Test Method Validations



In woodworking, the old adage goes “Measure Twice, Cut Once”, but I quickly learned that even this didn’t always guarantee perfect parts. Two ‘identical’ parts measured with a different ruler or off of a different reference face might not line up as perfectly as I had hoped. It makes me wonder how anything was built back in the days of units of measure such as the cubit or when a foot was actually an anatomical foot in length. Fortunately, the medical device field has far advanced from using our forearms as a measurement system with the addition of precision machinery, calibrated tools, and advanced optical systems. But, just like I learned in woodworking, does using tight-tolerance, calibrated calipers really guarantee that specifications have been met?

At Poly-Med, our 25 years of experience have helped us to learn that what we measure and what we measure with are only accurate and valid if we also control how we measure. When developing a new product, we go to great lengths to specify exactly how measurements are to be taken. By performing measurements in a repeatable way, we can help ensure that the data collected is comparable to the same data collected during validation runs and lot-to-lot in manufacturing.

Ideally, this process includes both a Test Method (TM) protocol and a Test Method Validation (TMV) protocol. The TM document describes the how of data collection and the TMV assesses the TM to confirm that how we collect that data is actually repeatable and consistent. In TMVs, the measurement process is put to the test across multiple trained operators and a range of the specifications. This allows insight into whether the method is valid for use with a given product, highlights areas to improve the consistency and precision of the method, and demonstrates the inherent variability of the measurement system. .

For example, a TMV might show that using a scale with demarcations every nanometer is really only useful and consistent to measure to the closest millimeter if used with an unaided human eye. For some specifications, this might be perfectly adequate. For others, this measurement method would not suffice. By changing the how from the unaided uman eye to a microscope, we can keep what is being measured and the measurement tool the same, while the precision of the measurement dramatically increases. Further assessment with a TMV would allow us to determine whether this method is now compatible with the product and whether the method is dependable across all operators or only possible with the expert who designed the method. This same process holds true with simple measurements such as dimensions, more complex measurements such as moisture content, and even qualitative attributes of the product. Only by properly performing TMVs for each specific product and specification can we ensure that our measurement system and methods are compatible with the device specifications.

If you are working on a medical device application and are interested in learning more about biodegradable polymers and how to validate test methods to assess them, contact us to learn how we can advance your idea.

Andrew Hargett, M.S.