A case note on the Federal Circuit’s September 3, 2026 nonprecedential decision affirming a claim construction that resulted in judgment of non-infringement in a dispute over an iron-sugar complex manufacturing patent.
The dispute in Biofer S.p.A. v. Vifor (International) AG was not whether Vifor’s process operated within a pH of 7.0 to 9.0 at some point during the reaction. Biofer’s own testing showed that it did — for approximately 90% of the oxidation reaction. The issue was what the claim required: whether the pH had to be maintained within that range throughout the oxidation step, or whether it was sufficient for the reaction to enter the range at some point.
The Federal Circuit agreed with the district court that the claim required the pH to be maintained between 7.0 and 9.0 during the oxidation step. Once that construction was affirmed, Biofer conceded that Vifor did not infringe.
The Patent and the Process
Biofer’s U.S. Patent No. 8,759,320 covers a process for preparing trivalent iron complexes with sugars, including dextrins and dextrans, for use in treating iron deficiency. The specification describes the need for iron/sugar complexes with appropriate physical and chemical stability, low toxicity, and good bioavailability, and identifies shortcomings in prior-art manufacturing processes.
The patented process has four steps: (1) activation of the sugar, (2) complexation of the activated sugar with an iron compound, (3) purification, and (4) stabilization. The appeal concerned only the first step, referred to as the activation or oxidation step.
During activation, an aldehyde end group on the sugar is oxidized to a carboxylic acid. The specification explains that dextrins and dextrans contain multiple aldehyde sites and that selective oxidation of the end groups is desirable. Oxidation at other sites can cause the sugar to break down — what the patent describes as “depolimerization phenomena.” The specification identifies pH control as a means of controlling that oxidation.
Claim 1 recites a process for preparing an activated sugar comprising the step of reacting a sugar having an aldehyde end group with bromine “in a solution at a pH between 7.0 and 9.0” with the specific oxidation of the end aldehyde. The claim also contains limitations concerning the type of sugar and the in-situ generation and addition of bromine.
The appeal therefore turned on the meaning and effect of the phrase “pH between 7.0 and 9.0.”
The Claim Construction Dispute
The district court framed the issue as whether the claim covered only a process that occurs entirely at a pH between 7.0 and 9.0, or also a process in which the pH falls within that range at some point, even briefly. It construed “pH between 7.0 and 9.0” to mean that the pH “is maintained in the interval separating 7.0 and 9.0.”
Biofer sought clarification, specifically asking whether the construction required the pH to remain within the range throughout the oxidation reaction. The district court declined to clarify the order, stating that the Markman order “speaks for itself” and that there was no ambiguity.
Biofer’s own testing then became significant. Its testing showed that Vifor’s manufacturing process operated within the 7.0–9.0 range for approximately 90% of the oxidation reaction. Biofer therefore stipulated that Vifor did not infringe under the district court’s construction, while preserving the construction for appeal.
The Federal Circuit’s Analysis
The Federal Circuit reviewed the claim construction de novo. Because the district court had relied solely on intrinsic evidence, the appeal turned on the claim language, specification, and prosecution history.
The claim language ties the pH limitation to the entire oxidation step
The court began with the language of claim 1.
Grammatically, “in a solution at a pH between 7.0 and 9.0” modifies “the step of reacting a sugar.” The court noted that there was no dispute that this “step” referred to the entire oxidation step of the four-step manufacturing process.
That mattered. The claimed pH range therefore defines the solution environment for the duration of the oxidation step. It was not merely a numerical range that the reaction needed to enter at some point.
The specification repeatedly describes pH as something to be maintained
The specification reinforced that reading.
It states that “it is important to maintain the reaction pH” between 5.0 and 12.0, preferably between 7.0 and 9.0. More importantly, it states that “[t]hroughout the activation reaction of the sugar, the pH value is controlled and maintained in the fixed range, preferably between 7.0 and 9.0.”
The examples addressing the oxidation step likewise describe maintaining the pH within the relevant range. The Federal Circuit therefore found that the specification consistently described the claimed pH condition as one that is maintained during the reaction, rather than merely reached at some point.
