United States Court of Appeals 

for the Federal Circuit ______________________ 

G. DAVID JANG, M.D.,

Plaintiff-Appellant

v.

BOSTON SCIENTIFIC CORPORATION, SCIMED 

LIFE SYSTEMS, INC., NKA BOSTON SCIENTIFIC 

SCIMED, INC.,

Defendants-Cross-Appellants

______________________ 

2016-1275, 2016-1575

______________________ 

Appeals from the United States District Court for the 

Central District of California in No. 5:05-cv-00426-VAPMRW, Judge Virginia Anne Phillips.

______________________ 

Decided: September 29, 2017

______________________ 

 DARYL JOSEFFER, King & Spalding LLP, Washington, 

DC, argued for plaintiff-appellant. Also represented by 

JED I. BERGMAN, Kasowitz, Benson, Torres & Friedman 

LLP, New York, NY; MARCUS BARBER, DARCY L. JONES,

HEATHER KIM, JONATHAN K. WALDROP, Redwood Shores, 

CA; JEFFREY J. TONEY, PAUL GUNTER WILLIAMS, Atlanta, 

GA.
2 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

 MATTHEW WOLF, Arnold & Porter Kaye Scholer LLP, 

Washington, DC, argued for defendants-cross-appellants. 

Also represented by EDWARD HAN, JOHN NILSSON. 

______________________ 

Before PROST, Chief Judge, O’MALLEY and CHEN, Circuit 

Judges.

CHEN, Circuit Judge.

This dispute between G. David Jang, M.D. (Dr. Jang) 

and Boston Scientific Corp. and Scimed Life Systems, Inc. 

(collectively, BSC), more than a decade old, returns to us 

for a fourth time. In the latest appeal of this case involving U.S. Patent No. 5,922,021 (ʼ021 Patent) and BSC’s 

sales of several coronary stents (collectively, Express 

stent), Dr. Jang challenges the district court’s denial of 

his motion for judgment as a matter of law (JMOL) on the 

ground that no reasonable jury could have found that 

BSC’s Express stent did not literally infringe claims 1 and 

8 (the asserted claims) of the ’021 Patent. Dr. Jang also 

challenges the district court’s vacatur of the jury’s finding 

that the Express stent infringed the asserted claims 

under the doctrine of equivalents, as well as the entry of 

judgment of non-infringement in favor of BSC, on the 

ground that the district court incorrectly held that he 

failed to provide an acceptable hypothetical claim for an 

ensnarement analysis, and thereby failed to prove that 

his doctrine of equivalents theory did not ensnare the 

prior art. Dr. Jang’s appeal is accompanied by a purported cross-appeal from BSC, which assigns error to the 

district court’s holding that BSC was contractually obligated to pay royalties for past sales of the Express stent if 

it infringed the asserted claims, notwithstanding the U.S. 

Patent and Trademark Office’s (PTO) eventual cancellation of them in an ex parte reexamination. 

Because we affirm the district court’s denial of Dr. 

Jang’s motion for JMOL, its vacatur of the jury verdict of 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 3

infringement under the doctrine of equivalents, and its

entry of judgment of non-infringement, we dismiss BSC’s

cross-appeal and need not reach the arguments it raised. 

INTRODUCTION

A. The ’021 Patent

Dr. Jang is the named inventor of the ’021 Patent, 

which is generally directed to a coronary stent. A representative embodiment of the claimed stent is below.

’021 Patent fig. 9D (annotated). Inside the dotted boxes

are expansion columns made up of a plurality of pairs of 

expansion struts. The solid box outlines a connecting 

strut column made up of connecting struts. Each connecting strut has: (i) a section at the “proximal” end that 

connects to an expansion strut pair in one expansion 

column; (ii) a section at the “distal” end that connects to 

an expansion strut pair in another expansion column; and 

(iii) an intermediate section that is not parallel to the two 

end sections. See, e.g., id. col. 13 ll. 5–18, 38–48. Given 
4 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

the connecting strut’s proximal and distal connections, 

each connecting strut links expansion strut pairs from 

two expansion columns in a “peak-to-peak” configuration. 

The connecting struts are designed to increase the longitudinal flexibility of the stent. See id. col. 6 ll. 29–36; id.

col. 8 ll. 45–47. 

Independent claim 1 is representative of the asserted 

claims:

1. A stent in a non-expanded state, comprising:

a first expansion strut pair including a first expansion strut positioned adjacent to a second expansion strut and a joining strut of the first

expansion strut pair that couples the first and 

second expansion struts at a distal end of the first 

expansion strut pair, a plurality of the first expansion strut pair forming a first expansion column; 

a second expansion strut pair including a first expansion strut positioned adjacent to a second expansion strut and a joining strut of the second 

expansion strut pair that couples the first and 

second expansion struts of the second expansion 

strut pair at a proximal end of the second expansion strut pair, a plurality of the second expansion 

strut pair forming a second expansion column; 

a first connecting strut including a first connecting strut proximal section, a first connecting strut 

distal section and a first connecting strut intermediate section, the first connecting strut proximal section being coupled to the distal end of the 

first expansion strut pair in the first expansion 

column and the first connecting strut distal section being coupled to the proximal end of the second expansion strut pair of the second expansion 

column, a plurality of the first connecting strut 

forming a first connecting strut column that cou-
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 5

ples the first expansion column to the second expansion column, the first connecting strut intermediate section being nonparallel to the first 

connecting strut proximal and distal sections, 

wherein the first expansion strut of the first expansion strut pair in the first expansion column 

has a longitudinal axis offset from a longitudinal 

axis of the first expansion strut of the second expansion strut pair in the second expansion column.

