`
`United States Court of Appeals
`for the Federal Circuit
`______________________
`
`PHARMA TECH SOLUTIONS, INC., DECISION IT
`CORP.,
`Plaintiffs-Appellants
`
`v.
`
`LIFESCAN, INC., LIFESCAN SCOTLAND, LTD.,
`JOHNSON AND JOHNSON,
`Defendants-Appellees
`______________________
`
`2019-1163
`______________________
`
`Appeal from the United States District Court for the
`District of Nevada in No. 2:16-cv-00564-RFB-PAL, Judge
`Richard F. Boulware, II.
`______________________
`
`Decided: November 22, 2019
`______________________
`
`JOHN J. SHAEFFER, Fox Rothschild LLP, Los Angeles,
`CA, argued for plaintiffs-appellants. Also represented by
`JEFFREY H. GRANT; WILLIAM A. RUDY, Denver, CO.
`
` EUGENE M. GELERNTER, Patterson Belknap Webb &
`Tyler LLP, New York, NY, argued for defendants-appel-
`lees. Also represented by GREGORY DISKANT; CHARLES
`DAVISON HOFFMANN, SEAN REEVES MARSHALL, Hoffmann
`Marshall Strong LLP, New York, NY.
` ______________________
`
`

`

`2
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`
`Before MOORE, REYNA, and STOLL, Circuit Judges.
`STOLL, Circuit Judge.
`This is an appeal from the district court’s summary
`judgment of noninfringement under the doctrine of equiv-
`alents. Because prosecution history estoppel bars the
`claims for infringement under the doctrine of equivalents,
`we affirm.
`
`BACKGROUND
`I
`Pharma Tech Solutions, Inc. sued LifeScan, Inc. for in-
`fringement of its U.S. Patent Nos. 6,153,069 and 6,413,411,
`which concern blood glucose monitoring systems for home
`use by individuals with diabetes. To test blood glucose, an
`individual typically draws blood by pricking a finger, plac-
`ing the blood on the end of a test strip, and placing the test
`strip into a meter. The test strip contains a pair of elec-
`trodes, including a working electrode and a second elec-
`trode. The working electrode is coated with an enzyme that
`oxidizes glucose in the blood sample. Following an incuba-
`tion period, the meter (1) applies a known electric potential
`across the electrodes, creating a diffusion limiting electric
`current (referred to as the “Cottrell current”) through the
`sample; and (2) measures Cottrell current. A proportional
`relationship exists between the measured current and
`blood glucose concentration. Based on this proportional re-
`lationship, a microprocessor in the meter converts the
`measured electric current to a blood glucose level and then
`reports the blood glucose level to the user.
`The shared specification of Pharma Tech’s ’069 and
`’411 patents states that the claimed inventions improve on
`these prior art blood glucose monitoring systems by “elim-
`inat[ing] several of the critical operator depend[e]nt varia-
`bles that adversely affect the accuracy and reliability” of
`these systems. ’069 patent col. 4 l. 66–col. 5 l. 3. The
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`3
`
`specification explains that the invention accomplishes this
`objective by performing multiple Cottrell current measure-
`ments and comparing the results. “In a system that is op-
`erating correctly, the results should agree within
`reasonable limits.” Id. at col. 4 ll. 51–52. Results outside
`of a prescribed percentage of each other, however, gener-
`ally indicate a system error, and the system will alert the
`user of a potential measurement error.
`With emphasis added to highlight the claim limitation
`at issue on appeal, illustrative claim 1 of the ’069 patent
`recites:
`1. An apparatus for measuring compounds in a
`sample fluid, comprising:
`a) a housing having an access opening
`therethrough;
`b) a sample cell receivable into said access opening
`of said housing, said sample cell being composed of;
`(i) a first electrode which acts as a working elec-
`trode;
`(ii) a second electrode which acts to fix the sys-
`tem potential and provide opposing current flow
`with respect to said first electrode, said second
`electrode being made of the same electrically
`conducting material as said first electrode, and
`being operatively associated with said first elec-
`trode, the ratio of the surface area of said second
`electrode to the surface area of said first elec-
`trode being 1:1 or less;
`(iii) at least one non-conducting layer member
`having an opening therethrough, said at least
`one non-conducting layer member being dis-
`posed in contact with at least one of said first
`and second electrodes and being sealed against
`at least one of said first and second electrodes to
`
`

