Wounded patent survives - Smith & Nephew v Convatec Technologies
The patent was about antimicrobial wound dressings impregnated with silver.
The IPKat can do no better than copy the judgement for the background to the technology:
- Wound dressings have advanced over the years and in the 1990s wound dressings were developed which were intended to keep the wound surface moist. One method of achieving this aim was to use materials which formed a gel. One class of gelling wound dressing used alginate materials. Another kind used carboxymethyl cellulose (CMC).
- Infection is a problem associated with wounds and consequently there is a need to both prevent and treat infection resulting from wounds. Antimicrobial agents can be used topically to achieve this result. A dry wound environment was not conducive to bacterial, fungal or viral growth. However, as gel dressings became more popular the problem of bacterial growth became more apparent. One antimicrobial agent known for many years is silver. Silver has a number of advantages for topical application including low toxicity. However there is a practical problem associated with the use of silver in wound dressings. It is light stability. This sensitivity is well known. For example the light sensitive nature of silver salts was used in photography for many years.
- The patent relates to a method of preparing a light stabilized antimicrobial material for use in wound dressings and medical devices. Essentially the method is one whereby a wound dressing material can be made which comprises silver as an antimicrobial agent but which is stable in the presence of light.
The patent was acknowledged to be invalid as granted but applied to be amended as follows (underlined passages to be added):
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.
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| Is this how the dressing is used? |
The first amendment provided novelty over an old (1946) piece of prior art which did not include gel-forming fibres (Kreidl) and the second amendment provided novelty over a recent piece of prior art (Gibbins). Simplifying enormously, the judge found inventive step over the first piece of prior art because it was not obvious to apply its teaching to modern wound dressings including gel forming fibres, in particular because it was not obvious how Kreidl worked. Concerning the second piece of prior art, it was the situation that to hypothetically arrive within the scope of the amended claim it would be necessary to select one particular example of the prior art patent application that there was no particular reason to select, and then modify it (increase chloride concentration), in the absence of any particular reason to do so.
There was a great deal of discussion about an added matter objection to the first amendment. The IPKat was particularly interested in the seriousness with which the judge addressed the assertion by Convatec that the statement in the application as filed:
Materials which are particularly adapted for the inventive method include gel-forming fibers such as Aquacel™
could be read in the sense that "such that" limits rather than exemplifies "gel-forming fibers".
The decision says on this point at para 83:
Smith & Nephew's best point is the argument that when the gel forming fibres idea is introduced at the top of p5 of the application the language would be understood as a disclosure not that any gel forming fibres would do and Aquacel was simply an example but that the gel forming fibres being discussed are those like Aquacel. [feline emphasis]
The IPKat believes that usage of the limiting type would in fact be rather rare in a patent document.
However, it was only having considered the common general knowledge that the judge accepted the meaning that the patentee argued for and presumably originally meant, namely that "such that" was followed by an example, not a limiting qualification.
A point on insufficiency with regard to "photostable" was rejected.
Final result - amended patent held to be valid.
Or perhaps this is not the final result, as Merpel has noticed that the European patent is under opposition by Smith & Nephew, so this case will run for some time...