Id. col. 18 ll. 9–40 (emphases added).1 

B. BSC’s Express Stent

The Express stent comprises two types of alternating 

columns or “elements”—referred to as “macroelements” 

and “microelements”—that are joined together. Microelements, depicted inside the box in the schematic below, 

are smaller and narrower than the macroelements on 

either side of the microelements. The microelements 

include horizontal bars that join the microelements and 

the macroelements together in a “peak-to-valley” configuration. 

 

1 As our previous opinion recognized, the PTO cancelled asserted claims 1 and 8 on February 11, 2014 in a 

second ex parte reexamination. Jang v. Boston Sci. Corp., 

767 F.3d 1334 (Fed. Cir. 2014). Because we affirm the 

district court’s non-infringement determination, and 

therefore need not address BSC’s cross appeal, the PTO’s 

cancellation of claims 1 and 8 has no bearing in our 

decision.

JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 7

2013, BSC requested an ex parte reexamination of the 

asserted claims before the PTO. 

In conjunction with its reexamination request, BSC 

sought leave to amend its answer to include invalidity 

defenses, under the theory that the assignment agreement should be interpreted so as to relieve BSC of any 

obligation to pay royalties for already-made sales of its 

Express stent, if the asserted claims were determined to 

be invalid or unpatentable. See J.A. at 6091. The district 

court denied BSC leave to amend, deeming any invalidity 

defenses “irrelevant” as to whether BSC owed Dr. Jang 

royalties for past sales under the terms of the assignment 

agreement. Id. The district court reasoned that BSC’s 

interpretation of the assignment agreement “would lead 

to an absurd result, namely, that BSC could avoid payment . . . under the [a]greement, even if the [’021 Patent] 

[were] declared invalid years after the [royalty] payments 

were due.” Id. 

BSC then moved for summary judgment using the 

same tack after the PTO cancelled the asserted claims as 

unpatentable in the ex parte reexamination. See id. at 

50–56. BSC contended that it owed Dr. Jang no royalties 

under the assignment agreement even if they had accrued 

well before the cancellation because unpatentable claims 

cannot be infringed. See id. at 50. The district court 

denied summary judgment, holding that BSC still owed

royalties to Dr. Jang for any past sales of stents covered 

by the asserted claims under the assignment agreement, 

despite the PTO’s subsequent cancellation of those claims. 

See id. at 50–56. 

The parties then proceeded to trial as to whether the 

Express stent infringed the asserted claims of the ’021 

Patent. Before trial, BSC moved in limine to preclude Dr. 

Jang from presenting a doctrine of equivalents theory to 

the jury, accusing him of merely rehashing his literal 

infringement theory in the guise of a doctrine of equiva-
8 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

lents theory, and thus, failing to provide particularized 

testimony as to how the Express stent is insubstantially 

different than the asserted claims. See id. at 66–69. The 

district court denied the motion, finding that Dr. Jang’s 

experts, Michael J. Lee and Nicolas A.F. Chronos, M.D.,

sufficiently explained his doctrine of equivalents theory in

their expert reports. See id. at 68–69. 

Collateral to this motion in limine was BSC’s invocation of an ensnarement defense. See id. at 9–12. BSC 

insisted that Dr. Jang’s doctrine of equivalents theory

would ensnare the prior art, referencing three prior art 

patents. See id. at 11. The district court decided to

conduct a post-trial ensnarement hearing, if the jury 

returned a verdict of infringement under the doctrine of 

equivalents. See id. at 12207.

The jury ultimately found no literal infringement, but 

found infringement under the doctrine of equivalents. 

Following through on its earlier decision, the district 

court conducted an evidentiary hearing on ensnarement. 

Dr. Jang objected, asserting that BSC belatedly raised

ensnarement, and thus waived it. See id. at 9–12; see also

id. at 34. The district court found no waiver. See id. at 9–

12. 

On the merits of the ensnarement inquiry, Dr. Jang 

elected to use a hypothetical claim analysis to establish a 

range of equivalents to which he believed he was entitled, 

above and beyond the actual scope of his asserted claims. 

