       NOTE: This disposition is nonprecedential.


  United States Court of Appeals
      for the Federal Circuit
                ______________________

              PURDUE PHARMA L.P.,
                   Appellant

                           v.

                  DEPOMED, INC.,
                       Appellee
                ______________________

           2015-2029, 2015-2030, 2015-2032
               ______________________

   Appeals from the United States Patent and Trade-
mark Office, Patent Trial and Appeal Board in Nos.
IPR2014-00377, IPR2014-00378, IPR2014-00379.
                ______________________

               Decided: March 24, 2016
               ______________________

   GREGORY A. CASTANIAS, Jones Day, Washington, DC,
argued for appellant. Also represented by JENNIFER
LORAINE SWIZE; JOHN JOSEPH NORMILE, JR., GASPER
LAROSA, LISAMARIE LOGIUDICE, New York, NY; ISRAEL
SASHA MAYERGOYZ, Chicago, IL.

    PAUL J. ANDRE, Kramer Levin Naftalis & Frankel
LLP, Menlo Park, CA, argued for appellee. Also repre-
sented by LISA KOBIALKA, HANNAH YUNKYUNG LEE.
                ______________________
2                     PURDUE PHARMA L.P.   v. DEPOMED, INC.



    Before PROST, Chief Judge, NEWMAN and LOURIE,
                    Circuit Judges.
LOURIE, Circuit Judge.
     Purdue Pharma L.P. (“Purdue”) appeals from the final
written decisions of the United States Patent and Trade-
mark Office (“PTO”) Patent Trial and Appeal Board (“the
Board”) affirming the patentability of all of the challenged
claims of U.S. Patent 6,340,475 (“the ’475 patent”) and
U.S. Patent 6,635,280 (“the ’280 patent”) in three related
inter partes review proceedings. See Purdue Pharma L.P.
v. Depomed, Inc., No. IPR2014-00377, 2015 WL 4150832
(P.T.A.B. July 8, 2015) (“Purdue I”); Purdue Pharma L.P.
v. Depomed, Inc., No. IPR2014-00378, 2015 WL 4150833
(P.T.A.B. July 8, 2015) (“Purdue II”); Purdue Pharma L.P.
v. Depomed, Inc., No. IPR2014-00379, 2015 WL 4150834
(P.T.A.B. July 8, 2015) (“Purdue III”). Because the Board
did not err in determining that Purdue, the petitioner,
failed to prove that the challenged claims are unpatenta-
ble as obvious over the cited prior art, we affirm.
                       BACKGROUND
     Depomed, Inc. (“Depomed”) owns the ’475 and ’280 pa-
tents, which share the same specification in relevant part,
and are both directed to a controlled-release oral dosage
form of a soluble drug and a method of use thereof. The
claimed dosage form comprises a solid matrix of polymers
with the drug dispersed therein. After dosing orally, the
polymeric matrix swells as a result of imbibition of water
to promote its retention in the stomach during the fed
state, viz., in the presence of food, and remains substan-
tially intact when the drug is released in the stomach.
Accordingly, the claimed dosage form allows a soluble
drug to be administered orally in a way that prolongs its
release. That prolonged release reduces the risk of tran-
sient overdosing and controls the drug dosage to safer and
more effective levels over an extended period of time.
PURDUE PHARMA L.P.   v. DEPOMED, INC.                      3


     In 2013, Depomed sued Purdue in the United States
District Court for the District of New Jersey, alleging
infringement of the ’475 and ’280 patents. Purdue then
filed three petitions at the PTO requesting inter partes
review of the asserted claims on grounds that those
claims are unpatentable as, inter alia, obvious over
Baveja et al., Zero-Order Release Hydrophilic Matrix
Tablets of β-Adrenergic Blockers, 39 Int’l J. Pharmaceutics
39 (1987) (“Baveja”), U.S. Patent 5,582,837 (“Shell”), and
other references. In July 2014, the Board instituted three
separate proceedings to review the patentability of the
following claims: (1) claims 1, 8–10, 13–15, 43, 45, and 46
of the ’280 patent; (2) claims 1, 8–10, 13–15, 61, and 62 of
the ’475 patent; and (3) claims 43, 54, 55, 57, 58, and 66 of
the ’475 patent. The district court stayed the litigation
pending the Board’s review.
    Claims 1 and 43 of the ’475 patent are representative
of the challenged claims and read as follows:
    1. A controlled-release oral drug dosage form for
       releasing a drug whose solubility in water is
       greater than one part by weight of said drug in
       ten parts by weight of water,
       said dosage form comprising a solid polymeric
       matrix with said drug dispersed therein at a
       weight ratio of drug to polymer of from about
       15:85 to about 80:20,
       said polymeric matrix being one that swells
       upon imbibition of water thereby attaining a
       size large enough to promote retention in the
       stomach during said fed mode [“the swelling
       limitation”],
       that releases said drug into gastric fluid by the
       dissolution and diffusion of said drug out of
       said matrix by said gastric fluid,
4                     PURDUE PHARMA L.P.   v. DEPOMED, INC.


