Originally published in Law360 on Sept. 15, 2025 (subscription may be required).

In a series of decisions issued between March and August, the U.S. Court of Appeals for the Federal Circuit clarified several important principles governing patent claim construction.

These rulings — Maquet Cardiovascular LLC v. Abiomed Inc., Eye Therapies LLC v. Slayback Pharma LLC, FMC Corp. v. Sharda USA LLC and Acufloor LLC v. EvenTile Inc. — offer valuable insights into the role of prosecution history, transitional phrases and specification evolution in defining patent scope.

The cases clarify doctrinal standards and provide practical guidance for patent prosecutors and litigators. Below, we summarize each decision and highlight key litigation and prosecution practice tips.

Maquet v. Abiomed: Prosecution disclaimer requires common limitations.

In the March 21 decision in Maquet Cardiovascular v. Abiomed, the Federal Circuit vacated the U.S. District Court for the District of Massachusetts’ judgment of noninfringement based on erroneous claim constructions in Maquet’s U.S. Patent No. 10,238,783, which covers intravascular blood pump systems.

The district court construed “guide mechanism comprising a lumen” to include a negative limitation — specifically, that the guide wire lumen must not be distal to the cannula — based on amendments made during prosecution of a related patent. It also added a limitation to the guide wire terms in claims 1 and 24, concluding that the guide wire could not pass through the free space between rotor blades.

The Federal Circuit rejected both constructions, emphasizing that prosecution disclaimer must be based on “clear and unmistakable” statements and that when relying on the prosecution history of a related patent, such disclaimers must relate to common limitations, not merely common subject matter.¹

The district court found that the related patents had common subject matter, i.e., related to intravascular pump systems, but the claim language at issue did not have common limitations.²

“Differences in claim language matter,” the court wrote. “Unless there is parity between the limitations, we cannot assume that the claims of an earlier, related patent present similar issues of validity to the later patent.”³

The court also clarified that silence in response to an examiner’s notice of allowance does not constitute disclaimer, nor do vague statements made during inter partes review proceedings.⁴

Litigation Practice Tips

When arguing disavowal or disclaimer during claim construction, the movant must overcome a high bar.

• Scrutinize whether the language relied on for disavowal or disclaimer is open to multiple reasonable interpretations. If so, the court will likely find no disavowal or disclaimer.
• When using the prosecution history of a related patent, distinguish between common limitations and common subject matter. Remember, common subject matter is not enough.
• Identical claim language across related patents may support disclaimer; differing language likely does not.

Prosecution Practice Tips

• Prosecution of related patents can be relevant if the cases have a limitation in common.
• Consider keeping claim language consistent across related applications or varying it intentionally.
• An applicant’s silence in response to a notice of allowance is generally not disavowal; however, consider using standard language when responding to notices of allowance — e.g., “We agree claims are allowable, but we don’t necessarily agree with your reasons.”

Eye Therapies v. Slayback: Transitional phrases can be redefined in prosecution.

In the June 30 decision in Eye Therapies v. Slayback Pharma, the Federal Circuit vacated the Patent Trial and Appeal Board’s finding of unpatentability, holding that the board had misconstrued the transitional phrase “consisting essentially of” in Eye Therapies’ U.S. Patent No. 8,293,742.

The patent claims methods for reducing eye redness using low-concentration brimonidine. During prosecution, the applicant amended the claims to replace “comprising” with “consisting essentially of” in response to prior art that disclosed brimonidine in combination with other active ingredients.

The board interpreted “consisting essentially of” in its typical, semi-open sense — allowing unlisted ingredients that do not materially affect the invention’s basic and novel properties. But the Federal Circuit found that the applicant had clearly redefined the phrase during prosecution, particularly through its use of the abbreviation “i.e.” to equate the claimed methods with those that exclude other active agents.⁵

“Use of ‘i.e.’ signals an intent to define the word to which it refers,” the Federal Circuit explained, citing its 2009 decision in Edwards Lifesciences v. Cook Inc. and its 2017 decision in Rembrandt Wireless v. Samsung.⁶

The court held that the prosecution history altered the typical meaning of “consisting essentially of,” narrowing it to exclude any additional active ingredients.

Litigation Practice Tips

• Transitional phrases like “consisting essentially of” can be redefined through prosecution.
• Carefully examine whether prosecution history alters the typical meaning of claim language.
• Even lawyers can misuse common terms, phrases or acronyms, such as “e.g.” versus “i.e.” here. Do not assume that the drafter of the patent knew the difference.
• Raise the issue that claim construction can affect other validity arguments to avoid affirming on alternate grounds.

Prosecution Practice Tips

• Consider differences between transitional phrases: “comprising,” “consisting essentially of,” and “consisting of.”
• Be cautious when using “i.e.” versus “e.g.” — the former may signal definitional intent.
• Even typical meanings of transitional phrases can be altered by prosecution history.
• Ask whether “consisting of” would have been a better choice than “consisting essentially of” if exclusion is desired.

FMC v. Sharda: Progression between provisional and patent specs can be significant.

In the Aug. 1 decision in FMC v. Sharda, the Federal Circuit vacated a preliminary injunction, finding that the district court had erred in construing “composition” in FMC’s pesticide patents.

The U.S. District Court for the Eastern District of Pennsylvania had limited composition to stable formulations, relying on language from a provisional application and a related patent. However, the issued patents — U.S. Patent Nos. 9,107,416 and 9,596,857 — omitted all references to stability.

The Federal Circuit held that the deletion of stability-related language from the provisional application was highly significant, citing its Dec. 9, 2024, decision in DDR Holdings LLC v. Priceline.com LLC.

