. We discuss the effects of the average length of NIPA chains between two crosslinkers on the volume phase transition as well as the effects of inhomogeneity in gels caused by a low fraction of crosslinker.