       that upon immersion in gastric fluid retains at
       least about 40% of said drug one hour after
       such immersion and releases substantially all
       of said drug within about eight hours after
       such immersion,
       and that remains substantially intact until all
       of said drug is released [“the substantially in-
       tact limitation”].
    43. A method of administering to a subject a drug
        that is therapeutic to said subject when ab-
        sorbed in the stomach where said drug has at
        least one ionized group in the pH range 5
        through 8,
       said method comprising orally administering
       to said subject a dosage form of said drug
       while said subject is in a fed mode,
       said dosage form comprising a solid polymeric
       matrix with said drug dispersed therein at a
       weight ratio of drug to polymer of from about
       0.01:99.99 to about 80:20,
       said polymeric matrix being one that:
       (a) swells upon imbibition of gastric fluid to a
       size large enough to promote retention in the
       stomach during said fed mode [“the swelling
       limitation”],
       (b) releases said drug into gastric fluid by the
       dissolving of said drug by said gastric fluid and
       either erosion of said matrix or diffusion of
       said dissolved drug out of said matrix,
       (c) retains at least about 40% of said drug one
       hour after such immersion in gastric fluid,
       (d) releases substantially all of said drug with-
       in about ten hours after such immersion, and
PURDUE PHARMA L.P.   v. DEPOMED, INC.                      5


        (e) remains substantially intact until all of
        said drug is released [“the substantially intact
        limitation”],
        thereby extending the release rate of said drug
        with time during said fed mode while releasing
        substantially all of said drug within said
        stomach where said drug is maintained in an
        acidic environment.
’475 patent col. 17 ll. 45–59, col. 25 ll. 39–64.
    In July 2015, after briefing and a consolidated oral
hearing, the Board issued three final written decisions
with similar reasoning in relevant part, in which it con-
cluded that Purdue failed to establish by a preponderance
of the evidence that the challenged claims would have
been obvious over the cited prior art. 1
    The Board found that Baveja discloses most of the
limitations of independent claims 1 and 43 of the ’475 and
’280 patents, except for the “swelling” and “substantially
intact” limitations. In so finding, the Board specifically
rejected Depomed’s argument that Baveja teaches away
from the claimed invention. Purdue I, 2015 WL 4150832,
at *12; Purdue II, 2015 WL 4150833, at *11; Purdue III,
2015 WL 4150834, at *12. The Board next found that
Shell discloses those limitations that are missing from
Baveja. However, despite finding that the cited prior art
teaches each limitation of claims 1 and 43 of both patents,
Purdue I, 2015 WL 4150832, at *14, *20; Purdue II, 2015
WL 4150833, at *13; Purdue III, 2015 WL 4150834, at
*14, the Board found that Purdue failed to establish a



    1   Among the instituted grounds, the Board also
found that Purdue failed to prove that claims 43, 54, 55,
57, 58, and 66 of the ’475 patent were anticipated by U.S.
Patent 6,120,803. But that finding is not at issue in this
appeal.
6                     PURDUE PHARMA L.P.   v. DEPOMED, INC.


