The Number That Makes the Case Memorable: 90%
Claim 1 required reacting a sugar with bromine “in a solution at a pH between 7.0 and 9.0.” During discovery, Biofer’s testing confirmed that Vifor’s manufacturing process operated within that range for approximately 90% of the oxidation reaction.
At first glance, that sounds close to infringement. But under the district court’s claim construction, the relevant limitation required the pH to be maintained between 7.0 and 9.0 throughout the oxidation step. Biofer therefore stipulated to non-infringement while preserving its right to appeal that construction.
On September 3, 2026, the Federal Circuit affirmed. The disposition is nonprecedential, so it does not announce a new general rule. Its value is practical: it shows why numerical overlap cannot be analyzed in isolation.
It was whether the claim required that pH range to define the reaction environment for the duration of the oxidation step.
The Court Started With the Claim Language
Biofer argued that “between 7.0 and 9.0” simply defined a numerical interval and did not add a separate functional requirement that the pH remain inside that interval for the entire reaction.
The Federal Circuit began with the claim language. Claim 1 recited a process “comprising the step of reacting a sugar … with bromine in a solution at a pH between 7.0 and 9.0.” Grammatically, the court viewed the pH phrase as modifying the entire reacting step.
The parties did not dispute that the “step” was the complete oxidation step of the disclosed manufacturing process. On that reading, the pH range described the solution environment for the duration of that step—not a parameter that could merely pass through the claimed range at some point.
The Specification Reinforced That Reading
The intrinsic record then made that interpretation harder to escape. The specification repeatedly described the importance of maintaining reaction pH and stated that, throughout the activation reaction of the sugar, the pH was controlled and maintained in a fixed range, preferably 7.0 to 9.0.
The examples associated with the oxidation step likewise described maintaining pH within the claimed range during oxidation. That repeated and consistent usage mattered because claim terms are read as a skilled person would understand them in the context of the patent as a whole.
The court therefore did not simply import a preferred embodiment into the claim. It used the specification to determine what the claim language itself most naturally meant in context.
The Prosecution History Pointed in the Same Direction
The prosecution record was especially important. During examination, Biofer relied on inventor evidence and experimental data to explain why the pH range mattered.
The experiments compared maintaining the reaction at approximately pH 7.8–8.2 with maintaining it at approximately pH 9.8–10.2. Biofer told the USPTO that outside the claimed range the reaction was not effective in avoiding destructive attack on the sugar. The Federal Circuit noted that the relevant claims were allowed on that basis.
Those statements had been useful in obtaining allowance. Years later, they became part of the intrinsic record used to understand the scope of the same claim.
This does not mean every prosecution statement automatically creates prosecution-history disclaimer. The point is narrower: when a later claim-construction dispute arises, courts may examine how the applicant itself explained the invention and why a technical condition was said to matter.
A Concrete Illustration of the Phillips Framework
Biofer makes the Phillips framework unusually tangible. Claim construction begins with the words of the claim, but it does not end with isolated words or numbers.
A phrase such as “pH between 7.0 and 9.0” may look self-contained when lifted out of the patent. In the actual infringement analysis, however, the court considered:
- the grammar and structure of the claim;
- how the specification repeatedly described the reaction condition;
- how the examples implemented that condition; and
- how the applicant relied on the same condition and supporting experiments during prosecution.
The result was a narrower practical reading than Biofer wanted at the infringement stage: the pH had to be maintained within the range for the oxidation step.
The Prosecution Lesson: Arguments Used to Obtain Allowance Do Not Disappear
This is particularly relevant to China-origin U.S. applications. Patent teams often focus intensely on claim wording while treating the specification and Office Action responses as separate drafting exercises.
When responding to a §103 rejection, however, practitioners may repeatedly argue that a parameter must be maintained, that a particular relationship is essential to a technical effect, or that experimental results demonstrate the special significance of a numerical range.
Those arguments may be exactly what is needed to obtain allowance. But after issuance, they remain in the prosecution record. If claim construction later becomes contested, a court may return to those statements to understand what the applicant told the USPTO the invention required.
The practical lesson is not to avoid making strong prosecution arguments. It is to make them deliberately, with an eye to both prosecution and future enforcement.
The FTO Lesson: Do Not Stop at a Numerical Comparison Table
The same logic matters in freedom-to-operate analysis. Suppose a competitor’s claim recites a temperature of 20–30°C, a pressure of 5–10 MPa, or a concentration below 5%.
It is not enough to place those numbers next to the product or process parameters and conclude that overlap means high infringement risk. The analysis should continue:
- Does the patent describe the parameter as a momentary value or something that must be maintained through an entire step?
- Do the examples consistently use the range in a particular way?
- Did the applicant emphasize the parameter during prosecution?
- Was experimental evidence used to connect the range to a particular technical effect?
- Does the claim language, read in the intrinsic record, impose a temporal or functional condition that is not obvious from the number alone?
Sometimes the limitation that determines the infringement result is not expressed through the single word you expected to find in the claim. It emerges from how the claim language is understood in context.
The Takeaway
Biofer v. Vifor is nonprecedential, but it illustrates a recurring patent-practice reality: technical boundaries emphasized to obtain a patent can later return when the patent is enforced.
A U.S. patent is therefore worth reading as more than its issued claims. The specification, prosecution arguments, and experimental evidence can all become relevant again during litigation and FTO.
And that is why the case’s final number is so striking:
Approximately 90% of the reaction occurred within pH 7.0–9.0. Under the governing claim construction, the remaining 10% was enough to put the infringement result on the other side.