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Petition for revocation - Obviousness - Defendant company holding patent
Smith & Nephew plc v Convatec Technologies Inc: Chancery Division, Patents Court (Judge Birss QC (Sitting as a Judge of the High Court)): 13 June 2012
The defendant company held a patent, European Patent (UK) No 1,343,510 (510), concerned with methods of making a wound dressing which used silver as an antimicrobial agent and which was photostable. Claim 1 of 510 stated: ‘A method of preparing a light stabilised antimicrobial material, characterised in that the method comprises the steps of: (a) preparing a solution comprising an organic solvent and a source of silver in a quantity sufficient to provide a desired silver concentration in said material; (b) subjecting a material which includes gel-forming fibres containing one or more hydrophilic, amphoteric or anionic polymers to said solution for a time sufficient to incorporate said desired silver concentration into said polymer, wherein said polymer comprises a polysaccharide or modified polysaccharide, a polyvinylpyrrolidone, a polyvinyl alcohol, a polyvinyl ether, a polyurethane, a polyacrylate, a polyacrylamide, collagen, or gelatin or mixtures thereof; and (c) subjecting said polymer, during or after step (b) to one or more agents selected from the group consisting of ammonium salts, thiosulphates, chlorides and peroxides which facilitate the binding of said silver on said polymer, the agent being present in a concentration between 1% and 25% of the total volume of treatment, which material is substantially photostable upon drying, but which will dissociate to release said silver upon rehydration of said material.’
The claimant company sought the revocation of 510 on the grounds of obviousness over two items of prior art and insufficiency. The first item of prior art, WO 01/24839 (Gibbins), comprised methods and compositions for making a silver-containing antimicrobial hydrophilic material. The second item of prior art, US Patent 2,396,514 (Kreidl), had been published in 1946 and related to disinfectant products which contained silver in combination with a halogen and methods for making them.
The defendant had conceded that 510 was invalid and applied to amend it by limiting the claim to methods applied to materials including gel-forming fibres. The defendant maintained that claim 1 of 510 in its amended form would be valid. The claimant opposed the amendments on the basis that they were an example of intermediate generalisation and constituted added matter contrary to section 76(3) of the Patents Act 1977 as the application as filed: (i) only referred to sodium carboxymethyl cellulose, whereas the amended claim referred to gel-forming fibres generally; (ii) only concerned a polymer containing gel-forming fibres, whereas the amended claim related to gel-forming fibres containing a polymer; and (iii) the invention was not limited to the use of gel-forming fibres as the application taught that the nature of the material was not central to the invention, whereas the amended patent would do.
It fell to be determined: (i) the identity of the skilled person; (ii) whether silver chemistry and light stability fell within common general knowledge; (iii) whether the meaning of ‘photostable’ in 510 was clear; (iv) whether the amendments constituted intermediate generalisation; (v) whether the amendments disclosed additional matter; (vi) whether 510 was obvious over Gibbins and Kreidl; and (vii) whether 510 insufficiently described ‘substantially photostable’. The application would be dismissed.
(1) Given the nature of the technology, the skilled person would be a team comprising a biomedical engineer, a chemist and a materials scientist. Further, the team might also comprise (or consult with) a life scientist with an understanding of microbial organisms and experience of antimicrobial testing and biocompatibility (see  of the judgment).
(2) It would be part of the common general knowledge that silver had a number of advantages for topical application as an antimicrobial agent that had included low toxicity. However, light stability had been a practical problem associated with the use of silver in wound dressings. A further part of the common general knowledge would include interactions that had been known as absorption and adsorption, and physisorption and chemisorptions. Another area of common general knowledge would be silver chemistry and that silver carboxymethyl cellulose would be light unstable, albeit it would be more light stable than silver chloride (see , , ,  of the judgment).
(3) In the instant case, the meaning of claim 1 of 510 had been clear enough. The claim had meant that once the method had been finished and upon drying the material, the change in colour afterwards should be ‘minimal’ and the claim itself would only require the material to be ‘substantially’ photostable. Those had been words of degree but they had not been regarded as so vague as to render the claim hopelessly ambiguous (see ,  of the judgment).
(4) The established law with respect to intermediate generalisation had provided that, if the specification had disclosed distinct sub-classes of the overall inventive concept, then it should be possible to amend down to one or another of those sub-classes, whether or not they had been presented as inventively distinct in the specification before amendment (see  of the judgment). In the circumstances, the application as filed had disclosed the idea of using gel-forming fibres generally and not just sodium carboxymethyl cellulose gel-forming fibres (see  of the judgment).
(5) The test for added matter was that the decision in respect of whether there had been an extension of disclosure should be made on a comparison of the two documents that had been read through the eyes of a skilled addressee. The task for the court would be threefold: (i) to ascertain through the eyes of the skilled addressee what had been disclosed, both explicitly and implicitly in the application; (ii) to do the same in respect of the patent as granted; and (iii) to compare the two disclosures and decide whether any subject matter relevant to the invention had been added whether by deletion or addition.
The comparison would be strict in the sense that subject matter would be added unless such matter had been clearly and unambiguously disclosed in the application either explicitly or implicitly (see  of the judgment).
In the instant case, the attack of added matter would be rejected and the amendments would be allowed. The amended claim 1 of 510 had disclosed a material which had within it gel-forming fibres, those gel-forming fibres would contain within them polymers. That had been disclosed in the application as filed and there had been no added matter (see , - of the judgment). Bonzel v Intervention Ltd (No 3)  RPC 553 followed; European Central Bank v Document Security Systems Inc  All ER (D) 277 (Mar) applied.
(6) On the facts of the instant case, claim 1 of 510 had not been obvious over Gibbins as the disclosure of Gibbins had been complex and it had not been clear how a skilled person, without knowledge of the invention, could be said to have arrived at a process within the defendant’s claim by nothing more than an obvious step or steps. At the filing date, it would not have been obvious to the skilled person which of two methods had explained Kreidl’s results and would work with the defendant's gel-forming fibre. To run the test and see if the Kreidl conditions would work would be the act of an inventive person.
Accordingly, the defendant’s claim had not lacked an inventive step and it would be valid over Kreidl (see , , , - of the judgement). Pozzoli SPA v BDMO SA  All ER (D) 275 (Jun) applied; Gedeon Richter plc v Bayer Pharma AG  All ER (D) 87 (Mar) applied.
(7) The insufficiency argument would be rejected. There had been nothing before the court to suggest that the skilled person would not know what ‘substantially photostable’ in 510 had meant. Nor had there been anything to suggest that the skilled person would have difficulty knowing whether any given method had fallen within the claim or determining how to perform a method in a way which would meet the criterion (see  of the judgment).
James Mellor QC and Charlotte May (instructed by Bristows) for the claimant; Piers Acland QC and Geoffrey Pritchard (instructed by Bird & Bird) for the defendant.
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