In dermatological research, in vitro studies such as histopathology, biochemistry, and cell biology are popular. In vivo studies have been far smaller in number probably because physiological tests are not of great importance in making a diagnosis of skin disorders and measures for such studies have been limited. In recent years, thanks to rapid progress in electronic and computer technology, various fine instruments have been developed and have become commercially available for physiological evaluation of the skin. These instruments enable us to evaluate and/or monitor various characteristics or conditions of the skin quantitatively and non-invasively. This new field of studies for measuring the skin in vivo by technological methods is called bioengineering of the skin.” In this article, application of bioengineering methods to clinical and experimental dermatology is reviewed.

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The combination of an emulsifier and an emollient often decides particle size of the emulsion obtained and its storage stability. In the present report emulsions were assembled according to the CAPICO method developed by Foerster et al. and were subjected to measurement of particle size by means of particle analyzer, SALD 2000A, Shimazdu. Alkylethoxylates were employed as emulsifiers and covered structures of C-chain length, 12-22 and number of ethylene oxide units, 10-20. Emollients covered structures of hydrocarbons, alkylether, mono-, di- and triesters. The ratio of emulsifiers/emollient/water was 1:3:6 w/w/w. Phase inversion temperature was set between 65-85°C by the calculation. In order to meet this temperature a 1:1 emollient mixture was chosen with one part always cetyl octanoate or hexadecane and the second emollient selected from the collection described above. As the third components glycerol, 1, 3-butyleneglycol, propyleneglycol, ethyl alcohol, and ascorbyl phosphate magnesium salt were selected. Particles with less than 100nm in diameter were always generated regardless of emulsifier structure when isopropyl myristate was used in emulsion. Emollients and emulsifiers, both having low or high inorganic character were a good combination for making fine particles. On the other hand, combination of emulsifiers with 20EO plus emollients of low inorganic character or combinations with 10EO plus emollients of high inorganic character produced very large particles. Storage stability test is also carried out to confirm the correlation to the particle size.

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We studied human head odors by sensory test and GC-MS analysis of hairs and head-space components. We thought that head odors mainly consisted of mixed odors of fatty acids (from lower to higher fatty acids), and these fatty acids were produced from triglycerides in the lipids by lipase of resident flora on the scalp. We developed the fatty acids formation model by lipase and bacteria, and found many fragrance materials controlling fatty acids formations. And we verified the effect of controlling head odors by hair shampoo and rinse use test.
Furthermore, we found that several fragrance materials form the esters with fatty acids.

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Stratum corneum collected by the tape stripping shows various appearances in terms of the amount, the thickness and the unevenness. The variations of the stripped states are considered to reflect the states of the outermost stratum corneum as well as the epidermis. Accordingly, the quantitative study of the stripped stratum corneum pattern is considered to enable us to evaluate the skin condition. Therefore, we developed a numerical method with image analysis to study the stripped stratum corneum pattern.
In measuring the pattern of the stripped stratum corneum, the light transmission images of the stripped tapes were input into the image analysis system to make the analyzed image. According to intensity and distribution of analyzed image on a gray level, the following five parameters were defined as numeric value; 1. the stripped amount, 2. the thickness of the stripped stratum corneum, 3. the unevenness of the size of the stratified stripped part, 4. the unevenness of the steric position of the stratified stripped part and 5. the unevenness of the distribution of the stripped amount.
Each parameter of the stripped stratum corneum patterns showed negative correlations with hydration state as well as water holding capacity, while it showed a positive correlation with transepidermal water loss (TEWL).
The numeric method with the image analysis of these stripped stratum corneum was useful for evaluating the effect of humectants.

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Our investigation on the effects of thiol structures in permanent wave solutions on reduction of hair led to following discoveries:
1) Partition coefficients (P) of thiols between water and 1-octanol was measured to determine the permeability of thiols into hair. Results from this method, there was a high correlation between the hydrophobic character, logP and the efficiency of the permanent wave solutions.
2) It is generally thought that the reduction of hair by thiols is strongly affected by the acidity of SH groups. The dissociation constants of SH groups was determined by spectrophotometric titrations. Using this method, we found no significant relationship between the acidity of SH groups and permanent wave efficiency. Ellman's Reagent (5, 5′-dithiobis[2-nitrobenzoic acid]:DTNB) was used to determine the reaction rate constant of thiols and DTNB. A significant correlation was found between the rate constants and SH group acidity as determined by spectrophotometric titrations, From these results, it appears that the effects of permanent wave are not solely dependent on the kinetics of homogeneous reaction in a liquid phase, and the action of thiol in permanent waving should be regarded as a diffusion controlled process.

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Understanding the microstructure of emulsions is indispensable for further improvements of cosmetic formulations. In the present study, we describe the application of a field-emission scanning electron microscope that incorporates a cryo-system (cryo-FESEM) to achieve high resolution, therefore enabling the characterization of the microstructures of emulsions. The emulsions used in this study were oil-in-water types composed of surfactant-cetostearyl alcohol-water system. To prepare a flat cross section of the emulsion specimen with good reproducibility, a cryomicrotome was adopted after rapidly freezing the emulsion with slush nitrogen. The cryo-FESEM images revealed clearly that the emulsion was formed of spherical lamellae with concentric circles. Thus we confirmed that the preparation of cross sections of frozen specimens with the cryomicrotome and their observation by the cryo-FESEM were useful to clarify the microstructures of emulsions. This methodology will be able to contribute both to understand the relation between microstructures and rheology of emulsions and to design novel emulsions for cosmetic products.

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Besides product effects, sensory performance is one of the most important criteria of cosmetic products. In recent years much effort has been made to develop devices for the measurement of sensory properties.
In present study, the smoothness of intact oily components and formulations containing them was measured in a distribution model by means of a frictional analyzer. The smoothness at the beginning, middle, end, and after distribution of sample was expressed as the average coefficient of friction (MIU). This determination showed that high viscous oily components controlled the smoothness of the formulation while distributed on the skin and that the final skin fiction after 30min of distribution was attributed to the oily components.

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