Smith & Nephew Plc v Convatec Technologies Inc

Post-grant amendment is allowable where the amended claim is clearly and unambiguously disclosed, expressly or implicitly, in the application as filed. The added-matter comparison is strict, but it must be made through the eyes of the skilled reader and must avoid hindsight. Features disclosed in a particular context cannot be extracted from that context, although a patentee need not identify every disclosed feature as independently inventive.

For obviousness, the court must identify the skilled person, common general knowledge, the inventive concept and the differences from the prior art. The question is whether those differences would have been obvious without knowledge of the invention. A simple experiment is not necessarily obvious where the skilled person cannot identify which of competing explanations for the prior art is correct.

Smith & Nephew sought revocation of European Patent (UK) No. 1,343,510, concerning methods of preparing light-stabilised antimicrobial materials containing silver for wound dressings. Convatec conceded that the unamended patent was invalid and applied to amend claim 1.

The disputed issues were whether the proposed amendment introduced added matter, whether amended claim 1 was obvious over Gibbins and Kreidl, and whether the claim was insufficient because the term photostable was unclear or lacked teaching. The court also considered the construction of photostable and the required order and concentration of the processing steps.

1. Construction. “Substantially photostable upon drying” allowed a controlled colour change during drying, provided that the change thereafter was minimal. The claim did not require the product to remain white, and the expression was not hopelessly ambiguous.
2. Added matter. Under section 75 of the Patents Act 1977, subject to section 76(3)(a), the proposed claim had to be compared with the application as filed. Applying the principles in European Central Bank v DSS [2008] EWCA Civ 192, Bonzel v Intervention Ltd [1991] RPC 553 and Vector v Glatt [2008] RPC 10, the application disclosed the cumulative combination of gel-forming fibres, the relevant polymer properties and the listed polymer types. The disclosure was not limited to sodium CMC fibres. The amended claim therefore did not add matter.
3. The reference to gel-forming fibres containing the relevant polymers did not create a new technical disclosure. Read by the skilled person, the allegedly awkward wording in the application conveyed the same teaching. The fact that gel-forming fibres were not presented as independently inventive did not prevent their use in the amended claim, because the feature was disclosed in its proper context.
4. Obviousness. Applying the structured approach in Windsurfing International Inc v Tabur Marine [1985] RPC 59 and Pozzoli v BDMO [2007] EWCA Civ 588, and the fact-sensitive approach approved in Conor v Angiotech [2008] UKHL 49, claim 1 was not obvious over Gibbins. Gibbins provided motivation to improve light stability, but the route to the claimed concentration and sequence required hindsight. Its references to complexes were too slender to provide the necessary direction.
5. Claim 1 was also not obvious over Kreidl. A skilled person would consider applying Kreidl’s successful cotton-gauze process to Aquacel, but would face competing explanations: surface adsorption of complexes or physical shielding within the material. It would not be obvious which explanation was correct, and a mere willingness to test the process was insufficient.
6. Insufficiency. The term photostable was sufficiently clear, and the patent enabled the skilled person to know whether and how the claimed result could be achieved.

The amendment was allowed. As amended, the patent was valid.

This was a first-instance decision of the High Court (Patents Court). No appellate history was stated in the judgment.