See id. at 12–19. In other words, he attempted to construct a hypothetical claim—predicated on representative 

claim 1—that would be broad enough to literally cover 

BSC’s Express stent, yet not so broad that it would be

unpatentable over the prior art. See, e.g., Intendis GmbH 

v. Glenmark Pharm. Inc., USA, 822 F.3d 1355, 1363–64 

(Fed. Cir. 2016). In the course of trying to draft such a 

hypothetical claim, Dr. Jang constructed approximately 

ten different claims, and ultimately chose to assert two of 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 9

them: hypothetical claim three and hypothetical claim 

five. See J.A. at 14–19. The district court concluded, 

however, that Dr. Jang failed, as a threshold matter, to 

draft a proper hypothetical claim for the ensnarement 

analysis. See id. The district court rejected hypothetical 

claim three because it impermissibly narrowed claim 1

and hypothetical claim five because it failed to broaden 

claim 1 at all. See id. Because Dr. Jang did not meet his 

burden of persuasion, which includes providing a proper 

hypothetical claim that does not ensnare the prior art, the 

district court vacated the jury verdict of infringement 

under the doctrine of equivalents and entered judgment of 

non-infringement in favor of BSC. See id. at 18–19. 

Dr. Jang then moved for JMOL with respect to, inter 

alia, literal infringement. See id. at 23–32. The district 

court found substantial evidence to support the jury’s 

verdict of no literal infringement, concluding that the jury 

could have reasonably found either that the Express 

stent’s microelements corresponded to the claimed expansion columns rather than the claimed connecting strut 

columns or that the Express stent’s macroelement (first 

expansion column) was connected to the microelement 

(second expansion column) in a “peak-to-valley” configuration instead of a “peak-to-peak” configuration. See id. at 

27. Dr. Jang also moved for a new trial, asserting several 

bases, all of which the district court rejected. See id. at 

33–35. 

Dr. Jang appeals the district court’s denial of his 

JMOL for literal infringement, as well as his motion for a 

new trial, and its vacatur of the jury verdict of infringement under the doctrine of equivalents. BSC purports to 

cross-appeal the district court’s denial of its summary 

judgment motion. We have jurisdiction over Dr. Jang’s 

appeal pursuant to 28 U.S.C. § 1295 (a)(1) (2012). 
10 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

DISCUSSION

A. Literal Infringement

The parties do not dispute that the Express stent’s 

macroelements literally meet all expansion columnrelated limitations of claim 1, leaving them to contest only 

whether the jury had a reasonable basis to find that the 

Express stent’s microelements do not meet all connecting 

strut-related limitations in the claim. Dr. Jang maintains

that a reasonable jury could not have found no literal 

infringement in this limited context because the undisputed facts showed otherwise and BSC’s noninfringement arguments were legally erroneous. At the 

very least, according to Dr. Jang, he is entitled to a new 

trial that is not tainted with the legally erroneous arguments. We disagree with Dr. Jang’s arguments. 

Denials of motions for JMOL or a new trial are reviewed according to the law of the regional circuit—here, 

the Ninth Circuit. See, e.g., TVIIM, LLC v. McAfee, Inc., 

851 F.3d 1356, 1362 (Fed. Cir. 2017). A district court’s 

denial of a motion for JMOL is reviewed de novo. See, 

e.g., id. (citing Harper v. City of Los Angeles, 533 F.3d 

1010, 1021 (9th Cir. 2008)). A grant of a motion for JMOL 

is proper only when “the evidence, construed in the light 

most favorable to the nonmoving party, permits only one 

reasonable conclusion, and that conclusion is contrary to 

that of the jury.” White v. Ford Motor Co., 312 F.3d 998, 

1010 (9th Cir. 2002) (quoting Forrett v. Richardson, 112 

F.3d 416, 419 (9th Cir. 1997)). That is, the district court 

must uphold a jury’s verdict “if it is supported by substantial evidence, which is evidence adequate to support the 

jury’s conclusion, even if it is also possible to draw a 

contrary conclusion.” Harper, 533 F.3d at 1021 (quoting 

Pavao v. Pagay, 307 F.3d 915, 918 (9th Cir. 2002)). Substantial evidence is “such relevant evidence as a reasonable mind might accept as adequate to support a 

conclusion.” Theme Promotions, Inc. v. News Am. Mktg. 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 11

FSI, 546 F.3d 991, 1000 (9th Cir. 2008) (quoting Syufy 

Enters. v. Am. Multicinema, Inc., 793 F.2d 990, 992 (9th 

Cir. 1986)).

The Ninth Circuit reviews the denial of a motion for a 

new trial for abuse of discretion. Incalza v. Fendi N. Am., 

Inc., 479 F.3d 1005, 1013 (9th Cir. 2007). It reverses the 

denial only if the record lacks any evidence supporting the 

verdict or if the district court made a mistake of law. 

Molski v. M.J. Cable, Inc., 481 F.3d 724, 729 (9th Cir. 

2007).

Dr. Jang contends that the district court erred in 

denying his motion for JMOL because it failed to consider 

whether Dr. Jang proved that the Express stent’s microelements were connecting strut columns, notwithstanding 

the fact that they may also be expansion columns. In 

other words, that there was sufficient evidence for the 

jury to find that the Express stent’s microelements were 

expansion columns is irrelevant to the resolution of his 

motion for JMOL, Dr. Jang argues, so long as he showed 

that the microelements were connecting strut columns. 

