How to prove that Cr oxide makes a stent biocompatible (e-polished 316LVM)

P

Plamen Petkov

#1
Dear friends,
Our firm manufactures coronary stent systems where the stent is made from ?surgical? 316LVM stainless steel. Now we apply for a certificate under Directive 93/42/EEC Annex II Section 4. The Assessor of our documentation wants me to prove him that the passive layer of chromium oxide, formed on the surface of our device through electropolishing, is responsible for the biocompatibility and corrosion resistance of the stent. I made for him literature review with the conclusion that without chromium oxide, stents made from 316LVM are of little use, but now he asks me ?How do you know that the equivalent to your devices, Boston Sc ? Liberte Monorail, Terumo ? Tsunami Gold, and Abbot ? Multilink Zeta, have the same layer of chromium oxide on the surface?? Looking into the catalogues for these devices I could not find evidence for that, even that they undergo electropolishing. Could anybody give some advice how to convince the Assessor that there is chromium oxide on the equivalent devices?
Thanks,
Plamen
 
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#2
Re: How to prove that Cr oxide makes a stent biocompatible

Not really sure I understand your problem, but maybe this helps to point you into the right direction:
To provide evidence of biocompatibility you'd look into ISO 10993 and perform all the relevant testing. Part of that would be corrosion testing per 10993-15 (or ASTM F2129 for the US) which would show that the passive layer (the chromium oxide) on the surface of the device is stable and prevents corrosion. You'd maybe have to validate your e-polishing process to show that it is reproducible.

Now, I read it that (as e-polished 316LVM is not exactly new) you'd like to leverage literature and/or predicate data instead of performing all the tests per 10993. In that case I'd start with certificates of the chemical composition and provide corrosion testing to show that the device is corrosion resistant. Next step might be a full chemical analysis per 10993-18 and an Auger analysis of the surface. If you need to use the predicates to generate your acceptance criteria then you need to test those also.

From your post I could not determine what exactly the concerns of your "Assessor" (internal, notified body, consultant?) really are and who actually brought up the competitor devices, so maybe my answer will not help you very much. In that case please let us know more details...
 

somashekar

Staff member
Super Moderator
#3
~~~ Welcome to the COVE Plamen Petkov ~~~
Your technical file for the stents must have test reports of bio-compatibility performed per ISO10993 on your manufactured stents. Literature review cannot be a substitution for tests towards assessing your stents bio-compatibility.
 
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M

MIREGMGR

#4
Your technical file for the stents must have test reports of bio-compatibility performed per ISO10993 on your manufactured stents. Literature review cannot be a substitution for tests towards assessing your stents bio-compatibility.
I don't think this is correct. Conformance to standards is one means of demonstrating conformance to Essential Requirements, but it is not the only allowed means. Demonstration by means of literature review might be accepted by an assessor, though in this case it apparently wasn't deemed sufficient. Comparison to predicate devices might be accepted as well, and in this case clearly such a comparison is relevant to the assessor since comparative questions have been asked.
 

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#5
I agree with MIREGMGR. There is some degree of freedom regarding the way you demonstrate meeting the essential requirements and in my experience there are some NBs who would accept an approach based on literature and predicate devices.
Also 10993-1 talks about using existing data and (in annex 3) gives you suggestions regarding how to evaluate literature data. And throughout all 10993 there is the requirement not to unnecessarily repeat animal testing when there is already data and to prefer in-vitro testing over in-vivo if you can get to the same conclusions. So if e-polished 316LVM has been sufficiently (-> gap analysis!) tested in the past, all you have to do is summarize that data and show that your surface is equivalent using in-vitro characterization techniques. So even the standard does not force you to perform all the testing...
 
Q

QuaProQuo

#8
~~~ Welcome to the COVE Plamen Petkov ~~~
Your technical file for the stents must have test reports of bio-compatibility performed per ISO10993 on your manufactured stents. Literature review cannot be a substitution for tests towards assessing your stents bio-compatibility.
I would definitely agree, some level of biocompatibility testing is required, to show that your materials, polishing techniques, etc. are at least bio-inert in vitro. The tests are fairly standard and may even yield supportive marketing results as well. Implantables in EU are really being scrutinized these days.
 
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P

Plamen Petkov

#9
Many thanks,
All of you have given me very precious advices. The Assessor is the notified body who is going to give the recommendation for the issue of the certificate under Directive 93/42/EEC Annex II Section 4. We have chosen 316L because it has been studied a lot and if reasonable rationale is given, we?d be able to waive actual testing. Of course the most proper way is to perform all testing to the relevant parts of 10993, but because this is time and money consuming, my boss ordered me to follow the literature route. Moreover the clinical investigation performed on the basis of the comparison between our device and the mentioned predicate ones, showed one and the same clinical outputs for all devices after all periods of follow-up ? 30 days, 6 and 12 months ? no patient died, nobody developed any disease as a result of stenting, all show health improvement etc. The mentioned before predicate devices have been chosen because ours is equivalent to them ? we try to prove that with a document Demonstration of Equivalence ? and since they are already legally on the market, they must have passed all relevant testing. I was hoping that if I find a documental evidence that the predicate devices have been e-polished (I am certain about that!), I?d be able to argue the statement that the surface properties of our stent are the same as these of the devices already on the market. The weak point that I see is to prove the quality of our e-polishing process which is perfect, but not validated.
I will stop boring you but remain open for any other suggestions.
Regards,
Plamen
 

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#10
This now makes it a little bit clearer. So some more things to think about:

1) The fact that the predicates are legally marketed does not mean that they passed all relevant testing, just that the company convinced their NB that they met all requirements. If you could look up their documentation then maybe you'd find a chain of rationales dating back to some device that was discontinued 2003... That is the main problem with predicates: most of the time you do not have all the data you'd actually need, especially for showing equivalence.
2) Next problem with predicates is that their clinical/market history does not tell you all that much. Which changes occured since introduction? Which problems did they have that did not lead to reportable actions, so you do not know about them? How is the detectability regarding the risks for which you'd like to leverage post market data from your competitors?

But back to your situation: You should find in the literature enough SEM pictures of e-polished 316L and also other surface treatments. So some inexpensive SEMs comparing literature, your device and the predicates might be the start of your showing equivalency. Next would be chemical certs and corrosion testing acc. to 10993-15. Maximum I would initially do is Auger analysis of the surface.
Although your NB is not allowed to act as a consultant, it is not uncommon to approach them with your concept and ask them if that would be acceptable and if not what they think is missing. They cannot tell you how to address the missing items/links, but in that case you could come back to the Cove...

Hope that helps...
 
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