`

`4
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`form a known electrode area within said opening
`such that said opening forms a well to receive
`the sample fluid and to allow a user of said ap-
`paratus to place the sample fluid in said known
`electrode area in contact with said first electrode
`and said second electrode;
`c) means for applying an electrical potential to both
`said first electrode and said second electrode;
`d) means for creating an electrical circuit between
`said first electrode and said second electrode
`through the sample fluid;
`e) means for measuring a first Cottrell current
`reading through the sample fluid at a first prede-
`termined time after the electrical potential is ap-
`plied and for obtaining at least one additional
`Cottrell current reading through the sample fluid,
`the at least one additional Cottrell current reading
`occurring at a second predetermined time following
`the first predetermined time;
`f) microprocessor means for converting the first Cot-
`trell current reading into a first analyte concentra-
`tion measurement using a calibration slope and an
`intercept specific for the first Cottrell current meas-
`urement, for converting the at least one additional
`Cottrell current reading into an additional analyte
`concentration using a calibration slope and an in-
`tercept specific for the at least one additional Cot-
`trell current measurement, and for comparing the
`first analyte concentration measurement with the at
`least one additional concentration measurement to
`confirm that they are within a prescribed percent-
`age of each other; and
`g) means for visually displaying the results of said
`analyte concentration measurements.
`Id. at col. 13 ll. 10–61.
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`5
`
`II
`The product accused of infringing under the doctrine of
`equivalents is LifeScan’s OneTouch® Ultra® system, a
`blood glucose meter for home use. When blood is detected
`on a test strip inserted into LifeScan’s meter, the meter
`measures current from two working electrodes during a
`five-second countdown period. LifeScan’s meter obtains fi-
`nal current measurements from the first and second work-
`ing electrodes at “5 seconds + 40 milliseconds (±25ms) after
`the measurement period begins” and “5 seconds + 340 ms
`(±25ms) after the measurement period begins.” J.A. 57.
`LifeScan’s meter then conducts a “Current Difference
`Test” to ensure that the difference between the recorded
`currents is within a defined limit. J.A. 57. “If the Current
`Difference Test passes, then the total final current (com-
`bining both working electrodes) is calculated.” J.A. 58. “[A]
`single glucose result is calculated from the total final cur-
`rent using a strip slope and intercept based on the strip’s
`calibration code.” J.A. 58.
`It is undisputed that LifeScan’s meters neither convert
`multiple Cottrell current readings to analyte concentration
`measurements nor compare multiple analyte concentra-
`tion measurements. Pharma Tech agrees that the accused
`products therefore do not literally infringe the claim. But
`Pharma Tech asserts that “an analyte measurement can be
`expressed as a current at a given time or as a concentra-
`tion” and, thus, the accused device infringes under the doc-
`trine of equivalents. Appellant’s Br. 40.
`III
`Because this appeal involves prosecution history estop-
`pel, a discussion of the relevant prosecution history is help-
`ful. Pharma Tech agrees that any prosecution history
`estoppel determined to apply to the ’069 patent extends to
`the related ’411 patent, so we focus on the prosecution his-
`tory of the ’069 patent.
`
`

