Federal Circuit Confirms Prosecution Statements Permanently Limit Patent Claim Scope—Puradigm Decision

The U.S. Court of Appeals for the Federal Circuit held on April 1, 2026, in Puradigm, LLC v. DBG Group Investments LLC, that statements made by a patent applicant during prosecution history can permanently narrow patent claim scope, even when the examiner rejected those statements. The decision (No. 24-2299, nonprecedential) underscores the high stakes of applicant language choices in patent prosecution.

At issue was U.S. Patent No. 8,585,979, directed to photocatalytic air purification cells that use UV light striking catalyst-coated targets to generate ions eliminating airborne contaminants. The asserted claims defined the distinguishing feature as a pair of “specular UV reflectors” that bounce UV light “directly” onto targets rather than diffusing it.

The accused DBG Group products incorporated unpolished aluminum reflectors instead of polished mirrors. The district court granted summary judgment of noninfringement, finding that during prosecution, the applicant had disclaimed polished aluminum and that this disclaimer logically extended to all forms of aluminum reflectors. The Federal Circuit affirmed this reasoning.

The critical finding: even though the original examiner disagreed with Puradigm’s prosecutorial statement, that statement became binding “prosecution disclaimer”—a form of claim estoppel. In other words, once an applicant asserts that certain subject matter falls outside the claim scope during prosecution, that assertion is legally binding and cannot later be revisited, regardless of examiner reaction.

The practical implications are profound for patent practitioners and applicants. Every word choice in specifications and amendment papers carries potential liability in future litigation. When an examiner rejects claims, the applicant’s arguments to overcome that rejection become permanently binding on claim interpretation. This demands extraordinarily careful, forward-looking prosecution strategy.

Puradigm serves as a cautionary tale. Imprecise terminology or inadequate claim definitions during prosecution can fatally undermine enforceability. For applicants pursuing international patent strategies—where language differences and jurisdictional variations require careful specification drafting—this lesson is particularly acute. Practitioners must balance immediate prosecution success against long-term claim security.