Convatec Ltd & Anor v Smith & Nephew Healthcare Ltd & Ors

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.

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.”

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 (e.g. from different species of seaweed), the materials can have different ratios of these monosaccharides.

26.

At the priority date there were a number of alginate fibre based dressings with different gelling properties and different absorbency properties. Two particular alginates are referred to in the evidence: Sorbsan and Kaltostat. Sorbsan is a straight calcium alginate while Kaltostat is a mixture of 80:20 calcium and sodium alginate. There were also alginate products in which the alginate fibre was mixed with other things. For example, Kaltocarb consisted of alginate fibres together with charcoal cloth and Sorbsan Plus was alginate fibres bonded to a viscose layer. Fibracol was a product consisting of alginate fibres together with collagen. There was also an alginate product called Carbonet but that was not a gelling product.”

Others were based on CMC gelling fibres. One of these was ConvaTec’s own wound dressing called Aquacel. Aquacel has been enormously successful and has achieved worldwide sales of $2 billion since it was launched in 1996, and is said to be worth £100 million per year with sales of £13.45 million in the UK for the first nine months of 2010. Another, which was also well known, was called Super AB, and was launched in the mid 1980s.

The judge summarised the common general knowledge in the following non-contentious terms at [33] – [34]:

“33.

The common general knowledge was not in dispute. It included all the matters I have set out above by way of technical background and the following (taken from ConvaTec’s closing):

i)

Production of gel-forming CMC fibres: was common general knowledge from as early as the 1970s.

ii)

The use of CMC gel-forming fibres in commercial products: for example, the Super AB wound dressing was common general knowledge in the mid 1980s.

iii)

How to make CMC gel-forming fibres: amongst other things by etherification was common general knowledge from the mid 1980s.

iv)

Variation of the gelling and absorbency properties of cellulose derivatives by varying the degrees of substitution and/or cross-linking: was common general knowledge from the mid 1980s.

v)

The difference in crystal structure and thermodynamic stability between Cellulose I and Cellulose II fibres: was common general knowledge. In particular, it was well-known that Cellulose II has a modified crystal structure and is thermodynamically more stable than the naturally occurring cellulose, Cellulose I.

vi)

Alginate fibre wound dressings: had been on the market since the 1970s.

vii)

Different fibres can have different absorption capacities and rates of absorbency: for example, CMC is generally more absorbent and has a higher rate of absorption than alginates.

34.

Another aspect of common general knowledge related to fibre processing to make webs for use in products like wound dressings. Techniques such as carding were very well known as was the making of non-woven felts e.g. by needle punching. Mixing or blending batches of fibre together was also common general knowledge.”

The Patent is entitled “Wound Dressing” and the description begins by explaining that the invention relates to a wound dressing and, in particular, a non-adherent wound dressing comprising fibrous material, and to a method of treating a wound comprising the application of the dressing to a wound.

Paragraph [0003] is important and reads:

“It is well known that the cleansing and debriding of wounds and the removal of wound exudate is important to the process of healing wounds. Commonly used wound dressings comprise gauze, foams, sponges, cotton wads or other fibrous materials. Gauze and other fibrous materials absorb fluids by capillary action. Some absorbent fibres are capable of forming a gel on contact with exudate which can give the advantage of non-adherence to the wound. Such fibres when used alone in contact with a wound tend to preferentially absorb a particular type of exudate. In addition such fibres when used alone in contact with a wound tend to be capable of absorbing exudate at only one rate or in one rate pattern. For instance those fibres based on cellulose tend show high absorptive capacity for water which tends to be initially very high and then tail off. Since wound exudates are variable and can have different ion contents and viscosities optimum treatment of a particular wound is not always achieved when such fibres are used alone.”

Here the patentee explains the advantage of gel forming fibres is that they absorb exudate and do not stick to the wound. But then, importantly, the patentee identifies the disadvantage of such fibres as being that when they are used alone in contact with the wound they tend preferentially to absorb a particular type of exudate and do so at only one rate or in one rate pattern. The particular disadvantage of fibres based on cellulose is said to be that they show an absorptive capacity for water which tends to be initially very high but then tails off. As was generally known, wound exudates are variable and have different ion contents and viscosities with the result that the use of cellulose based fibres alone may not achieve optimum wound treatment.

