Hi Ronen, when you say "finished device form" are you referring to the grinding up (homogenisation) of the entire device prior to biocompatibility testing?
The reason I ask is because only part of the device contacts the body - a good percentage (more than 80%) of the device remains outside of the body during use. In this case would you still say that biocompatibility testing should be done at the finished device form?
The rationale for "finished device form" is simply because certain manufacturing processes may subject materials to changes that might affect biocompatibility (interaction with other materials, contamination, etc.).
If a material was previously tested by iteself, you can certainly make the case that a given material, in its "finished form" is no different.
But you have to make the case by demonstrating that the material doesn't undergo any processing during manufacture that may influence its biocompatibility.
With respect to general testing: As Ronen suggests, consult with a test lab.
In my experience, they request materials in specific small quantities (no need to grind up your MRI

). ...and these quantities are proportional to the intended contact with the patient.
For example, an electrode may consist of fabric with plastic rim. When in use, say, 95% of the contact will be the fabric, and the plastic rim accounts for the remaining 5%.
So, when the test lab requests X square cm of material, you'd provide them with the relative proportions of intended patient contact. They will carry out the homogenization/extraction process according to the 10993 standard being tested against at their lab.
As I say, this is just my experience...but it makes sense...