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Physics

Radical sterilization

Microorganisms are eliminated with plasma-based equipment at a low temperature

STERILILYEquipment and ultraviolet radiation inside the chamberSTERILILY

When present in medical equipment and food, funguses and bacteria can cause serious problems of contamination and intoxication. The solution, as everyone knows, is to sterilize them, eliminating these tiny organisms that are capable of multiplying so quickly. To do so, a large arsenal has already been developed to combat them, with chemical substances, heat, and even radioactive elements. Now, the turn of plasma has arrived. Regarded as the fourth state of matter, plasma is produced by applying an intense electric field to some kinds of gases. The action of this field supplies the ions and electron with energy, which cause collisions with the atoms and molecules. This situation excites the molecules, generating free radicals and ultraviolet radiation. The result is a joint action against membranes, enzymes and nucleic acids that make up the cells of the microorganisms, which destroys their vital functions. The novelty in this kind of sterilizer is a piece of equipment fitted with a chamber in which the process is carried out dry and at a low temperature, developed in Campinas by researchers from a company called Sterlily, with the financial support of FAPESP’s Small Business Innovation Research Program (PIPE).

The first prototype of the device, called Esteriliza 1000, is installed in the Campinas High Technology Complex Development Company (Ciatec), an incubator that houses Sterlily. It has already been used in the sterilization of over 12,000 plastic containers for cultivating cloned plants, besides disposable syringes and containers for lab tests. The agility of the process is one of the advantages over other methods. Heat treatment does not eliminate completely some kinds of bacteria that are resistant to high temperatures. Furthermore, excessive heating causes damage in materials that have a low melting point, like the majority of pieces produced with polymers. Ultraviolet radiation, much used, is efficient only for surfaces directly exposed to the radiation. Sterilization with ethylene oxide (ETO) is the one that is most similar to the process with plasma. But as it is regarded as carcinogenic, is increasingly being rejected. Sterilization by cobalt irradiation, also used on thermally sensitive materials, has a high cost and requires an isolated area.

Rapid process
The plasma sterilization cycle, of about an hour and a half for plastic materials, is considered rapid. With several kinds of plasma and exposure times, from five to 20 minutes, it is possible to verify the destruction of the body of the bacterium. Total elimination is important, because microorganisms like Escherichia coli, even when dead, can produce toxins. “As a standard for validating the process, we use the Bacillus subtilis variety niger bacterium, the most resistant to plasma processes”, explains Tadashi Shiosawa, who runs Sterlily in partnership with Tony Sadahito China and José Alonso Corrêa Júnior.

The plasma process is also suitable for sterilizing organic materials. “At the moment, we are doing tests with edible mushrooms, verifying the active properties of the product after sterilization. In this case, we carry out a reduction in the microbial load and not complete sterilization, in order not to kill the mushroom”, Shiosawa explains. For the time being, the greatest demand is for sterilizing plastic products. But glass and metal products can also be sterilized with plasma. To cater to a wide range of applications, the Esteriliza 1000 was planned to be adapted to different parameters. The process is controlled by a computer, using software developed for the equipment and a microprocessor that monitors the power source.

“During the development of the project, at the Plasma Physics Laboratory of the State University of Campinas (Unicamp), we carried out experiments to find out what the process of characterizing the plasma would be, setting its potency according to the source of electricity”, Shiosawa comments. This is because, depending on the components and the environment in the inside of the chamber, different kinds of plasma can be created. Having defined the characteristics, the parameters were adjusted in tests carried out at the Microbiology Laboratory of the College of Food Engineering at Unicamp.

The equipment is made up of a stainless steel cylinder. In the inside, an atmosphere is created with a reduced pressure, to generate a vacuum. Inside, drawers with apertures hold the materials. They are covered with a polypropylene wrapping developed in Brazil for this use, made of a non-woven trilaminate, which lets gases pass through, but prevents microorganisms from doing so. Next, hydrogen peroxide gas is released in the inside of the chamber, where a high frequency electric field is applied, which generates ultraviolet radiation. This kind of sterilization has some specific aspects, such as its low temperature, from 35ºC to 40ºC, making it suitable for applying to several materials.

The researchers are not going so far as to wager that the use of plasma should replace the other processes, but they do see advantages, above all in the case of food, for permitting a controlled reduction in the bacterial load. Shiosawa says that the cost of producing the Esteriliza 1000 varies according to usage. But he recognizes that the initial sales price, estimated at between R$ 400,000 and R$ 500,000, is high for the domestic market.

For this reason, the focus of the company, originally created to market the equipment, has given way to the provision of services. The technology employed, with the exception of the vacuum system, imported from Germany and Britain, was developed in Brazil. After it is given a registration by the Ministry of Health, the equipment will be ready to be included definitively in the market.

The Project
Development of a Plasma Sterilizer (nº 97/07411-1); Modality Small Business Innovation Research Program (PIPE); Coordinator Tadashi Shiosawa – Sterlily; Investment R$ 147,890.00 and US$ 18,494.75

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