A reader asks:
I am new at medical devices biocompatibility. I've been asked to perform a MEM cytotoxicity assay on an arteriovenous fistula needle. I am not really clear on how to perform the extraction of the device; as I've been asked to do it on the final device which has the needle plus the tube. Would it be appropriate to calculate the volume for the extraction based on surface for the tube and weight for the needle, and sum up both volumes, and submerge the device in that volume?You want to test the fluid pathway of the device and any other part of the device that is inserted into the body, i.e. the route the fluid would take as it enters the body and exterior of the needle. As you said, in your case it sounds like the area comes from the interior of the tube (and plunger surface), the needle, and some extra for the exterior portion of the needle that is inserted into the body. I would stick to the ISO 10993 standard and just use the surface area calculation, I'm not sure if the standard allows a combination of the weight and surface area calculations.
It sounds like you may be performing the testing yourself, but the easiest way for me to get answers or at least some direction for medical device biocompatibility testing (assuming you end up using them) is to call Nelson Laboratories, NAMSA, Pacific Biolabs, or WuXi Apptec. If this is your first time getting testing done- call all four (or at least the first two) and see which one you like, if this is not the first time, generally someone in the company has some strong opinions on which one is best.
Good luck with your testing.