The Federal Circuit decision in Bio-Rad Laboratories, Inc. v. 10X Genomics Inc., addresses several interesting issues. This article focuses on the affirmance of the district court decision that the “tangentiality” exception to prosecution history estoppel permitted Bio-Rad to show infringement under the doctrine of equivalents of an amended claim limitation.

The Patent And Prosecution History At Issue

The patent asserted under the doctrine of equivalents was U.S. Patent No. 8,889,083. Claim 1 was treated as representative:

1. A microfluidic system comprising:
a non-fluorinated microchannel;
a carrier fluid comprising a fluorinated oil and a fluorinated surfactant comprising a hydrophilic head group in the microchannel;
at least one plug comprising an aqueous plug-fluid in the microchannel and substantially encased by the carrier-fluid,
wherein the fluorinated surfactant is present at a concentration such that surface tension at the plug-fluid/microchannel wall interface is higher than surface tension at the plug-fluid/carrier fluid interface.

According to the Federal Circuit decision, the highlighted terms were added during prosecution to overcome a prior art rejection based on a reference (“Quake”) that “disclosed microchannels formed or coated with Teflon (a fluorinated polymer) or other fluorinated oils.” The Federal Circuit summarizes the arguments made during prosecution as follows:

The inventors distinguished the prior art by arguing that, unlike Quake, the as-filed application … attempts to prevent droplets from sticking to the walls of microchannels and requires that the “surfactant should be chemically similar to the carrier fluid and chemically different from the channel walls.” J.A. 16640. The inventors amended the claims to require non-fluorinated microchannels and a fluorinated surfactant, which would not react with each other. They explained that, as amended, the claims were distinct from Quake, which did not teach microchannels and carrier fluids that were chemically distinct. Rather, in their view, Quake taught coating the microchannels with a fluorinated oil and using fluorinated surfactants in the carrier fluid. The fluorinated microchannels and surfactants could, therefore, react with each other.

The Accused Products

The accused products at issue contained microchannels with 0.02% Kynar, which is said to be a “fluorine-containing coating resin.” As noted in the Federal Circuit decision, “[t]he jury found that 10X’s accused products … do not literally satisfy the ‘non-fluorinated microchannels; limitation but meet the limitation under the doctrine of equivalents.” Underpinning that finding was a finding that the accused products had “minute or negligible quantities of fluorine that have no function in the product and do not react with the microchannels.”

The Federal Circuit Decision

The Federal Circuit decision was authored by Judge O’Malley and joined by Judges Newman and Taranto.

The decision explains basic principles of prosecution history estoppel as follows:

Prosecution history estoppel arises when a patent applicant narrows the scope of his claims during prosecution for a reason “substantial[ly] . . . relating to patentability.” See generally Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359, 1366–67 (Fed. Cir. 2003) (en banc) (“Festo II”). A narrowing amendment is presumed to be a surrender of all equivalents within “the territory between the original claim and the amended claim.” Festo I, 535 U.S. at 740. This presumption can be overcome if the patentee can show that one of the following “exceptions” to prosecution history estoppel applies: (1) the rationale underlying the amendment bears no more than a tangential relation to the equivalent in question; (2) the equivalent was unforeseeable at the time of the application; or (3) there was some other reason suggesting that the patentee could not reasonably be expected to have described the equivalent. Id. at 740–41

At issue here is exception (1), the “tangentiality” exception.

The district court found the amendment at issue to be tangential to the accused equivalent because the amendment was made “to distinguish the microchannels in their system from fluorinated prior art microchannels that would react with the carrier fluid.” On the other hand, the accused products had “minute or negligible quantities of fluorine that have no function in the product and do not react with the microchannels,” and so “could meet the ‘non-fluorinated’ limitation under the doctrine of equivalents.” The Federal Circuit agreed:

The prosecution history of the ’083 patent establishes that the objectively apparent reason for adding the “nonfluorinated microchannels” limitation was no more than tangentially related to the equivalent at issue. In amending the claims, the patentees sought to distinguish the claimed invention from Quake, which disclosed fluorinated microchannel wall coatings that would react with the carrier fluid. …. By claiming non-fluorinated microchannels and a fluorinated surfactant, the inventors made sure that, in contrast to the Quake disclosure, the carrier fluid and microchannels in the claimed invention would not react with each other, thereby preventing droplets from sticking to the walls of the microchannels. …. As such, Bio-Rad was not barred from asserting that microchannels containing negligible amounts of fluorine are equivalent to “non-fluorinated microchannels.”

The Federal Circuit also considered and rejected arguments that the doctrine of claim vitiation barred a finding of infringement under the doctrine of equivalents, and found substantial evidence to support the jury verdict of infringement of the ’083 patent. Thus, the judgment of infringement of that patent was affirmed.

Protecting Inventors From Copyists

While not cited in this decision, the court’s characterization of the accused devices brings to mind the important role the doctrine of equivalents can play in protecting inventors from “copyists” who would “evade liability for infringement by making only insubstantial changes to a patented invention” to avoid the literal scope of the claims. See, e.g., Festo Corp. v Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002) (citing Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U. S. 17 (1997) and Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U. S. 605 (1950)). The decision here protected the patentee from accused devices that had “minute or negligible quantities” of the fluorine excluded by the amended claim language, but still performed the same function, in the same way, to achieve the same result.