Convatec Ltd and Others v Smith & Nephew Healthcare Ltd and Others

JurisdictionEngland & Wales
CourtCourt of Appeal (Civil Division)
JudgeLord Justice Kitchin,Lord Justice Tomlinson,Lord Justice Mummery
Judgment Date02 May 2012
Neutral Citation[2012] EWCA Civ 520
Date02 May 2012
Docket NumberCase No: A3/2011/2528, A3/2011/2530 & A3/2011/2514

[2012] EWCA Civ 520

[2011] EWHC 2039 (Pat)





Royal Courts of Justice

Strand, London, WC2A 2LL


Lord Justice Mummery

Lord Justice Tomlinson


Lord Justice Kitchin

Case No: A3/2011/2528, A3/2011/2530 & A3/2011/2514

(1) Convatec Ltd
(2) Convatec Technologies Inc
(3) Convatec Inc
(1) Smith & Nephew Healthcare Ltd
(2) Smith & Nephew Plc
(3) Speciality Fibres and Materials Ltd

Piers Acland QC and Dr Brian Nicholson (instructed by Messrs Latham and Watkins) for the Appellants/Claimants

Justin Turner QC and Mark Chacksfield (instructed by Messrs Slaughter and May and Messrs Bristows) for the Respondents/Defendants

Hearing dates: 21/22 March 2012

Lord Justice Kitchin



In these proceedings the claimants ("ConvaTec") asserted that a wound dressing sold by the first and second defendants under the name Durafiber infringed their European Patent UK No 0 927 013 ("the Patent"). Durafiber consists of a mixture of cellulose fibres called Tencel and fibres made from a derivative of cellulose called cellulose ethyl sulfonate ("CES"). The CES fibres are made by the third defendant ("Speciality Fibres").


The defendants denied infringement and challenged the validity of the Patent on the grounds that it was obvious over the common general knowledge and three items of prior art referred to in the proceedings as Qin, Lassen and Bahia, and that it was insufficient.


The action came on for trial before HHJ Birss QC sitting as a judge of the High Court. At trial, ConvaTec conceded claim 1 of the Patent was invalid over Qin but maintained that claim 3 was valid and infringed.


In his judgment, handed down on 27 July 2011, the judge rejected all the attacks on the validity of claim 3 but held it was not infringed. He also held that if ConvaTec had established infringement then claim 3 would have been invalid over Bahia.


ConvaTec now appeal against the judge's finding of non-infringement. They contend the judge fell into error in construing claims 1 and 3 of the Patent and that, on their proper interpretation, Durafiber falls within their scope. They also contend the judge fell into error in concluding that if ConvaTec had established claim 3 was broad enough to encompass Durafiber then it would have been invalid over Bahia.


The defendants cross-appeal against the finding that claim 3 is valid over Qin.

The skilled addressee


It was common ground that the Patent is addressed to a team consisting of a scientist with experience in developing wound dressings, a chemist with knowledge and experience of cellulose chemistry and, if necessary, a clinician. The judge described the constitution of the team in these terms at [32]:

"There was no dispute that in this case the person skilled in the art would likely be a team. The team would consist of (i) a scientist with experience in developing wound dressings (such a person would typically have a science degree and may or may not have a PhD); (ii) a chemist with knowledge and experience of cellulose chemistry, experienced in developing cellulose fibres and fabrics, and additionally (iii) a clinician who could provide guidance on the required clinical properties of the products being considered. The clinician would only be consulted if necessary. Whether these three sets of skill and knowledge were to be found in a single individual or a group of two or three persons is irrelevant."

Technical background


The judge set out the technical background at [14] – [31]. He also held that all of this background formed part of the common general knowledge of the skilled team as at the priority date of the Patent, 5 September 1996. Neither side disputed the judge's findings. For the purposes of this appeal, I would emphasise the following.


The Patent is concerned with wound dressings made of fibrous materials which are able to absorb relatively large quantities of aqueous liquids and, on doing so, do not dissolve but instead form a gel comprising highly swollen fibres which retain some solid structure.


Cellulose is a polymer consisting of a linear chain of glucose molecules linked together. Naturally occurring cellulose (sometimes called Cellulose I) consists of many such chains lying together in such a way that they form crystalline and amorphous regions. Water may only penetrate the amorphous regions with the result that natural cellulose is only able to absorb a relatively small amount of water.


Cellulose has been used as a source of industrial fibres for very many years. These fibres may be made by a variety of processes and are often referred to collectively as regenerated cellulose. Such regenerated cellulose (sometimes called Cellulose II) is chemically identical to natural cellulose but it tends to be thermodynamically more stable and the crystalline structure of its ordered regions is different. Tencel is a regenerated cellulose produced by a process of solvent spinning.