After referring to an earlier disclosure of a co-spun composite fibre, the specification then explains the solution at paragraph [0005]:

“We have now found that the disadvantages of the prior art can be mitigated by mixing different types of gelling fibres together. Accordingly the present invention provides a wound dressing comprising, in sheet form, a mixture of different types of gel forming fibres.”

Such a wound dressing is said in paragraph [0006] to have the advantages that it provides good absorbency for a range of exudates and is also relatively inexpensive. In addition, it creates a moist wound environment.

Paragraph [0007] explains that the gel forming fibres of the invention are hygroscopic and, upon uptake of wound exudate, become moist and slippery or gelatinous and so reduce the tendency of any surrounding fibres to adhere to the wound.

Paragraph [0008] identifies various different types of gel forming fibre which may be used and refers specifically to those made of CMC, pectin, alginate, chitosan, hyaluronic acid or other polysaccharides and to fibres derived from gums.

The specification continues at paragraphs [0009] and [0010] by explaining that the gel forming fibres for use in the invention preferably have a particular degree of absorbency of water or saline as measured in the free swell absorbency method, a particular degree of substitution and a particular tenacity. Importantly, it is said that the fibres are preferably mixed to give a dressing which comprises fibres of different absorbencies and also different absorbency rates and profiles.

The dressing may comprise other fibres, whether natural or synthetic, with much lower absorbencies and which do not form gels, as explained in paragraph [0011]. Then, at [0014], various common general knowledge techniques for making wound dressings and mixing the gel forming fibres of the invention are described.

Finally, I should refer to the examples. Example 1 describes the production of a web comprising alginate fibres used in the commercial dressing Kaltostat with CMC fibres of the kind used in Aquacel. In Example 2, a dressing made of this composite web was tested for absorbency, together with another dressing made in the same way but with a different ratio of alginate to CMC fibres, together with a control dressing containing CMC fibres alone.

The key claims are 1 and 3:

We were also referred to claims 4, 5, 8 and 9 which read:

The proper meaning of claims 1 and 3 lies at the heart of all the issues on this appeal. The approach to be adopted to the interpretation of a patent claim was summarised by this court in Virgin v Premium Aircraft [2009] EWCA Civ 1062, [2010] RPC 8 at [5]:

“One might have thought there was nothing more to say on this topic after Kirin-Amgen v Hoechst Marion Roussel [2005] RPC 9. The judge accurately set out the position, save that he used the old language of Art 69 EPC rather than that of the EPC 2000, a Convention now in force. The new language omits the termsof from Art. 69. No one suggested the amendment changes the meaning. We set out what the judge said, but using the language of the EPC 2000:

[182] The task for the court is to determine what the person skilled in the art would have understood the patentee to have been using the language of the claim to mean. The principles were summarised by Jacob LJ in Mayne Pharma v Pharmacia Italia [2005] EWCA Civ 137 and refined by Pumfrey J in Halliburton v Smith International [2005] EWHC 1623 (Pat) following their general approval by the House of Lords in Kirin-Amgen v Hoechst Marion Roussel [2005] RPC 9. An abbreviated version of them is as follows:

(i)

The first overarching principle is that contained in Article 69 of the European Patent Convention;

(ii)

Article 69 says that the extent of protection is determined by the claims. It goes on to say that the description and drawings shall be used to interpret the claims. In short the claims are to be construed in context.

(iii)

It follows that the claims are to be construed purposively—the inventor's purpose being ascertained from the description and drawings.

(iv)

It further follows that the claims must not be construed as if they stood alone—the drawings and description only being used to resolve any ambiguity. Purpose is vital to the construction of claims.

(v)

When ascertaining the inventor's purpose, it must be remembered that he may have several purposes depending on the level of generality of his invention. Typically, for instance, an inventor may have one, generally more than one, specific embodiment as well as a generalised concept. But there is no presumption that the patentee necessarily intended the widest possible meaning consistent with his purpose be given to the words that he used: purpose and meaning are different.

(vi)

Thus purpose is not the be-all and end-all. One is still at the end of the day concerned with the meaning of the language used. Hence the other extreme of the Protocol—a mere guideline—is also ruled out by Article 69 itself. It is the terms of the claims which delineate the patentee's territory.

(vii)

It follows that if the patentee has included what is obviously a deliberate limitation in his claims, it must have a meaning. One cannot disregard obviously intentional elements.

(viii)

It also follows that where a patentee has used a word or phrase which, acontextually, might have a particular meaning (narrow or wide) it does not necessarily have that meaning in context.