Biofer’s prosecution history provided the technical reason for the claimed range
The prosecution history provided further support.
Biofer submitted a declaration from named inventor Dr. Egidio Marchi “to corroborate the criticality” of the claimed pH interval. Marchi recreated Example 5 and reported that maintaining the pH between 7.8 and 8.2 resulted in selective oxidation without increased depolymerization. By contrast, maintaining the pH between 9.8 and 10.2 resulted in a depolymerizing attack on the sugar.
Biofer relied on this evidence before the examiner, stating that outside the claimed range the reaction was not effective in preventing destructive attack on the sugar. The claims were allowed on that basis. The Federal Circuit therefore viewed the prosecution history as supporting the conclusion that maintaining the pH between 7.0 and 9.0 was tied to achieving the claimed selective oxidation while avoiding depolymerization.
This is important because the prosecution history did not merely confirm that the 7.0–9.0 range was preferred. It provided evidence of why the claimed range mattered to the process.
The broader pH range disclosed in the specification did not expand the claim
Biofer argued that the district court’s construction improperly limited the claim to a preferred embodiment because the specification disclosed a broader pH range of 5.0 to 12.0.
The Federal Circuit rejected that argument. The fact that the specification disclosed a broader range did not mean that claim 1 had to cover it. Claim 1 expressly recited the narrower 7.0–9.0 range. As the court noted, not every claim must cover every embodiment disclosed in the specification.
The distinction is straightforward: the specification may describe what is suitable across a broader range, but the scope of the issued claim is determined by what the claim actually recites. Biofer’s “brief excursions” theory came too late
At oral argument, Biofer advanced a narrower position: the process should be covered if it operated primarily between pH 7.0 and 9.0, with only “brief excursions” outside that range, provided the claimed specific oxidation was achieved.
The Federal Circuit did not reach the merits of that formulation because Biofer had not presented it to the district court. In fact, Biofer had taken the opposite position below, arguing that the solution only needed to hit the 7.0–9.0 range for a very brief period.
The court therefore treated the “brief excursions” argument as forfeited and declined to consider a new claim construction position on appeal.
The second claim-construction issue was not before the court
Biofer also challenged the construction of the claim limitation requiring hypochlorite to be added in stoichiometric quantities with respect to the aldehyde end groups.
The Federal Circuit declined to review that issue. The parties’ stipulation and the resulting judgment of non-infringement were not based on that limitation, so the issue was not implicated by the judgment being appealed.
What the Decision Illustrates
Biofer is a useful reminder that a numerical range in a process claim cannot always be treated as merely defining numerical endpoints.
Here, the surrounding claim language tied the pH limitation to an identified process step. The specification repeatedly described the pH as something that had to be maintained during that step. The prosecution history then supplied experimental evidence supporting why maintaining the claimed range mattered to the claimed oxidation process.
Several points stand out:
- Claim language matters in context. The phrase “at a pH between 7.0 and 9.0” was read together with the “step of reacting,” which the parties agreed encompassed the entire oxidation step.
- Repeated specification language can reinforce a duration requirement. The specification did not merely identify 7.0–9.0 as a numerical range; it repeatedly described the pH as being controlled and maintained throughout the activation reaction.
- Prosecution history can provide more than disclaimer. Here, the inventor’s declaration supplied experimental evidence connecting the claimed pH range to selective oxidation and avoidance of depolymerization.
- A broader disclosure does not necessarily broaden a narrower claim. The specification’s disclosure of a 5.0–12.0 range did not alter the express 7.0–9.0 limitation in claim 1.
- Claim construction positions need to be preserved. Biofer’s attempt to advance a “brief excursions” theory on appeal was forfeited because that was not the position it had presented to the district court.
- A stipulated judgment can limit the issues available on appeal. Because Biofer stipulated to non-infringement under the district court’s construction, the Federal Circuit’s task was principally to decide whether that construction was correct. Once the court affirmed it, non-infringement followed from Biofer’s own stipulation.
The Federal Circuit ultimately affirmed the construction that “pH between 7.0 and 9.0” means the pH is maintained within that interval, and affirmed the resulting judgment of noninfringement.
Reference: Biofer v. Vifor Judgement
