Sample Size for Biocompatibility Tests

[Freddo]

Hi all,

So far, i was of the opinion that a sample size of 1 is sufficient for biocompatibility tests (given that your device provides a reasonably large surface area).
However, my QA department now wants to have a sample size justification. I can't find anything in the ISO 10993 series. I do not know how i can argue that a sample size of 1 is sufficient.
Did anybody else encounter this issue? Any ideas on how to resolve this?
Thanks

Freddo

 

[yodon]

My experience has been that the test labs require a specific amount of surface area of the material. "Sample counts" are mostly irrelevant.

 

[Freddo]

Yes, that is exactly what my understanding is. But is there any way to justify this?

 

[ScottK]

Yes, that is exactly what my understanding is. But is there any way to justify this?

present the recommendations of the lab that you intend to use as your justification.
I've done cytotoxicity and endotoxin studies with one sample each from three lots of the material in question for indirect contact materials.

 

[Bev D]

The issue here is that "sample sizes" are calculated based the variability of the population. so the intent of the test, the science of the test, and thing under test and the inherent variability of the thing to the characteristic being tested all matter: sometimes this gives us a probabilistic situation and sometimes it gives us a deterministic situation. traditional sample size calculations are used in a probabilistic situation.

biocompatibility testing is to determine if the inherent design choices are acceptable or not. if you think your design choices will be variable you probably need a better design - or at least a more controlled set of material suppliers or manufacturing processes. If your design is appropriate then it isn't a matter of how many things you test, it's about the area of the specimen - is it large enough to provide an adequate opportunity? So your "sample size" is not the number of things but the area of the specimen of one thing...

If you suspect that there may be some manufacturing variability (contamination, coating thickness, whatever) then it's a matter of getting a single sample from multiple manufacturing events (3 being the minimum and usually sufficient number). But this really should be done during development or during verification when brining on a new supplier or manufacturing line...