Brian Tifft, Program Manager, Applications Development ; and Dr. Jean Daou, Research & Development Manager, EMEA Aptar CSP Technologies discuss why advancements in medical device sterilisation have been slow in coming – until recently.
Medical device sterilisation is a critical process in healthcare, ensuring that instruments and equipment are free from harmful microorganisms that could cause infections. Unfortunately, sterilisation innovation has long been… well, somewhat sterile. As in less than fruitful.
Indeed, over the last 50 years there has been little innovation in sterilisation techniques, with one modality, Ethylene Oxide (ETO) Sterilisation, dominating the global landscape. However, due to concern over carcinogenic properties, ETO has understandably undergone significant scrutiny in recent years, leading the industry to reassess options for properly sterilising medical devices while mitigating safety risks.
This paper provides a brief overview of the most commonly used sterilisation techniques and, from there, explores a new innovation in sterilisation technology – one with the potential to reduce reliance on ETO while minimising patient risk and, most importantly, delivering equivalent sterilisation results.
The current landscape
One of the most widely used sterilisation methods is steam sterilisation. Also known as autoclaving, this non-toxic, cost-effective1 approach uses high-pressure saturated steam to kill microbial life, including spores, within a relatively short timeframe. However, this method is unsuitable for heat-sensitive materials, as its high temperatures can damage certain plastics and electronic components2. Dry heat sterilisation is a similar but less efficient methodology, due to the longer exposure times required.
Elsewhere, gamma radiation sterilisation employs high-energy gamma rays to destroy microorganisms3 on a wide range of materials, including plastics and metals. This approach can be particularly useful for pre-packaged items, since it can penetrate packaging materials. However, gamma radiation sterilisation has been known to cause changes in the physical properties of some materials, and infrastructure is costly. Another pricey prospect is hydrogen peroxide plasma sterilisation, which uses vaporised hydrogen peroxide and low-temperature plasma to sterilise devices.4 Effective and fast, with cycle times typically under an hour, this method is safe for most materials, including heat-sensitive ones; however, true to its name, it is unsuitable for materials that absorb hydrogen peroxide.
In terms of chemical sterilisation, sporicidal chemicals require lengthy contact time to destroy pathogens, and their effectiveness cannot be monitored via a biological indicator. Sporicidal chemicals are often used within a hospital reprocessing department to decontaminate heat-sensitive devices like flexible endoscopes, scissors and stethoscopes, as well as oral and rectal thermometers.
However, while some devices can be effectively sterilised via sporicidal chemicals, the CDC reports that “liquid chemical sterilants may not convey the same sterility assurance level as sterilisation achieved using thermal or physical methods.”5 There are a few reasons for this. For one, medical devices cannot be wrapped during processing to maintain sterility after processing and during storage. In addition, devices may need to be rinsed after liquid chemical sterilants have been applied, and the water itself may not be adequately sterile.
Lastly, what has typically been the most common sterilisation method is ethylene oxide sterilisation (ETO). This chemical sterilisation method uses ETO gas to sterilise medical devices at low temperatures, making it ideal for heat-sensitive items. Highly effective, the approach can penetrate complex device structures6, but its lengthy cycle time, large infrastructure and thorough aeration requirements, and toxicity and carcinogenic properties leave the door open for innovations in sterilisation methodologies. Among the most promising of these next-generation techniques are chlorine dioxide-based approaches.
Chlorine Dioxide Sterilisation
Chlorine dioxide is a widely available, broad-spectrum antimicrobial that has been used in contact with food and water for many years. In fact, it has been safely and effectively employed in municipal water treatment programs since the 1950s, and as a liquid surface sterilant since the early 2000s. However, current solutions using ClO2 for medical device sterilisation are often limited by the expansive infrastructure it has historically required.
Encouragingly, recent material science breakthroughs have yielded the development of a sterilisation method leveraging ClO2 gas, but without the need for extensive infrastructure, training – or, for that matter, even electricity. This novel chlorine dioxide generation method uses a highly engineered active film material to disperse a controlled amount of chlorine dioxide gas within a sealed environment to sterilise heat- and moisture-sensitive medical devices and surgical instruments.
