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I. Introduction

Direct patent infringement has two types: literal infringement and infringement under the doctrine of equivalents (DOE). See John C. Evans, Addressing Default Trends In Patent-Based Section 337 Proceedings In The United States International Trade Commission, 106 Mich. L. Rev. 745, 765 (2008). “Literal infringement occurs if each and every element of the asserted claim, as construed, can be identified in the accused product.” Id. The DOE “allows the patentee to claim those insubstantial alterations that were not captured in drafting the original patent claim but which could be created through trivial changes.” Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 535 U.S. 722, 733, 122 S. Ct. 1831, 1838 (2002)(“Festo VIII”).

The DOE can broaden the patent protection scope, and “is premised on language's inability to capture the essence of innovation, but a prior application describing the precise element at issue undercuts that premise.” Id., 535 U.S. at 734, 122 S. Ct. at 1839. However, if the claims were amended during patent prosecution, the DOE may be limited by Prosecution History Estoppel (“PHE”). See Marc D. Sharp, Notes, Festo X: The Complete Bar By Another Name?, 19 Berkeley Tech. L.J. 111, 113 (2004).

This memo will focus on the discussion about PHE and, particularly, on one defense measure against PHE, which is “unforeseeable at the time the claim was drafted.” In the following content, Part II of this memo will discuss PHE, and Part III will discuss “unforeseeable at the time the claim was drafted.” Finally, Part IV will review three recent cases of the United States Court of Appeals for the Federal Circuit (“Federal Circuit Court”).

II. Prosecution History Estoppel
A. General Concept
PHE serves two purposes. The first purpose is to “require[] that the claims of a patent be interpreted in light of the proceedings in the PTO during the application process.” Festo VIII, 535 U.S. at 733, 122 S. Ct. at 1838. “Estoppel is a [‘]rule of patent construction[‘] that ensures that claims are interpreted by reference to those []that have been cancelled or rejected.” Id., 535 U.S. at 733, 122 S. Ct. at 1838.

The second purpose is to limit the application of the DOE. See Id. This is because “[w]hen [] the patentee originally claimed the subject matter alleged to infringe but then narrowed the claim in response to a rejection, he may not argue that the surrendered territory comprised unforeseen subject matter that should be deemed equivalent to the literal claims of the issued patent.” Id., 535 U.S. at 733-734, 122 S. Ct. at 1838.

PHE “ensures that the doctrine of equivalents remains tied to its underlying purpose. Where the original application once embraced the purported equivalent but the patentee narrowed his claims to obtain the patent or to protect its validity, the patentee cannot assert that he lacked the words to describe the subject matter in question.” Id., 535 U.S. at 734, 122 S. Ct. at 1839. The prosecution history helps decide whether “the inventor turned his attention to the subject matter in question, knew the words for both the broader and narrower claim, and affirmatively chose the latter.” Id., 535 U.S. at 735, 122 S. Ct. at 1839.

B. Amendments that Trigger PHE
PHE “applies to amendments made for a []substantial reason related to patentability[.]” Id., 535 U.S. at 735, 122 S. Ct. at 1839. “[E]ven if the amendment's purpose were unrelated to patentability, [a] court might consider whether it was the kind of reason that nonetheless might require resort to the estoppel doctrine.” Id. “[A] narrowing amendment made to satisfy any requirement of the Patent Act may give rise to an estoppel.” Id., 535 U.S. at 736, 122 S. Ct. at 1839. It is clear that an amendment made for of claims 35 U.S.C. §§ 101-103 is related to patentability, but an amendment made for 35 U.S.C. § 112 is still related to patentability because “[w]hat is claimed by the patent application must be the same as what is disclosed in the specification; otherwise the patent should not issue.” Id., 535 U.S. at 736, 122 S. Ct. at 1840. However, “[i]f a § 112 amendment is truly cosmetic, then it would not narrow the patent's scope or raise an estoppel.” Id., 535 U.S. at 736-37, 122 S. Ct. at 1840.

“A patentee who narrows a claim as a condition for obtaining a patent disavows his claim to the broader subject matter, whether the amendment was made to avoid the prior art or to comply with [35 U.S.C.] § 112. [A court] must regard the patentee as having conceded an inability to claim the broader subject matter or at least as having abandoned his right to appeal a rejection. In either case estoppel may apply.” Id., 535 U.S. at 737, 122 S. Ct. at 1840. Additionally, “a [‘]voluntary[‘] amendment may give rise to prosecution history estoppel.” Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 344 F.3d 1359, 1366 (Fed. Cir. 2003)(“Festo X”).

Moreover, “[w]hen the patentee is unable to explain the reason for amendment, estoppel not only applies but also []bar[s] the application of the doctrine of equivalents as to that element.[ But, t]hese words do not mandate a complete bar; they are limited to the circumstance where [‘]no explanation is established.[‘]” Festo VIII, 535 U.S. at 740, 122 S. Ct. at 1842.

