Many bioengineering techniques to elucidate functions and characteristics of the skin have been developed until now. They measure the water content of stratum corneum, transepidermal water loss (TEWL), skin surface contour, mechanical properties, blood flow, sebum secretion rate, wrinkles, skin pigmentation and so on. These instrumental measurements are applied to validation of the efficacy of the cosmetics. Recently, a few in vivo bio-microscopes which non-invasively visualize horizontal image or vertical cross section of the skin with subcellular resolution, have been developed by using non-linear optics phenomenon. In this paper, I describe how skin measurement technologies have been changed with time and applied to cosmetic science, and also review in vivo bio-microscopes, they are optical coherence tomography (OCT), confocal laser scanning microscope (CLSM), second harmonic generation (SHG) microscope, multi photon microscope (MPM), and coherent anti-Stokes Raman scattering (CARS), which will be very helpful to examine the effects of the cosmetics on the skin.
The skin which is located at the surface of our body is not only a sensory organ but also a defensive organ. We are able to be perceptible for environmental stimuli such as dryness, temperature and even solar lights, through the skin and to protect our body against invaders, such as chemicals and microorganisms by the skin. Defenses by the skin are divided into two types, one is physical defense and another is a physiological one. The physical defense which is called as the physical barrier function is realized by corneocytes, intercellular lipid lamellar structure, tight junction and so on. On the other hands, physiological defense is constructed by collaboration of langerhans cells, antimicrobial peptides and physical barrier functions. The article introduces the skin functions adapting against environmental stimuli.
Non-invasive evaluation technology of the skin is highly required for understandings of its properties as well as maintenance of healthy skin by cosmetic approach. Recently, various optical technologies have been proposed to measure inside of the skin. In this review, we introduce two topics. Confocal Raman spectroscopy enables us to detect not only water gradient beneath the skin surface, but also various constituents of the skin. Multi-photon microscopy provides visualization of dermal matrices including collagen fibers and elastin, and differences between subjects with less or much UV exposure history were successfully demonstrated, suggesting alteration in photo-aging. Such optical systems offer new insights thorough evaluation of inside of the skin with non-invasive fashion.
The most important and principal function of the skin is to provide a protective interface between human body and external environment. Ceramides exist as main components of intercellular lipids of stratum corneum, and play an essential role of a barrier function of the skin. It is well known that natural ceramides are optically active, and consist of (2S, 3R)-configuration (D-erythro configuration) at the sphingosine moiety. Thus, the optically active (2S, 3R)-ceramides have been developed based on the strategy of asymmetric synthesis. In order to embody the function of the ceramides in various cosmetic products, effective and stable novel formula of the ceramides have been devised with consideration of lamellar structure of natural intercellular lipids. As a consequence of studies especially focused on stereochemistry, compositions containing the optically active ceramides showed significant recovering effect of water-holding capacity and barrier function of the skin. The following article reviews recent developments in the functional properties of the optically active ceramides as well as various formulating techniques of these materials.
Evaluation of the adhesion properties of dermal and transdermal patches (i.e. poultice and tape) applied to the skin is very important. Several physical test methods are used as quality tests of patch adhesion. However, it has been well-known that physical test and human sensory may not correlate well, particularly in case of poultice. We have developed a novel tack method using the phosphor-bronze thin plate and have evaluated adhesiveness of poultice and compared human sensory results. Additionally, cohesiveness of poultice has also evaluated using the filter paper. These methods are thought to evaluate the adhesive properties of patch products and also apply for the evaluation of novel formulation development.
Lipid lamellar structure in intercellular space of stratum corneum is recognized as main physical barriers against dehydration and invasion of foreign substances. For development of effective transdermal drug delivery, it is necessary to decrease those barriers temporally and reversibly. Co-administration of components which has drug absorption enhancing effect is one of the essential methodologies to increase absorption of drugs via skin. The change in lipid lamellar structure was determined by synchrotron X-ray diffraction. When the stratum corneum was pretreated by l-menthol, lipid lateral packing became liquid crystal. It was considered that disorder of lamellar structure brought about increasing in drug permeation. It means that the lipid lamellar structure is one of the key parameters to evaluate physical barrier function of the skin. The structure analysis of lipid lamellar employing synchrotron X-ray diffraction is thought to be a meaningful technique possibly applied for promoting mechanism of transdermal absorption enhancer and evaluation of barrier function of skin.
Sunscreen cosmetics show UV-protection function by the application of organic UV absorbers and/or inorganic UV scattering agents. In 2012, the expression of UVA protection efficacy was amended from three grades (PA+ ∼ PA+++) to four grades (PA+ ∼ PA++++). In accordance with this revision, cosmetic manufacturers have directed their efforts toward the development of sunscreens with strong UVA protection. In our company, a broad-spectrum sunscreen product, BSUS Milk-1, which shows a strong UVA protection efficacy by the composition of four kinds of UV absorbers and one UV scattering agent, has developed. BSUS Milk-1 was tested on 39 patients with photosensitive dermatoses at six university hospitals. The results demonstrated that BSUS Milk-1 is highly useful, especially for UVA-sensitive patients.
Sun protection is simply guarding a body from the adverse effects of sunlight. Aside from the hazards of heat, the sun poses the danger of sunburn, which can permanently damage the skin, precancerous changes in the skin, as well as premature wrinkling and signs of aging. UVB (Ultraviolet-B) rays are short wavelengths responsible for sun burns. UVB protection is indicated by SPF (sun protection factor) levels. UVA (Ultraviolet-A) rays penetrate deep into the skin, which can cause premature signs of aging, including sunspots, wrinkles and uneven skin tone. The PA rating system is used to indicate the level of UVA protection. In this report, the mechanism of UV protection by using titanium dioxide and zinc oxide particles are explained. Zinc oxide fine particles have excellent shielding property. We demonstrated the property using zinc oxide particles prepared by a homogeneous precipitation method from aqueous solution of zinc salts. The morphology of the zinc oxide precipitates was significantly changed depending on the precursor composition, the concentration of precipitant, and the reaction temperature. Different UV-vis absorption/reflection characteristics were observed for the particles with different morphologies.
The growth of single-walled carbon nanotubes (SWCNTs) by hot-filament chemical vapor deposition using Co as a catalyst and Co silicide as a catalyst support was investigated at 450°C. Ethanol vapor was used as the carbon source. The density of grown nanotubes was much higher for the sample formed using Co silicide as the support than for that formed using Si dioxide as the support. Co silicide was found to be more suitable than Si dioxide as the support for nanoparticles of the Co catalyst that triggers nanotube growth. Moreover, Co silicide was suitable for growing SWCNTs with a relatively uniform diameter.
It is known that zwitterions acquire a positive electrical charge under the isoelectric point (I.P.), which increases its adsorption to hairs. We focused on this unique property of zwitterions to increase the amount of adsorption to hair. The target compound was 2-(dimethyldocosylammonio)ethyl octadecyl ethyl phosphate (DOEP), which shows I.P.= 4.3. The adsorption of DOEP to hair was clearly higher at under its I.P. than at higher pH, and the coefficient of friction decreased at the under I.P..