The claims of an issued patent describe the metes-and-bounds of the invention. However, that depends on the court’s interpretation, i.e., construction, of the claimed terms. Statements made by an inventor in her patent application, or those made during prosecution, may be deemed during claim construction to have disavowed subject matter which an inventor thought was embraced by her patent. When considering whether or not subject matter was disavowed, two recent opinions emphasize that such disavowal must be unambiguous and made in the context of the issued claims. Statements made in a patent application hold greater weight than do statements made during prosecution since “[u]ltimately, the only meaning that matters in claim construction is the meaning in the context of the patentPoly-America, L.P. v. API Industries, Inc., p. 10 (emphasis added).

Poly-America relates to a patent infringement suit about trash bags. The accused infringer successfully argued that the claimed term “short seal” should be interpreted to include, inter alia, a feature extending inwardly from the interior edge of the side seal, even if this additional feature was not recited in the claim. The defendant argued that the inventor had disavowed a broader interpretation. The defendant’s allegedly infringing bag did not have this inwardly extended feature but rather had a single width for the entire bag. The patent taught that prior trash bags would not wrap securely around the rim of a trash receptacle. Instead, the bags disclosed in the patent specification, with inwardly extended short seals, did wrap so securely. Despite intentionally reciting the inwardly extended feature in some but not all claims, the court noted that “[e]very embodiment described in the specification has inwardly extended short seals and every section of the specification indicates the importance of inwardly extending short seals.” Id. at p. 10. The abstract even stated that the bag of the present invention had a reduced upper opening. Moreover, the patentee argued during prosecution that prior art trash bags were distinguishable because they had linear and parallel side seals, not inwardly facing ones. The court found that the inventor had disavowed an interpretation of “short seal” that didn’t include this inwardly extended feature.

The court in Poly-America instructs in dictum that while disavowal must be clear and unequivocal, it need not be explicit. An inventor may disavow claims lacking a particular feature when the specification describes the “present invention” as having that feature. An inventor may also disavow claims lacking a particular feature when the specification distinguishes or disparages prior art based on the absence of that feature. The specification thus remains the single best guide for claim construction.

The court will look at a patent’s prosecution history to see if disavowal by prosecution history disclaimer is appropriate. In M.I.T. v Shire Pharmaceuticals, Inc., the court looked at prosecution history but found it was insufficient to meet the disavowal standard. MIT’s patent claimed a cell-scaffold which included cells derived from vascularized tissue. Shire argued that vascularized tissue excluded skin cells due to MIT’s allegedly disavowing statements, but this argument failed. Unlike in Poly-America, the clear and unequivocal disavowal standard was not met because the allegedly disavowing statements were made out of context. While Shire was able to select statements MIT made during an examiner interview that the prior art was distinguishable because it was limited to skin cells, the court found these statements insufficient to disavow skin cells from the claims. When MIT made these statements, the then-pending claims were not those that ultimately issued. Shire’s advantageous selection of MIT’s declarant remarks were also unpersuasive as to whether skin cells were disavowed from the claims. Though these declarant’s remarks, absent context, suggested that vascularized tissue did not include skin cells, the court stated that in “the context of the overall prosecution history” the isolated statements didn’t meet the high standard for prosecution disclaimer. When the statements were made, the claim limitations at issue were not under examination. Thus, these statements did not alter or disclaim the ordinary meaning of vascularized organ tissue as used in the specification.

As evident from the holding in Poly-America and M.I.T., claim scope disavowal must be proven by clear and unequivocal evidence. Courts will limit claim scope when the patentee unambiguously states that the present invention does or does not include certain features even if those features are not recited in the claims. Such unambiguous disavowal is most readily found, if at all, in the patent application though it may also be found in the prosecution history if it is made in the context of the claimed terms which ultimately issue. Practitioners should consider whether statements in a patent application or those made during prosecution may be deemed to have disavowed claim scope which is valuable to the inventor. Where appropriate, practitioners should qualify these statements or provide the correct context for interpreting them to avoid claim scope disavowal.