`

`6
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`access
`
`opening
`
`an
`
`As originally filed, claim 4 of the patent application
`that ultimately issued as the ’069 patent (application claim
`4) read as follows:
`4. An apparatus for measuring compounds in a
`sample fluid, comprising
`a) a housing having
`therethrough[,]
`b) a sample cell receivable into said access opening
`of said housing, said sample cell being composed of
`a first electrode which acts as a working elec-
`trode,
`a second electrode which acts to fix the system
`potential and provide opposing current flow with
`respect to said first electrode, said second elec-
`trode being of substantially the same size as said
`first electrode and being made of the same elec-
`trically conducting material as said first elec-
`trode, said second electrode being operatively
`associated with said first electrode,
`at least one non-conducting layer member hav-
`ing an opening therethrough said layer member
`being disposed in contact with at least one of
`said electrodes and said layer member being
`sealed against at least one of said first and sec-
`ond electrode to form a known electrode area
`within said opening such that said opening
`forms a well to receive said sample fluid and to
`place said fluid in said known electrode area in
`contact with said first electrode and said second
`electrode,
`(c) means for applying an electrical potential to
`said first electrode and said second electrode,
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`7
`
`(d) means for creating an electrical circuit between
`said first electrode and said second electrode
`through said sample,
`(e) means for measuring Cottrell current through
`said sample and
`(f) means for visually displaying results of said
`measurement.
`J.A. 220–21. As Pharma Tech’s expert acknowledged, this
`originally presented claim was “broad enough to essen-
`tially cover any test strip with two working electrodes.”
`J.A. 698.
`In a first office action, the examiner rejected the inven-
`tors’ pending claims in view of U.S. Patent No. 5,385,846
`(Kuhn), U.S. Patent No. 5,288,636 (Pollmann), and U.S.
`Patent No. 5,108,564 (Szuminsky). The inventors’ October
`1997 response to the examiner’s office action amended ap-
`plication claim 4 (which later issued as ’069 patent claim
`1). Among other things, the claim was amended to require:
`(1) obtaining at least two Cottrell current readings; (2) con-
`verting the plurality of Cottrell current readings to analyte
`concentration measurements; and (3) linearly comparing
`the plurality of analyte concentration measurements:
`e) means for measuring a first Cottrell current
`reading though said sample at a first predeter-
`mined time after said electrical potential is applied
`and for obtaining at least one additional Cottrell
`current reading through said sample, said at least
`one additional Cottrell current reading occurring
`at a second predetermined time following said first
`predetermined time,
`f) means for converting said first Cottrell current
`reading into a first analyte concentration measure-
`ment, and for converting said at least one addi-
`tional Cottrell current reading into an additional
`analyte concentration measurement, and
`for
`
`

`

`8
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`linearly comparing said first analyte concentration
`measurement to said additional analyte concentra-
`tion measurement[.]
`J.A. 303 (underlined text added by amendment).
`In the remarks accompanying the October 1997
`amendment, the inventors emphasized the new claim lan-
`guage and distinguished the asserted prior art based
`thereon. For example, the inventors argued, “Kuhn is not
`applicable to claims 4 or 66 as now amended, in that ob-
`taining a plurality of readings by taking repeated measure-
`ments is not the same as the multiple readings now
`claimed, wherein those readings are converted to analyte
`concentration and then linearly compared to one another.”
`J.A. 307 (emphasis added). The inventors distinguished
`Pollmann and Szuminsky on the same basis, asserting:
`“Pollmann likewise does not suggest the present claimed
`means for comparing the concentration derived from the
`first measurement and at least one additional concentra-
`tion derived from an additional measurement to verify the
`result.” J.A. 307–08 (emphasis added); see also J.A. 308
`(“Claims 66–69 all include the additional multiple meas-
`urement limitation, wherein the multiple measurements
`are used to verify the result by comparing concentrations
`determined at different times during the measurement.”1
`(emphasis added)).
`In a second office action, the examiner rejected the
`pending claims as anticipated by U.S. Patent No. 5,508,171
`
`
`1 The October 1997 amendment amended application
`claim 66 to depend from application claim 4. Claims 67–
`69, which issued as independent claims 4–6 of the ’069 pa-
`tent, were amended to recite limitations requiring obtain-
`ing a plurality of current readings and comparing analyte
`concentrations derived
`from said current readings.
`J.A. 304–06.
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`9
`
`(Walling) and as obvious over Walling in view of Szumin-
`sky or U.S. Patent No. 5,243,516 (White). J.A. 359–61. The
`examiner explained that Walling discloses “means for ap-
`plying an electrical potential between the electrodes and
`means for measuring a resulting diffusion limiting current
`at multiple times.” J.A. 360 (citing Walling col. 3 l. 29,
`col. 8 l. 55–col. 12 l. 55). Noting that Szuminsky and White
`each disclose a microprocessor to take measurements in a
`sensor similar to that of Walling, the examiner concluded
`that “[i]t would have been obvious for Walling to adopt a
`microprocessor in view of Sz[u]minsky or White.” J.A. 361.
`The examiner further concluded that the applicants’ “line-
`arly comparing” limitation did not change the obviousness
`analysis, because “any microprocessor is capable of carry-
`ing out that function.” J.A. 361.
`In response, the inventors again highlighted the “con-
`verting” and “comparing” claim language added by the Oc-
`tober 1997 amendment. For example, the inventors
`emphasized that “Walling et al and Szuminsky et al do not
`even disclose taking multiple analyte concentration meas-
`urements and comparing such to confirm proper operation
`of a measuring system.” J.A. 378. Similarly, to distinguish
`White, the inventors argued that “[i]n contrast to the teach-
`ings in White, the present invention compares analyte con-
`centration readings at different times.” J.A. 378.
`The examiner again rejected the claims as obvious over
`Walling in view of White in a third office action. Following
`an examiner interview, the inventors filed another re-
`sponse in which they repeatedly distinguished the prior art
`based on the “converting” and “comparing” limitations.
`The inventors asserted:
`the present invention is directed to a system which
`takes two different Cottrell current readings, con-
`verts them to two different analyte concentration
`measurements, and then compares the two analyte
`concentration measurements to each other to
`
`

