Low Temperature Plasma Sterilization
Some medical devices are made of materials that can withstand the high temperatures of a sterilization autoclave (134°C) : metals, glass, polymers such as PEEK, polypropylene, acetal copolymers or polyphenylsulfone, etc. But innovations in the medical device have led to the use of more fragile materialseither that they cannot withstand heat (heat-sensitive materials), or that they are not resistant to sterilization products (chemical-sensitive or radio-sensitive materials). They are called fragile medical devices. Aurora plasma sterilization meets the needs of manufacturers of these medical devices : low temperature sterilization that does not damage the materials. Low temperature for medical devices is below 60°C.
The first is required from manufacturers of fragile medical devices, which must provide patients with pathogen-free devices with a probability of less than one in a million cases.
The most common low temperature sterilization (LTS) techniques for single-use devices are gamma irradiation and ethylene oxide fumigation.
X and beta rays, nitric oxide, peracetic acid and supercritical CO2 are other modes of industrial low temperature sterilization. But their use is very limited in the sterilization industry.
Industrial sterilization is carried out at 75% by subcontracting, due to the complexity and dangers posed by the processes mentioned.
The other type of low temperature sterilization applies to reusable devices. It is the responsibility of the hospital or medical practice. It is sometimes subcontracted. In such reprocessing, only one to three devices are sterilized at a time.
There is a low temperature sterilizer model that uses ozone (O3) combined with hydrogen peroxide. The dangers posed by ozone to the human respiratory system render this solution unpalatable, even if the sterilization results are undeniable.
The most common low-temperature sterilization method in healthcare centers is vaporized hydrogen peroxide (VHP) sterilization. It consists of exposing the device to be sterilized to H2O2 in the form of vapor in an enclosure under primary vacuum (about one mbar). The enclosure is heated to around 55°C, depending on the VHP sterilizer models.
A single dose of hydrogen peroxide is used for an entire cycle. To this dose corresponds a certain mass to be sterilized. Manufacturers implement various means to overcome the hydrogen peroxide present at the end of the cycle. Questions remains about the validity of the concentrations. One model creates a plasma discharge at the end of the cycle, which is supposed to break down the H2O2 into water and oxygen.
The only true low-temperature plasma sterilization process in the care center is Aurora’s. Aurora exclusively uses an air gas plasma to sterilize medical devices. Aurora does not use any chemical agent to sterilize. From this point of view, Aurora differs from supercritical CO2 sterilization, which still uses H2O2 or peracetic acid as additives.
To generate the Aurora plasma, the tank must reach a much higher vacuum than for the VHP. The vacuum for plasma is a secondary vacuum. During the vacuum descent phase, the device to be sterilized is purged of any liquid or gas. It is thus perfectly dry, with no risk of ice formation.
There is also no risk of condensation since the tank is not heated, and the injected oxygen cannot liquefy at such a pressure. There is therefore no concern of condensation of the sterilizing agent, contrary to what can happen in VHP, and which affects the effectiveness of this technique.
Aurora Plasma also allows long narrow lumens to penetrate much farther than VHP. Indeed, due to its design, a VHP sterilizer will come up against the constraints of fluid mechanics to enter and exit a tube of more than 89 cm and 1 mm inside diameter. The Aurora plasma is not subject to this constraint, and it has demonstrated its effectiveness on tubes 5 m long and 1 mm in internal diameter.
With the Aurora plasma, no desorption phase or elimination of chemical residues is necessary at the end of a sterilization cycle. Indeed, the reactive species composing the plasma do not survive the interruption of the electromagnetic field which ignites the plasma. Simply cut off the radio frequency for the oxygen ions to recompose into harmless gases in the air.
And since the temperature reached during the plasma sterilization cycle does not exceed 40°C, operators do not have to wait for a temperature drop.
NB: sterilization is a probability, while disinfection is a reduction in microbial load (by a factor of 10,000 for high-level disinfection). The level of health safety between sterilization and disinfection is therefore without comparison.
The qualities of Aurora plasma make it particularly suitable for complex shapes such as long and narrow lights, fragile polymers, electronics, cellulose, foams. Its temperature does not exceed 40°C. The time of a sterilization cycle lasts about 1 hour currently. These performances are constantly improving.
A sterilant is a physical or chemical means used in a sterilization process. Its objective is to reduce to 0.000001% (1 in 1 million) the probability of finding pathogenic microorganisms on a medical device.
