Does the application of inter partes review to a patent that issued before the enactment of the AIA violate the Due Process Clause because it retroactively diminishes vested rights by lowering the burden of proof required to revoke a patent in an adversarial proceeding?

QUESTION PRESENTED In 2006, the Patent Office issued petitioner’s patent under a statutory scheme that guaranteed that an issued patent is presumed valid in adversarial proceedings until a challenger proves that it is invalid by clear and convincing evidence. Years later, the Leahy-Smith America Invents Act (“AIA”) eliminated that guarantee by creating, for the first time, an adversarial proceeding that allows a challenger to obtain revocation of a patent by merely a preponderance of the evidence: inter partes review. Unlike any previous administrative process for reexamining a patent, inter partes review requires full participation by the challenger and operates as an adjudication on the relative strength of the parties’ disputed arguments. The AIA expressly subjected patents that issued before its enactment to that new regime. Does the application of inter partes review to a patent that issued before the enactment of the AIA violate the Due Process Clause because it retroactively diminishes vested rights by lowering the burden of proof required to revoke a patent in an adversarial proceeding?