reason to combine the prior art to achieve the claimed
invention with a reasonable expectation of success, Pur-
due I, 2015 WL 4150832, at *16, *20; Purdue II, 2015 WL
4150833, at *15; Purdue III, 2015 WL 4150834, at *16.
    Specifically, the Board found that, although Baveja
and Shell may have interrelated teachings, Purdue failed
to explain persuasively “how or why” a person of ordinary
skill in the art would have combined the “swelling” and
“substantially intact” features of the Shell formulation
with the Baveja formulation.         Purdue I, 2015 WL
4150832, at *16; Purdue II, 2015 WL 4150833, at *15;
Purdue III, 2015 WL 4150834, at *16. The Board also
found that, to the extent that Purdue relied on the nature
of the problem to be solved to supply a reason to combine
the prior art, it improperly used hindsight by defining the
problem with a recitation of the challenged claims.
    Moreover, the Board found that Purdue failed to es-
tablish that a skilled artisan would have had a reasonable
expectation of success to achieve the claimed invention.
Purdue I, 2015 WL 4150832, at *17, *20; Purdue II, 2015
WL 4150833, at *16; Purdue III, 2015 WL 4150834, at
*17. The Board considered expert testimony regarding
the large number of variables in play when designing a
drug formulation, as well as co-inventor Helm’s testimony
that it took her years of research to develop the claimed
dosage form. The Board also noted that Purdue failed to
address why one of ordinary skill in the art would have
reasonably expected that modifying the Baveja formula-
tion to incorporate the “swelling” and “substantially
intact” features would not affect the other desired proper-
ties of the Baveja formulation, such as the drug release
profile.
    The Board therefore concluded that claims 1 and 43 of
both patents were not shown to be unpatentable as obvi-
ous. For similar reasons, the Board concluded that Pur-
due failed to prove that the other challenged claims,
which depend from either claim 1 or 43, would have been
PURDUE PHARMA L.P.   v. DEPOMED, INC.                     7


obvious over the cited prior art, and therefore did not
consider Depomed’s evidence of secondary considerations.
    Purdue timely appealed to this court. We have juris-
diction pursuant to 28 U.S.C. § 1295(a)(4)(A).
                        DISCUSSION
    We review the Board’s legal determinations de novo,
In re Elsner, 381 F.3d 1125, 1127 (Fed. Cir. 2004), and the
Board’s factual findings underlying those determinations
for substantial evidence, In re Gartside, 203 F.3d 1305,
1316 (Fed. Cir. 2000). A finding is supported by substan-
tial evidence if a reasonable mind might accept the evi-
dence to support the finding. Consol. Edison Co. v.
NLRB, 305 U.S. 197, 229 (1938).
     A claim is unpatentable as obvious if the differences
between the claimed subject matter and the prior art are
such that the subject matter as a whole would have been
obvious at the time of invention to a person having ordi-
nary skill in the art. 35 U.S.C. § 103(a) (2006). 2 Obvi-
ousness is a question of law premised on underlying
issues of fact, including: (1) the scope and content of the
prior art; (2) the level of ordinary skill in the pertinent
art; (3) the differences between the claimed invention and
the prior art; and (4) objective evidence, such as commer-
cial success, long-felt need, and the failure of others. KSR
Int’l Co. v. Teleflex Inc., 550 U.S. 398, 427 (2007); Graham
v. John Deere Co., 383 U.S. 1, 17–18 (1966); In re Baxter,
678 F.3d 1357, 1361 (Fed. Cir. 2012). Similarly, the
determinations of what a reference teaches and the exist-
ence of a reason to combine references are questions of



   2     Because the applications leading to the ’475 and
’280 patents were filed before March 16, 2013, the pre-
Leahy-Smith America Invents Act version of § 103 applies
in this appeal. See Pub. L. No. 112-29, § 3(n)(1), 125 Stat.
284, 293 (2011).
8                     PURDUE PHARMA L.P.   v. DEPOMED, INC.


