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Antibacterial surface mimicking structure of cicada wings to be put to practical use

Kansai University professor Takeshi Ito, who developed a material having bactericidal effects by mimicking the structure of a cicada wing, is seen in this photo taken in the Osaka Prefecture city of Suita on Aug. 23, 2018. (Mainichi)

SUITA, Osaka -- A group of researchers at Kansai University here has developed a material with significant germ-killing effects by copying the structure of cicada wings.

The achievement is expected to facilitate the development of safe and lasting antibacterial products without using drugs that can have a harmful effect on the human body.

The group led by Kansai University professor Takeshi Ito imitated the structure of the wings of the "kumazemi" or cryptotympana facialis -- a large cicada unique to Japan. Ito is a specialist on nanostructure and microstructure biomimetics, which involves studying and imitating tiny natural structures to solve human problems.

"Kumazemi," or cryptotympana facialis cicadas with transparent wings that are antibacterial, are seen lined up on a tree trunk at Osaka Castle Park in Osaka Chuo Ward on July 16, 2004. (Mainichi)

The development came following a 2012 study by an Australian research team which determined that transparent wings like that of the kumazemi have antibacterial effects.

The surface of a kumazemi wing has around 30 to 40 tiny protrusions per micrometer (one-millionth of a meter), each with a height of about 200 nanometers (1 nanometer is one-billionth of a meter) lined up in an orderly fashion. Such a structure minimizes the reflection of light, repels water, and punctures germ cell membranes that come into contact with the wing.

The researchers reproduced this structure by coating a silicone board with numerous resin beads about 200 nanometers in diameter and then covering it with an ultrathin gold sheet. When dipped into a special solution, the parts where the silicone and gold meet are trimmed away, creating cylindrical protrusions of about 200 nanometers in height, similar to those found on a kumazemi wing.

Food-poisoning E. coli bacteria, when placed on this artificial material, died over time, and after 24 hours their survival rate was far below 1 percent, which is the baseline for having germ-killing effects under Japanese Industrial Standards (JIS). The bacteria survival rate on the surface of a normal silicone board is in the range of several tens of percent.

A configuration of protrusions artificially reproduced on the surface of a silicone board is seen on the top, and that of a "Kumazemi," or cryptotympana facialis wing, is seen on the bottom. (Photo courtesy of Takeshi Ito)

Bacteria that have become resistant to antibiotics have emerged as a serious problem. Antibacterial agents that use metallic particles such as silver and zinc are said to be harmful to human health. The nanostructure material developed by Ito's team could be applied to bathroom, kitchen, and medical equipment to keep items clean and safe.

One of the biggest challenges for the material's commercialization is the production cost of making the material larger. Ito said that he intends to cooperate with businesses to commercialize a product.

(Japanese original by Shuichi Abe, Osaka Science & Environment News Department)

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