Prosecution history estoppel applies to narrowing amendment for a purpose, but not for all purposes

| September 25, 2020

Bio-Rad Laboratories, Inc., Et Al. v. 10X Genomics Inc.

August 3, 2020

Newman, O’Malley (Opinion author), and Taranto


The Federal Circuit held that 10X infringes Bio-Rad’s ‘083 patent under the doctrine of equivalents because a tangential exception to the prosecution history estoppel applies in this case.


Bio-Rad Laboratories, Inc. and the University of Chicago (collectively, “Bio-Rad”) accused 10X Genomics Inc. (“10X”) of infringing three patents: U.S. Patent Nos. 8,888,083 (“083 patent”); 8,304,193 (“193 patent”); and 8,329,407 (“407 patent”). The United States District Court for the District of Delaware held that 10X willfully infringed all three patents and awarded damages in an amount of $23,930,716.

The patents-in-suit are directed to systems and methods for forming microscopic droplets (also called “plugs”) of fluids to perform biochemical reactions. Claim 1 of the ‘083 patent, as below, is representative:

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.

During prosecution, the inventors amended the claims, as underlined above, to distinguish from a prior art, U.S. Patent No. 7,294,503 (“Quake”). Quake disclosed microchannels formed or coated with Teflon (a fluorinated polymer) or other fluorinated oils. Furthermore, the inventors argued that their invention 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.” That is, the non-fluorinated microchannels and the fluorinated surfactant are required not to react with each other. This is the purpose of the amendment. In contrast, Quake did not teach that microchannels and carriers fluids were chemically distinct, and the fluorinated microchannels and surfactants could, therefore, react with each other.

After the litigation was filed, 10X modified its products to add 0.02% Kynar-a non-reactive amount of a fluorine-containing resin-to its microchannels. 10X concedes that the addition of this amount of Kynar is irrelevant to the functioning of its products. In the District Court, the jury found that 10X’s accused products, as modified, do not literally satisfy the “non-fluorinated microchannels” limitation, but meet the limitation under the doctrine of equivalents. On appeal, among other issues, 10X argued that prosecution history estoppel and claim vitiation barred Bio-Rad’s theory of equivalence. The District Court held that prosecution history estoppel does not apply in this case because the amendment at issue was only tangentially related to the accused equivalent.

On appeal, 10X continued to argue that prosecution history estoppel applies because the inventors’ amendment narrowed the claims to recite a “non-fluorinated microchannel” to overcome Quake, which taught “fluorinated” microchannels. As such, the inventors surrendered the right to expand their monopoly to cover microchannels containing fluorine, “for whatever purpose.” In response, Bio-Rad counter argued that the reason for narrowing the claims was peripheral, or not directly relevant to the alleged equivalent. Bio-Rad contends that the patentees amended the claims to make clear that the carrier fluid and the microchannel wall should be chemically distinct, which bears no more than a tangential relation to the alleged equivalent-microchannel walls containing a nominal amount of fluorine that is not chemically distinct from the carrier fluid. The Federal Circuit agreed with Bio-Rad, and reasoned that inventors surrendered microchannels coated with fluorine that reacted with carrier fluids, not those containing de minimis amounts of fluorine that have no effect on how the microchannel functions in the system. The narrowing amendment can only be said to have a tangential relation to the equivalent at issue-negligibly fluorinated microchannels, or microchannels with non-fluorinated properties. That is, the inventors surrendered microchannels coated with fluorine for a purpose, but not for all purposes.

Take away

  1. During prosecution, inventors should also explain in detail the purpose of the amendment of claims in order to narrow the scope surrendered by the amendment.

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