Disavowal of Claim Scope Must be Unambiguous

NMT Medical, Inc. v. Cardia, Inc., [06-1645](June 6, 2007)[GAJARSA, Michel, Mayer] The Federal Circuit vacated summary judgment of infringement of U.S. Patent No. 5,451,235 on a device for repairing heart defects, because of errors in claim construction, and remanded for further proceedings.
SIGNIFICANCE: (1) Whether a structure is insubstantially different from the structure disclosed in the specification corresponding to a means-plus-function claim is a fact question best left to the jury. (2) Disavowal of claim scope must be unambiguous.
BRIEF: Construction of a means plus function claim requires the court to identify the claimed function, and then to locate the structure in the specification which has been clearly linked to that function. Once a means plus function claim is construed, literal infringement is analyzed by determining whether the accused device employs structure identical or equivalent to the structure disclosed in the patent, and the accused device performs the identical function specified in the claim. LOF: Infringement of a means plus function claim is a question of fact. When the accused device is not identical to the structure corresponding to the means plus function element, the issue is whether the difference between the accused structure and the structure disclosed in the specification are "insubstantial". The Federal Circuit found that it was error to resolve the factual question of insubstantial differences on summary judgment.
Turning to claim 12, the Federal Circuit found error in the trial court's construction that required the devices to be "directly" connected. The Federal Circuit noted that the specification used the term directly when directly connection was intended, and concluded it was error to impose the requirement of "directly" when the claim language did not. Defendant argued that the patentee had disclaimed a broader interpretation, but the Federal Circuit has declined to apply the doctrine of prosecution disclaimer where the alleged disavowal of claim scope is ambiguous. Noting that amendments were made, the Federal Circuit found that they did not unambiguously limit the claim to directly connected.