fact. In re Beattie, 974 F.2d 1309, 1311 (Fed. Cir. 1992);
In re Hyon, 679 F.3d 1363, 1365–66 (Fed. Cir. 2012). In
an inter partes review proceeding, the petitioner bears the
burden of proving a proposition of unpatentability by a
preponderance of the evidence. 35 U.S.C. § 316(e).
    Purdue argues that the Board erred by deviating from
the Supreme Court’s guidance in KSR that an obvious-
ness analysis involves an expansive and flexible approach
that accounts for the interrelated teachings of the prior
art and the nature of the problem to be solved. Applied
here, Purdue contends, those principles necessarily
demonstrate how and why a skilled artisan would have
had a reason to combine the interrelated teachings of
Baveja and Shell, as both references teach similar con-
trolled-release profiles of similar formulations with over-
lapping drug-to-polymer ratios. Purdue also argues that
the problem to be solved provides a further reason to
combine Baveja and Shell, for those references already
solved the problem by teaching the drug release profile
and other limitations of the challenged claims. Purdue
maintains that its definition of the problem to be solved
came directly from Shell, not from the challenged claims.
    Depomed responds that the Board applied the correct
legal standard in its obviousness analysis, recognizing
that this case involves complex and unpredictable formu-
lation technology. According to Depomed, a skilled arti-
san would not have had a reason to combine Baveja and
Shell to make the claimed dosage form. Depomed asserts
that Baveja teaches away from the non-zero-order drug
release profiles shown in Figures 1 and 2, on which Pur-
due relies, by characterizing them as a “major disad-
vantage.” J.A. 1805. Depomed contends that Purdue’s
generic and conclusory statements of interrelated teach-
ings of the prior art are indicative of the fact that Purdue
presented no credible evidence on a motivation to combine
the prior art. Depomed responds, moreover, that Purdue
improperly relied on hindsight to formulate the problem
PURDUE PHARMA L.P.   v. DEPOMED, INC.                       9


to be solved, which cannot be derived from Shell because
Shell focuses on drugs of limited solubility and only
depicts drug release profiles up to seven hours.
    Purdue additionally argues that Baveja and Shell
demonstrate actual success, far more than a reasonable
expectation of success, and that the Board overlooked the
evidence that Baveja discloses actual dosage forms having
the claimed drug release profiles and that Shell provides
clear direction as to which parameters are critical. Ac-
cording to Purdue, the Board improperly relied on the
testimony of co-inventor Helm, who admitted that she
was not aware of the cited references, as well as the
testimony of Depomed’s expert Hopfenberg because that
testimony was divorced from the explicit teachings of
Baveja and Shell.
    Depomed responds that Baveja and Shell do not es-
tablish a reasonable expectation of success, and that both
parties’ experts testified that there were numerous varia-
bles affecting controlled-release formulations. Depomed
argues that changing any one of those variables could
significantly affect the drug release profile. Depomed also
responds that Helm is more than qualified to offer testi-
mony as one of ordinary skill in the art, and that Hopfen-
berg’s opinion was properly based on his review of the
prior art. Depomed emphasizes that the claimed inven-
tion was the product of testing different combinations of
polymers and drugs through years of research.
     We agree with Depomed that the Board applied the
correct legal standard in its obviousness analysis and that
substantial evidence supports its finding that Purdue
failed to establish that a person of ordinary skill in the art
would have had a reason to combine Baveja and Shell to
pursue the claimed invention with a reasonable expecta-
tion of success. As the petitioner before the Board in an
inter partes review proceeding, Purdue bore the burden of
establishing obviousness of the challenged claims by a
preponderance of the evidence. 35 U.S.C. § 316(e). The
10                    PURDUE PHARMA L.P.   v. DEPOMED, INC.


Board did not err in finding that Purdue failed to satisfy
that burden.
    The record shows that the Board correctly determined
that each limitation of the challenged independent claims
was known in the art, as evidenced by the teachings of
Baveja and Shell. In particular, the Board correctly found
that Baveja teaches almost all of the limitations of claims
1 and 43 of the ’475 and ’280 patents, and that Shell
teaches the “swelling” and “substantially intact” limita-
tions not otherwise disclosed in Baveja.
    Moreover, substantial evidence supports the Board’s
finding that Baveja does not teach away from the claimed
dosage form. Although Baveja expresses a preference for
oral dosage forms that exhibit a zero-order release profile
over those that do not, that preference does not amount to
teaching away from dosages forms with a non-zero-order
release profile. See In re Mouttet, 686 F.3d 1322, 1334
(Fed. Cir. 2012) (“[J]ust because better alternatives exist
in the prior art does not mean that an inferior combina-
tion is inapt for obviousness purposes.”).
    Nevertheless, the Board correctly recognized that “a
patent . . . is not proved obvious merely by demonstrating
that each of its elements was, independently, known in
the prior art.” KSR, 550 U.S. at 418. Indeed, it remains
“important to identify a reason that would have prompted
a person of ordinary skill in the relevant field to combine
the elements in the way the claimed new invention does.”
Id. (emphases added). As the Board correctly recognized,
one may look to “interrelated teachings” of multiple
references, id., or a “problem known in the field of en-
deavor,” id. at 420, to determine whether there was an
“apparent reason” to combine the prior art teachings “in
the fashion claimed by the patent at issue,” id. at 418.
    Although the obviousness analysis may not be con-
fined by any formalistic test, or by overemphasis on the
explicit teachings of prior art publications, a petitioner
PURDUE PHARMA L.P.   v. DEPOMED, INC.                   11


