Patent

Infringement - Obviousness

Convatec Ltd and other companies v Smith & Nephew Healthcare Ltd and others: Chancery Division, Patents Court (Judge Birss QC): 27 July 2011

The claimant owned a wound dressing product called Aquacel, which was based on a cellulose derivative, carboxymethyl cellulose (CMC). The claimant also owned, inter alia, patent EP (UK) 0 927 013 (the patent), granted on 5 September 1996, entitled Wound Dressing.

The specification of the patent began by explaining that the invention related to a wound dressing and in particular to a non-adherent wound dressing comprising fibrous material. The invention was intended to address the problem of cellulose based fibres which had a high absorptive capacity initially but then tailed off.

The specification acknowledged that a mixture of alginate and other water soluble materials had been proposed before albeit as a co-spun composite fibre and that the disadvantages of prior art could be mitigated by mixing different types of gelling fibres together. Such wound dressings provided good absorbency for a range of exudates and were relatively inexpensive. In addition, a moist wound environment might be created which was beneficial to healing. The specification explained that to make the wound dressing, gel forming fibres were intimately mixed to form a web of mixed fibres. The methods of mixing those fibres were all part of the skilled person's common general knowledge.

The relevant claims of the patent were claims 1, 3, 5 and 9. Claim 1 described: 'A wound dressing comprising a blend of discrete modified cellulose gel forming fibres with one other type of discrete gel forming fibres.' Claim 3 described: 'A wound dressing as claimed in any preceding claim wherein the dressing comprises a wound contacting surface consisting of a blend of discrete modified cellulose fibres with at least one other type of discrete gel forming fibres.'

Claim 5 described: 'A wound dressing as claimed in any preceding claim wherein the dressing comprises a blend of discrete alginate fibres and discrete modified cellulose fibres.' Claim 9 described: 'A wound dressing as claimed in any preceding claim wherein the gel forming fibres have an absorbency of at least 2g of liquid per fibre.' There was no dispute that in the instant 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 might or might 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 those three sets of skill and knowledge were to be found in a single individual or a group of two or three persons was irrelevant.

The first and second defendant companies wished to sell a wound dressing called Durafiber, which was made from a blend of cellulose fibres called Tencel and fibres made from cellulose ethyl sulfonate (CES). CES fibres for Durafiber were made by the third defendant company. The fourth defendant was an ex-employee of the claimants then working for the third defendant.

The claimant contended that Durafiber infringed various of their intellectual property rights relating to wound dressings. The defendant counterclaimed for revocation of the patent on the ground of invalidity on the bases of obviousness and common general knowledge. In respect of its counterclaim, the defendants relied on three items of prior art, referred to as Qin, Lassen and Bahia, all published before the priority date of the patent. Qin was published on 9 May 1996. The abstract was a fair summary of its disclosure and stated: 'A wound dressing comprises in combination (i) a first wound contact layer which preferably has a positive effect on the healing of the wound, and (ii) a second layer of greater hydrophilicity than the first layer.'

Qin was therefore based on the idea of a two-layer dressing, as the specification explained, to ensure that bulk exudate was removed from the wound and peripheral skin to reduce or eliminate maceration. Prior art dressings had not always proved satisfactory in venting the large amount of fluid production (exudate) present in a wound. Examples of materials to be used in layer (i) were given. They included, inter alia, calcium alginate to provide calcium ions for haemostasis. Layer (i) might be provided as a woven, non-woven or knitted material or as a gel. The Lassen patent was published in 1981, and its disclosure related to chemically modified cellulose fibres and a method of extracting them into filaments.

The filaments were then used to lay down a web which could be used to make disposable diapers and other such absorbent products. It was common ground that Lassen disclosed (or at least rendered obvious) a swab or surgical sponge made using the web which would be the wound contacting surface. The web would be made from composite filaments made from phosphorylated cellulose fibres and fibres of Buckeye brand cross-linked CMC. Those two fibres were both gel forming fibres.