C. Question of Law
Whether PHE is applied is decided by a court. Id. And, “rebuttal of the presumption of surrender is [also] a question of law” Festo X, 344 F.3d at 1367. “Questions relating to the application and scope of prosecution history estoppel thus fall within the exclusive province of the court. Accordingly, the determinations concerning whether the presumption of surrender has arisen and whether it has been rebutted are questions of law for the court, not a jury, to decide.” Id., 344 F.3d at 1368.

D. Patentee/Plaintiff’s Defenses against PHE
“[A] patentee should bear the burden of showing that the amendment does not surrender the particular equivalent in question[,]” Festo VIII, 535 U.S. at 740, 122 S. Ct. at 1842, because “[t]he patentee, as the author of the claim language, may be expected to draft claims encompassing readily known equivalents.” Id. “A patentee'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.” Id.

The Supreme Court of the United States (“Supreme Court”) provided three categories for the patentee to overcome PHE: “[(1) t]he equivalent may have been 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; [(3)] there may be some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” Id., 535 U.S. at 740-41, 122 S. Ct. at 1842. In the following discussion, I will focus on the first category.

III. “Unforeseeable at the Time the Claim was Drafted”
A. General Concept
“When [a] patentee has chosen to narrow a claim, courts may presume the amended text was composed with awareness of this rule and that the territory surrendered is not an equivalent of the territory claimed.” Id., 535 U.S. 722, 741, 122 S. Ct. 1831, 1842. The Supreme Court has ruled that the patentee may rebut by “show[ing] that at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.” Id. Additionally, the “discussion of the relevant factors encompassed by each of the rebuttal criteria [would be judged] on a case-by-case basis.” Festo X, 344 F.3d at 1368.

B. Basic Definition of “Unforeseeable”
According to the Federal Circuit Court, the “unforeseeable” criterion “presents an objective inquiry, asking whether the alleged equivalent would have been unforeseeable to one of ordinary skill in the art at the time of the amendment.” Festo X, 344 F.3d at 1369.

“Usually, if the alleged equivalent represents later-developed technology (e.g., transistors in relation to vacuum tubes, or Velcro® in relation to fasteners) or technology that was not known in the relevant art, then it would not have been foreseeable. In contrast, old technology, while not always foreseeable, would more likely have been foreseeable. Indeed, if the alleged equivalent were known in the prior art in the field of the invention, it certainly should have been foreseeable at the time of the amendment.” Id.

C. Evidentiary Rules
“By its very nature, objective unforeseeability depends on underlying factual issues relating to, for example, the state of the art and the understanding of a hypothetical person of ordinary skill in the art at the time of the amendment. Therefore, in determining whether an alleged equivalent would have been unforeseeable, a district court may hear expert testimony and consider other extrinsic evidence relating to the relevant factual inquiries.” Id.

D. Application
The Federal Court held that “the Supreme Court in Festo VIII []ties foreseeability to whether the applicant would have been expected to know of, and thus properly claim, the proposed equivalent at the time of amendment.[]” Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 493 F.3d 1368, 1378 (Fed. Cir. 2007)(“Festo 2007”). It further held that “the Supreme Court in [Festo VIII does not excuse] an applicant from failing to claim ‘readily known equivalents' at the time of application.” Id. Thus, “an equivalent is foreseeable when the equivalent is known in the pertinent prior art at the time of amendment.” Id.

E. Rejected Foreseeability Test
In Festo 2007, the Federal Court rejected “the foreseeability test [which] requires application of the function/way/result or insubstantial differences test[,]” id., 493 F.3d at 1379, where the patentee argued that “[t]he proper unforeseeability test is to determine whether the proven equivalent would have been foreseeable to a person of ordinary skill in the art to accomplish the claimed invention, i.e., perform the same function in substantially the same way to achieve the same result, looking only at the information available at the time of the amendment.” Id. at 1378-79. The most important reason to reject this argument is that “[t]he question is not whether after the narrowing amendment the alternative was a known equivalent, but rather whether it was a known equivalent before the narrowing amendment.” Id. at 1381.

IV. Federal Circuit Court Case Studies
A. Cross Medical Products, Inc. v. Medtronic Sofamor Danek, Inc. (March 20, 2007)-Literal Infringement Dispute May Effect the “Unforeseeable” Determination.

In Cross Medical Products, Inc. v. Medtronic Sofamor Danek, Inc., the original claim language is “said seat means including a vertical axis and first threads.” See Id., 480 F.3d 1335, 1340 (Fed. Cir. 2007). The language was amended to have “threads” followed by a limitation, “which extend in the direction of said vertical axis toward said lower bone interface to a depth below the diameter of the rod when it is in the rod receiving channel.” See Id. The amendment was related to patentability. See Id. The alleged equivalent was an undercut or recess. See Id. at 1343.

