Scientists from Tomsk Polytechnic University and Saratov State University teamed up with colleagues from Taiwan and proposed to make a laser “blade” for a medical scalpel with a specified curved shape using a photonic “hook.” Currently there are laser scalpels only with an axisymmetric focus area, i.e., with a cylindrical blade. According to scientists, changing the shape of the blade will expand the possibilities of using the laser in medicine, while it is about two times thinner than the cylindrical option. The concept and its rationale are published in the Journal of Biophotonics.

A laser scalpel is a surgical instrument used to cut or remove biological tissues by using laser energy. In a limited area of tissue the beam sharply raises the temperature up to 400 °C, thus making the irradiated area to burn out instantly. This way, the laser immediately seals small blood vessels along the edges of an incision. The laser scalpel makes very thin incisions and reduces bleeding, and the radiation itself is absolutely sterile.

The laser scalpel makes very thin incisions and reduces bleeding. (Credit: Journal of Biophotonics/jbio.202000342)

“A conventional surgical scalpel has a variety of blade shapes to suit specific applications. Laser scalpels do not have such a variety, or rather, there is only one form of radiation localization — axisymmetric,” says Igor Minin, project manager and professor in the department of electronic engineering at TPU. “Therefore, we proposed a simple way to make the tip shape curved using a photonic hook. This is a new type of curved self-accelerating light beam, shaped like a hook. Earlier, we theoretically predicted and experimentally confirmed the existence of such a hook.”

An indispensable element of a laser scalpel is the fiber for transmitting laser energy. At its end, a focused laser beam of several wavelengths is formed. With its help, the surgeon performs all necessary manipulations.

“To bend the laser beam, we proposed one of the simplest possible solutions: place an amplitude or phase mask at the end of the fiber,” says Minin. “It is a thin plate made of metal or a dielectric material like glass. The mask redistributes the energy flow inside the fiber and forms a curved region of radiation localization at the end of the fiber, that is, a photonic hook.”

Through simulation, a curved blade is proved to have a length of up to 3 mm and a thickness of about 500 μm (100 μm is the thickness of a human hair), with a wavelength to be 1,550 nm. In other words, the scientists add one small element without affecting the general design and performance of the device and get changes in the area of the fiber end alone (at the tip).

“The shape and thickness of the blade is changing: it is approximately two times thinner than the axisymmetric option,” Minin explains.

In the journal article, the scientists provided a theoretical basis for the concept, and now they are preparing to confirm it experimentally at National Yang-Ming University (Taiwan). The research was supported by a grant from the Russian Foundation for Basic Research. (No. 20-57-S52001).

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