From The Field

August 10, 2020

On August 3, the Federal Circuit issued a decision addressing, among other things, the doctrine of equivalents (the “DOE”).  The case, Bio-Rad Laboratories, Inc., et al. v. 10X Genomics Inc, provided an opportunity for the Federal Circuit to address long-established DOE principles that it has visited less frequently in recent years than during the 1990s and early 2000s.     

The case involves three patents directed to microfluidic systems and methods for forming microscopic droplets (also called “plugs”) of fluids to perform biochemical reactions.  Microfluidic systems utilize chips that have microfluidic channels, i.e., hair-width pathways, through which cells and fluids flow and perform biochemical reactions.  The Federal Circuit addressed a number of interesting patent issues in this decision, but for the purposes of this post, we will focus on the court’s discussion of the doctrine of prosecution history estoppel and the doctrine of claim vitiation, both of which may act as a bar to the application of DOE. 

The patent relevant to the DOE issue is U.S. Patent No. 8,889,083 (the “’083 patent”).  Claim 1, a representative claim of the ’083 patent, reads (with emphasis added):

 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.

During prosecution, the applicant amended the claims to overcome a rejection based on the prior art U.S. Patent No. 7,294,503 (“Quake”), which disclosed microchannels coated with a fluorinated polymer or other fluorinated oils.  The inventors distinguished Quake by arguing that Quake taught coating the microchannels with a fluorinated oil and simultaneously using fluorinated surfactants in the carrier fluid, which would result in reactions between the microchannels and surfactants, while the’083 invention attempted to prevent fluid from sticking to the walls of the microchannels and therefore required the surfactant and the channel walls to be chemically different.  The inventors further amended the claims to add “non-fluorinated” before “microchannels” and “fluorinated” before “surfactant” to make clear that these two components are chemically different and would not react with each other.    

It appears that the devices at issue originally had non-fluorinated microchannels, but after the litigation was filed, 10X Genomics (“10X”) modified its products to add 0.02% Kynar, a non-reactive amount of a fluorine-containing resin, to its microchannels.  10X conceded that the addition of the Kynar had no impact on the functioning of its products.  At trial, the jury found that the accused products, as modified, did not literally satisfy the “non-fluorinated microchannels” limitation but met the limitation under the DOE.

10X argued that the DOE should not apply here due to prosecution history estoppel and claim vitiation.  Prosecution history estoppel arises when a patentee narrows the scope of his claims during prosecution for a reason substantially related to patentability.  In this situation, a narrowing amendment is presumed to be a surrender of all equivalents within the territory between the original claim and the amended claim.  There are three exceptions to the application of this presumption: (1) the rationale for 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 explanation suggesting that the patentee could not reasonably be expected to have surrendered the equivalent.  The doctrine of claim vitiation ensures that the application of the DOE is not applied so broadly as to render an element in the claim effectively eliminated or read an element completely out of the claim.

On prosecution history estoppel, 10X argued that because the applicant specifically added “non-fluorinated” to limit microchannels in prosecution to distinguish Quake, the patentee should not be allowed to recapture 10X’s modified products with fluorinated microchannels.  The Federal Circuit disagreed, finding that the “tangential relation” exception applied here.

The court first noted that whether prosecution history estoppel applies is a question of law, but courts should look to the specifics of the relevant prosecution history to determine whether estoppel precludes the particular DOE argument at issue.  In other words, prosecution history estoppel is always a case-specific analysis.

In this particular case, the court noted that the applicant’s decision to add the “non-fluorinated microchannels” limitation must be considered together with its decision to add, at the same time, the limitation of a “fluorinated surfactant.”  This history makes clear that the applicant added the limitation of “non-fluorinated microchannels” for a particular purpose, namely, preventing droplets from sticking to the walls of the microchannels by making the channel walls chemically different from the fluorinated surfactant, and relied on this purpose to distinguish Quake.  The accused devices, however, contained only negligible amounts of fluorine in the microchannels, which could not react with the surfactant.  Based on these facts, the court concluded that the narrowing amendment had only a tangential relation to the equivalent at issue, i.e., negligibly fluorinated microchannels, and therefore, the patentee was not barred from invoking the DOE for its infringement claim. 

On claim vitiation, 10X argued that because “fluorinated” and “non-fluorinated” are “diametric opposites,” and because a fluorinated microchannel is the “antitheses” of a non-fluorinated microchannel, allowing the patentee to capture 10X’s now fluorinated microchannels would entirely vitiate the “non-fluorinated microchannel” limitation.

The Federal Circuit panel rejected 10X’s attempt to limit the inquiry to a binary choice between “fluorinated” and “non-fluorinated.”  Instead, the court stated that the appropriate inquiry is whether a reasonable fact finder could have found that a negligibly-fluorinated microchannel performs the same function, in the same way, and achieves the same result, as a non-fluorinated one.  If the answer is “yes,” then the difference between the claim limitation and the equivalent would be deemed insubstantial and allowing the patentee to capture 10X’s negligibly-fluorinated microchannels would not render the “non-fluorinated microchannel” limitation meaningless.  Here, because 10X essentially conceded that a 0.02% Kynar-containing microchannel was insubstantially different from a non-fluorinated microchannel, claim vitiation did not apply.

The Federal Circuit’s analysis in this case provides good guidance for future applications of the doctrine of prosecution history estoppel and the doctrine of claim vitiation.  

Author: Hui Liu