`

`10
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`confirm that they are within a prescribed percent-
`age of each other. That operation in the present
`invention is neither taught nor suggested by Wall-
`ing et al or White (’516), or any combination
`thereof.
`J.A. 397–98. The inventors then distinguished Walling on
`the basis that “Walling et al does not convert two different
`Cottrell current readings to first and second analyte con-
`centration measurements, and then compare the first and
`second analyte concentration measurements to each other,
`as in the present invention.” J.A. 398. Rather, they as-
`serted, Walling “utilize[s] the multiple [current] measure-
`ments
`together
`to determine a proper analyte
`concentration.” J.A. 398. Turning to White, the inventors
`asserted that “White (’516) discloses an operation in which
`Cottrell current measurements at two different times are
`taken and a ratio of the measured Cottrell currents [is]
`evaluated.” J.A. 398. The inventors explained that the
`claimed “converting” limitation and the claimed “compar-
`ing” limitation each provided a basis to distinguish “the
`present invention” over White:
`First, in the present invention the two different
`Cottrell current readings are converted into first
`and second analyte concentration measurements.
`Further, in the present invention the first and sec-
`ond analyte concentration measurements based on
`the first and second Cottrell current readings are
`compared to each other to confirm that they are
`within a prescribed percentage of each other.
`J.A. 398. Continuing, the inventors emphasized that be-
`cause neither Walling nor White “disclose[s] or suggest[s]
`comparing first and second analyte concentration measure-
`ments based on first and second Cottrell current readings
`to each other,” the combination of White and Walling can-
`not render the claims obvious. J.A. 399.
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`11
`
`In response, the examiner issued a notice of allowabil-
`ity, and the ’069 patent issued. The ’411 patent, which is a
`continuation of the ’069 patent, issued subsequently.
`IV
`After Pharma Tech filed a complaint for infringement
`of the ’069 and ’411 patents, LifeScan moved to dismiss
`Pharma Tech’s complaint based on failure to state a claim
`upon which relief could be granted for both literal and
`equivalent infringement.
` The district court denied
`LifeScan’s motion, allowed Pharma Tech to amend its com-
`plaint, granted expedited discovery limited to infringement
`of the “converting” and “comparing” limitations, and per-
`mitted LifeScan to file an early motion for summary judg-
`ment. For its doctrine of equivalents infringement claims,
`Pharma Tech’s amended complaint identified the relevant
`equivalent as “the
`functionality of a system that
`(a) measures current at two different times, (b) compares
`the current[s] to ensure they are within a prescribed per-
`centage and (c) converts the current readings into a glucose
`concentration.” J.A. 1047–48.
`After Pharma Tech dismissed its literal infringement
`allegations, LifeScan filed a motion for summary judgment
`of no infringement under the doctrine of equivalents.
`LifeScan asserted that argument-based and amendment-
`based prosecution history estoppel barred Pharma Tech’s
`doctrine of equivalents infringement theory. Specifically,
`LifeScan asserted that when the inventors amended their
`claims to require conversion of Cottrell current readings to
`analyte concentration measurements and subsequent com-
`parison of those analyte concentration measurements, they
`surrendered any claim scope covering systems and meth-
`ods that do not compare analyte concentration measure-
`ments.
` In addition, LifeScan maintained that the
`inventors’ arguments distinguishing the prior art consti-
`tuted clear and unambiguous disclaimers of meters that do
`not perform the claimed conversion and comparison steps.
`
`