In DDR Holdings, the court found that removing “services” from a definition of “merchants” narrowed the claim scope to “goods.” The court held that because the references to “stability” were removed from the application as filed and the patent as issued, that the term “composition” was not limited solely to stable formulations, but included unstable formulations as well.

“A skilled artisan would find that evolution meaningful,” the court wrote.⁷ “Every textual reference in the provisional application that a skilled artisan might reasonably have relied upon for interpreting ‘composition’ was removed from the asserted patent.”

The court also reiterated that invalidity need not be proven to defeat a motion for a preliminary injunction and that it is sufficient for a non-movant to present a substantial question of invalidity.

Litigation Practice Tips

• Differences between the scope of the provisional application and the issued patent can be material for claim construction.
• A substantial question of invalidity is sufficient to defeat a preliminary injunction.
• Patent owners should factor the burden on the non-movant (for a preliminary injunction) into litigation strategy and cost-benefit analysis.

Prosecution Practice Tips

• Review provisional applications for overly limiting language.
• Consider whether changes to the provisional impact the priority date.
• Be deliberate about what language is retained or removed during prosecution.

Acufloor v. EvenTile: Construction should provide planing, preserve validity and align with prosecution.

In the May 28 decision in Acufloor v. EvenTile, the Federal Circuit addressed two claim construction issues in patents covering tile leveling devices: the meaning of “edge” and the interpretation of “majority of an area.”

The U.S. District Court for the Middle District of Florida had construed the edge narrowly as “the line at which a surface of a tile terminates,” which would exclude embodiments where mortar contact occurs near — but not at — the very edge. The Federal Circuit modified this construction, holding that “edge” means “the area around and including the very edge of the tile.”

The court noted that a line does not have a surface area, “so restricting the edge to only a line would render the word ‘contact’ meaningless” and a “claim construction that gives meaning to all the terms of the claim is preferred over one that does not do so.”⁸

During prosecution, Acufloor repeatedly distinguished their invention from the prior art on the ground that the prior art devices do not permit the tile to be in contact with the mortar all the way to the very edge of the tile.

In litigation, Acufloor argued that an edge does not necessarily include the very edge. However, the Federal Circuit disagreed holding Acufloor to its distinguishing statements made in prosecution. In support of its position Acufloor tried to rely on figures in the patent. But the Federal Circuit noted that the court has held that “arguments based on drawings not explicitly made to scale in issued patents are unavailing.”⁹

The dissent argued for Acufloor’s construction but noted that its construction may render the claims invalid. In response the majority points out that indefiniteness is a factor that cuts against adopting that construction in appropriate cases. When there is doubt as to the proper construction of a claim term, the construction that preserves the validity of the claim should be adopted.¹⁰

The court also rejected the district court’s construction of “majority of an area,” which had compared the area of the notches to the solid portions of the base. Instead, the court held that the phrase refers to the area of tile-to-mortar-to-subfloor contact, not the base itself. Thus, the term should have been construed based on the plain terms of the claim limitation.

Litigation Practice Tips

• Prosecution history can be a treasure trove for supporting your desired construction.
• Do not overlook the benefit of visual aids in briefing, the court included annotated images in the final opinion.
• When in doubt, courts will adopt constructions that preserve validity.

Prosecution Practice Tips

• The edge includes some surface area and the very edge — consider using terms like “edge portion” or “edge margin” as an alternative.
• Important spatial relationships should be shown in the drawings and explained in the specification.
• Consider providing drawings that are to scale and stating so in the specification.
• Prosecution history is key to claim construction.

Conclusion: Precision, context and strategy matter.

These four decisions collectively reinforce five key principles:

• These cases demonstrate the importance and impact prosecution history and intrinsic evidence have on claim construction. It can be tempting to argue extrinsic evidence, but these cases show such reliance is dangerous.
• Know the prosecution history. Small errors by the patent drafter such as misusing phrases and terms — like e.g. and i.e. — can have a material impact on the outcome of claim construction.
• Say and show what you mean in the claims, description and drawings. Courts will favor interpretations that are consistent with prosecution, avoid invalidity and impart meaning.
• Be precise with language such as terminology selected for the claims and arguments made in prosecution.
• Statements in prosecution can alter typical meanings. Well-established terms like “consisting essentially of” are not immune to redefinition through prosecution.

For patent prosecutors, these cases highlight the importance of strategic drafting and careful argumentation in prosecution. For litigators, they underscore the need to scrutinize prosecution history and the intrinsic evidence.

John Carpenter is senior counsel and William Broman is an associate at Taft.

The opinions expressed are those of the author(s) and do not necessarily reflect the views of their employer, its clients, or Portfolio Media Inc., or any of its or their respective affiliates. This article is for general information purposes and is not intended to be and should not be taken as legal advice.

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¹ Id. at 1340.
² Id.
³ Id. at 1339.
⁴ Id. at 1342.
⁵ Id. at 1270-1271.
⁶ Id.
⁷ Id. at 1333.
⁸ See Merck & Co. v. Teva Pharms. USA, Inc. , 395 F.3d 1364, 1372 (Fed. Cir. 2005).
⁹ Nystrom v. TREX Co. , 424 F.3d 1136, 1149 (Fed. Cir. 2005).
¹⁰ See Phillips v. AWH Corp. , 415 F.3d 1303, 1327 (Fed. Cir. 2005); Liebel-Flarsheim Co. v. Medrad, Inc. , 358 F.3d 898, 911 (Fed. Cir. 2004).