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Claim Cancelation Limits but Doesn’t Prohibit Assignor Estoppel Defense

On remand from the Supreme Court, the US Court of Appeals for the Federal Circuit reconsidered the boundaries of the doctrine of assignor estoppel. The Federal Circuit found that the patent assignor was estopped from challenging the validity of an asserted patent because the asserted claim was not materially broader than the specific claims assigned to the patent owner. Hologic, Inc. v. Minerva Surgical, Inc., Case Nos. 2019-2054; -2081 (Fed. Cir. Aug. 11, 2022) (Stoll, Clevenger, Wallach, JJ.)

Csaba Truckai filed a patent application for a device that was designed with a moisture-permeable head to treat abnormal uterine bleeding while avoiding unintended burning or ablation. Truckai assigned the pending patent application to his company, Novacept, which was later acquired by Hologic. Truckai then founded a new company, Minerva Surgical, and developed a new device that used moisture impermeability to avoid the unwanted ablation. Hologic subsequently filed a continuation application to expand the scope of its claims to encompass applicator heads in general, regardless of moisture permeability. The US Patent & Trademark Office issued a patent on the expanded claims in 2015, and Hologic subsequently sued Minerva for patent infringement.

Hologic argued that doctrine of assignor estoppel barred Minerva from challenging the validity of the patent claims. The district court agreed and granted summary judgment of infringement. On appeal, the Federal Circuit affirmed the summary judgment of no invalidity. The Supreme Court granted certiorari and declined Minerva’s request to discard the doctrine of assignor estoppel but clarified that it comes with limits, holding that “assignor estoppel applies only when an inventor says one thing (explicitly or implicitly) in assigning a patent and the opposite in litigation against the patent’s owner.” The Supreme Court remanded to the Federal Circuit to address whether Hologic’s claim was materially broader than the one Truckai assigned. The Supreme Court explained that if the asserted claim was materially broader than the assigned claim, “then Truckai could not have warranted its validity in making the assignment and without such a prior inconsistent representation, there is no basis for estoppel.”

On remand, the Federal Circuit considered whether Truckai warranted the assigned claim’s validity at the time of assignment and whether the assigned claim was materially broader than the asserted claim.

The Federal Circuit concluded that Truckai had represented that the assigned claim was valid. The Court explained that the assigned claim was initially rejected as being anticipated, but Truckai successfully argued for its allowance. The claim was then canceled in response to a restriction requirement, but such cancellation did not speak to the claim’s patentability because an assignee would understand that it could later prosecute the claim’s subject matter under standard patent practice. Therefore, cancelation did not nullify the claim, and it “remained viable for further prosecution.” Additionally, the assignment was not just to the rights to the application, but to the rights to any continuation, continuation-in-part or divisional patent applications not yet filed. When presenting the application, Truckai signed [...]

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Missed Connection: Avoid Claim Construction Rendering Independent Claim Narrower Than Dependent Claim

The US Court of Appeals for the Federal Circuit vacated a district court’s claim constructions concerning generic independent claims that were amended after a species restriction requirement, because the district court disregarded the doctrine of claim differentiation after incorrectly concluding that the examiner had mistakenly rejoined withdrawn claims. Littelfuse, Inc. v. Mersen USA EP Corp., Case No. 21-2013 (Fed. Cir. Apr. 4, 2022) (Prost, Bryson, Stoll, JJ.)

Littelfuse owns a patent directed to a fuse end cap for providing an electrical connection between a fuse and an electrical conductor. The specification teaches three embodiments of the invention:

  1. A single-piece machined end cap comprising a mounting cuff and a terminal
  2. A single-piece stamped end cap comprising a mounting cuff and a terminal
  3. A two-piece assembled end cap comprising a mounting cuff, a terminal and a fastening stem attaching the mounting cuff to the terminal.

The originally filed claims included independent claims covering an end cap with a mounting cuff and a terminal, and dependent claims directed to the three embodiments. The claims directed to the two-piece assembled end cap embodiment contained the limitation that the terminal is press-fit onto the fastening stem.

During prosecution, the examiner issued a restriction requirement, asserting that the independent claims were generic to the three species in the dependent claims. Littelfuse elected to prosecute the assembled end cap species and the examiner withdrew the claims directed to the other embodiments. In response to a novelty rejection, Littelfuse amended the independent claims by adding the fastening stem element without specifying that the terminal is press-fit onto the stem. After allowing the amended independent claims, the examiner concluded that the previously withdrawn claims “require all the limitations of the . . . allowable claims,” and thus rejoined them.

Littelfuse sued Mersen for selling allegedly infringing fuses. The parties asked the district court to determine whether the fastening stem element in the independent claims limited Littelfuse’s patent to multi-piece end caps, despite the rejoined dependent claims being directed to one-piece embodiments. The district court found that the claim language, the specification and the prosecution history required the invention to have a multi-piece construction. First, the district court determined that the plain meaning of “fastening stem” was “a stem that attached or joins the other two components of the apparatus.” The district court then noted that the fastening stem was only mentioned in the specification in relation to the multi-piece embodiment in which the terminal is joined to the mounting cuff by the fastening stem. While Littelfuse argued that the US Patent & Trademark Office’s rejoining of the withdrawn claims meant that the independent claims covered unitary and multi-piece embodiments, the district court reasoned that the claims were rejoined based on a “misunderstanding” because they referred to the original independent claim, which did not include a fastening stem. In light of the district court’s finding that the independent claims covered only a multi-piece apparatus, the parties stipulated to non-infringement. Littelfuse appealed.

Applying the doctrine of claim differentiation, the [...]

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