The Federal Circuit Court held that the alleged equivalent was foreseeable because “the evidence of record clearly demonstrates that the use of an undercut or recess, the alleged equivalent here, is an old and well known fundamental of basic machining that was entirely foreseeable at the time of the amendment to one of ordinary skill in the art.” Id. (citing John R. Walker, Machining Fundamentals, Fundamentals Basic to Industry, at 185-86 (1981); U.S. Patent No. 5,129,900; U.S. Patent No. 5,190,543). Moreover, the Federal Circuit Court cited patentee’s literal infringement arguments to hold that the patentee “suggest[ed] that an [‘]undercut[‘] was known in the art to serve effectively as a thread.” Id.

Therefore, according to Cross Medical Products, Inc., a court may refer to plaintiff’s literal infringement arguments to decide whether the alleged equivalent was unforeseeable. It is necessary for a plaintiff/patentee to review whether literal infringement arguments would affect DOE infringement arguments.

B. Festo 2007 (July 5, 2007)-Equivalents May be Foreseeable in Light of the Cited Prior Arts.
In Festo 2007, when the disputed patent was prosecuted, the applicant amended the one claim and added “a cylindrical sleeve made of a magnetizable material” to define the composition of the sleeve in the original claim. See Id. at 1374. The applicant did so in response to the examiner’s rejection. See Id. at 1373.

The alleged equivalent was the aluminum sleeve. See Id. at 1374. The Federal Circuit Court held that the aluminum sleeve was not unforeseeable because the applicant cited one prior art patent that “disclosed a []guide tube [that] is surrounded by a carriage [sleeve], which has the shape of a slit ring and is also made from a non-magnetic material.” Id. at 1382. It also held that “[w]hile the prior art does not specifically disclose an aluminum alloy sleeve, it is undisputed that aluminum alloy is a non-magnetizable material.” Id.

Thus, according to Festo 2007, the cited prior arts may be a relevant source to take the un/foreseeability test. It is necessary to review all cited prior arts before the amendment is submitted in order to decide whether claims should surrender the foreseeable equivalents expressly mentioned or implied in the cited prior arts.

C. Schwarz Pharma, Inc. v. Paddock Laboratories, Inc. (October 12, 2007)-The Claim Language is the Center of the “Unforeseeable” Determination.
In Schwarz Pharma, Inc. v. Paddock Laboratories, Inc., “the independent claims recited a [‘]metal containing stabilizer[‘] and [‘]an alkali or alkaline earth-metal salt,[‘] respectively, but, following the rejection, each was amended to instead recite [‘]an alkali or alkaline earth metal carbonate.[‘]” Id., 504 F.3d 1371, 1373 (Fed. Cir. 2007). The alleged equivalent is magnesium oxide. See Id.

The plaintiff referred to the specification, arguing that the original independent claims did not include magnesium oxide. See Id. at 1375. But the Federal Circuit Court disagreed, holding that the original claim language was broad enough to cover magnesium oxide. See Id. The specification only mentions “borates, silicates, and carbonates,” see id. at 1376, and the Federal Circuit Court held that those references “reflects preferences, not limitations inconsistent with both the original claims and broader language in the specification.” Id.
The plaintiff also tried to narrow the field of the invention from pharmaceutical compositions to pharmaceutical stabilizers that inhibit cyclization in ACE inhibitors, so that magnesium oxide can be excluded. See Id. at 1377. However, the Federal Circuit Court held that the argument was not right because the claim began with the words “a pharmaceutical composition which contains.” See Id.

Thus, according to Schwarz Pharma, Inc., courts will rely on original claim language to decide what was encompassed and what was surrendered. The specification or the field of the invention may not be relevant to the foreseeability test.

V. Conclusion
During patent prosecution, an applicant shall be very careful about each amendment s/he makes. It is important to check the scope of foreseeable equivalents regarding an amended claim limitation before an amendment application is filed. Otherwise, during a patent litigation, when arguments related to the infringement under the DOE are made, they will be barred by PHE. It is because a court will think the patentee surrendered foreseeable equivalents at the time when the amendment was made.

Additionally, the recent Federal Circuit Court cases show that (1) a court may refer to plaintiff’s literal infringement arguments to decide whether the alleged equivalent was unforeseeable; (2) the cited prior arts may be a relevant source to take the un/foreseeability test; (3) a court will rely on original claim language to decide what was encompassed and what was surrendered. Thus, during patent prosecution, it is important to write well-designed claims in the beginning while it is also critical to review all documents submitted or received during the prosecution and to check each argument during a litigation.