Smith & Nephew Plc v Convatec Technologies Inc.
| Jurisdiction | England & Wales |
| Judge | Lord Justice Kitchin,Lord Justice Jackson,Lady Justice Arden |
| Judgment Date | 14 December 2012 |
| Neutral Citation | [2012] EWCA Civ 1638 |
| Court | Court of Appeal (Civil Division) |
| Docket Number | Case No: A3/2012/1456 |
| Date | 14 December 2012 |
[2012] EWCA Civ 1638
IN THE COURT OF APPEAL (CIVIL DIVISION)
ON APPEAL FROM THE HIGH COURT OF JUSTICE
CHANCERY DIVISION (PATENTS COURT)
His Honour Judge Birss QC
Royal Courts of Justice
Strand, London, WC2A 2LL
Lady Justice Arden
Lord Justice Jackson
and
Lord Justice Kitchin
Case No: A3/2012/1456
James Mellor QC and Miss Charlotte May (instructed by Bristows) for the Appellant
Piers Acland QC (instructed by Bird & Bird LLP) for the Respondent
Hearing date: 30 October 2012
Introduction
This appeal concerns moist wound dressings which contain gel-forming polymers and ionic silver as an antimicrobial agent. The antimicrobial properties of ionic silver have been known for very many years but it suffers from the drawback that it is not stable in the presence of light. The respondent (Convatec) is the proprietor of European Patent (UK) No 1,343,510 ("the patent") which has a priority date of 29 November 2001 and, in its amended form, describes and claims of ways of making moist wound dressings containing ionic silver in a light stable form. The patent is of great commercial importance to Convatec because it protects a number of silverised wound dressing products with sales in the UK of about £14.7m each year.
In these proceedings the appellant (Smith & Nephew) applied to revoke the patent on the basis that it was obvious in the light of two earlier publications referred to as Kreidl and Gibbins, and that it did not describe the invention sufficiently and clearly enough for it to be performed by a person skilled in the art. Convatec conceded that the patent was invalid in the form in which it was granted but applied to amend it. Smith & Nephew resisted the application to amend the patent both on the basis that the amendment would result in the specification disclosing additional matter and on the basis that the patent as proposed to be amended would still be invalid for obviousness and insufficiency.
The action came on for trial before HHJ Birss QC in March 2012. In his judgment of 13 June 2012, the judge held that the amendment was allowable and rejected all the attacks upon the patent in its amended form. Upon this appeal, Smith & Nephew contends that the judge fell into error in failing to find the patent obvious in the light of Kreidl. It does not seek to challenge any of the judge's other findings.
The skilled team and the expert evidence
The patent is addressed to a notional skilled but unimaginative team likely to have a practical interest in its teaching. In this case there was no dispute as to the composition of that team. It would include a biomedical engineer, a chemist and a materials scientist. The biomedical engineer would have practical experience of wound dressing development; the chemist would have an understanding of silver chemistry; and the materials scientist would have practical experience of dressing structures and components.
The judge heard evidence from two witnesses, Professor Burrell for Smith & Nephew and Professor Kennedy for Convatec. Professor Burrell is Professor of Chemicals and Materials Engineering at the University of Alberta in Canada, has worked in the field of wound dressing since 1991 and has a particular interest in the use of silver in wound management.
Professor Kennedy spent his academic life up to the priority date at Birmingham University, gaining his first degree in Chemistry, then a PhD and, in due course, becoming a lecturer and then a senior lecturer. He has always had a particular interest in monomolecular and macromolecular carbohydrates. As the judge explained, Professor Kennedy was faced with a difficulty in this case in that he was instructed only shortly before the trial when Convatec's expert up to that point, Professor Qin, fell seriously ill. As a result, Professor Kennedy's evidence consisted of annotated versions of the reports Professor Qin had already prepared.