See Appellant Br. at 55 (“If the [microelements] satisfy 

the claim terms of a connecting-strut column, then they 

are connecting-strut columns for literal infringement 

purposes, regardless of whether they might also be considered something else (such as expansion columns).”). 

Dr. Jang also maintains that the district court erred in 

denying his motion for JMOL because BSC’s arguments 

rest on legally erroneous premises and so they cannot 

support the jury’s verdict of no literal infringement. 

The issue of literal infringement was a question of 

fact for the jury. The jury heard Dr. Jang’s theory of 

infringement and his supporting evidence but nevertheless found that the Express stent did not literally infringe. 

The district court did not fail to consider Dr. Jang’s theory 

of infringement and it correctly found substantial evidence to support the jury’s finding that the Express 
12 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

stent’s microelements do not literally meet the connecting-strut-column-related limitations in claim 1. See J.A. 

at 25–28. BSC’s expert, James Moore, Ph.D., testified 

that the Express stent’s macroelements and the microelements were more akin to the claimed expansion columns than the claimed connecting strut columns in the 

asserted claims because both elements expand the Express stent when needed, which causes foreshortening of 

the stent. See id. at 9330–43, 9389–90. These elements

stood in contrast to the claimed connecting strut columns

that do not expand when the claimed stent expands, and 

instead, compensate for the foreshortening caused by the

expansion of the claimed expansion columns. See id. 

Moreover, the Express stent’s macroelements and microelements are joined together in a “peak-to-valley” configuration by a connecting strut with a parallel intermediate 

section, i.e., a straight, horizontal connector—as opposed 

to the claimed expansion columns that are joined in a 

“peak-to-peak” configuration by a connector with a nonparallel intermediate section.3 See id. Dr. Jang’s experts 

conceded as much. See id. at 8877–79 (Mr. Lee acknowledging that the Express stent’s microelements could be

expansion columns); id. at 8869–73 (Mr. Lee recognizing 

that the Express stent’s microelements and macroelements could be viewed as being joined by straight connectors); id. at 9260–61 (Dr. Chronos acknowledging that 

the Express stent’s microelements behave like expansion 

columns); id. at 9284–85 (Dr. Chronos recognizing that if 

the Express stent’s microelements and macroelements are 

viewed as expansion columns, then they are joined by a 

straight connector). The jury’s verdict of no literal infringement, therefore, is supported by substantial evidence.

 

3 Despite the fact that the asserted claims do not 

use the term “peak-to-peak,” the parties agree that this is 

an inherent limitation of the asserted claims. 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 13

Dr. Jang failed to persuade the district court that 

BSC’s non-infringement arguments were legally erroneous. We are similarly unpersuaded. Dr. Jang characterizes BSC’s position as one of mutual exclusivity and 

argues that this purported “‘either/or’ position effectively 

imported a negative limitation into the definition of 

‘connecting strut column.’” Appellant Reply Br. at 33. Dr. 

Jang misrepresents BSC’s non-infringement arguments. 

BSC did not argue, as Dr. Jang contends, that microelements could only be deemed either exclusively expansion 

columns or exclusively connecting strut columns. Rather, 

BSC fairly argued at trial that the microelements, like the 

macroelements, simply are expansion columns. J.A. at 

8413–14, 10573. In particular, BSC argued that there 

was no literal infringement because those two expansion 

columns are joined by straight connectors in a peak-tovalley configuration. Id. at 10570, 11366. 

Dr. Jang also contends that BSC misled the jury to 

find no literal infringement because BSC told the jury 

that the Express stent’s microelements could not be the 

claimed connecting strut columns due to the presence of 

“extra metal” in the microelements that is not recited in 

the asserted claims. This was erroneous according to Dr. 

Jang because the asserted claims use the transitional 

phrase “comprising,” i.e., open-ended claim language, and 

so the addition of “extra metal” in the Express stent

cannot preclude a finding of literal infringement. But this

was not one of BSC’s non-infringement positions at trial. 

To the extent that BSC introduced this “extra metal” 

concept to the jury, BSC did so, not as an alternative noninfringement position, but as an explanation that Dr. 

Jang’s experts ignored certain structural features of the 

Express stent in their infringement analyses, thereby 

undermining the strength of their testimony on whether 

the microelements were connecting strut columns. See id.

at 9343, 10579–80. 
14 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

In sum, a reasonable jury could have returned a verdict of no literal infringement based on the evidence 

presented at trial. We consequently have no basis to 

order a new trial. 

B. Ensnarement in View of a Hypothetical Claim

In an appeal relating to the doctrine of equivalents, a 

party often challenges the fact finding made below of 

infringement (or no infringement) under that doctrine, 

which is usually analyzed under the well-established 

“substantially the same function-way-result” or “insubstantial differences” inquiry. Here, however, the jury’s 

finding that the Express stent satisfies each claim element of the asserted claims under the doctrine of equivalents is not on appeal. Instead, this appeal centers on the 

district court’s application of a limitation on the reach of 

the doctrine, known as “ensnarement.” 

