Supercritical CO2 (scCO2) sterilization is a safe and highly efficient method for sterilization with many applications in the MedTech industry. While ethylene oxide (EtO) has long been the leading industrial sterilization modality, its emissions have raised concerns regarding its impact on human health and the environment. In this context, scCO2 has emerged as a promising and sustainable alternative to EtO sterilization.
In this article, Tony Eisenhut, CEO, NovaSterilis Inc. sheds light on the particularities of this technology, exploring the challenges that need to be overcome for its successful expanded implementation. He also delves into the advantages of transitioning to scCO2, highlighting that these benefits extend beyond sustainability.
What is Supercritical CO2?
Before we explore the potential challenges and opportunities surrounding scCO2 technology, it’s essential to understand some key definitions:
Supercritical CO2 is a fluid in which CO2 has liquid and gas-like properties. The supercritical state is achieved when the temperature and pressure are above its critical points (~31°C and 1,070 psi or 73 atm).
Applications of SCCO2 in Medtech and Beyond
As Tony explains, scCO2 has been broadly used in the MedTech space for decades. Early uses focused on the extraction of natural compounds for medicinal purposes, such as the extraction of paclitaxel (Taxol) from the bark of yew trees. More recently, scCO2 has been used to extract cannabinoids from cannabis, which has become a large market.
However, the applications of scCO2 in the MedTech industry extend beyond extraction and include:
- Material cleaning and terminal sterilization of medical devices, including synthetic and biological-based devices.
- Decellularization of human and animal tissues without the use of harsh chemicals such as Triton X.
- Product manufacturing, whether via the impregnation of bioactives into scaffolds or the creation of scaffolds such as aerogels.
The uses of supercritical CO2 are growing rapidly in the medical device, regenerative medicine, and therapeutics industries, says Tony.
Most of the applications are mid to low-volume because of the current equipment limitations for the MedTech applications.
Making the Switch: Why Choose ScCO2 Over EtO?
EtO sterilization is the most widely used method to terminally sterilize medical and pharmaceutical products. According to the Food and Drug Administration, EtO is used to treat approximately 50% of sterile medical devices.
However, according to the U.S. Environmental Protection Agency (EPA), regular exposure to EtO over long periods can increase the risk of developing cancer.
For this reason, in April 2023, the EPA proposed measures to reduce risk in communities and to workers. This includes cutting EtO emissions from commercial sterilization facilities by 80% annually. In parallel, the FDA is working to increase the awareness of alternatives to EtO for sterilizing medical supplies.
Manufacturers have expressed concerns regarding the capability, scalability, and approvability (the ability to obtain regulatory clearance) of this alternative method. The question that arises is whether scCO2 would be capable of meeting the challenge.
“I would assert that all sterilization modalities impact the materials they are sterilizing to some degree. What we are all working to achieve is a minimization of the impacts of sterilization such that the sterilized materials still function as intended.”, Says Tony.
“Although EtO is broadly compatible, it still has compatibility limitations, especially with bio-based materials. We have been working with scCO2 as a sterilant for over 20 years at this point, and we have shown the ability to terminally sterilize a broad array of materials and devices. Our scCO2 sterilization platform has been used commercially in the tissue banking industry since 2008. There have been well over 300,000 devices implanted in humans over that period without any reported adverse reactions relative to sterilization.”, Tony adds.
Benefits of Supercritical CO2 Compared to EtO for Sterilization
When comparing scCO2 to EtO, there are several benefits worth considering, for example:
- CO2 is an inert, non-reactive molecule. In and of itself, it is advantaged over EtO from a reactivity standpoint.
- To successfully sterilize with scCO2, you must include an entrainer (such as a peracetic acid-based additive). There is a synergistic effect between the scCO2 and the peracetic acid, so you can use minimal amounts to achieve a sterility assurance level of 10^-6.
- The conditions under which scCO2 is created result in deep penetration of the sterilant in the device, even through torturous packaging configurations. scCO2 is the most effective sterilization modality when it comes to penetration.
- Similar to EtO, scCO2 is a low-temperature sterilization modality (with an operating temperature of 35°C).
- Unlike EtO, scCO2 does not require an outgassing period of tens of hours. It requires no outgassing time.
It is often believed that supercritical CO2 processing is only cost-effective on high-value, low-volume products. Tony explains that this is not true. “The cost of operation is lower than that of EtO and often radiation when you evaluate the total cost of sterilization.”, he says.
Towards More Sustainable Sterilization: scCO2 as a Green Alternative to EtO
There has been much talk about the potential for supercritical CO2 to expand and solidify its’ position as an eco-friendly sterilization option, replacing many of the applications currently served by EtO. Tony Eisenhut believes in this possibility. “NovaSterilis won the Presidential Green Chemistry Small Business award in 2007 based on the use of CO2 as an alternative to EtO.”, he says.
He emphasizes: “I do not think there is a “silver bullet” for the replacement of EtO. I think there will be multiple sterilization modalities that will be viable alternatives based on the needs of the products being sterilized. I think that for the foreseeable future, EtO will be a part of the solution as well, albeit a smaller percentage, as the regulatory pressures grow and the costs continue to rise. I do believe that alternative sterilization solutions, including scCO2, are more economical than EtO when you look at the total cost of processing.”
Challenges To Overcome
However, the transition may not go as seamlessly as expected. There are still barriers to overcome to implement this technology on a larger scale.
According to Tony, the principal obstacles to implementing scCO2 technology are:
- Economic investment in the scaled-up infrastructure.
- Awareness of the alternative.
- Professional risk as the willingness to try a “newer” sterilization modality is tempered by decision-makers fear of career repercussions should it fail, even if the risk of failure is no greater than that of EtO sterilization.
“Although scale is a perceived problem, it is not a true problem. Supercritical CO2 is used in some very large industrial applications, including extraction applications of coffee and hops. We are aware of an installation with 60,000L of scCO2 capacity. The infrastructure used for extraction can also be used for sterilization. The difference is related to the process, not the equipment. This is a long-winded way to say that the ability to scale scCO2 sterilization to volumes processed with EtO is not a technology or engineering hurdle; it is a finance hurdle. There needs to be a forward-thinking company with the resources that will make the investment or the federal government will have to step in with a tax incentive program as it has done with solar energy if broad adoption at scale is to be realized .”, Says Tony.
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