In disclaiming claim coverage in light of certain prior art, the applicant does not thereby act as a lexicographer, redefining individual words.

On June 3, 2013, in Regents of the Univ. of Minn. v. AGA Med. Corp., the Federal Circuit affirmed the district court's summary judgment that AGA did not infringe U.S. Patents No. 6,077,281 and No. 6,077,291, which related to septaloccluder medical devices for repairing heart defects, and that the '281 patent was invalid for anticipation.

[T]he court held that the asserted claims of the '281 patent were anticipated. Like an infringement analysis, an anticipation analysis has two parts: first, the disputed claim terms are construed, then the construed claims are compared to the prior art. A patented invention is anticipated by a prior art reference if that reference discloses all elements of the claimed invention, including means-plus-function structures or their equivalents. "While anticipation is a question of fact, 'it may be decided on summary judgment if the record reveals no genuine dispute of material fact,'" a decision that we review de novo. Whether the prosecution history imposes a limitation on the range of equivalents is a legal determination reviewed de novo.

In this case, the question is whether the prior art device described in the Lock article anticipated claims 1, 4, and 5 of the '281 patent. [T]he district court determined that all three claims were anticipated by the Lock device, which [used] umbrella-like radial frames. The University agrees that the Lock device has all the limitations of the three asserted claims, with the exception of the following two elements: (1) a structure satisfying the means-plus-function limitation, and (2) structures "in communication with" each other, and having "at least substantial portions of the[ir] central portion[s]" in communication with one another.

Although claim 1 of the '281 patent was not drafted in standard means-plus-function language, the court determined, and the parties now agree, that the [claim includes] a means-plus-function element, with the function of "moving the member from a compressed orientation to an expanded orientation," Under section 112 ¶ 6, now recodified as 35 U.S.C. section 112(f), a means-plus-function claim limitation includes both the corresponding structures disclosed by the specification as means of performing the function, and the equivalents of those structures. Here, the district court concluded that the specification disclosed two corresponding structures: "a frameless membrane made of a thin piece of a superelastic material," and "a flexible, elastically deformable frame carried around the periphery of the member" (the "peripheral frame structure"). . . . For purposes of section 112(f), an equivalent of the disclosed structure performs the same function as the disclosed structure, insubstantially the same way, with substantially the same result. . . . When an applicant tells the PTO that a prior art reference lies outside the scope of his claim, he is bound by that argument. In this case, no one disputes that the University effected a clear and unambiguous disclaimer of King's radial frame with respect to the language describing the "elastically deformable frame" in amended claim 1 of the '951 application. Nor is there any apparent dispute that the University's disclaimer of King's radial frame is also applicable to the similar radial frame disclosed by Lock. The question is whether the University's disclaimer carries forward to the means-plus-function language used in claim 1 of the '281 patent. . . .

Our law makes clear that "[j]ust as prosecution history estoppel may act to estop an equivalence argument under the doctrine of equivalents, positions taken before the PTO may bar an inconsistent position on claim con¬struction under § 112, ¶ 6." Thus, prosecution history disclaimer may limit the range of equivalent structures that fall within the scope of a means-plus-function limitation. We have also held that a disclaimer made during the prosecution of a patent application may operate as a disclaimer with respect to later patents of the same family. The problem for the University is that this limitation of the '951 application was not carried forward to the '281 patent. . . . We have explained that "[w]hen the purported disclaimers [made during prosecution] are directed to specific claim terms that have been omitted or materially altered in subsequent applications (rather than to the invention itself), those disclaimers do not apply." In general, a prosecution disclaimer will only apply to a subsequent patent if that patent contains the same claim limitation as its predecessor. Thus, our cases establish that the two patents must have the same or closely related claim limitation lan¬guage. If the language of the later limitation is significantly different, the disclaimer will not apply. [A]n inventor's arguments with respect to certain claim limitations in a parent should not apply to significantly different claim limitations in a divisional application. . . .

The proper inquiry is whether the scope of the claim limitation is substantially the same in the subsequent application as it was in the earlier application. In disclaiming claim coverage in light of certain prior art, the applicant does not thereby act as a lexicographer, redefining individual words. The appropriate focus is on the scope of the claim element, not the meaning of particular words in isolation. This is why our cases evaluate the similarity between the earlier and later claim limitations, carrying disclaimer forward if there are only immaterial differences . . . . Our requirement that the patents share "limitations in common" is not a mere technicality: it is necessary to support the inference that the patentee's earlier arguments are also applicable to the claim limitations of the patent-in-suit. Without claim language that makes that linkage clear, neither the PTO examiner nor the patentee's com¬petitors would be on notice as to the true scope of the later patent's claims. We have held that it is permissible for a patentee to take a different approach to claiming an invention in subsequent patents, either by adding limitations or by altering the claims' format. When the patentee does so, however, we cannot rely on the dubious argument that dissimilar claims present equivalent issues of validity, or that the applicant's disclaimer with respect to one claim would be equally applicable to another claim.

Here, the basis for distinguishing prior art in the second application is not the same as in the first. . . . The scope of claim 1 in the second application is plainly not the same as it was in the first application, and it would be inappropriate to import the first application's limitations into the different context of the second application. "Although statements in a file history may of course be used to explain and potentially limit the meaning of claim limitations," they "cannot be used to add an entirely new limitation to the claim." It is likewise inappropriate to apply a narrowing disclaimer to limitations that are materially different from the limitation to which it originally applied. . . . In other words, claim 1 of the '281 patent contains a different claim limitation than its predecessors and captures different subject matter. . . . Thus, the original disclaimer does not carry over to limit the range of equivalents here, and does not negate the district court's anticipation finding.