Dr. Jang insists that the district court erred in several 

respects in overturning the jury’s verdict of infringement 

under the doctrine of equivalents based on BSC’s ensnarement defense. Dr. Jang argues that his hypothetical 

claims three and five are properly broader in scope than 

representative claim 1, and if they were flawed, the 

district court was required to proceed with an ensnarement analysis, even if that meant the district court would 

have to devise an acceptable hypothetical claim for Dr. 

Jang that was broader in scope than representative claim 

1. Dr. Jang is wrong on both counts. 

A doctrine of equivalents theory cannot be asserted if 

it will encompass or “ensnare” the prior art. DePuy Spine, 

Inc. v. Medtronic Sofamor Danek, Inc., 567 F.3d 1314, 

1322 (Fed. Cir. 2009). “This limitation is imposed even if 

a jury has found equivalence as to each claim element.” 

Id. at 1323 (citing Wilson Sporting Goods Co. v. David 

Geoffrey & Assocs., 904 F.2d 677, 683, 687 (Fed. Cir. 

1990), overruled in part on other grounds, Cardinal Chem. 

Co. v. Morton Int’l, Inc., 508 U.S. 83, 92 n.12 (1993)). A 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 15

“[h]ypothetical claim analysis is a practical method to 

determine whether an equivalent would impermissibly 

ensnare the prior art.”4 Intendis, 822 F.3d at 1363–64 

(citing Ultra-Tex Surfaces, Inc. v. Hill Bros. Chem. Co., 

204 F.3d 1360, 1364 (Fed. Cir. 2000)). We have explained: 

Hypothetical claim analysis is a two-step process. 

The first step is “to construct a hypothetical claim 

that literally covers the accused device.” Next, 

prior art introduced by the accused infringer is 

assessed to “determine whether the patentee has 

carried its burden of persuading the court that the 

hypothetical claim is patentable over the prior 

art.” In short, [the court] ask[s] if a hypothetical 

claim can be crafted, which contains both the literal claim scope and the accused device, without 

ensnaring the prior art. 

Id. at 1363 (quoting DePuy, 567 F.3d at 1324, 1325); see 

also Ultra-Tex Surfaces, 204 F.3d at 1364–65 (“Under a 

hypothetical claim analysis, a patentee proposes a hypothetical claim that is sufficiently broad in scope to literally

encompass the accused product or process. If that claim 

would have been allowed by the PTO over the prior art, 

then the prior art does not bar the application of the 

doctrine of equivalents.” (citations omitted)). “The burden 

of producing evidence of prior art to challenge a hypothetical claim rests with an accused infringer, but the burden 

 

4 The hypothetical claim analysis is not the only 

method in which a district court can assess whether a

doctrine of equivalents theory ensnares the prior art. See

Conroy v. Reebok Int’l, Ltd., 14 F.3d 1570, 1576–77 (Fed. 

Cir. 1994); Int’l Visual Corp. v. Crown Metal Mfg. Co., 991 

F.2d 768, 772 (Fed. Cir. 1993). We note that Dr. Jang 

never asked the district court to assess the scope of his 

doctrine of equivalents theory using a method other than 

the hypothetical claim analysis. 
16 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

of proving patentability of the hypothetical claim rests 

with the patentee.”5 Interactive Pictures Corp. v. Infinite 

Pictures, Inc., 274 F.3d 1371, 1380 (Fed. Cir. 2001) (citing

Streamfeeder, LLC v. Sure-Feed, Inc., 175 F.3d 974, 984 

(Fed. Cir. 1999)). “We review a district court’s conclusion 

that a hypothetical claim does not encompass the prior art 

de novo and resolution of underlying factual issues for 

clear error.” Intendis, 822 F.3d at 1363 (citing DePuy, 567 

F.3d at 1324). 

The district court correctly concluded that Dr. Jang’s 

hypothetical claims three and five were flawed and 

properly declined to conduct any hypothetical claim 

analysis as a result. See J.A. at 12–19. Dr. Jang’s hypothetical claim three reads: 

the first connecting strut intermediate section be

ing non parallel to the first connecting strut prox

imal and distal sections column configured to 

provide increased flexibility compared to the first 

and second expansion columns. 

Id. at 14 (strikethrough and emphasis to reflect amendments to claim 1).6 Although hypothetical claim three is 

broader than claim 1 by deleting the non-parallel intermediate section limitation (thereby encompassing connecting struts with a parallel intermediate section), it also 

 

5 We have described the ensnarement inquiry as 

one of determining the patentability of the hypothetical 

claim, rather than its validity. That is because “[t]he 

pertinent question” is “whether that hypothetical claim 

could have been allowed by the PTO over the prior art” as 

the PTO has never actually issued it. Wilson Sporting 

Goods, 904 F.2d at 684.

