Abstract:

Objective Naturally green-colored silk has excellent antioxidant property due to the intrinsic flavonoid-based pigments. It is a promising alternative antioxidant functional natural fiber for being as healthcare textiles. However, the transdermal characteristics, influencing factors and dose effect relationship of antioxidant components from naturally green-colored silk to skin have not been reported, so it is necessary to study them in order to clarify the antioxidant effect toward the human skin when using its products.

Method Transdermal permeation test were carried out on a transdermal permeation device and pork skins were used to simulate the permeation process of the antioxidant substances to the skin from the silk fiber. The pure water extract of natural green-colored silk and the extract of above skin tissues were analyzed by high performance liquid chromatography. The Folin phenol method was used to quantitatively detect the antioxidant extracts in each cortex. The classical DPPH radical scavenging method was used to evaluate the antioxidant activity of pig skin tissues after migration test.

Results The results of high-performance liquid chromatography analysis show that the antioxidant components in the fibers can migrate to the stratum corneum layer and dermis layer of the skin (Fig. 2). The antioxidants were found to be present mainly in the stratum corneum layer when the contact time was less than 12 h, but they were accumulated mainly in the dermis layer when the contact time exceeded 12 h (Fig. 4). The antioxidants could not permeate the whole skin layers. Under humidity conditions similar to skin sweating, the total polyphenol content in the skin reached at (11.7±2.9) μg/cm², accounting for 11.0% of the total fiber phenol content (Tab. 1). Antioxidant components migrated in general in acidic skin environments and migrated more to the deeper layers of the skin under the normal skin environment. In the acidic skin environment, the polyphenol content in the stratum corneum and dermis layer were 2.9 μg/cm² and 10.5 μg/cm² (Fig. 3), respectively. Both of the stratum corneum layer and dermis layer showed considerable improvement in antioxidant activity, and it obeyed the dose-response effect, and the more antioxidant components absorbed by the skin layers, the greater the free radical scavenging capacity of the skin layers. Volunteer trials were also carried out. After 24 h of fabric-to-skin contact, the content of polyphenols detected in the stratum corneum of the skin ranged from 5.1 to 6.6 μg/cm², with an average value of (5.7±0.5) μg/cm² (Fig. 5). Due to the high content of antioxidant components presented in the skin, the average scavenging rate toward the free radicals in the stratum corneum of the skin of volunteers was(76.7±8.2)%, which was significantly higher than the antioxidant activity of the stratum corneum (37.8±3.7)% of the pig skin experimental group at the same condition.

Conclusion The antioxidant components in the fibers can migrate to the stratum corneum layer and dermis layer of the skin. The amount of antioxidant permeated to the skin depended on the contact time, moisture, and the acidity and basicity of the skin. The amount of antioxidants in the skin was positively related to the contact time. The skin surface with light moisture facilitated the permeation of antioxidants to the skin, but it is not that the moister the skin, the greater the migration, similar to the human body skin with slightly sweating environment which is better for the antioxidant to permeate to the skin. Acidic skin environment enabled a deeper permeation of the antioxidants as compared with the basic skin environment. The antioxidant components in the fibers can migrate into the human skin and endow the skin with excellent antioxidant capacity. This enables naturally green-colored silk to be used as a promising antioxidant textile material.

Key words: naturally green-colored silk, antioxidant substance, antioxidant fiber, flavonoids, skin, transdermal characteristic