Choosing the right artificial soil for cleaning validation. Blog post by Andres Dumas

February 18, 2024

In the development of a cleaning validation protocol, a critical initial phase involves the selection of an artificial test soil. This formulation aims to replicate the contaminants encountered by a medical device during clinical use. Since there is no universal soil ideal for all medical devices, this process requires collaboration among the testing lab, sponsor or manufacturer, and clinical staff to collectively determine the most optimal test soil for the device in question.

What is required for the cleaning validation?

When performing a cleaning validation according to ANSI AAMI ST98:2022, the standard requires that the intended use and clinical conditions are assessed and applied to the medical device during the cleaning validation. For the test soil, it has to represent the worst-case soil exposure and its formulation should have a supporting scientific justification of its relevance. The test soil has to include substances representative of tissues, fluids, and any other chemicals or contaminants that are intended to be removed during the cleaning of the device. 

What to consider when selecting the correct test soil?

The selection of the test soil starts by assessing the intended clinical use of the device. This assessment should include the location(s) in the body where it will be used and all tissues and fluids exposed to the device. For example, if testing an oscillating saw blade used in orthopedic surgeries, an optimal standardized soil may be ATS2015-Bone which simulates contamination from blood and bone fragments.

When selecting a soil where blood is the predominant component, it is essential to assess coagulation. If blood is the predominant component during clinical use and no other components interfere with coagulation, then a coagulating blood test soil should be considered. If on the contrary, other components are present in higher proportions or anticoagulants are used in the procedure, then a non-coagulating blood test soil should be used. 

Mixtures of test soils can also be used to simulate clinical use best. For example, if testing flexible scopes, used to investigate the gastrointestinal tract and perform biopsies a combination of two soils that represent both mucus and blood could be used. Adjusting the ratios of the soils allows for tailoring based on the expected proportions of each contaminant during the device's clinical use.

All non-patient-derived contaminants and chemical compounds expected during the clinical procedure should be simulated during the soiling process. If the medical device requires lubrication before use, which is the case of some probes, dilators, catheters, and others, the lubricant could be incorporated into the soil or applied directly to the device during the soiling process. The same applies to the use of bone cement, the use of ophthalmic viscosurgical devices (OVDs), and any other compound that is applied when using the device and that could contribute to the soiling process. 

Finally, it is important to recognize that even though there are several standardized soil formulations listed in ASTM and ISO standards, these recipes do not encompass every single residue with which a medical device will come into contact. Formulations not included in these standards may be more relevant and are allowed as long as scientific justification is provided. 

With extensive experience in Cleaning Validation protocol development and execution, we will guide you in selecting the artificial test soil that best suits your device and clinical application. Don’t hesitate to reach out to the expert team at SteriLabs