6 We will not recite the other limitations of claim 1 

that remain unchanged in Dr. Jang’s hypothetical claims 

three and five. 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 17

is narrower by adding the requirement that the connecting strut column must provide more flexibility as compared to the expansion columns. Our precedent has been 

clear, however, that a patentee’s hypothetical claim may 

not add any narrowing limitations. See Streamfeeder, 175 

F.3d at 983 (“While use of a hypothetical claim may 

permit a minor extension of a claim to cover subject 

matter that is substantially equivalent to that literally 

claimed, one cannot, in the course of litigation and outside 

of the PTO, cut and trim, expanding here, and narrowing 

there, to arrive at a claim that encompasses an accused 

device, but avoids the prior art. Slight broadening is 

permitted at that point, but not narrowing.”). Whereas 

claim 1 previously covered embodiments where the connecting strut column has the same or lesser degree of 

flexibility when compared to the first and second expansion columns, hypothetical claim three narrows claim 1 

so that the connecting strut column must have an increased degree of flexibility when compared to the first 

and second expansion columns. See J.A. at 16. The 

district court thus correctly rejected Dr. Jang’s hypothetical claim three. 

Dr. Jang contends that the combination of the added

comparative flexibility limitation with the deletion of the 

non-parallel intermediate section limitation results in an 

overall broader claim scope than claim 1, because, in his 

view, the comparative flexibility limitation recites the 

function that the non-parallel intermediate section of the 

connecting strut is designed to achieve. In other words, 

Dr. Jang argues that he simply is replacing a structural 

limitation for a functional limitation that encompasses 

the structural limitation, as well as all other structures 

that perform that function. But this argument is problematic because nothing in the ’021 Patent or elsewhere

in the record indicates that the claimed connecting strut 

columns provide increased flexibility in comparison to the

claimed expansion columns. Although the specification 
18 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

explains that the connecting strut columns improve a 

particular form of flexibility (i.e., longitudinal) of the stent 

as a whole, see ’021 Patent col. 6 ll. 29–36; id. col. 8 ll. 45–

47, it never discusses the flexibility of the connecting strut 

columns vis-à-vis the expansion columns. We thus cannot 

agree with Dr. Jang that the limitation he added in 

hypothetical claim three is merely a broader version of 

the limitation he deleted from claim 1.

As for Dr. Jang’s hypothetical claim five, it reads: 

a first connecting strut including at least a first 

connecting strut proximal section, a first connecting strut distal section and a first connecting strut 

intermediate section[.]

J.A. at 17 (emphasis to reflect amendment to claim 1). 

This hypothetical claim does not broaden claim 1 at all. 

Claim 1 already uses the transitional phrase “comprising” 

to establish an open-ended claim. See, e.g., Vehicular 

Techs. Corp. v. Titan Wheel Int’l, Inc., 212 F.3d 1377, 

1383–84 (Fed. Cir. 2000) (“A drafter uses the term ‘comprising’ to mean ‘I claim at least what follows and potentially more.’”). Thus, the addition of “at least” to

hypothetical claim five is redundant with claim 1’s recitation of “comprising.” In short, hypothetical claim five and 

claim 1 have the same claim scope. 

Following Dr. Jang’s troubles in drafting a proper 

hypothetical claim that encompassed the Express stent

yet was also patentable in the face of seemingly crowded 

prior art (a venture that began with generating approximately ten different hypothetical claims), the district 

court was under no obligation to undertake a hypothetical 

claim analysis on his behalf. A patentee, like Dr. Jang, 

bears the burden of proving that it is entitled to “the 

range of equivalents which it seeks.” Wilson Sporting 

Goods, 904 F.2d at 685. And, when utilizing the hypothetical claim tool, that burden starts with proposing a 

proper hypothetical claim that only broadens the issued 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 19

asserted claims. See Streamfeeder, 175 F.3d at 983. Dr. 

Jang cannot effectively transfer the responsibility of 

defining the range of equivalents to which he is entitled to 

the district court.7 See Ultra-Tex Surfaces, 204 F.3d at 

1364 (“Under a hypothetical claim analysis, a patentee 

proposes a hypothetical claim . . . .” (emphasis added)). 

Because, as a threshold matter, Dr. Jang failed to submit 

a proper hypothetical claim for consideration, he was 

unable to meet his burden of proving that his doctrine of 

equivalents theory did not ensnare the prior art. The 

district court thus correctly vacated the jury verdict of 

infringement under the doctrine of equivalents. 

Failing on the merits, Dr. Jang turns to several purported procedural infirmities in the district court’s handling of BSC’s ensnarement defense. Dr. Jang specifically 

argues that BSC waived its ensnarement defense because: 

(1) BSC failed to raise the defense in a motion for either 

summary judgment or JMOL; (2) the defense was a proxy 

for invalidity defenses that were excluded by the district 

court earlier in the case; (3) BSC’s belated notice to Dr. 

Jang of the defense was prejudicial because it deprived 

him of any pre-trial discovery related to the defense; and 

(4) the defense was never listed in the pretrial order as 

required by Ninth Circuit law. We address each of these 

unpersuasive arguments in turn. 

