In Jang v. Boston Sci. Corp., 2017 U.S. App. LEXIS 18825, the Federal Circuit revisited a decade-old controversy. The case is a good opportunity to see the mechanics behind the ensnarement doctrine and a hypothetical claim analysis.
The Fed. Circuit reviewed claim 1 of U.S. Patent No. 5,922,021, which recites:
1. A stent in a non-expanded state, comprising:
a first expansion strut pair including a first expansion strut positioned adjacent [*4] 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 couples 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.
Dr. Jang's claimed stent is shown on the left, while BSC's Express Stent is shown on the right:
In its decision, the court first held that a reasonable jury could have returned a verdict of no literal infringement based on the evidence presented at trial and refused to order a new trial. Having lost on literal infringement, the case turned on whether the Express Stent infringed based on the doctrine of equivalents.
The more interesting aspect of the case is the ensnarement analysis. By way of background, under the doctrine of equivalents, analysis is to be performed under the "substantially the same function-way-result" or "insubstantial differences" inquiry. BSC's Express Stent was found to infringe under the doctrine of equivalents by the jury, but the district court judge vacated the jury verdict and entered judgment of non-infringement. Thus, the appeal centered on whether the doctrine of equivalents should have been limited by the ensnarement doctrine.
In such cases, a hypothetical claim analysis is performed, where 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." The burden of proof is split, with the burden of producing evidence of prior art to challenge a hypothetical claim resting with an accused infringer, while the burden of proving patentability of the hypothetical claim rests with the patentee.
One requirement of a proper hypothetical claim is that it must only broaden the issued asserted claims. This is where Dr. Jang failed. During the course of litigation, Dr. Jang had generated ten different hypothetical claims, and could not properly craft a proper claim that would encompass the Express Stent while remaining patentable over the crowded prior art. Moreover, the district court was under no obligation to step in and rectify Dr. Jang's failure to construct such a hypothetical claim, and correctly vacated the jury verdict of infringement under the doctrine of equivalents.
The takeaway appears to be that a patentee's hypothetical claim must be broader than the asserted claim in every sense. A hypothetical claim that broadens some limitations of the asserted claim, but narrows others is deficient and will be rejected by the court. Additionally, even if the hypothetical claim is deficient and can be easily rectified, the court will not step in to correct the hypothetical claim and relieve the patentee of his duty to craft such a claim.