Sterilization is intended to kill all pathogens. In hospitals, hot steam sterilization is usually used for this purpose. But there are a number of other procedures, each with advantages and disadvantages (Image: wip-studio/stock.adobe. Today, sterilization procedures are used to remove surgical instruments from the eye. Medical products routinely sterilized. But there are still challenges, such as sterilizing sensitive items. New gentle procedures may help. The sterilization of coated implants. Even vaccines against viral diseases become possible with it.
Tim Schroder Science journalist in Oldenburg, Germany
Hardly anyone has described the importance of hygiene as impressively as the great German surgeon Theodor Billroth, the middle of the 19. In the early twentieth century, the surgeon was known primarily for his advanced gastric surgeries. "So be it written in large letters about every hospital: Cleanliness to the point of debauchery," the physician warned at a time when many pathogens had not even been discovered yet.
The only known fact was that physicians could significantly reduce the mortality of their patients if they regularly cleaned their hands and surgical instruments with carbolic, an antiseptic chemical substance that is now known as a Phenol is called. Hygiene and cleanliness had already found their way into hospitals by then. From Disinfection or even sterilization but there was not yet any talk of. Only with the isolation and cultivation of the Cholera pathogen Vibrio cholerae through Robert Koch In 1884, the systematic development of sterilization methods slowly began in Germany. In the beginning, this mainly involved the flaming of surgical cutlery.
The beginnings of sterilization: All-purpose weapon: prere cooker
Fortunately, today there is a whole range of sterilization methods and corresponding industry standards that provide exact specifications. Thus, various values must be adhered to. For medical devices, for example, it is stipulated that the number of pathogens in a sample must be reduced to one millionth by sterilization.
In hospitals, it is a matter of repeatedly cleaning and sterilizing a large number of medical devices after use (Image: Roger/stock.adobe.com)
Today, the main technique used for this purpose is the Steam sterilization. Especially in hospitals it is the workhorse. In a kind of modern Prere cooker, the autoclave, objects are sterilized with hot steam at mostly 134 degrees Celsius in positive prere. This destroys viruses and bacteria as well as their permanent forms, the spores that can cause disease. For temperature-sensitive items, the so-called low-temperature processes are used today – these include chemical treatments or various types of irradiation.
Clinics and industry use various methods for sterilization
Which process is used depends on what the Sterilization is used. In a hospital, things are different from those in a company that sells sterile-packaged medical products. "In the hospital, the Steam sterilization of surgical instruments accounts for the lion's share because it is quick and easy to handle," says Maik Roitsch, assistant to the executive board at the German Society for Sterile Supply. "From the time the autoclave is filled to the time it is removed, only about an hour goes by."In addition, no additional chemicals are needed and no special occupational health and safety regulations that might affect them have to be taken into account – unlike the handling of chemicals required for some low-temperature processes. Today, this includes above all Low-temperature steam and formaldehyde sterilization (NTDF), where the additional Formaldehyde is used as a sterilizing agent. Formaldehyde Destroys proteins in the cells of microorganisms. Since formaldehyde is harmful to health, such facilities must be operated in accordance with the Ordinance on Hazardous Substances.
NTDF sterilization: gentle but time-consuming
A major advantage of the NTDF sterilization consists in the fact that it works at 60 to 70 degrees Celsius. This process can also be used to sterilize plastic items several times without causing damage. The formaldehyde is added to the Low-temperature steam added. To ensure that steam and formaldehyde also flow through hollow bodies such as syringes or tubes, the steam containing formaldehyde is extracted several times – and the chamber is then refilled. This technique is known as Fractionation designates. "The fact remains, however, that handling formaldehyde involves an additional workload," says Maik Roitsch. Also, because waiting times would have to be observed for the formaldehyde to evaporate completely from the sterile material again. Thus a NTDF sterilization could take six hours.
Matachana Germany GmbH in Selmsdorf offers two low-temperature sterilization processes. Currently, both are being tested to sterilize disposable FFP mouth masks for reuse (Image: Matachana)
Peroxide plasma sterilization: the power of radicals
For some years now, another alternative has been the peroxide plasma sterilization, where Hydrogen peroxide is used. hydrogen peroxide decays in the Sterilization chamber into reactive so-called radicals, which attack and destroy the surfaces of bacteria, viruses and prions. After the reaction, the radicals are broken down again with a so-called plasma. Plasma is a gas consisting of free charge carriers, electrons and ions. It is created by exposing air or gases to strong electric fields.
The plasma causes the radicals to combine to form water and oxygen. And this is the great advantage of Peroxide plasma sterilization: No problematic substances remain. One disadvantage, says Maik Roitsch, is that this method can only be used to a limited extent on instruments with hollow bodies, since the active ingredient can hardly penetrate the cavities. 20 years on the market. Established in Germany. For a long time it was only offered by one manufacturer, but now others have joined the ranks.
Plasma: on the rise for sterilization
While hydrogen peroxide is the actual active component in the peroxide process, processes in which the plasma itself is used for sterilization have also been available for some time. After all, plasmas are very good at killing germs. This is because they have multiple effects.
The charged particles react with the surface or the membrane of the bacteria and damage or perforate it. In addition, the plasmas can release UV radiation, which damages the genetic material of the microorganisms. Even pathogens that are resistant to antibiotics are killed by this treatment. The Crailsheim-based Groninger& Co. GmbH, for example, has been using plasma for some time to sterilize tubs and syringe barrels prior to filling.
