The Federal Circuit has denied David Jang’s petition for en banc rehearing in Jang v. Boston Scientific.  The basic issue surrounds Boston Scientific’s “ensnarement defense” and whether it had been waived.

The ensnarement doctrine limits the scope of the doctrine of equivalents – barring the patentee from asserting a scope of equivalency that will encompass or “ensnare” the prior art. DePuy Spine, Inc. v. Medtronic Sofamor Danek, Inc., 567 F.3d 1314 (Fed. Cir. 2009).  This approach is closely akin to the ordinary claim construction canon of construing terms in order to preserve validity. However, the ensnarement doctrine is actually applied while the construe-to-preserve-validity approach is generally a limited afterthought if even considered.

The doctrine makes perfect sense at this high level – patents should not cover what is found in the prior art.  The difficulty comes in the doctrinal and procedural details.

  • Who should decide (CAFC: the judge);
  • What is the standard (CAFC: it is question of law);

The particular issue in the en banc setup was whether Boston Scientific’s belated raising of the ensnarement doctrine constituted waiver of the doctrine – BSC did not raise the defense in the pretrial order.  In its decision, the Federal Circuit ruled that it was not necessary to raise the defense at that point since the District Court had already indicated that the issue would be decided post-trial.

[CAFC Decision][Jang En Banc Petition]

15 thoughts on “

  1. 3

    If an equivalent of a claimed invention is known, how is it even possible that the claimed invention is even patentable?

    1. 3.1

      While I understand your concern, I believe Phillips v. AWH provides some latitude here, particularly in those instances where a claim is susceptible to multiple constructions. As the Federal Circuit indicated in Phillips, “[W]e have looked to whether it is reasonable to infer that the PTO would not have issued an invalid patent, and that the ambiguity in the claim language should therefore be resolved in a manner that would preserve the patent’s validity.” Hence, in the instance when an ambiguity causes a claim to be read on both an equivalent and an embodiment that is not invalid, then, in accordance with Phillips, it might be conceivable that a court could, under certain circumstance, be justified in construing the claim in such a way as to avoid invalidity.

      1. 3.1.1

        Gary Cohen (sounds like link to, but this is an issue of infringement asserted by the patent owner. One can take this assertion to be an admission against interest such that if it is shown that the alleged equivalent was known prior to the critical date then the patent necessarily is invalid.

    2. 3.2

      How is it possible? Ned, see this:

      link to

      Suppose you (like Lilly here) have a case in which the claim you are asserting is limited to pemetrexed disodium but your infringer is using dipotassium instead.

      On the evidence, the Supreme Court (reversing the High Court and the Court of Appeal) finds dipotassium to be an equivalent to the disodium you have claimed, notwithstanding that every single one of the attacks on the validity of the claim failed. Bingo!

      Interesting is why the claim that went to issue was not directed to the pemetrexed ion (which would cover both Na and K) but instead was confined to just the one specific salt. Importantly, it was NOT to establish patentability over the art. There was no file history of narrowing to disodium to get over the art.

      So it is possible, at least in England under the EPC (but only since July of this year when this very case ushered into UK law for the very first time in history a Doctrine of Equivalents).

      1. 3.2.1

        Oops. Sorry Ned. The variant of the claimed subject matter, using the dipotassium salt was not “known”.


            Ned, in my eagerness to discuss your point, I failed to mention the key point, that the Activis case not only introduces into English law a DoE but also raises the likelihood of something like an ensnarement doctrine being needed in future infringement cases before the courts of the UK.

            But any such Doctrine will be different in the UK.

            What the UK now does is to construe the claim for the purposes of validity over the prior art. That claim construction also determines whether the accused embodiment infringes, except in the case of an infringement by equivalent (IbE). The embodiment accused of infringing by equivalent falls (by definition) outside the ambit of the claim for purposes of assessing the validity of the claim.

            It follows that the accused infringer who is doing something like the prior art cannot raise the defence that always used to be rock solid, that if you construe the claim wide enough to cover what I’m doing, the claim must be invalid. Hence the need now for something akin to an ensnarement doctrine.

            Of course, Europe has its personal “right of continued use” claim to protect those who fall within a not invalid claim, but are doing no more than what they were already doing before the date of the claim. The new issue, as yet unresolved, will arise when the accused infringer asserts in defence that the accused act (which he has only just started doing) is an act that the art prior to the date of the claim already rendered obvious to perform.

            It strikes me that we shall not have long to wait, in the UK, before such a situation arises. Meanwhile, UK litigators are curious how the courts in London will handle it.


              The new issue, as yet unresolved, will arise when the accused infringer asserts in defence that the accused act (which he has only just started doing) is an act that the art prior to the date of the claim already rendered obvious to perform.


              Act and Art are not similar enough, but are similar enough?


                anon, suppose that your accused act, published “after”, infringes. Now suppose that its publication instead came “before” the claim. Would it then have destroyed the claim’s validity?

                Up until Activis, yes, axiomatic. After Activis, maybe not.

                Consider the claim, and the “gap” between it and the art that is the foundation of its patentability and validity. Now consider that your accused act sits somewhere in that gap, close enough to the area protected by the claim to infringe by equivalent, yet obvious in view of the prior art that can be deployed against the validity of the claim. But the claim, properly construed for purposes of assessing its validity, does not reach as far as your accused act of infringement by equivalent.

                The good old English Gillette Defence (if you stretch the claim wide enough to catch me, you render it invalid) is powerless. So now England needs some sort of “ensnarement” doctrine, to avoid that the claim can be enforced against those who practice what the prior art rendered obvious.

                And why? Because of what its Supreme Court decreed in July this year, in the Activis case. Why Activis? To harmonise English law on infringement with the provisions of the EPC, written in 1973.

                Is it not amazing how long it takes, sometimes, for the law to adjust to a new statutory regime?

                1. Your explanation does not suffice, as you merely added more words to your shorter statement.

                  Act and Art are still being postulated as not similar enough, but are similar enough.

                2. Your link does not even reference “ensnarement.”

                  What it does seem to indicate is a distinction between novelty and nonobviousness and the application of DOE between the two different legal tests.

  2. 2

    Based on extensive legal research I’ve previously performed in the area of claim construction, I’d say it’s fair to characterize the Federal Circuit’s application of the “construe-to-preserve-validity” approach as reticent. Indeed, you probably would be hard pressed to find a case in which the approach is examined up front as a primary theme. Hence, no matter how you characterize it, I don’t believe that the subject approach has much visibility in the Federal Circuit caselaw.

    1. 2.1

      Reticent – as applied? or as being acknowledged to having been applied?

      (not sure if “primary theme” matters here)

  3. 1

    “However, the ensnarement doctrine is actually applied while the construe-to-preserve-validity approach is generally a limited afterthought if even considered.”

    It would be interesting to see some data support that assertion.

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