Cellulose may also be chemically modified by replacing the hydroxyl groups along the polymer chain with much larger substituents by, for example, etherification. One of the most commonly used cellulose ethers is carboxymethylcellulose ("CMC"). The effect of chemical modification is to disrupt the crystalline regions of the fibres and so increase their absorbency. Depending upon the degree of etherification and cross-linking between the polymer chains, the ability of the fibres to absorb water will be affected to a greater or lesser extent. These derivatives have proved extremely useful, as the judge explained:

"19. Cellulose ethers have been widely used in a variety of industries such as food production and pharmaceuticals. They have long been used as absorbents both in powder form and in the form of fibres. When using powdered cellulose ethers to absorb water, the idea is to render the cellulose water soluble by derivatisation and then crosslink the molecules. Thus when water is added the material forms a gel rather than dissolving completely. When using fibres the idea is either to partially derivatize or else to completely derivatize and then cross-link. Either way the end result is again a gel.

20. Cellulosic gel forming fibres, in particular ones made of CMC, were well established commercial products in the 1980s. There was one particular high profile application referred to in the evidence called Rely. Rely was a tampon launched by Proctor & Gamble which took approximately 45% of the US tampon market in 1980. It employed CMC fibres and was highly absorbent. It made headline news at least in part because it was associated with deaths from what was called toxic shock syndrome. Mr Woodings explained that this was not due to CMC as a material. In any case there is no doubt that the skilled team would have been very well aware of this at all material times."


It has been known since the 1960s that wounds heal more quickly if they are kept moist. As a result, those involved in the development of wound dressings have looked to incorporate into their dressings absorbent materials which will absorb exudate from the wound while maintaining a moist wound environment. The matter is complicated because the nature of the exudate varies from wound to wound and may change during the course of the healing process, as the judge said at [21] – [22]:

"21. The production of fluid (known simply as "exudate") is a normal feature of wound healing. Exudate is composed of serum-like watery fluid together with other things such as cellular debris. Serum-like watery exudate is called "serous" exudate. Exudate can be bloody (called "sanguinous") and it can be infected (called "purulent"). Purulent exudate is pussy in nature. It includes white blood cells (in particular neutrophils).

22. Over the course of the healing of a wound, the nature and amount of the exudate produced changes. Typically, wounds all produce copious amounts of serous watery exudate in the initial stages and as healing takes place, the level of exudate drops off. Serous exudate is a very complex mixture of electrolytes, glucose and other solutes. One of the properties of serous exudate which can change is the concentration of ions in the exudate."


Accordingly, a variety of different gel forming materials have been used in wound dressings, some based upon hydrocolloid powders and others upon gelling fibres. A number have been based upon alginate, a natural product derived from seaweed. The judge explained these at [24] – [26]:

"24. … The principle on which alginate dressings work is by ion exchange. Two forms of alginate are relevant: calcium alginate and sodium alginate. Calcium alginate is insoluble while sodium alginate is soluble and forms a gel. So when a calcium alginate wound dressing is used in a wound, the sodium ions in the wound exudates can be exchanged with the calcium ions in the alginate. This allows the fibres to absorb water and form a gel. Another effect of this ion exchange is that calcium ions are released. These calcium ions can have a haemostatic effect – that is they prevent bleeding.

25. The gelling characteristic and the absorbent properties of the alginates can be modified by varying two characteristics: the ratio of calcium to sodium alginate and the ratios of two particular monosaccharide residues, known as M and G. Alginates with a high M ratio swell very rapidly; with high G they gel less well but have greater strength. Depending on the source of the alginate...

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  • IP Snapshot May 2012
    • United Kingdom
    • Mondaq United Kingdom
    • 6 June 2012
    ...prior art. For the full text of the decision, click here Convatec Ltd and others v Smith & Nephew Healthcare Ltd and others [2012] EWCA Civ 520, 2 May 2012 The Court of Appeal has upheld the decision of the Patents Court in 2011, which had held that one claim of the patent was valid but......
  • Patent Costs When The Claimant Discontinues
    • United Kingdom
    • Mondaq United Kingdom
    • 16 May 2012
    ...information before they had established that they had cause to complain. In a judgement which has now been upheld on appeal, see [2012] EWCA Civ 520, ConvaTec failed to establish that a Smith & Nephew wound dressing called Durafiber infringed their patent. However, Claim 3 of the patent......

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