Convatec Ltd. & Ors v Smith & Nephew Healthcare Ltd & Ors

Patent claims are construed purposively, but the court must respect the language actually chosen and must not add or disregard a deliberate limitation. A product claim is not converted into a product-by-process claim merely because the product will commonly be made by a particular process.

A claim requiring a blend of modified cellulose gel-forming fibres with another type of gel-forming fibre requires the presence of gel-forming fibres which are not modified cellulose. Dependent claims must be construed in their statutory and linguistic context. Obviousness is assessed by reference to the skilled team, the common general knowledge, the inventive concept and the differences from the prior art, while guarding against hindsight.

The claimants alleged infringement of European patent EP (UK) 0 927 013 by Durafiber, a wound dressing comprising Tencel fibres and cellulose ethyl sulfonate fibres. The defendants counterclaimed for revocation on grounds including lack of novelty, obviousness and insufficiency.

The trial concerned the construction of claims 1, 3 and 5, infringement, and validity over Qin, Lassen, ‘746 (Bahia) and common general knowledge. The central issues were whether claim 1 required a manufacturing process, what constituted another type of gel-forming fibre, and whether the claimed combination was obvious.

1. Construction. Claim 1 was a product claim, not a product-by-process claim. It required an intimate mixture of discrete gel-forming modified cellulose fibres and at least one other type of discrete gel-forming fibre. The other fibres had to be gel-forming fibres not made of modified cellulose. The fibres retained their separate identities and did not comprise a composite or co-spun fibre.
2. The expressions “modified cellulose” and “gel forming” were construed in context. “Modified cellulose” was not limited to chemically derivatised cellulose. However, claim 3, although omitting the words “gel forming” before “modified cellulose fibres”, referred back to the gel-forming fibres in claim 1. Its wound-contacting surface therefore had to consist solely of a blend of gel-forming modified cellulose fibres and at least one other type of gel-forming fibre. The familiar distinction between “comprising” and “consisting of” applied.
3. Infringement. Durafiber contained non-gel-forming Tencel and gel-forming cellulose ethyl sulfonate fibres. The only gel-forming fibres were modified cellulose fibres. It therefore did not infringe claim 1, and consequently did not infringe dependent claim 3. The second defendant had committed no relevant act and the action against it was dismissed.
4. The alternative infringement case based on differences between batches and alleged differences in absorbency was not established. The experimental evidence was unreliable and did not demonstrate distinct fibre types or materially different underlying absorbency properties.
5. Validity. Claim 1 was anticipated by Qin. Claim 3 was not obvious over Qin because its two-layer teaching and the positive wound-healing function of the wound-contacting layer gave rise to a concern that combining CMC and alginate could interfere with haemostasis. Claim 3 was not invalid over Lassen because Lassen disclosed modified cellulose fibres of the same type, and its fibres were fused into a mass rather than being discrete. Claims 3 and 5 were not invalid over ‘746 (Bahia). The common-general-knowledge attack on combining CMC and alginate was rejected, partly because the absence of such a product despite longstanding knowledge supported the conclusion that the combination was not obvious. The conditional insufficiency case did not arise.

First-instance decision of the High Court (Patents Court). No prior appellate decision is stated in the judgment.