Amending a granted patent to avoid invalidity - the silver lining | Fieldfisher
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Amending a granted patent to avoid invalidity - the silver lining



United Kingdom

Innovate - Amending a granted patent to avoid invalidity

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Smith & Nephew Plc v Convatec Technologies Inc.

This was an application by Smith & Nephew Plc for revocation of Convatec's European Patent No.1,343,510 filed in 2001 and entitled "Light Stabilised Antimicrobial Materials", on the grounds of added matter, obviousness citing two pieces of prior art (Kreidl and Gibbins) and insufficiency.

The patent relates to light stabilised antimicrobial materials and methods of preparing antimicrobial polymers for use in wound dressings. The background addresses the problem of infection in wounds, the use of silver as an antimicrobial agent and overcoming the difficulty that silver containing materials are typically light sensitive.

Claim 1 invalid in its original form

Convatec conceded during the course of proceedings that the patent, as granted, was invalid and applied for it to be amended as follows (amendments underlined):

[44] 1. A method of preparing a light stabilized 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.

Added Matter

Smith & Nephew Plc contended that the amendments should not be allowed because they constituted added matter contrary to s76(3) of the 1977 Act. The amendments were an example of intermediate generalisation and there was no disclosure of gel forming fibres generally.

[56] The test adopted for added matter was explained by Aldous J in Bonzel v Intervention Ltd [1991] R.P.C. 553 at 574 is as follows:

"The decision as to whether there was an extension of disclosure must be made on a comparison of the two documents read through the eyes of a skilled addressee. The task of the Court is threefold:

(a) To ascertain through the eyes of the skilled addressee what is disclosed, both explicitly and implicitly in the application.

(b) To do the same in respect of the patent as granted.

(c) To compare the two disclosures and decide whether any subject matter relevant to the invention has been added whether by deletion or addition.

The comparison is strict in the sense that subject matter will be added unless such matter is clearly and unambiguously disclosed in the application either explicitly or implicitly."

HHJ Birss QC, after having reminded himself that it is important to distinguish between the disclosure of the subject matter and the scope of the claim [59], applied the law on amendments in detail comparing the post-grant amendments to the application as filed and rejected the attack of added matter finding the amendments proposed by Convatec acceptable:

[99] In any event I do not believe this argument about the phrasing of that passage in the application has much to do with the question of added matter. The question is whether the amendments give rise to added matter. In step (b) the amended claim refers to "a material which includes gel-forming fibres containing one or more hydrophilic, amphoteric or anionic polymers … wherein said polymer comprises a polysaccharide (etc.)". In my judgment all this discloses is a material which has within it gel forming fibres, those gel forming fibres containing within them polymers which satisfy both lists of properties. That is disclosed in the application as filed. There is no added matter.


The pertinent question was whether the invention was obvious to the skilled person at the filing date having regard to any matter which forms state of the art (Section 2(2) and 3 of the 1977 Act).

Gibbins was the first piece of prior art provided by Smith & Nephew, which comprised methods and compositions for making a silver-containing antimicrobial hydrophilic material, addressing the need to maintain an optimum level of moisture for wound healing. The disclosure in Gibbins was complex and it was not clear to HHJ Birss QC how a skilled person, without knowledge of the invention, could be said to arrive at a process within the Convatec claim by nothing more than an obvious step or steps [133].

The second piece of prior art that came under scrutiny cited dated back to 1946, Kreidl, and was a clear teaching of a method of preparing a light stabilised antimicrobial material for use in the wound dressings with the same basic steps as the Convatec invention. HHJ Birss QC considered this point in detail but found that Convatec's claim did not lack an inventive step (i.e. it was not obvious) and declared it valid. He was not persuaded that it was obvious to the skilled person to apply the teachings in Kreidl, focussing on cotton gauze, to modern gel forming dressing materials.


HHJ Birss QC dismissed the insufficiency argument in relation to photostability very briefly in 4 paragraphs of the judgment.


Thus Smith & Nephew's challange to the patents failed. The European Patent is, however, under opposition by Smith & Nephew – so it's unlikely the case will end here.

Key Practical Note

Deciding what amendments to make to a granted patent essentially constitutes a balancing act. On the one hand the amendments need to take the claims beyond the ambit of the prior art but on the other must not be such as to leave the patentee open to an attack of having added matter.

Beverley Potts, Senior Associate (PSL) in the IP and Technology Dispute Resolution Group at Field Fisher Waterhouse LLP