`

`12
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`Pharma Tech opposed summary judgment, asserting that
`its October 1997 amendment of the claims to include the
`“conversion” and “comparison” steps was tangential to the
`real purpose of the amendment, which was to require a lin-
`ear comparison of multiple measurements.
`The district court held that amendment-based prosecu-
`tion history estoppel barred Pharma Tech’s claims of in-
`fringement under the doctrine of equivalents. The court
`reasoned that LifeScan’s accused system falls within the
`claim scope surrendered by the inventors during prosecu-
`tion of the ’069 patent. In so ruling, the district court con-
`cluded that the tangentiality exception did not apply
`because the inventors’ remarks during prosecution indi-
`cated that “comparison of analyte concentration measure-
`ments was, at a minimum, a significant aspect of the
`[October 1997] amendment.” Pharma Tech Sols. Inc. v.
`LifeScan Inc., 348 F. Supp. 3d 1076, 1084 (D. Nev. 2018).
`The district court further held that argument-based estop-
`pel likewise barred Pharma Tech’s claims, noting that the
`inventors “consistently relied on the comparison of two an-
`alyte concentration measurements as a distinguishing fea-
`ture of [their] claims.” Id. Accordingly, the district court
`granted LifeScan’s motion for summary judgment.
`Pharma Tech appeals. We have jurisdiction under
`28 U.S.C. § 1295(a)(1).
`
`DISCUSSION
`I
`We apply the standard of review of the regional circuit
`in reviewing a grant of summary judgment. Enfish, LLC
`v. Microsoft Corp., 822 F.3d 1327, 1334 (Fed. Cir. 2016).
`The Ninth Circuit reviews a district court’s grant of sum-
`mary judgment de novo. Forester v. Chertoff, 500 F.3d 920,
`923 (9th Cir. 2007). “Viewing the evidence in the light most
`favorable to the non-moving party, we must decide whether
`any genuine issues of material fact exist and whether the
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`13
`
`district court correctly applied relevant substantive law.”
`Id. “Whether prosecution history estoppel applies, and
`thus whether the doctrine of equivalents is available for a
`particular claim limitation, is a question of law reviewed
`de novo.” Spectrum Pharm., Inc. v. Sandoz Inc., 802 F.3d
`1326, 1337 (Fed. Cir. 2015).
`
`II
`“Prosecution history estoppel applies as part of an in-
`fringement analysis to prevent a patentee from using the
`doctrine of equivalents to recapture subject matter surren-
`dered from the literal scope of a claim during prosecution.”
`Trading Techs. Int’l, Inc. v. Open E Cry, LLC, 728 F.3d
`1309, 1322 (Fed. Cir. 2013). Prosecution history estoppel
`can occur in two ways: “either (1) by making a narrowing
`amendment to the claim (‘amendment-based estoppel’) or
`(2) by surrendering claim scope through argument to the
`patent examiner (‘argument-based estoppel’).” Conoco,
`Inc. v. Energy & Envtl. Int’l, L.C., 460 F.3d 1349, 1363
`(Fed. Cir. 2006).
`With respect to amendment-based prosecution history
`estoppel, the Supreme Court has recognized that a “pa-
`tentee’s decision to narrow his claims through amendment
`may be presumed to be a general disclaimer of the territory
`between the original claim and the amended claim.” Festo
`Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S.
`722, 740 (2002). The presumption may be overcome if the
`patentee can show the applicability of one of several excep-
`tions identified by the Supreme Court: (1) the equivalent
`was “unforeseeable at the time of the application”; (2) “the
`rationale underlying the amendment may bear no more
`than a tangential relation to the equivalent in question”; or
`(3) “there may be some other reason suggesting that the
`patentee could not reasonably be expected to have de-
`scribed the insubstantial substitute in question.” Id.
`at 740–41.
`
`