We therefore expect a sterilant to be biocidal. Thus, by definition, it presents a threat to living organisms, and therefore to human health and the environment.
But thanks to Aurora, the world of health now has plasma with a non-toxic sterilant that does not present a danger to health or the environment.
Water vapor saturated at 134°C is the oldest and best known sterilant. It is implemented in autoclaves, sealed enclosures under pressure of 2 bars. The process is well controlled. It refers to the sterilization of reusable medical devices in healthcare centers and hospitals.
In addition to its high energy consumption, it presents a danger of explosion and burns. Recent questions have been raised about its effectiveness in certain long and narrow lights. Above all, such temperatures damage many heat-sensitive materials. The autoclave is therefore reserved for robust medical devices.
However, saturated water vapor leaves no residue. It does not require a desorption phase. Its precursor, liquid water, is also safe if it is cold. This is not the case with the following sterilants.
Ionizing radiation is another family of sterilants. It is made up of gamma rays, X-rays, and beta rays.
The advantage of ionizing rays is to sterilize cold. They can thus process a wider range of materials.
Ionizing rays sterilize by transferring energy to the molecules they pass through. They thus damage the components of the cells they pass through, creating lesions that can cause cell death if the dose is high enough.
Sterilization with ionizing radiation must therefore be implemented with the precautions that apply to nuclear activities. Ionizing rays can cause skin burns, vomiting and internal pain. In the long term they increase the risk of cancer.
The most common ionizing sterilant is Cobalt 60. It accounts for 40% of cold sterilization of medical devices worldwide. This cobalt isotope is obtained by exposure of this metal in the heart of certain nuclear reactors.
In a sterilization plant, the source of Co60 is isolated from its surroundings by thick concrete walls. It is immersed in a vast pool of water when the sterilization cycle is interrupted.
These industrial constraints are justified because the gamma rays of Cobalt 60 are the only ones which make it possible to cold sterilize materials in their mass. Indeed, the gamma rays of Cobalt 60 are able to cross consistent thicknesses.
Irradiation has the effect of altering the polymer chains. This is an effect that can be desired in modifying materials. In general, it is rather a consequence that one wants to avoid, because it produces an accelerated aging of the materials and damages them.
Due to industrial constraints, it is complicated for manufacturers to extend their sterilization capacities to ionizing radiation. Producing Cobalt 60 in the future will pose challenges as the reactors capable of generating it are nearing the end of their life.
The use of chemical sterilants encounters similar problems.
The two main chemical sterilants used in sterilization are ethylene oxide and hydrogen peroxide.
The latter (H2O2) is well suited to the reprocessing of reusable devices in hospitals and in care centers which perform their own sterilization. With some protection (gloves and goggles) to avoid skin burns and a desorption phase so as not to harm the patient, one can quite simply mitigate its toxicity.
This is not the case with ethylene oxide (C2H4O), explosive, irritant, carcinogenic and mutagenic.
Still used for hospital sterilization in some countries, it was banned for this use in European hospitals 10 years ago. It is now reserved for industrial sterilization, i.e. contract sterilization of single-use medical devices.
It has, however, come under increased scrutiny since 2019, when the US Environment Agency shut down two ethylene oxide sterilization plants in the US, following environmental releases, considered to be a threat to the health of local residents. In agreement with the FDA, these factories were reopened because of the disruption that the supply disruptions of certain devices were causing in health establishments. The use of ethylene oxide has become a political issue in the states of Illinois and Georgia, as well as during the 2020 presidential elections.
European authorities joined these concerns at the end of 2020, calling or the dissemination of technologies to replace ethylene oxide in sterilization due to the toxicity of this product.
This is because Aurora’s sterilant is obtained by transforming small amounts of gaseous oxygen (O2) into plasma, via a low-power RF electromagnetic source. Reactive oxygen species have very short lifespans (of the order of a second at most). When the electromagnetic source is cut, the plasma is instantly recomposed into O2.
The method does not pose any cytotoxicity problems.
The residues of the microorganisms eliminated by the plasma are volatilized in the form of carbon dioxide or nitrogen dioxide, without danger to health or the environment in the quantities produced, and in the ventilated environment of a sterilization department.
Finally, the Aurora process does not require a major energy source: the Aqsaniit sterilizer plugs into a simple socket.