must nevertheless make a sufficient showing that is more
than “mere conclusory statements,” to establish a reason
that would have prompted a skilled artisan to combine
the prior art teachings in the way of the claimed inven-
tion. Id. at 418–19. As we have explained, a patent
challenger must demonstrate that a skilled artisan would
have had reason to combine the teachings of the prior art
references to achieve the claimed invention, and that the
skilled artisan would have had a reasonable expectation
of success from doing so. See PAR Pharm., Inc. v. TWI
Pharm., Inc., 773 F.3d 1186, 1193 (Fed. Cir. 2014).
    Here, the Board found that Purdue failed to sufficient-
ly show that a skilled artisan would have had a reason to
combine the teachings of Baveja and Shell to achieve the
claimed invention. That determination is supported by
substantial evidence, which we must uphold, rather than
revisit de novo. The record shows that Purdue presented
limited evidence of a reason to combine the teachings of
Baveja and Shell. E.g., J.A. 1956–62, 1985–86 (¶¶ 127–
28, 131–33, 193–94); Appellant’s Br. 38–39. Its expert
opined generally on the interrelated teachings of those
references, but did not explain in sufficient detail how or
why a skilled artisan would have been motivated to
combine the “swelling” and “substantially intact” features
of the Shell formulation with the Baveja formulation to
attain the claimed dosage form.
    Moreover, to the extent that Purdue relies on the
problem to be solved to supply the reason to combine the
prior art, it failed to demonstrate to the Board that the
problem was known in the art or that Purdue’s formula-
tion of the problem was derived directly from the prior
art, rather than from the challenged claims. The Board
therefore did not err in finding that Purdue improperly
relied on hindsight in formulating the problem to be
solved. Insite Vision Inc. v. Sandoz, Inc., 783 F.3d 853,
859 (Fed. Cir. 2015) (“Defining the problem in terms of its
12                    PURDUE PHARMA L.P.   v. DEPOMED, INC.


solution reveals improper hindsight in the selection of the
prior art relevant to obviousness.”).
     We also conclude that substantial evidence supports
the Board’s finding that Purdue failed to sufficiently show
that a skilled artisan would have had a reasonable expec-
tation of success in combining Baveja and Shell to achieve
the claimed dosage form. As the Board noted, both par-
ties’ experts testified on the large number of formulation
considerations in play when designing a drug formulation.
In light of that, Purdue did not sufficiently explain why a
skilled artisan would have expected that the Baveja
formulation could be modified to incorporate the “swell-
ing” and “substantially intact” features of Shell, without
affecting the other desired properties. In other words,
Purdue did not address whether adding the “swelling”
and “substantially intact” features to the Baveja formula-
tion would have been reasonably expected to lead to a
dosage form that satisfies the other limitations of the
challenged claims.
    Accordingly, we conclude that the Board did not err in
finding that Purdue failed to establish a reason to com-
bine the cited prior art to achieve the claimed invention
with a reasonable expectation of success. Because the
Board did not reach the merits of Depomed’s evidence of
secondary considerations, we similarly decline to do so in
the first instance on appeal.
                       CONCLUSION
    We have considered the remaining arguments, but
find them to be unpersuasive. The Board did not err in
determining that Purdue failed to make a sufficient
showing that the challenged claims of the ’475 and ’280
patents would have been obvious over the cited prior art.
We therefore affirm the Board’s decision.
                      AFFIRMED
