Tracking of cutaneous vascular structural changes post-UV irradiation using optical coherence tomography angiography.

BACKGROUND: Ultraviolet (UV) irradiation to skin induces biological responses to protect and heal the wounded tissue. Cutaneous blood vessels play an important role in maintaining skin homeostasis, by inducing angiogenesis and vasodilation. However, the vascular dynamics in vivo, such as morphological changes over time and their depth dependency, are not fully understood. METHODS: Ten Asian males were enrolled in this study and received UV (UVA + UVB) irradiation at two minimal erythema dose (MED) to the inner upper arm. Changes in epidermal thickness and vascular structures associated with UV irradiation were evaluated over time for 28 days by optical coherence tomography angiography (OCTA). This technique enables non-invasive visualization of three-dimensional vascular networks in human skin based on OCT assessment of skin structures with near-infrared light. RESULTS: Notable dilation of vascular structures and increases in epidermal thickness were observed after UV irradiation. Vessel density was markedly increased from the papillary dermis to the upper reticular dermis at a depth of 200 µm. These increases in vascular density showed significant persistence even at 28 days after UV irradiation. CONCLUSION: We visualized the vascular structural changes caused by UV irradiation and revealed that the effects of a single UV irradiation at 2 MED persisted for up to 28 days after exposure. The OCTA technique allows not only the in situ assessment of micro-vasculature in human skin but also its monitoring of vascular dynamics over time.

Free-energy model of phase inversion dynamics in binary phase separation.

We propose here an alternative way to understand the characteristic pattern formation found in the so-called viscoelastic phase separations. Since the viscoelastic phase separations have been observed in systems with strong viscoelastic nature such as polymer solutions, numerical modelings for them have been conducted so far by introducing dynamic properties such as concentration-dependent mobility or elastic relaxation moduli to a usual scheme of phase separations. In contrast to these approaches, we propose the introduction of a small change, a bump, in the local free-energy function, keeping a parameter representing dynamic properties constant. We show that the bump in the local free-energy function successfully induces desired pattern formations in a controlled way, while it does not change equilibrium states. The mechanisms by which this free-energy approach reproduces experimentally observed pattern formations are discussed.

Finger-like pattern formation in dilute surfactant pentaethylene glycol monododecyl ether solutions.

We report here peculiar finger-like patterns observed during the phase separation process of dilute micellar pentaethylene glycol monododecyl ether solutions. The patterns were composed of parallel and periodic threads of micelle-rich domains. Prior to this pattern formation, the phase separation always started with the appearance of water-rich domains rimmed by the micelle-rich domains. It was found that these rims played a significant role in the pattern formation. We explain this pattern formation using a simple simulation model with disconnectable springs. The simulation results suggested that the spatially inhomogeneous elasticity or connectivity of a transient gel of worm-like micelles was responsible for the rim formation. The rims thus formed lead rim-induced nucleation, growth, and elongation of the domains owing to their small mobility and the elastic frustration around them. These rim-induced processes eventually produce the observed finger-like patterns.