In nature, plasma is formed in connection with lightning (Image: Libor/stock.adobe.com)
Ethylene oxide: Dealing with hazardous materials during sterilization
While the Plasma sterilization is still quite new, the industry has long been using the chemical Gas sterilization used – especially ethylene oxide sterilization. Ethylene oxide Also damages the membranes of pathogens. Since it penetrates easily into cavities, it is very suitable for sterilizing tubes and syringes.
The problem with this process: Ethylene oxide (EO) is carcinogenic. Therefore, one has to be very careful that the sterilized items do not contain any EO when they are delivered.
Items usually have to rest for several hours to allow the EO to outgas. "For companies that sterilize large batches, it's not a problem," says Maik Roitsch. "For everyday hospital operations, however, this is hardly practicable."As a result, the number of EO systems in hospitals has declined sharply in recent years, while in industry the technology is currently on the rise.
Since it is difficult to measure EO residues on the goods directly, the corresponding systems must be tested and standardized in a relatively complex manner before they are used – to ensure that the goods actually no longer contain any EO after passing through the process.
Sterilization of entire pallets: Irradiation is the method of choice
The irradiation of goods with gamma radiation, which is released when atomic nuclei decay, is also particularly suitable for industrial use. The advantage: the radiation penetrates packages. Maik Roitsch: "You can move a whole pallet into the irradiation facility, which is very convenient."The gamma particles cause the air to be ionized in a similar way to plasma, producing free ozone radicals. These radicals then damage germs and viruses.
Since the gamma particles also penetrate into shrink-wrapped goods, sterilization can even take place in the closed package. Nothing could be simpler. Unlike EO, the load on the goods can be easily measured afterwards with a Geiger counter, because radioactive sources are used for gamma sterilization. Thus, radioactivity also occurs, which must be measured after sterilization. Therefore, as with EO, it takes some time before the goods can be released and shipped.
Sterilization of sensitive products: Particularly gentle electron beam
Gaby Gotzmann knows all the different sterilization processes and their weaknesses very well. "The problem with most sterilization processes is that they attack materials or surfaces to a greater or lesser extent," says biotechnologist from the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP in Dresden. The Steam sterilization is not suitable for most plastics because of the high heat involved. And even for the low-temperature process as Ethylene oxide and NTDF there are restrictions. Especially when it comes to sensitive surfaces – for example, implants.
Sterilization with electron beams is suitable for sensitive products. These can be automatically held in the beam (Image: Fraunhofer FEP)
Implants are increasingly coated with certain molecules to help them grow into the body or to keep bacteria at bay. "The trend is to even coat implants individually for each patient," Gotzmann says. However, with the common Sterilization process such surfaces are destroyed.
At FEP has therefore become an alternative gentle sterilization method over the past ten years Low-temperature process the low-energy electron-beam sterilization process. Similar to classic television tubes, a high-energy electron beam is generated and passed over the object to be sterilized.
The energy applied to the surface of the object only has a short-term effect. The surface remains undamaged. And just like a television, you can simply turn the beam on and off. "We can even process surfaces coated with biomolecules such as proteins without destroying the proteins," says Gaby Gotzmann. "The electrons damage the genetic material of the pathogens faster than the proteins are affected."
Electronics can also be sterilized
The new process is particularly suitable for prostheses and implants with electronic components – such as heart and brain pacemakers or blood prere sensors. Gamma radiation and steam sterilization are ruled out here because both would destroy the sensitive electronics. EO and NTDF, in turn, are ruled out because ethylene oxide and formaldehyde could easily settle in the porous or coated surfaces. The electron beam is significantly cleaner and faster. Gotzmann: "We have developed a 3D gripper arm that automatically and quickly guides an object through the electron beam."
The only disadvantage of this approach is that objects are only sterilized where the electron beam hits them. Cavities cannot be processed. But for surface sterilization, as envisaged by Gaby Gotzmann, this is negligible.
The Electron beam technology is now ready for use. In a next step, the Dresden-based company wants to test the process in cooperation with clinics or sterilization service providers.
Skillful sterilization processes can also speed up the processing of vaccines
In this context, the FEP technology not only suitable for surfaces, but also for the Sterilization of vaccines, such as those needed to combat influenza or, in the future, corona. Such vaccine solutions contain inactivated viruses. Formaldehyde is usually added to the vaccine solutions, which destroys the viruses in the solution before it is injected into patients.
The problem: The formaldehyde also partially destroys the proteins on the surface of the viruses – of all things, those structures that are recognized by the human immune system. Experiments have shown that the electron beam works much more gently here. Formaldehyde destroys the genetic material of the viruses, but does not damage the protein molecules on the surface of the viruses. In addition, the electron beam is much faster. Formaldehyde-added vaccine solutions must sit for several days for the formaldehyde to take effect and then be removed again. The electron beam can scan and sterilize entire batches in a matter of minutes.
Keeping sterilization in mind already during development
"Of course, it remains the case that every sterilization process has its advantages and disadvantages," says Gaby Gotzmann. It is simply a matter of finding the right procedure for the corresponding application. She knows from experience that this is often not taken into account. Particularly in the development of new medical devices. "It's amazing, but in fact it happens again and again that developers don't think at the beginning to design their product in such a way that the function must also survive sterilization in the end."In this respect, Gaby Gotzmann advises to pay more attention to the sterilization of medical devices in the future.
The number of germs should also be reduced by washing hands and possibly arms with disinfectant (image: Peter Atkins/stock.adobe.com)
Sterilization, disinfection, cleaning
In times of Corona, sterility is a major ie. Experts make a clear distinction between Disinfection and Sterilization. Both methods aim to kill or inactivate pathogens in order to prevent infections.
With the Disinfection the number of reproducible germs must be reduced by a factor of at least 10-5. This means that from 1.000.000 reproducible germs, no more than ten are allowed to survive.