(ix)

It further follows that there is no general "doctrine of equivalents."

(x)

On the other hand purposive construction can lead to the conclusion that a technically trivial or minor difference between an element of a claim and the corresponding element of the alleged infringement nonetheless falls within the meaning of the element when read purposively. This is not because there is a doctrine of equivalents: it is because that is the fair way to read the claim in context.

(xi)

Finally purposive construction leads one to eschew the kind of meticulous verbal analysis which lawyers are too often tempted by their training to indulge.”

In a case such as the present it is important to have in mind that the exercise to be undertaken is one of interpretation of the actual language used in the claim with the aim of ascertaining what the skilled person would have understood the patentee to be using that language to mean. As Lord Hoffmann said in Kirin Amgen Inc v Hoechst Marion Roussel [2004] UKHL 46, [2005] RPC 9 at [34]:

“"Purposive construction" does not mean that one is extending or going beyond the definition of the technical matter for which the patentee seeks protection in the claims. The question is always what the person skilled in the art would have understood the patentee to be using the language of the claim to mean. And for this purpose, the language he has chosen is usually of critical importance. The conventions of word meaning and syntax enable us to express our meanings with great accuracy and subtlety and the skilled man will ordinarily assume that the patentee has chosen his language accordingly. As a number of judges have pointed out, the specification is a unilateral document in words of the patentee's own choosing. Furthermore, the words will usually have been chosen upon skilled advice. The specification is not a document inter rusticos for which broad allowances must be made. On the other hand, it must be recognised that the patentee is trying to describe something which, at any rate in his opinion, is new; which has not existed before and of which there may be no generally accepted definition. There will be occasions upon which it will be obvious to the skilled man that the patentee must in some respect have departed from conventional use of language or included in his description of the invention some element which he did not mean to be essential. But one would not expect that to happen very often.”

I come then to apply these principles in considering the proper interpretation of claims 1 and 3. It is necessary to begin with claim 1 because claim 3 is dependent upon it and because the judge found that Durafiber did not fall within its scope.

The judge was faced with a most unusual situation in that he was not attracted by the interpretation contended for by either side.

ConvaTec argued that claim 1 includes wound dressings comprising two types of modified cellulose gel forming fibre with different absorbencies, whether because they are based on different polymers or because they have different degrees of substitution or cross-linking.

The defendants argued that “type” in claim 1 means a particular polymer, and that “other types” would be seen as other polymers. So alginate is different from CMC; and CMC is different from CES. This interpretation, they argued, is straightforward and consistent with the general teaching of the specification.

The judge rejected both of these arguments, concluding that claim 1 required a blend of gel forming modified cellulose fibres and at least one other type of gel forming fibres, that is to say fibres which are not modified cellulose. He put it this way at [64] – [65]:

“64.

The claim reads “a blend of discrete modified cellulose gel forming fibres with at least one other type of discrete gel forming fibres”. The claim is perfectly clear. One “type” of discrete gel forming fibre is “modified cellulose”. As well as fibres of that type, in order to be within the claim you must use fibres of at least one “other type”, in other words some discrete gel forming fibres which are not modified cellulose. Focussing on just the word “type” misses the way claim 1 is written.

65.

In my judgment the meaning of claim 1 is actually rather simple. If all the gelling fibres in the wound dressing are modified cellulose then the claim is not satisfied. The claim requires a blend of (gel forming) modified cellulose fibres and some other type of fibres, that is to say some other fibres which are not modified cellulose. If I ask in a shop for a bowler hat and another type of hat, I do not expect to be given two bowler hats, differing only in their size or colour or whatever.”

On this appeal, ConvaTec maintained the interpretation for which they contended before the judge. The defendants, on the other hand, abandoned the interpretation for which they had contended and instead supported that of the judge.

ConvaTec’s argument proceeded as follows. As explained in paragraph [0003] of the specification, it was known that different kinds of alginates have different absorbency properties. It was also known that different kinds of cellulose fibres have different absorbency properties depending upon the choice of derivative and the degree of substitution and cross-linking.

Against this background, the solution to the problem is stated in paragraph [0005] to be the use of a mixture of different types of gel forming fibres in the wound dressing. This is followed almost immediately afterwards, in paragraph [0007], by an unambiguous reference to fibres having different gelling properties as being different “types”. Fibres having different gelling properties have different absorbencies – the two go together. Accordingly, the different types of gel forming fibres referred to in paragraph [0007] necessarily have, and would be understood to have, different absorbencies.

