On August 3, 2020, in Bio-Rad Labs., Inc. v. 10X Genomics, Inc.1, the Federal Circuit clarified its decision in TomTom v. Adolph2 regarding limiting claim preambles, holding that the preamble of the claim at issue could not be separated, as was done in TomTom, into limiting and non-limiting portions.
In 2015, Bio-Rad Laboratories, Inc. (“Bio-Rad”) sued 10X Genomics, Inc. (“10X”), alleging infringement of several patents covering systems and methods for forming microscopic fluid droplets to perform microscale biochemical reactions. These types of systems can be separated into two camps: 1) systems where the reaction takes place in the microfluidic system (known as “on-chip”), and 2) systems where the reaction takes place outside of the microfluidic system (known as “off-chip”).
After a trial in late 2018, the jury found the asserted patents valid and infringed, and awarded damages to Bio-Rad. On appeal, 10X argued, among other things3, that the district court misapplied the Federal Circuit’s ruling in TomTom, when it construed only certain words from the claim’s preamble as limiting, rather than the entire preamble. The claim at issue covered:
A method for conducting a reaction in plugs in a microfluidic system, comprising the steps of:
providing the microfluidic system comprising at least two channels having at least one junction; …
forming at least one plug of the aqueous fluid containing the at least one biological molecule and the at least one reagent by partitioning the aqueous fluid with the flowing immiscible carrier fluid at the junction of the at least two channels, the plug being substantially surrounded by the immiscible carrier fluid flowing through the channel, wherein the at least one plug comprises at least one biological molecule and the at least one reagent for conducting the reaction with the at least one biological molecule; and…4
The lower court construed the preamble of the claim at issue to be limiting “only to the extent that it provides an antecedent basis for the terms ‘microfluidic system’ and ‘reaction.’”5 Relying on TomTom, the lower court found that the claim preamble “states an intended use for the invention, ‘followed by the body of the claim, in which the claim limitations describing the invention are recited.’”6
In TomTom, the Federal Circuit held that a district court need not “construe the entire preamble if it construed a portion of it.”7 The preamble of the claim at issue in TomTom recited “ a method for generating and updating data  for use in a destination tracking system of at least one mobile unit comprising…”8 The Federal Circuit held that the first part of the preamble was not limiting, whereas the second part was limiting because it provided antecedent basis for terms recited in the body of the claim; thus, TomTom held that it is possible for one part of the preamble to be limiting even though another part is not.
On appeal, 10X argued that TomTom does not apply to the claim at issue and it was error to give limiting effect to certain terms in the preamble, but not to other surrounding terms. Specifically, 10X argued that the preamble clearly provides antecedent basis for the claim limitations “the microfluidic system” and “the reaction,” and the terms “conducting … in” should also have limiting effect, such that the claim is limited to methods where the reaction takes place in the microfluidic system (i.e., “on-chip” reactions). By contrast, 10X’s accused product employs the “off-chip” method, wherein the reaction takes place after the droplets have left the microfluidic system. Bio-Rad argued that the district court correctly applied TomTom when it construed only certain words of the preamble to be limiting.
The Federal Circuit agreed with 10X, declining to split up the preamble as it did in TomTom. “Crucially, unlike TomTom, the preamble in this case cannot be neatly packaged into two separate portions. Nor does it simply recite a method for an intended use or purpose.”9 The Court agreed with the lower court that the terms “microfluidic system” and “reaction” provide antecedent basis and should be construed, but held that “these limiting terms can[not] be read separately from the remainder of the preamble. The language relied upon for antecedent basis in the preamble at issue is intertwined with the rest of the preamble.”10 The Court found that “[b]ased on the antecedent relationship, it is clear the claim drafters intended to limit the claimed methods to on-chip reactions, using both the preamble and the body of the claim to define the claimed invention.”11 The Court buttressed its conclusion that the entire preamble is limiting by noting that “[d]uring prosecution, the examiner amended both the preambles and the titles of the patents to specify that the reactions are conducted ‘in plugs in the microfluidic system.’”12 Therefore, the Court found the district court’s claim construction erroneous, vacated the judgment of infringement and remanded for a new trial under the proper claim construction.