`

`14
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`Pharma Tech does not dispute that the October 1997
`amendment was narrowing, and relies on one of these ex-
`ceptions on appeal: that the rationale of its amendment
`bore no more than a tangential relation to the equivalent
`in question. “The tangential relation inquiry ‘focuses on
`the patentee’s objectively apparent reason for the narrow-
`ing amendment,’ which ‘should be discernible from the
`prosecution history record.’” Integrated Tech. Corp. v. Ru-
`dolph Techs., Inc., 734 F.3d 1352, 1358 (Fed. Cir. 2013)
`(quoting Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki
`Co., 344 F.3d 1359, 1369 (Fed. Cir. 2003)).
`Turning to argument-based prosecution history estop-
`pel, “the prosecution history must evince a clear and un-
`mistakable surrender of subject matter.” Conoco, 460 F.3d
`at 1364 (quoting Deering Precision Instruments, L.L.C. v.
`Vector Distribution Sys., Inc., 347 F.3d 1314, 1326 (Fed.
`Cir. 2003)). We have explained that “[c]lear assertions
`made during prosecution in support of patentability,
`whether or not actually required to secure allowance of the
`claim, may also create an estoppel . . . because [t]he rele-
`vant inquiry is whether a competitor would reasonably be-
`lieve that the applicant had surrendered the relevant
`subject matter.” PODS, Inc. v. Porta Stor, Inc., 484 F.3d
`1359, 1368 (Fed. Cir. 2007) (alterations in original) (cita-
`tions omitted).
`
`III
`We hold that amendment-based and argument-based
`prosecution history estoppel bar Pharma Tech’s infringe-
`ment claims under the doctrine of equivalents. Pharma
`Tech’s asserted equivalent is within the territory that the
`inventors surrendered during prosecution of the ’069 pa-
`tent. Moreover, the inventors’ arguments accompanying
`and following the October 1997 amendment clearly and un-
`mistakably surrendered systems that do not convert Cot-
`trell
`current
`readings
`to analyte
`concentration
`measurements and compare those analyte concentration
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`15
`
`measurements. The inventors’ clear statements not only
`establish argument-based estoppel, but also negate
`Pharma Tech’s reliance on the tangential relation excep-
`tion.
`
`A
`Prior to the inventors’ October 1997 amendment, appli-
`cation claim 4 was broad enough to cover any bioelectrical
`blood glucose monitoring system. The October 1997
`amendment narrowed the claims to systems that convert a
`plurality of current readings to analyte concentration
`measurements and compare said analyte concentration
`measurements. The applicants thus presumptively sur-
`rendered any bioelectrical blood glucose monitoring sys-
`tems that do not convert a plurality of current readings into
`analyte concentration measurements and compare the re-
`sulting analyte concentration measurements. Pharma
`Tech’s asserted equivalent—“the functionality of a system
`that (a) measures current at two different times, (b) com-
`pares the current[s] to ensure they are within a prescribed
`percentage and (c) converts the current readings into a glu-
`cose concentration”—falls squarely within the territory be-
`tween the original claim and the amended claim.
`J.A. 1047–48.
`Resolution of the amendment-based prosecution his-
`tory estoppel issue turns on whether the inventors’ objec-
`tively apparent rationale underlying the narrowing
`amendment bore no more than a tangential relation to the
`accused LifeScan systems. See Integrated Tech., 734 F.3d
`at 1358. Resolution of the argument-based estoppel issue
`turns on whether the prosecution history evinces a clear
`and unmistakable surrender of systems that do not convert
`and compare analyte concentration measurements. See
`Conoco, 460 F.3d at 1364. Here, the inventors clearly and
`unambiguously distinguished their invention over the
`prior art based on the converting and comparing limita-
`tions added by the October 1997 amendment. We thus
`
`

`

`16
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`agree with the district court that the inventors’ remarks
`accompanying the October 1997 amendment make clear
`that the amendment was made to achieve patentability—
`and for reasons more than tangentially related to the
`equivalent at issue. The objectively apparent reason for
`the October 1997 amendment was to distinguish the inven-
`tion over prior art systems that measured and displayed a
`diffusion limiting current reading.
`The inventors consistently asserted that the Octo-
`ber 1997 amendment overcame the prior art cited by the
`examiner because the prior art did not compare analyte
`concentration measurements derived (i.e., converted) from
`diffusion limiting current readings. See, e.g., J.A. 307
`(“Kuhn is not applicable to claims 4 or 66 as now amended,
`in that obtaining a plurality of readings by taking repeated
`measurements is not the same as the multiple readings
`now claimed, wherein those readings are converted to ana-
`lyte concentration and then linearly compared to one an-
`other.” (emphasis added)); J.A. 307–08 (“Pollmann likewise
`does not suggest the present claimed means for comparing
`the concentration derived from the first measurement and
`at least one additional concentration derived from an addi-
`tional measurement to verify the result.”); J.A. 308
`(“Claims 66–69 all include the additional multiple meas-
`urement[s] . . . [that] are used to verify the result by com-
`paring concentrations determined at different times during
`the measurement. There is no teaching or suggestion in
`Pollmann or Szuminsky to verify the measurement in the
`way claimed in claim[s] 66–69.” (emphasis added)).
`The inventors’ arguments to the PTO throughout the
`remainder of the prosecution history confirm our conclu-
`sion. The inventors repeatedly and unequivocally de-
`scribed “the present invention” as “a system which takes
`two different Cottrell current readings, converts them to
`two different analyte concentration measurements, and
`then compares the two analyte concentration measure-
`ments.” J.A. 397–98. And they continually argued that
`
`