Paragraph [0008] then identifies CMC fibres as being preferred gel forming fibres and goes on to list a number of other preferred kinds of gel forming fibres, one of which is “chemically modified cellulosic fibres”. This term is not limited to CMC and embraces a variety of other cellulose derivatives.

Finally, paragraph [0010] teaches that the gel forming fibres are preferably mixed to give a dressing comprising fibres of “different absorbencies and also different absorbency rates and profiles”. The reference here to “absorbencies” is a reference to the absorptive capacity of fibres measured in grams of liquid per gram of fibre. The phrase “absorbency rates and profiles” is clearly a reference to something else – the pattern of absorbency over time. None of the claims expressly refer to gelling fibres having “different absorbencies”. However, claim 4 introduces a requirement for the different types of gel forming fibres to have “different rates of liquid absorbency”. This is a clear indication that the focus of paragraph [0010] (in other words that which is said to be preferable) is a dressing comprising fibres which have different absorbency rates and profiles.

So, in summary, ConvaTec submitted:

Attractively though these submissions were presented, I find myself unable to accept them.

In my judgment, claim 1 is clear. It calls for a blend of two different types of discrete gel forming fibres; one must be based upon modified cellulose such as CMC or CES; the other must be made of some other material, such as pectin, alginate, chitosan or hyaluronic acid.

This interpretation is entirely consistent with and supported by the body of the specification which, in paragraph [0003], explains that gelling fibres based on cellulose show a high absorptive capacity for water but suffer from the drawback that this capacity tails off over time.

Paragraph [0004] then says that co-spinning different polymer types to produce what were described during the course of the appeal as alloys may not achieve optimum treatment.

Against this background the solution provided by the Patent is to mix different types of gelling fibres together. In context, the skilled person would understand this to be a description of the mixing of gelling fibres based upon cellulose with gelling fibres of some other basic chemistry. This understanding would be confirmed by paragraph [0007] which describes the various different types of gelling fibre to which I have referred and which, in the light of the common general knowledge, the skilled person would expect generally to have different absorbencies and also different absorbency rates and profiles, a plainly desirable characteristic, as described in paragraph [0010].

This interpretation is also consistent with the subsidiary claims which variously call for the different fibre types to have different rates of absorption (claim 4); to comprise a blend of alginate fibres and modified cellulose fibres (claim 5); and to have an absorbency of at least 2 grams of liquid per gram of fibre (claim 9).

If it occurred to the skilled person to consider the interpretation contended for by ConvaTec, I have no doubt he would reject it for the following further reason. He would appreciate the specification contains no description or teaching of the difference in absorbency which would be sufficient to distinguish one fibre type from another.

ConvaTec sought to overcome this difficulty by relying upon the evidence of the defendants’ expert in cellulose chemistry, Mr Woodings. ConvaTec submitted that Mr Woodings accepted in the course of his cross-examination that the wound care team would regard as material a difference in absorbency of 2-3 grams of liquid per gram of fibre.

We were taken to the whole of Mr Woodings’ cross-examination upon this issue during the course of the appeal. I have read and re-read that evidence but I am doubtful that it supports the proposition for which ConvaTec contends and, in particular, I do not think Mr Woodings ever accepted such a difference in absorbency was of any practical relevance. Certainly, I am wholly unpersuaded that the judge fell into error in concluding as he did at [70]-[71]:

“70.

ConvaTec’s construction necessarily imports a word of degree. The types must be “materially” different. How different is that? Mr Acland submitted that the evidence was that a difference of 2-3g/g absorbency would be regarded by the skilled person as a material difference. This arose from some passages in his cross-examination of Mr Woodings. In my judgment Mr Woodings’ evidence as a whole was not as helpful to ConvaTec’s construction as it was submitted to be. In my judgment he did not regard the point as clear cut. When Mr Woodings was first asked about it I took his view to be that fibres which differed by 2-3 g/g absorbency would be regarded as having different absorbency properties in a laboratory. Asked about it a second time Mr Woodings was shown an Aquacel monograph from 1998 which gave figures for absorbency of various dressings including a group of alginate dressings. The absorbencies of these alginate dressings did differ between themselves by about 2-3g/g according to a graph. Mr Woodings accepted the differences between these dressings were material differences but was in doubt about the significance of those differences. He was also concerned about testing methods. I took Mr Woodings’ evidence as a whole on this to be that as a technical matter a skilled person working in a laboratory would regard a difference of that magnitude as a difference which was a genuinely measurable or real difference. But whether it was a difference of any significance from a practical point of view, Mr Woodings did not know and if anything my impression was that he doubted it.