 

7 In Streamfeeder, after we rejected the patentee’s 

hypothetical claim for impermissibly narrowing the 

patent claim in one respect while also broadening it in 

another, we additionally explained why a proper hypothetical claim in that case—one without the narrowing 

limitation—was unpatentable over the prior art. See 175 

F.3d at 983–84. Nothing in Streamfeeder, however, 

requires courts to engage in this additional inquiry when 

the patentee fails to come forward with a proper hypothetical claim.
20 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

First, Dr. Jang argues that in DePuy we held that

ensnarement must be raised in a motion for either summary judgment or JMOL. See Appellant Br. at 30 (citing 

DePuy, 567 F.3d at 1324). But that is an unduly narrow 

reading of DePuy. We considered in that case whether 

ensnarement is a factual question that must be tried to 

the jury. 567 F.3d at 1323. To answer that question, we 

turned to precedent, which has treated ensnarement and 

prosecution history estoppel on equal footing. See id.

(“We have called ensnarement and prosecution history 

estoppel, collectively, ‘two policy oriented limitations’ on 

the doctrine of equivalents, both of which are ‘applied as 

questions of law.’” (quoting Loctite Corp. v. Ultraseal Ltd.,

781 F.2d 861, 870 (Fed. Cir. 1985), overruled in part on 

other grounds, Nobelpharma AB v. Implant Innovations, 

Inc., 141 F.3d 1059, 1068 (Fed. Cir. 1998) (en banc)). 

Because prosecution history estoppel was a legal question

for a district court to consider, we concluded that ensnarement was one as well. See id. (“We see no reason 

why ensnarement should be treated differently, for procedural purposes, than prosecution history estoppel.”). We 

held that 

[E]nsnarement, like prosecution history estoppel, 

is “to be determined by the court, either on a pretrial motion for partial summary judgment or on a 

motion for judgment as a matter of law at the 

close of the evidence and after the jury verdict.” 

As a practical matter, both legal limitations may 

be readily addressed in the same set of motions. 

Id. at 1324 (quoting Warner-Jenkinson Co. v. Hilton Davis 

Chem. Co., 520 U.S. 17, 39 n.8 (1997)). Our “holding” in 

DePuy was not that these two motions were the only 

vehicles by which to raise ensnarement. Instead, when 

read in context, DePuy is most fairly understood as holding that ensnarement is a legal question for the district 

court to decide and that the district court could, but did 

not have to, decide that question through particular types 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 21

of motions. See id. This is especially so because the 

district court in DePuy conducted a separate ensnarement 

proceeding after a jury verdict of infringement under the 

doctrine of equivalents, just as the district court did here. 

See id. at 1321–22. We see nothing legally unsound in 

BSC raising ensnarement through its pretrial motion in 

limine, and the district court conducting a post-trial 

hearing on the defense contingent on an infringement 

verdict under the doctrine of equivalents. Moreover, 

based on a review of the record, we are satisfied that Dr. 

Jang received sufficient notice of BSC’s ensnarement 

argument.

Second, Dr. Jang argues that the district court should 

have barred BSC from presenting its ensnarement defense as a matter of law because BSC was not allowed to

challenge the validity of the asserted claims. Allowing 

BSC to repackage previously-excluded invalidity defenses 

in the guise of an ensnarement defense, he argues, is a 

“camouflaged or back-handed attack” on the validity of 

the asserted claims and effectively an end run around the 

right to a jury trial on validity. See Appellant Br. at 47, 

50 (quoting Thomas & Betts Corp. v. Litton Sys., Inc., 720 

F.2d 1572, 1580 (Fed. Cir. 1983)). 

We are unpersuaded by Dr. Jang’s attempt to conflate 

two different concepts. We have explained before that 

“[t]he ensnarement inquiry . . . has no bearing on the 

validity of the actual claims” asserted in a case. DePuy, 

567 F.3d at 1323 (citing Wilson Sporting Goods, 904 F.2d 

at 685). And that is because ensnarement concerns 

patentability with respect to a hypothetical patent claim 

as opposed to the validity of an actual patent claim. See

Wilson Sporting Goods, 904 F.2d at 685 (“Leaving this 

burden [of proving that the range of equivalents sought 

does not ensnare the prior art] on [the patentee] does not, 

of course, in any way undermine the presumed validity of 

[its] actual patent claims. In the present situation, [the 

patentee’s] claims will remain valid whether or not [it]
22 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

persuades us that it is entitled to the range of equivalents 

sought here.”). Thus, the fact that BSC could not pursue 

a validity challenge of the asserted claims in this litigation does not somehow mandate that it is likewise barred 

from challenging a necessarily-broader set of newlyminted, hypothetical claims. 

Dr. Jang’s reliance on Thomas & Betts is misplaced. 

There, we stated that “[w]here [the] validity [of a patent]

in view of the prior art has not been challenged, the

[district] court is less free to limit the application of the 

doctrine of equivalents than where invalidity is specifically urged . . . .” 720 F.2d at 1580. That observation about 

the relative application of the doctrine of equivalents in 

two different factual scenarios, however, is not a license 

for a patentee to obtain a range of equivalents that ensnares the prior art, even if an alleged infringer does not 

challenge the validity of the underlying patent claims. 

