Federal Circuit Finds Claim Is Not “Materially Broader” and Inventor Estopped From Challenging Asserted Claim

Previously, we reported on the Supreme Court’s limits on assignor estoppel and arguments on remand at the Federal Circuit. Last week, on August 11, 2022, the Federal Circuit issued its opinion deciding whether Hologic’s claims are “materially broader” than the claims at the time of assignment, barring application of the assignor estoppel doctrine. The Federal Circuit found the claims are not “materially broader” than what the inventor (now trying to challenge the patent) originally assigned, and accordingly, Minerva is estopped from challenging the validity of Hologic’s claims. 

The Federal Circuit opined on two issues: (1) whether Mr. Truckai, the inventor (and founder of Minerva), warranted the validity of the prior claim when the IP rights were assigned; and (2) whether the asserted claim is materially broader than the rights assigned—and specifically, whether the prior claim is broad enough to cover moisture-impermeable devices. We address each below:

First, Mr. Truckai must have warranted validity of the prior claim when the rights were assigned for estoppel to apply. The Federal Circuit found that Mr. Truckai did warrant the validity of the prior claim. The prior claim at issue was cancelled in response to a restriction requirement, not on the merits. 

The Examiner found that the apparatus claims, including the assigned claim at issue, were distinct inventions from the method claims. Mr. Truckai requested the Examiner withdraw the restriction requirement because the Examiner had already allowed the assigned claim at-issue, or alternatively, elected to prosecute the method claims. The Examiner maintained the restriction requirement, and in response, Mr. Truckai canceled the apparatus claims.

The Federal Circuit found the apparatus claims, including the assigned claim at issue, were canceled “for reasons other than patentability.”1 Because the claims were canceled or withdrawn in response to the restriction requirement, the applicant could have prosecuted those claims separately and “cancelation did not nullify the claim.”2 Thus, Mr. Truckai warranted the validity of the claim at the time of assignment, and assignor estoppel may apply if the asserted claims are found to be “materially broader.”

Second, because the assignment included a warranty as to validity, the asserted claim must be “materially broader” than the assigned claim, or estoppel will apply and bar a validity challenge. The difference here hinged on whether the assigned claim covered moisture-permeable and/or moisture-impermeable devices. 

The Federal Circuit previously found that the asserted claim covered endometrial treatment devices with moister impermeable applicator heads. But both parties agree that assigned claim does not have an express moisture-permeability limitation. Thus, on remand, the Federal Circuit construed the assigned claim, determining whether the claim language is broad enough to cover moisture-impermeable devices or is limited to moisture-permeable devices. The Federal Circuit found that it is broad enough to cover both.

Specifically, the Federal Circuit found that the assigned claim covers moisture-impermeable devices (as well as moisture-permeable devices) because “electrode array” is not limited to moisture-permeable devices. The Federal Circuit looked to claim differentiation and the written description: the inventor drafted other claims that require moisture permeability, but the assigned claim at issue was silent as to moisture permeability. And, even though the written description described “and/or a tendency to absorb moisture” as a preferable characteristic, moisture permeability was not described as a “requirement or mandatory characteristic.”3

Accordingly, the Federal Circuit held that Minerva is estopped from challenging the validity of the asserted claims based on assignor estoppel because the asserted claim is not “materially broader” than the original claims. The Federal Circuit thus affirmed the district court’s summary judgment that the asserted claim is not invalid and that the claim is infringed.


The August 11, 2022 Federal Circuit  decision stresses the importance and potential implications of assignors making representations and warranties that may bar validity challenges or assignees expanding the scope of assigned patent applications.  For example, an assignor should carefully consider whether to warrant the validity of post-assignment claims of any pending application, or not yet filed continuations, CIPs or divisional applications.   Moreover, it was not clear how “materially broader” would be interpreted and what evidence could be considered. But this decision makes clear that claim construction—and intrinsic evidence—are key.4   

Please contact the authors with any questions, and stay tuned for updates regarding this case or assignor estoppel.

Kasey E. Koballa is an associate in the Raleigh, NC, office and April Abele Isaacson is a partner in the San Francisco, CA office of Kilpatrick Townsend & Stockton, LLP.


1  Hologic, Inc. v. Minerva Surgical, Inc., Nos. 2019-2054, Doc. 106, at 10 (Fed. Cir. Aug. 11, 2022)
2  Id. at 11.
3  Id. at 15.
4  “Because this determination rests on principles of claim construction, it is ultimately a question of law [the Federal Circuit] review[s] de novo where, as here, it is decided only on the intrinsic evidence.” Id. at 12.
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