`

`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`17
`
`these features distinguished their invention over the prior
`art. For example, with respect to White, the inventors ar-
`gued: “In contrast to the teachings in White, the present in-
`vention compares analyte concentration readings at
`different times.” J.A. 378 (italics added). Distinguishing
`Walling, the inventors similarly asserted, “Walling et al
`does not convert two different Cottrell current readings to
`first and second analyte concentration measurements, and
`then compare the first and second analyte concentration
`measurements to each other, as in the present invention.”
`J.A. 398 (italics added). These same inventor statements
`establish a clear and unmistakable surrender of subject
`matter. The inventors’ remarks clearly and unambigu-
`ously indicate their view that the sequence of performing
`“converting” and “comparing” limitations was a distin-
`guishing feature of “the present invention.” See J.A. 398
`(“White (’516) differs from the present invention in the fol-
`lowing respects. First, in the present invention the two dif-
`ferent Cottrell current readings are converted into first and
`second analyte concentration measurements. Further, in
`the present invention the first and second analyte concen-
`tration measurements . . . are compared to each other.”
`(italics added)). Based on the inventors’ clear statements,
`a competitor reviewing the prosecution history of the
`’069 patent would reasonably believe that the inventors
`had surrendered systems that do not convert diffusion lim-
`iting current readings to analyte concentration measure-
`ments and
`then
`compare
`the
`resulting analyte
`concentration measurements. Accordingly, we also affirm
`the district court’s determination that argument-based
`prosecution history estoppel precludes Pharma Tech from
`asserting infringement under the doctrine of equivalents.
`Citing Pioneer Magnetics, Inc. v. Micro Linear Corp.,
`330 F.3d 1352, 1356 (Fed. Cir. 2003), Pharma Tech argues
`that the “converting” and “comparing” claim limitations
`were already disclosed in the prior art and, as such, these
`limitations must have been added for reasons not related
`
`

`

`18
`
`PHARMA TECH SOLS., INC. v. LIFESCAN, INC.
`
`to patentability. Appellant’s Br. 52. But Pioneer Magnetics
`does not support this argument. In Pioneer Magnetics, we
`held that the patentee’s narrowing amendment was “re-
`lated to patentability” and “clearly not tangential” to the
`asserted equivalent where the prior art contained the
`equivalent. 330 F.3d at 1357. That the October 1997
`amendment may have ceded more claim scope than neces-
`sary to overcome prior art does not mean that the tangen-
`tial relation exception applies here. Indeed, we have held
`that “[t]he fact that the inventors may have thought after
`the fact that they could have relied on other distinctions in
`order to defend their claims is irrelevant” to discerning the
`objective reason for their amendment. Int’l Rectifier
`Corp. v. IXYS Corp., 515 F.3d 1353, 1359 (Fed. Cir. 2008)
`(quoting Schwarz Pharma, Inc. v. Paddock Labs., Inc.,
`504 F.3d 1371, 1377 (Fed. Cir. 2007)); see also Eli Lilly &
`Co. v. Hospira, Inc., 933 F.3d 1320, 1332 (Fed. Cir. 2019)
`(“Amendments are not construed to cede only that which is
`necessary to overcome the prior art.” (citing Schwarz,
`504 F.3d at 1377)). Accordingly, we reject Pharma Tech’s
`argument based on Pioneer Magnetics.
`B
`Finally, Pharma Tech analogi