Medical device cleaning using an ultrasonic bath
Use of ultrasonic baths for cleaning is common in the medical device industry for products like guide wires and metal parts, assemblies and implants. This method is usually used after devices have been initially cleaned to remove bulky impurities, particles and greasy material residuals. This method is designed to remove fine impurities only. An ultrasonic bath may be used with water, detergent or solvents (such as ethanol) and operated at temperatures that vary from 15˚C to 140˚C. The detergent is to be chosen based on the physical and chemical characteristics of the impurities to be removed by the cleaning. For organic impurities, alkaline detergent is suitable. For inorganic impurities, acidic detergent is suitable. The process may be followed by rinsing with purified water.
Ultrasonic cleaning processes for medical devices involve generating ultrasound waves at a frequency of 20–130 kHz to create cavitation bubbles that inflect force against contaminants adhering to or embedded in the surface of the medical device part. At higher frequencies, the cavitation bubbles increase in number and decrease in size. Larger bubbles release more energy when they interact with the material. For smaller parts it is better to employ a large amount of smaller bubbles that are able to penetrate small areas.
Ultrasonic cleaning is suitable for devices with uneven or homogeneous surfaces that may “trap” impurities.
Ultrasonic cleaning has the potential to cause significant damage to small medical devices like stents, specifically devices that react to a resonant frequency close to that used in the ultrasonic bath.
An ultrasonic bath cleaning method should include the following parameters:
- Ultrasonic frequency
- Ultrasonic power
- Cleaning time
- Cleaning agents
- Ultrasonic bath temperatures
- Quantity of parts/medical device to be cleaned per cycle
- Ultrasonic bath location (clean room classification)
- Drying procedure
Medical device washing and disinfecting machines
This type of multi-stage cleaning process comprises several stages which may vary, depending on the type of impurities to be removed by the cleaning and and the desired level of cleanliness. An example of a typical medical device cleaning cycle is washing with highly alkaline pH, followed by rinsing to neutralize the pH, then continuing with a highly acidic rinse solution and, finally, rinsing with purified water. Cleaning of medical device sub-parts might necessitate additional soaking, enzyme incubation and ultrasonic treatment. The advantages of medical device cleaning using washing machines are that they use an automated process, are easy to operate, and usually minimize pre-treatment stages and labor.