71.

When the patent and in particular paragraph [0010] refers to “different absorbencies” it seems to me that the skilled reader would think the patentee was referring not just to differences which can be measured but to differences in the behaviour of two classes of fibre which are sufficiently great to make it worthwhile putting those classes of fibre together, from the point of view of the practical behaviour of a wound dressing. The brief cross-examination of Mr Woodings on this did not explore the issue in any depth. I doubt but do not have to decide whether the evidence is sufficient to make good a submission that a given difference in absorbency (in this case 2-3g/g) was different enough to be relevant from the point of view of wound dressing behaviour. If Mr Acland’s submission on construction is right then this analysis becomes vital. It is the key to ConvaTec’s infringement case. It seems to me that, as a matter of construction, these problems would be obvious to a skilled reader as a necessary facet of a construction which demanded two classes of fibre differing only in their relative absorbency properties and by some unspecified degree. Claims can be delimited by words of degree (see “large” in BTH v Corona (1922) 39 RPC 49) but the fact that ConvaTec’s construction introduces an issue of this kind into the construction of claim 1 is a point against it. The Protocol refers to reasonable certainty for third parties. In my judgment ConvaTec’s construction runs counter to that principle.”

In my judgment the skilled person would therefore be confirmed in the view that the patentee has chosen to define his monopoly on the more certain foundation of the requirement of a blend of gel forming fibres based on cellulose with gel forming fibres of some other basic chemistry.

For all these reasons, I have reached the conclusion that the judge arrived at the correct interpretation of claim 1.

Claim 3 differs from claim 1 in two respects. First, claim 3 requires the wound contacting surface to have a particular composition (“wherein the dressing comprises a wound contacting surface consisting of …”). Second, claim 1 uses the term “modified cellulose gel forming fibres” whereas claim 3 simply refers to “modified cellulose fibres”.

The parties were agreed both before the judge and on this appeal that the terms “comprising” and “consisting of” are used in this claim in their familiar sense, that is to say “comprising” means “includes but is not limited to” and “consisting of” means that nothing else may be included. Thus the wound contacting surface of claim 3 must contain the defined blend and nothing else.

The parties were not, however, agreed as to the nature of that defined blend and, in particular, the meaning of the expression “discrete modified cellulose fibres”.

ConvaTec contended, as they did before the judge, that the “modified cellulose gel forming fibres” of claim 1 are chemically modified forms of cellulose, for otherwise they would not be gel forming. However, the term “modified cellulose” which appears in claim 3 embraces chemically modified (derivatized) cellulose such as CMC and also non-derivatized cellulose such as Tencel.

Recognising that claim 3 is dependent on claim 1, ConvaTec contended it can be satisfied in a variety of ways and, in particular, by a dressing in which (i) the wound contacting surface consists of a blend of gelling fibres, at least one of which is modified cellulose; or (ii) the wound contacting surface consists of a blend of gelling fibres, at least one of which is modified cellulose, together with a non-derivatized cellulose fibre such as Tencel.

ConvaTec supported this interpretation by referring to paragraph [0011] of the specification which explicitly refers to the inclusion of non-derivatized cellulose fibres. They submitted the skilled person would note this description and consider that such fibres have been deliberately catered for in claim 3.

The judge rejected ConvaTec’s interpretation, concluding that the “discrete modified cellulose fibres” referred to are just the “discrete modified cellulose gel forming fibres” of claim 1. He considered that claim 3 is simply using a partial description “discrete modified cellulose fibres” to refer to the “discrete modified cellulose gel forming fibres” of claim 1.

I believe that the judge arrived at the correct interpretation of claim 3 for the following reasons. First, the skilled person would consider the claim to be directed to the composition of the wound contacting surface of the dressing and would consider this to be a particularly important element of the dressing because of the need to ensure non-adherence to the wound, the maintenance of a moist environment and a high absorptive capacity of the dressing. I believe he would therefore naturally understand the claim to be requiring the presence of the blend of claim 1 at the wound surface.

