Medical Device Sterilization Methodologies for Your Product

On the surface, the production of energy-driven minimally invasive, electrophysiology, patient monitoring, and electrosurgical devices may appear similar.

They usually tend to involve some sort of injection molding, extrusion, wire termination, PCB configuration, and final assembly.

Given the fact that these products typically use similar manufacturing processes, wouldn’t the sterilization method be similar if not identical?

Now..

Let’s discuss the common medical device sterilization methodologies and how you can select the correct one for your medical device.

Sterilization Methodology Symbols

Below is a chart of the most common medical device sterilization methodologies and their associated symbols.

Breaking down the common sterilization methodologies for medical devices.

Beyond the symbol, it’s important to know what differentiates each of these medical device sterilization methods.

Ethylene Oxide

Ethylene Oxide (“ETO”), also referred to as EO/EtO or Ethylene Oxide “Gas” Sterilization, is a common option for products that are otherwise sensitive to heat and or moisture, such as electronics.

In general, ETO sterilization operates within the following parameters, which impact its effectiveness:

• Temperature range of 37°C to 63°C
• Relative humidity between 40% and 80%
• Exposure time of 1 to 6 hours
• For heat or moisture-sensitive devices/components
• Compatible with plastics
• Usually compatible with electronics

It’s important to note that there can be other limiting factors that may increase gas concentration which are not listed above.

Compared to other sterilization methods, ETO has a longer sterilization cycle, which can be impacted by factors such as temperature.

Typically, there are five stages associated with ETO sterilization:

1. Preconditioning and Humidification
2. Gas Introduction
3. Exposure
4. Evacuation
5. Air Washes

Each step has its own requirements and evidences why total cycle time must be taken into consideration when considering ETO as your sterilization method.

Radiation

Introduced as a sterilization method to the medical industry in the 1960’s, radiation gamma sterilization using Cobalt 60 or electron beam irradiation (“E-beam”), kills microorganisms and operates in a very tightly controlled parameter: 25 kGy, radiation does not cause a significant rise in temperature.

Where ETO tends to have little to no impact on electronics, radiation has a significant impact on electronics.

Some plastic materials may be affected by radiation, such as polypropylene and polyvinyl chloride (“PVC”).

The impact of this type of sterilization on a given material can vary from altering material color to affecting the material integrity.

It’s important to note that plastic material companies can produce radiation resistant grades of these polymers.

In general, radiation has a short sterilization process which provides quick turnaround time for single use medical devices.

Steam

Steam sterilization, also known as “autoclave”, uses steam to sterilize equipment and other object.

This sterilization methodology is commonly utilized on reusable medical devices.

Steam sterilization typically operates within the following parameters:

• Temperature range from 121°C to 132°C
• Relative humidity between 40% to 80%
• 30 minutes in a gravity sterilizer or 4 minutes in a pre-vacuum sterilizer

Steam may be incompatible with certain plastics and some electronics.

In fact, if steam is your desired method of sterilization you must ensure that proper potting/epoxy and overmolding is performed.

Steam sterilization is influenced by the following four variables:

• Steam
• Pressure
• Temperature
• Time

During steam sterilization, the device or product is exposed to direct steam contact under specific time, temperature and pressure.

This is applicable whether you are utilizing a standard gravity cycle or a pre-vacuum sterilization process.

Where ETO and radiation sterilization must be done at a sterilization facility, steam sterilization is typically done on premise at places like hospitals, physicians’ offices, and other health-care facilities.

Sterilization units can be built-in “stationary” or portable “table-top” units.

Vaporized Hydrogen Peroxide

Vapor Hydrogen Peroxide (“VHP”) is performed through the vaporization of liquid hydrogen peroxide.

VHP is comparatively a rapid sterilization process.

Similar to steam sterilization VHP sterilization may be done on site at hospitals and other healthcare facilities.

Choosing the right sterilization methodology for your device.

Given the differences of the different sterilization methodologies, it is imperative that the device manufacturers consider the impact sterilization will have on their product.

Factors that should be considered include:

• Expected lifetime of your product (i.e., single use versus reusable)
• Material
• Packaging
• Shelf life
• Transportation

Though the list could go on and on, the key point is that if you want to select the right sterilization methodology for your device, you need to know your product and your requirements.

The last thing you want to do is get through the development phase and learn post-sterilization that the chosen method of sterilization wasn’t adequate or worse compromised your device or product.

If you need help selecting the appropriate sterilization methodology for your device, I recommend speaking with an expert.

Additional resources.

To learn more about how to approach the development of energy-driven devices from a holistic standpoint (considering the impact of sterilization, the importance of the interconnect, etc.), download our free eBook.