Each side attacked the other's expert but the judge found neither attack well founded. He formed the view that both experts gave their evidence fairly. He also recognised that Professor Burrell had much more experience of the use of silver in wound dressings than Professor Kennedy. Nevertheless, he found that in general he preferred the evidence of Professor Kennedy as to the thinking of the skilled team because Professor Burrell was a man of exceptional innovative talent and a problem solver who would persist in pursuing a hypothesis even in the face of negative experimental results. The judge considered Professor Burrell's evidence attributed too much of that persistence to the skilled team. Professor Kennedy's evidence, on the other hand, was generally straightforward and plausible.
Technical background and the common general knowledge
The judge set out the technical background and identified the common general knowledge of the skilled team at [6]-[8] and [31]-[38]. This has not been challenged by Smith & Nephew but I would mention the following matters which are of particular relevance to the issues arising on this appeal.
Traditional wound dressings were designed to absorb all exudates and so keep the wound dry. They were commonly made of cotton, a soft, naturally occurring cellulose based material which comprises many different fibres, each of which consists of a long tubular cell. The cell wall is rather thin and surrounds a lumen which occupies two thirds of the breadth of the fibre. Cotton absorbs water by drawing it into the lumen of each of its fibres by capillary action.
In the 1960s it was found that wounds heal more quickly if they are kept moist. In the 1980s and 1990s this knowledge led manufacturers to develop new gel-forming wound dressings based upon materials such as hydrogels and alginates which have the ability both to absorb wound exudates and maintain a moist wound surface. One well known dressing comprising a gel-forming material was made by Convatec and called Aquacel. It contains sodium carboxymethyl cellulose or simply NaCMC.
Moist wound dressings do, however, suffer from the drawback that they encourage infection. Hence there was a need to provide moist wound dressings with some kind of antimicrobial activity.
That brings me to the common general knowledge concerning silver chemistry. As I have said, ionic silver (normally in the form of Ag + ions) was known to have antimicrobial properties and indeed there were commercial products on the market which used ionic silver as an antimicrobial agent. A further advantage of ionic silver is that it has a low toxicity. However, it is highly light sensitive, that is to say that in the presence of light or other radiant energy it is reduced to silver metal which causes the loss of its antimicrobial activity and a significant discolouration of the material or solution in which it is contained.
It was also generally known that silver ions (Ag +) react strongly with chloride ions (Cl -) to form silver chloride (AgCl). Silver chloride has a low solubility and will precipitate out of solution, though due to the dynamic equilibrium between the ionic species and the salt, there will always be a small proportion of silver ions in solution. It was also known that in the presence of a large excess of chloride ions, coordination complexes can be formed, these being species in which the silver ion is bound to more than one chloride ion. So, for example, silver chloride with two chloride ions will have the formula AgCl2 -. Silver chloride complexes were known to be more soluble than silver chloride and the greater the excess of halogen, the more soluble they tend to be.
As for light stability, silver chloride was known to be unstable when exposed to light. Silver chloride coordination complexes are light stable or, at any rate, more light stable than silver chloride itself, but this was not generally known.
The judge also recorded (at [38]) that it was common ground that AgCMC was known to be unstable when exposed to light, although it was more light stable than AgCl. The judge had his doubts as to whether this was truly common general knowledge but since it was common ground, he accepted it.
The final aspect of the common general knowledge which I must mention concerns the difference between absorption and adsorption. As the judge explained, absorption involves the uptake of a substance into a material. Adsorption, on the other hand, is a gathering of a substance on the surface of a material where it may be held by electrostatic binding caused by the interaction of oppositely charged dipoles on molecules – so called Van der Waals forces.
The patent
The specification begins with the field of the invention and a statement that the invention relates to light stabilised antimicrobial materials and ways of preparing them.
There follows a description of the background of the invention and, at paragraph [0003], an acknowledgement that it was known to include silver as an antimicrobial agent in salt form in wound dressings but that such silver-containing materials are sensitive to light which causes uncontrolled discolouration. The specification explains there was therefore a need for hydrophilic polymeric materials containing silver in a light stable form.
Against this background the specification explains that the invention is directed to a way of preparing light stable materials comprising gel-forming polymeric fibres...
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