The claim construction issue in ABS Global, Inc. v. Cytonome/ST, LLC, No. 22-1761, — F.3d — (Fed. Cir. Oct. 19, 2023), was whether the claim language, “the sample stream,” was or was not limited to a single sample stream.

The patent-in-suit described and claimed a microfluidic device for processing a sample fluid. U.S. Patent No. 10,583,439. If one fluid is introduced into a microchannel and then a second fluid is introduced into the same microchannel, the two fluids travel in “laminar flow,” i.e., in parallel layers, without mixing. “Sheath flow” is a type of laminar flow in which a layer of “sample fluid” that contains particles is abutted on more than one side by a layer of particle-free sheath fluid. `439 patent, col. 1, lines 23–25 (“surrounded by another layer of focusing fluid on more than one side”). By introducing focusing fluid (e.g., sheath fluid) to “focus” (i.e., squeeze and confine) the sample fluid, a device user can accurately position particles (e.g., “in a single row file”) for inspection or other use at a point in the flow path.

            The specific claim language at issue is “a fluid focusing region configured to focus the sample stream.” The use of the definite article, “the,” means that the phrase “the sample stream” refers back to earlier language as an antecedent. The antecedent language is “a sample stream” in the preceding limitation, and it is the singular-only or plural-allowing meaning of that limitation which is determinative. The reference-back “the” language takes its meaning from the meaning of the antecedent, so if “a sample stream” has a plural-allowing meaning, so does the reference-back “the sample stream” phrase. See, e.g., Salazar v. AT&T Mobility LLC, 64 F.4th 1311, 1315 (Fed. Cir. 2023); LiteNetics, LLC v. Nu Tsai Capital LLC, 60 F.4th 1335, 1346 (Fed. Cir. 2023); Baldwin Graphic Systems, Inc. v. Siebert, Inc., 512 F.3d 1338, 1342–43 (Fed. Cir. 2008).

            Two familiar aspects of claim-construction analysis strongly support the plural-allowing meaning here. First, “at least in an open-ended ‘comprising' claim,” like claim 1 of the '439 patent, “use of ‘a' or ‘an' before a noun naming an object” requires that the phrase be construed to mean “‘one or more' unless the context sufficiently indicates otherwise.” Lite-Netics, 60 F.4th at 1345; see Salazar, 64 F.4th at 1315; Convolve, Inc. v. Compaq Computer Corp., 812 F.3d 1313, 1321 (Fed. Cir. 2016); Baldwin, 512 F.3d at 1342–43. The court has called this the “general rule,” adding that an exception “only arises where the language of the claims themselves, the specification, or the prosecution history necessitate a departure from the rule.” Baldwin, 512 F.3d at 1343. Second, the specification here states: “[F]or the purposes of the present disclosure, the term ‘a' or ‘an' entity refers to one or more of that entity. As such, the terms ‘a' or ‘an', ‘one or more' and ‘at least one' can be used interchangeably herein.” '439 patent, col. 18, lines 27–30. That definition reinforces, rather than negates, the applicability here of the “one or more” general rule concerning “a” or “an.” It also brings into play the lexicography principle—that, with narrow exceptions, “[w]here the specification instructs as to the meaning of a claim term, ‘the inventor's lexicography governs.'” Grace Instrument Industries, LLC v. Chandler Instruments Co., 57 F.4th 1001, 1010 (Fed. Cir. 2023) (quoting Phillips v. AWH Corp., 415 F.3d 1303, 1316 (Fed. Cir. 2005) (en banc)); see Thorner v. Sony Computer Entertainment America LLC, 669 F.3d 1362, 1365 (Fed. Cir. 2012); Martek Biosciences Corp. v. Nutrinova, Inc., 579 F.3d 1363, 1380 (Fed. Cir. 2009).

The Federal Circuit found there was no sufficient basis for rejecting the plural-allowing meaning of “a sample stream” here. Neither the prosecution history nor the specification supply a “clear and manifest disavowal” of that meaning, Martek, 579 F.3d at 1380, or “totally negate[]” it, id. at 1383 (Lourie, J., dissenting in part). While the specification disclosed single-sample-stream embodiments, they were described as nothing more than examples. Nor was there an operational impossibility that requires rejecting the plural-allowing meaning.

The Federal Circuit also found that a dependent claim requiring that the focusing fluid be “introduced into the flow channel symmetrically with respect to a centerline of the sample stream” did not compel a different result.

A “centerline of the sample stream” is merely a reference point for how focusing fluid should be introduced. It has not been shown that satisfaction of the claim 2 requirement precludes a sample-stream centerline from running through focusing fluid.

Thus, the Federal Circuit held that “the sample stream” is not limited to a singular-only sample stream. Because the PTAB had determined that the challenged claims were not unpatentable based on a singular-only sample stream, the IPR was reversed and remanded.

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