Bahia was a PCT application published on 4 August 1994, entitled Wound Dressings. It related to a wound dressing employing CMC fibres in the wound contacting surface. Following negotiations between the parties, the only live issue at the instant trial was the claim for infringement of the patent and the counterclaim for its revocation. By the end of the trial, the claimants had accepted that claim 1 had been anticipated by Qin. Consequently, the only live issues on the validity of claim 3 were obviousness over the three forms of prior art (Qin, Lassen and Bahia) and common general knowledge. On the basis that the second defendant was a holding company and did not trade in the United Kingdom, and there was no evidence of any act of infringement committed or threatened by it, the action against the second defendant was dismissed.

The issues for determination were: (i) the true construction of claims 1 and 3; (ii) whether Durafiber infringed the patent; and (iii) whether claim 3 was obvious over Qin, Lassen and Bahia; and (iv) whether claim 3 was invalid over common general knowledge alone.

The court ruled: (1) In the instant case, the common general knowledge included: (i) knowledge of cellulose as used in gel forming wound dressing products, (ii) knowledge of wound exudate; (iii) knowledge of moist wound dressings which promoted the maintenance of a moist wound environment by gelling; (iv) production of gel-forming CMC fibres; (v) the use of CMC gel-forming fibres in commercial products; (v) how to make CMC gel-forming fibres; (vi) knowledge of how to vary the gelling and absorbency properties of cellulose derivatives by varying the degrees of substitution and/or cross-linking; (vii) knowledge of the difference in crystal structure and thermodynamic stability between Cellulose I and Cellulose II fibres: in particular, it was well-known that Cellulose II had a modified crystal structure and was thermodynamically more stable than the naturally occurring cellulose, Cellulose I; (viii) Knowledge of Alginate fibre wound dressings, which had been on the market since the 1970s; and (ix) knowledge that different fibres could have different absorption capacities and rates of absorbency: for example, CMC was generally more absorbent and had a higher rate of absorption than alginates (see [14], [21], [23], [33] of the judgment).

(2) It was well established that construction of a patent claim was purposive in nature and the question was always to work out what the person skilled in the art would have understood the patentee to be using the language of the claim to mean. From that it followed that, first, the words of the claim were to be construed having regard to the patentee's purpose as set out in the rest of the specification.

Secondly, the exercise was one of interpretation of the words of the claim. Accordingly, it was not permissible simply to ignore an integer of the claim; nor was it permissible to write a new integer into the claim. Further, it was always important to bear in mind that the skilled person read the specification in the light of the common general knowledge and appreciating that its purpose was to describe and demarcate an invention, namely a practical idea for a new product or process (see [48], [50] of the judgment).

In the instant case, claim 1 was a product claim. It required the wound dressing to comprise a mixture of two classes of gel forming fibre. The mixture had to be intimate but the fibres had to retain their separate (discrete) nature. There should be modified cellulose gel forming fibres together with at least one other type of gel forming fibres, namely some gel forming fibres not made of modified cellulose. That construction of claim 1 was in truth quite plainly what a skilled person would understand the language of claim 1 to mean, in its proper context, in the light of the specification as a whole and in the light of the common general knowledge.

The two rival constructions of claim 1 advanced by the parties had not really been interpretations of the words of the actual claims at all, they had both been attempts to create new possible patent claims which could have been written in the light of the specification as a whole and which a skilled person might not have been surprised to see if they had read the specification first and then turned to the claims. In respect of claim 3, it simply required that the wound contacting surface of the dressing consisted of a mixture of gel forming modified cellulose fibres and at least one other type of gel forming fibre, namely something other than modified cellulose. All the fibres at the wound contacting surface of claim 3 had to be gelling fibres (see [77], [78], [100] of the judgment).

Kirin-Amgen Inc v Hoechst Marion Roussel Ltd; Hoechst Marion Roussel Ltd v Kirin-Amgen [2004] All ER (D) 286 (Oct) applied; Virgin Atlantic Airways Ltd v Premium Aircraft Interiors UK Ltd [2009] All ER (D) 235 (Oct) applied.

(3) The only gel forming fibres in Durafiber were made of CES. In other words, as regards gel forming fibres, Durafiber used modified cellulose alone and there was no other type of gel forming fibre present. Accordingly, on the true construction of the claims, Durafiber did not infringe claim 1. Further, since claim 3 was dependent on claim 1, Durafiber did not infringe that claim either, irrespective of the issues of construction of claim 3 (see [104], [105] of the judgment).

