Sterilizing Medical Devices that contain Electronic Components

[inforseeker]

I'm working on a medical device that contains sensitive electronic components (standard commercial-grade PCBs and surface-mount components). The device needs to be sterilized before clinical use, and I'm running into challenges finding a method that ensures sterility without damaging the electronics.
We've tried gamma sterilization at 45 kGy, but we're seeing failures in some components afterward. I’m now evaluating alternative methods like E beam.
I’d really appreciate insight from anyone who has experience with:

• Successfully sterilizing electronics in medical devices
• Specific components or PCB coatings that are more resistant to gamma radiation
• Known failure mechanisms from radiation or plasma exposure

 

[Astronuc]

Did one use an accelerator for the gamma sterilization, or ⁶⁰Co?

Were the electronic devices 'ON' or powered during the gamma sterilization process? That might induce a critical ionization event, even a single event upset (SEU). Gammas are much more penetrating than electrons. Depending on the energy, gammas will ionize atoms by photoelectric effect, Compton scattering, or pair production (e⁺e^-). The photo- and Compton electrons will also cause electron cascades in the matter through which they pass.

Electrons are attenuated quickly, so depending on the device dimensions, one might need to go in two directions from front and back, or top and bottom, i.e.,. from opposite directions.

What needs to be sterilized? Outside of the electronic components?

I have done simulations and dose calculations on medical devices, and various related materials, for photons (X-ray, gamma) and electrons. I have not done any simulations on electronics, but that could be done if a model is available.

I may be able to put you in touch with some people who do similar work, and I believe they are interested in radiation effects in electronics.

If interested, send me a DM. Do not put personal information in this (or any other) thread/post.

There is a separate effort at my organization to look at radiation effects on electronics.

 

[Tom.G]

Ethylene Oxide gas is used for sterilization in hospitals for things that can not withstand steam sterilization.

Edit: Problem is that IT IS EXPLOSIVE, so you better farm out that part of the project to the professionals!

Cheers,
Tom

 

[Filip Larsen]

If the device does not itself has direct contact with the patient then it may be an option to cover it with a sterile cover instead or as additional protection.

I work with software for OR ultrasound devices and I understand that for those devices the solution is to cover the main computer unit in sterile covers (allowing the surgeon to still see displays and control button) such that only the probes themselves needs to be able to withstand the special sterilization fluids that they are designed for.

 

[Technophile50]

ethylene oxide gas sterilization is relatively benign. temperatures can be as high as 60 degrees centigrade. The device will also need to withstand the vacuum cycles used to remove the gas. Internal cavities will need to be vented to the exterior so the gas can get in and quickly be removed under vacuum, hermetically sealed, or filled with inert impermeable material. Avoid mechanical joints and parts with crevices (e.g sockets, porous materials) where possible. Fill unavoidable cavities (e.g. under components) by vacuum impregnation with an EtO compatible epoxy. Design/use unavoidable connectors for easy gas flow in and out. Elastomers like silicone rubber are generally permeable to EtO and easy to sterilize, but thick sections require longer cycle times to allow full permeation and purging.

Case in point. An eye surgeon who was treating a teen who had been poked in the eye by a rotten stick and acquired bacterial, fungal, and viral infections brought me literature for a continuous medicine infusion device that had a squashed football shaped silicone rubber retainer connected to a small silicone tube threaded by a needle through the eyelid. It had been removed from the market because pathogens occasionally avoided sterilization in the stainless tubing used to connect the tubing to the retainer. He asked if i could construct one ASAP, because having nurses manually every half hour flush the patient's eye wasn't gaining on his complex infection. I worked late constructing a polished aluminum mold to cast the retainer integral with the end of the tubing, made a part, cleaned it, and gave it to the sterile processing night shift. About a week later, the doctor came by and said, "thank you for your work making that device: having it saved that kids eye."

From the intertubes - "Master Bond multiple ETO resistant adhesives offer a range of properties. High/low viscosity systems feature toughness, optical clarity, fast cures, thermal conductivity, electrical conductivity, low water absorption and vibration/impact resistance."
Also see https://sterigenics.com/technologies/ethylene-oxide/

Good luck; sometimes the intangible rewards are important.