In Jang v. Boston Scientific (Sept. 29, 2017), the Federal Circuit rejected Dr. Jang’s attempt to prove infringement under the doctrine of equivalents.  Here, “ensnarement” limits the doctrine of equivalents whenever a hypothetical patent claim that literally covers the accused product would also ensnare the prior art.  When ensnarement is invoked to avoid infringement, the accused infringer must simply identify the limiting prior art.  The patent owner then has the difficult burden to craft a hypothetical patent claim that (i) literally covers the accused product, (ii) is strictly broader than the issued claim, and (3) is still patentable over the identified prior art.  Dr. Jang’s first hypothetical claim was rejected because it added new narrowing language, despite removing an existing language.  His second claim was rejected because his addition of the words “at least” to introduce “at least a first . . . section” was not broadening when the “sections” were all part of an open-ended claim (one that uses the transition phrase “comprising”).  The words “at least” thus did not change the claim scope.  The Federal Circuit then noted that courts have no duty to step in and fix improper hypothetical claims.  Dr. Jang thus failed to carry his burden in proving infringement.