Earlier this month, in University of Strathclyde v. Clear-Vu Lighting LLC, the Court of Appeals for the Federal Circuit (“the CAFC”) reversed a decision by the Patent Trial and Appeal Board (“the Board”) that found claims 1-4 of the University of Strathclyde’s U.S. Patent No. 9,839,706 (“the ’706 patent”) invalid as obvious. Specifically, the CAFC determined there was not substantial evidence supporting either that the prior art disclosed all claim limitations of the ’706 patent or that there was a reasonable expectation of success in combining the references used by the Board in making its obviousness determination.


The ’706 patent, which issued on December 12, 2017, relates to a method for “photoinactivating” antibiotic-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA) without using a photosensitizing agent. On December 12, 2018, Clear-Vu filed a petition for inter partes review of claims 1-4 of the ’706 patent. The Board instituted Clear-Vu’s IPR on July 10, 2019. A year later, the Board determined that claims 1 and 3 of the ’706 patent would have been obvious over Ashkenazi[1] in view of Nitzan[2], and that claims 2 and 4 would have been obvious in further view of Jones[3]. Strathclyde appealed on the grounds that: 1) neither Ashkenazi nor Nitzan taught exposing bacteria to light without the use of a photosensitizing agent; and 2) the Board’s finding of a reasonable expectation of success in combining Ashkenazi with Nitzan.

The Prior Art Did Not Disclose All Claim Limitations

 The CAFC determined that the Board erroneously found that Ashkenazi and Nitzan disclosed all claim limitations for claims 1 and 3 of the ’706 patent. An obviousness determination generally requires a finding that “all claimed limitations are disclosed in the prior art.” PAR Pharm., Inc. v. TWI Pharms., Inc., 773 F.3d 1186, 1194 (Fed. Cir. 2014). Claims 1 and 3 of the ’706 patent require exposing the bacteria in question to 400-420 nm blue light without the use of a photosensitizer, and that this exposure inactivates the bacteria. Ashkenazi does not disclose or suggest inactivating bacteria without the use of a photosensitizer. Further, while Nitzan provides an example of exposing bacteria to 407-420nm blue light without a photosensitizer, nothing in the reference shows that this exposure inactivated the bacteria.

In its final written decision, the Board cited Clear-Vu’s argument that combining Ashkenazi with Nitzan “disclose[d] exposing bacteria to light without using a photosensitizer.” However, the CAFC reversed the Board, noting that “we fail to see why a skilled artisan would opt to entirely omit a photosensitizer when combining these references.” The CAFC also rejected an argument by Clear-Vu that Ashkenazi and Nitzan “disclose the particular ‘inactivating’ and ‘inactivates’ language.” In so doing, the CAFC declined to read the “inactivation limitation” in “isolation, divorced from the claim as a whole.”

No Reasonable Expectation of Success

The CAFC rejected the Board’s finding that a skilled artisan would have a reasonable expectation of success combining Ashkenazi with Nitzan, holding that the “only support for such a finding is pure conjecture coupled with hindsight reliance on the teachings in the’706 patent.” An obviousness determination generally requires a finding “that a person of ordinary skill in the art would have been motivated to combine or modify the teachings in the prior art and would have had a reasonable expectation of success in doing so.” Regents of Univ. of Cal. v. Broad Inst., Inc., 903 F.3d 1286, 1291 (Fed. Cir. 2018).

Neither Ashkenazi nor Nitzan contains any suggestion of successfully inactivating any bacteria without using a photosensitizer. The Board’s decision relied on Ashkenazi’s teaching that “blue light may” inactivate “other bacterial cells that produce porphyrins,” and that because Ashkenazi showed light-activated porphyrin molecules caused inactivation for one type of bacteria (with the use of a photosensitizer), then “the fact that MRSA has some level of endogenous porphyrin suggests to a skilled artisan that MRSA, too, would exhibit some amount of inactivation after exposure to 407-420nm blue light.”  In reversing the Board, the CAFC emphasized that “not only is there a complete lack of evidence in the record that any bacteria were inactivated after exposure to 407-420 nm blue light without using a photosensitizer, there is also evidence showing that others had failed to inactivated MRSA . . . without using a photosensitizer.” The CAFC rejected Clear-Vu’s attempt to rely on the ’706 patent itself to support the Board’s findings as improper hindsight analysis.

Notwithstanding its holding, the CAFC reiterated in its conclusion that “reasonable expectation of success” does not require “absolute predictability” or “guaranteed success.” “To be sure, we have repeatedly rejected that notion.”

The CAFC’s decision in University of Strathclyde reaffirms the importance to petitioners that they fully develop their obviousness arguments. Petitioners should ensure that their alleged prior art references disclose each and every claim limitation, and that a skilled artisan would combine their cited references with a reasonable expectation of success that is not reliant on hindsight reasoning.

[1] Helena Ashkenazi et al., Eradication of Propionibacterium acnes by its endogenic porphyrins after illumination with high intensity blue light, 35 J. FEMS Immunology & Med. Microbiology 17, 17–24 (2003).

[2] Yeshayahu Nitzan et al., ALA induced photodynamic effects on Gram positive and negative bacteria, 3 Photochemical & Photobiological Scis. 430, 430–35 (2004).

[3] U.S. Pat. App. Pub. No. 2005/00550070.