Durafiber did not infringe the patent (see [185] of the judgment).

(4) In assessing obviousness, it was settled law that the court had to adopt a structured approach which was to: '(1) (a) Identify the notional "person skilled in the art"; (b) Identify the relevant common general knowledge of that person; (2) Identify the inventive concept of the claim in question or if that cannot readily be done, construe it; (3) Identify what, if any, differences exist between the matter cited as forming part of the "state of the art" and the inventive concept of the claim or the claim as construed; (4) Viewed without any knowledge of the alleged invention as claimed, do those differences constitute steps which would have been obvious to the person skilled in the art or do they require any degree of invention?'

Further, the question of obviousness had to be considered on the facts of each case. The court had to consider the weight to be attached to any particular factor in the light of all the relevant circumstances (see [125] of the judgment).

In the instant case, the invention in question was a wound dressing and the claim would only be obvious if it was obvious to the relevant team as a whole. Qin did employ a material which included, inter alia, a combination of CMC and alginate at layer (i), but it was a co-spun alloy fibre (pectin/CMC/alginate). The wound expert's evidence was that alloys like that had not necessarily provided the benefit of both properties of alginate and pectin, and that the skilled person would be concerned about knowing what the properties of the combined layer would be.

The skilled person would be concerned that the CMC could disrupt the haemostatic potential of the alginate. Accordingly, mixing CMC fibres with alginates at the wound contacting surface, when the mixture might interfere with the alginate's function, could give you the worst of both worlds. Consequently, that was prima facie evidence that it would not be obvious over Qin to employ such a felt as the layer (1) wound contacting surface. Further, with respect to Lassen, it was common ground that Lassen disclosed (or at least rendered obvious) a swab or surgical sponge made using a web made from composite filaments made from phosphorylated cellulose fibres and fibres of Buckeye brand cross-linked CMC. Those two fibres were both gel forming fibres.

Since both those fibres were modified cellulose fibres on any view, there was therefore no other type of fibre in Lassen. It followed that claim 3 was not invalid over Lassen. In relation to Bahia, there were grave doubts whether there was anything patentably distinct between Bahia and the defendants' actions which were alleged to infringe.

Consequently, on the basis of the findings on the infringement side of the case that the claimants had failed to establish that the CES product of the defendants fell within the claim on their construction of it, there was no basis for finding that the product of example 1 of Bahia would fall within the claim (see [139], [140], [142], [170] of the judgment). Claim 3 was not obvious over Qin, Lassen or Bahia (see [185] of the judgment).

Windsurfing International Inc v Tabur Marine (Great Britain) Ltd [1985] RPC 59 applied; Pozzoli SPA v BDMO SA [2007] All ER (D) 275 (Jun) applied; Conor Medsystems Inc v Angiotech Pharmaceuticals Inc [2008] All ER (D) 107 (Jul) applied.

(5) When looking at a case based on nothing but the common general knowledge of the skilled person, it was not only legitimate, but vital, to look at what had actually happened in the field. Although the person skilled in the art was a legal construct, he or she was not supposed to be so divorced from reality that one could not consider such evidence when the question was one of that kind (see [180] of the judgment).

In the instant case, the case based on common general knowledge alone that it had been obvious to combine CMC and alginate fibres in a wound dressing would be rejected. If that combination had been obvious to a person skilled in the art in 1996, it would have been equally obvious for any time in the previous ten years since the relevant facts had become common general knowledge. However, no such product had emerged on the market.

The fact that it had not was sufficient in the instant case to dismiss the case based on obviousness over common general knowledge alone (see [181], [182] of the judgment). Abbott Laboratories Ltd v Evysio Medical Devices ULC [2008] All ER (D) 282 (Apr) applied.

Piers Acland QC and Brian Nicholson (instructed by Latham & Watkins) for the claimants. Justin Turner QC and Mark Chacksfield (instructed by Slaughter and May and Bristows) for the first, second and third defendants.