In 2018, Kao Corporation (President and CEO, Michitaka Sawada) developed a "Fine Fiber" technology method with direct spraying that creates a light, soft, and natural layered ultra-thin membrane on the skin surface composed of sub-micron sized super-fine fibers. Recently, our Skincare Research Laboratory and Analytical Science Laboratory have focused attention on technology used to create a membrane with moisture permeability*1 formed by a formula to control water evaporation on the surface of skin. Testing results showed that control of water evaporation on skin is related to the expression of proteins, the raw materials of the stratum corneum, which are associated with a healthy skin condition.
The findings of this study were presented at the 44th annual meeting of the Japan Cosmetic Society in Tokyo, Japan (June 28-29, 2019), and the 2019 Academic Meeting of the Japan Proteome Society in Miyazaki Prefecture, Japan (July 24-27, 2019), and will also be presented at the 25th IFSCC meeting in Milano, Italy (September 30-October 2, 2019).
The stratum corneum in the outermost skin layer has a barrier function that is important for maintaining homeostasis of the skin, as it acts to prevent external stimulatory substance invasion and control water evaporation. However, it is not uncommon for the barrier function of the stratum corneum to decline as an effect of environmental factors as well as aging, consequently causing deterioration in physical appearance and beauty. We have been conducting research in an effort to find solutions that complement the function of the stratum corneum, as currently available formulas have shown insufficient performance in regard to uniformity and durability.
The fine fiber technology developed by Kao Corporation has been shown to form an ultra-thin layered membrane consisting of fine fibers on the skin surface by direct spraying of a specialized polymer solution through a small-sized applicator nozzle developed exclusively for this use. The ultra-thin membrane is formed with interwoven thin fibers smaller than 1 μm in diameter, and characterized by not only lightness and softness, but also a high capillary force*2 . Use of this fine fiber membrane in combination with a liquid formula demonstrated a performance capability of quick and even distribution of that combined formulation throughout the application area, and then it remained firmly held by the entire membrane.
For wound treatment, a "moist healing" technique is widely used, in which the wound is treated with use of an artificially moisturized environment, thus taking advantage of the self-healing ability of the body. Inspired by related findings, we investigated methods to maintain a moderate hydric environment on the skin surface for enhancing skin improvement. Our results showed that application of the high capillary force of fine fibers improved the uniformity and durability of membranes applied to skin by use of a specially developed formulation. Furthermore, attention was given to control of water evaporation from the skin by the formula in combination with the fine fibers. In that regard, moisture permeation characteristics were compared among different preparations, namely, conventional formula alone, fine fibers alone, and fine fibers plus formula (Fig. 1).
Membranes formed by use of the conventional formula showed high moisture permeability as fine spaces were present. Accordingly, the control of water evaporation was limited. Similarly, those formed by use of the fine fiber alone showed porous spaces in the layered membrane composed of fine fibers and moisture permeability that was not considerably different from that of membranes formed with the conventional formula.
In contrast, when the fine fiber membrane was used in combination with the moisturizer formula, even spreading caused by the capillary force of the fine fibers to fill the fine spaces was noted, which lowered measured moisture permeability as compared to that of the conventional formula and provided suppression of moisture evaporation from the skin surface. Results of repeated experiments confirmed that moisture permeability could be controlled by the composition of the formula. Furthermore, it was considered that the water evaporation suppressive effect caused by control of moisture permeation may have a longer effective period with the fine fiber plus formula application, as the produced membrane was found to possess greater adhesion strength in comparison to that formed by the conventional formula.
Forty-five women in their 30s and 40s who had dry skin or awareness of skin dryness were enrolled for a 2-week application test using our moisturizing formula designed to control water evaporation without causing damage to the structure of the fine fiber membrane. They were divided into two groups; those who applied the formula alone and subjects who applied the fine fibers along with use of the formula.
For verifying the condition inside the stratum corneum to detect changes within a short period, we developed a time-series proteome analytical method with application of proteome analysis using mass spectrometry. Expression of 245 different proteins in the stratum corneum was comprehensively analyzed before and after application. Furthermore, the skin surface appearance was observed in each subject.
(1) Time-series proteome analysis – Expression of proteins in stratum corneum
Expression of proteins in the stratum corneum was analyzed before the start of continuous applications, and then again 7 and 14 days later. In the subject group that applied the fine fiber plus water evaporation-control formula, increased expression of a greater number of proteins within a short period as compared to that in the group that applied the formula alone was noted.
Notably, in the group with the combined formula, proteins (CAPN1, BLMH) that promote production of raw materials for natural moisturizing factor (NMF) showed a greater increase as compared to the formula alone group. Additionally, other proteins (GGCT, HAL, ARG1) known to promote the production of raw materials for NMF had a greater increase after 14 days of continuous application as compared to after 7 days. Our findings also confirmed that expression of the protein (SBSN) involved in promotion of production of lamellar granules*3, which are deeply involved in the barrier function of skin, was specifically increased (Fig. 2).
(2) Skincare effects
In both the fine fiber plus water evaporation-control formula and formula alone groups, water content in the skin showed a significant increase from the third day of application in comparison to that just prior to starting the applications. As for skin appearance, brightness and gloss were significantly improved within 3 days of starting applications in the combined use group, earlier as compared to the group with formula alone (Fig. 3).
Inspired by moist healing methods widely used for wound treatment, we studied application of a formula combined with fine fibers for water evaporation control. Our results showed that moisture permeability of the stratum corneum could be controlled by use of this novel combination formula. Furthermore, increased expression of several different proteins that provide favorable skin conditions in the stratum corneum within a short period of time, along with early improvements in dry skin appearance were observed.
Based on these findings, we intend to develop products with an added dimension gained by applying this fine fiber technology. In addition, we will continue to pursue technological developments for application in therapeutic settings to contribute to the needs of society.