See Wilson Sporting Goods, 904 F.2d at 684. 

Third, Dr. Jang was not prejudiced by any lack of pretrial discovery as to ensnarement. The district court 

ruled that Dr. Jang could proceed with a doctrine of

equivalents theory at trial only shortly before it started. 

See J.A. at 68–69. It also alerted the parties during this 

time frame that it would conduct an ensnarement hearing 

if the jury returned a verdict of infringement under the 

doctrine of equivalents. Id. at 12207 (post-verdict Minute 

Order: “After directing the [c]lerk to enter the jury’s 

verdict into the record, the [district court] reminded 

counsel for both parties of its prior ruling that in the event 

the jury found in favor of [p]laintiff under the doctrine of 

equivalents theory, it would proceed with an evidentiary 

hearing on the issue of ensnarement.” (emphasis added)). By then there was little to no time to reopen discovery, let alone a motion by Dr. Jang to do so, which could 

have resulted in a waste of the party’s resources and 

disrupted the district court’s case management, had the 

jury not returned a verdict of infringement under the 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 23

doctrine of equivalents. In between the jury’s verdict and 

the ensnarement hearing, the parties had “three weeks to 

develop evidence, expert opinion, and argument . . . [on 

the ensnarement] defense.” Appellant Br. at 34. Each 

party was presumably on a level playing field when they 

arrived at the hearing. If Dr. Jang deemed otherwise, he 

could have moved the district court for an enlargement of 

time to conduct additional discovery on the defense. 

Fourth and finally, Dr. Jang argues that “Ninth Circuit law is clear that any defense not listed in the 

[p]retrial [o]rder is waived,” and that because ensnarement was not listed in the pretrial order, the defense was 

waived. Appellant Br. at 31–32 (citing Pierce Cty. Hotel 

Emps. & Rest. Emps. Health Tr. v. Elks Lodge, 827 F.2d 

1324, 1329 (9th Cir. 1987); United States v. First Nat’l 

Bank of Circle, 652 F.2d 882, 886 (9th Cir. 1981)). But 

this puts the cart before the horse. Dr. Jang has not

adequately articulated why proper preservation of ensnarement required its explicit mention in the pretrial 

order. The pretrial order governs trial, see, e.g., Fed. R. 

Civ. P. 16(e), but ensnarement is a legal question for the 

district court to decide, and the district court here notified 

the parties before trial that it would resolve that question, 

if necessary, outside of the trial, see J.A. at 12207. We see 

no reason why the district court should have mentioned 

ensnarement or the contingent post-trial hearing on

ensnarement in the pretrial order under these circumstances. 

In sum, the district court permissibly conducted a 

post-trial ensnarement hearing after finding that BSC 

timely raised the defense, and it appropriately vacated 

the jury verdict of infringement under the doctrine of 

equivalents and entered judgment of non-infringement for 

BSC when Dr. Jang failed to demonstrate through a 

proper hypothetical claim analysis that his doctrine of 

equivalents theory did not ensnare the prior art. 
24 JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 

C. Cross-Appeal

BSC cross-appeals the denial of its motion for summary judgment, in which the district court held that it 

owed royalties to Dr. Jang, if the Express stent were 

covered by the asserted claims, notwithstanding the 

PTO’s eventual cancellation of those claims. We dismiss 

the cross-appeal because it does not seek to enlarge the 

district court’s judgment of non-infringement in its favor. 

Instead, the cross-appeal merely offers an alternative 

basis to affirm the judgment. See Howmedica Osteonics 

Corp. v. Wright Med. Tech., Inc., 540 F.3d 1337, 1343 n.2 

(Fed. Cir. 2008) (dismissing “cross-appeal as improper 

because it did not seek to enlarge the judgment but merely asserted an alternative ground to affirm the judgment”); see also Symantec Corp. v. Computer Assocs. Int’l, 

Inc., 522 F.3d 1279, 1294–95 (Fed. Cir. 2008). When an 

improper cross-appeal is dismissed, we may nonetheless 

consider the arguments raised as alternative grounds for 

sustaining the judgment. Symantec, 522 F.3d at 1294. 

Because we affirm the district court’s judgment on other 

grounds, we need not do so here. 

CONCLUSION

Based on the foregoing analyses, the district court 

correctly denied Dr. Jang’s motion for JMOL of literal 

infringement of claims 1 and 8 of the ’021 Patent as 

substantial evidence supported the jury’s verdict of no 

literal infringement. The district court properly vacated 

the jury’s finding of infringement under the doctrine of 

equivalents because it correctly concluded that Dr. Jang 

did not meet his burden of proving that his doctrine of 

equivalents theory did not ensnare the prior art as he 

failed to draft a proper hypothetical claim. The district 

court consequently entered judgment of non-infringement

in favor of BSC, and we affirm that entry of judgment. 

We dismiss the cross-appeal and need not reach the 

arguments it raised. 
JANG v. BOS. SCI. CORP. & SCIMED LIFE SYS., INC. 25

AFFIRMED.

COSTS

No costs.