[The patentee] may be correct that "practicing the prior art" is not a defense to patent infringement. See Ecolab Inc. v. Paraclipse, Inc., 285 F.3d 1362, 1377 (Fed. Cir. 2002). However, it does not follow that a defendant’s belief that it can freely practice inventions found in the public domain cannot support a jury’s finding that the intent required for induced infringement was lacking. The jury heard [the defendant's] founders explain why they did not believe they were infringing and had the opportunity to assess their credibility. We find no basis to overturn the jury’s decision with respect to inducement.

A link to the slip opinion is: Kinetic Concepts, Inc. v. Blue Sky Medical Group, Inc., CA Nos. 2007-1340-42 (Fed. Cir. February 2, 2009).