Crucially, this process can be performed quickly, thoroughly, and with little to no infrastructure or training virtually anywhere sterilisation is needed. Originally developed for use as a food safety antimicrobial solution, the technology was repurposed for N95 mask decontamination during the COVID-19 pandemic, and further developed to safely and effectively provide comprehensive medical device sterilisation in a matter of hours.
The ClO2 active film sterilisation solution leverages a proprietary active polymer technology currently used around the world to protect sensitive drug products, implantable devices, diagnostics and probiotics. The active film is comprised of a base majority polymer that provides the structure, a co-polymer (strands of “unmixed” co-polymer through the strip, referred to as the channeling agent), and active particles comprised of a proprietary material that generates ClO2 gas (see Figure 1).
The channels are hydrophilic, and draw external moisture into the polymer matrix to enable the chemical reaction that creates ClO2. Due to the concentration gradient, the ClO2 is diffused through the channels to the external environment. The technology enables control of small molecule transport through the polymer, and controls the sustained release of ClO2 gas into the headspace of a sealed environment. The ClO2 gas can be released to a defined dosage and validated to achieve Sterility Assurance Level (SAL) of 10-6.
To activate the technology, the active film is submerged in any aqueous solution to trigger a chemical reaction that releases a controlled amount of chlorine dioxide gas sterilant, killing 99.999% of bacteria, viruses, and fungi. The activated film is placed in a small, confined space (e.g. sterilisation chamber, Pelican™ case, etc.), along with the device(s) to be sterilised, to concentrate the gas to sporicidal levels (see Figure 2). The sterilisation process occurs at ambient conditions, (i.e. no elevated/reduced pressure or temperatures required) and does not require aeration steps prior to retrieving the sterilised devices from the container, as chlorine dioxide naturally and rapidly breaks down to safe chlorite ions. Again, this entire process can be done without electricity, and requires little training or maintenance.
This active-film based chlorine dioxide gas sterilisation method presents numerous safety improvements when compared to other chemical sterilants, including ethylene oxide (EtO). Chlorine dioxide is a non-carcinogenic and non-mutagenic molecule. Typically, exposure to chlorine dioxide occurs through drinking water that has been disinfected with the substance. Therefore, ingestion via treated water does not result in adverse effects, as the chlorine dioxide is quickly broken down to chlorite ions, which are harmless to the human body.7
Conclusion
The spike in hospital-acquired infections has prompted government agencies to formulate stringent frameworks to minimise occurrences. As healthcare facilities, including outpatient settings, seek alternatives to replace EtO sterilisation with other low-temperature methods, an opportunity arises to introduce new technological approaches to medical equipment sterilisation.
An active film-based chlorine dioxide gas sterilisation system has the potential to meet the evolving needs of the healthcare landscape simply and cost-effectively. Additionally, the technology’s portable, electricity-free nature could encourage its adoption beyond traditional healthcare settings, serving unmet needs of rural communities, remote emergency response teams, and even military personnel in combat zones.
References:
- https://esenssys.com/methods-of-medical-sterilisation/. Accessed November 19, 2024.
- https://pharmadocx.com/commonly-used-medical-device-sterilisation-methods/. Accessed November 19, 2024.
- Sterilisation of Biomaterials and Medical Devices, Book 2012, Edited by S. Lerouge and A. Simmons.
- https://www.cdc.gov/infection-control/hcp/disinfection-sterilisation/hydrogen-peroxide-gas-plasma-file-name.html, Accessed December 3, 2024.
- A. E. Acosta-Gío, J.L. Rueda-Patiño, L. Sánchez-Pérez. Sporicidal activity in liquid chemical products to sterilise or high-level disinfect medical and dental instruments. Am. J. Infect. Control, 2005, 33(5), 307-309.
- https://lso-inc.com/news/6-methods-for-medical-device-sterilisation-how-they-work-and-which-devices-are-ideal/. Accessed November 19, 2024.
- S.K. Raut, K. Singh, S. Sanghvi, V. Loyo-Celis, L. Varghese, E.R. Singh, S. Gururaja Rao, H. Singh H. Chloride ions in health and disease. Bioscience Reports, 2024, 44(5), BSR20240029.