Second, the use of the phrase “one other type of discrete gel forming fibres” appears to contemplate a wound contacting surface in which the discrete modified cellulose fibres are themselves gel forming fibres.

Third, I consider this interpretation derives further support from the subsidiary claims and, in particular, claims 5 and 8. Claim 5 is directed to a wound dressing which comprises a blend of discrete alginate fibres and discrete modified cellulose fibres. This makes little sense unless the discrete modified cellulose fibres are gel forming as called for by claim 1. Much the same point may be made in relation to claim 8 which calls for a dressing comprising a blend of from 30% modified cellulose fibres with 70% alginate fibres by weight. I consider the reader would understand the modified cellulose fibres must again be gelling fibres.

For all these reasons I agree with the judge that claim 3 requires the wound contacting surface to consist of a mixture of gel forming modified cellulose fibres and at least one other type of gel forming fibre.

It follows that Durafiber does not infringe the Patent. It comprises a blend of Tencel fibres and fibres made from CES. The only gel forming fibres are those made from CES and, since there is no other type of gel forming fibre present, Durafiber cannot infringe claim 1; nor can it infringe claim 3.

It also follows that there is no need to address the further finding of the judge that, even on ConvaTec’s construction, infringement had not been established. Nevertheless, since we heard argument upon it, I shall express my conclusions, albeit shortly.

ConvaTec’s case as opened at trial was founded upon photographs of the Durafiber product when viewed under a light microscope in hydrated and non-hydrated form. ConvaTec contended that, after hydration, two populations of gelling fibres could be seen, namely “thick” and “thin” fibres; and this observation showed that there were two distinct and distinguishable populations of gelling fibre, each having different absorbency properties.

After cross-examination of ConvaTec’s expert, Mr Bishop, ConvaTec effectively abandoned this case and instead sought to rely upon the batch records of the third defendant and the evidence given under cross-examination by Mr Woodings.

ConvaTec’s new case ran as follows. Speciality Fibres manufactures CES fibres in a batch process using a type of pressurised vessel called a kier. At the end of each reaction, the resulting fibre mass (called “tow”) is removed from the kier and two short pieces (representing the extremes of absorbency) are cut from each end. These two pieces are mixed together and four samples are removed for absorbency testing. The mean value is taken as the absorbency of the batch.

Four batches of tow are blended together into a mix and combined with Tencel. Each mix is used by Speciality Fibres to make a batch of fabric for use in Durafiber dressings. On occasions, dressings are made using a combination of different mixes.

Speciality Fibres gave disclosure of batch records for 25 representative batches. Two points emerged:

The judge rejected this case on the facts. First, he pointed to the intra-batch variations and the potential difficulty this created for ConvaTec on validity over Bahia:

“116.

I doubt 2-3 g/g was established to be a relevant (as opposed to measurable) difference. However the patentee’s argument suffers from a more fundamental flaw. The prior art ‘746 [Bahia] discloses at least making a wound dressing from fibres produced in a single batch. With an eye on this ConvaTec disputes the existence of evidence of differences in absorbency between samples from a single batch. The data ConvaTec relies on to establish infringement is the defendants’ absorbency data which on the face of it shows variation between batches of fibres. However the defendants point out that variation to a broadly similar degree can also be seen in the data taken for samples taken within a single batch. If there is such variation between samples from a single batch then using one batch of fibre to make a wound dressing as disclosed in ‘746 would, on ConvaTec’s construction of the claim, risk invalidity.”

Secondly, the judge concluded that the infringement case was simply not made good on the evidence:

“120.

The reason none of these points were properly explored in evidence was that, as Dr Turner submitted, the claimants’ case on infringement was transformed during the trial. Mr Bishop’s expert’s reports were focussed on the experiments and so was the claimants’ opening skeleton. I do not say it was illegitimate for the claimants to raise the point but they must take the evidential basis for it that they find. In my judgment even if the claim was to be read in the way the claimants contend, infringement would not have been established. In summary all the evidence amounts to is that some variation in the absorbency data will exist. There will be some intra-batch variation and some inter-batch variation. I am not satisfied the magnitude of intra-batch variation is any more or less that the inter-batch variation. There is no basis to distinguish safely between variability in results due to variability in the test as opposed to variability in the underlying material. I am not satisfied the differences in the numbers represents actual differences in the properties of the materials. There is no basis to say whether any two given samples of material (intra batch or inter batch) have sufficiently different absorbency properties to satisfy the claimants’ claim construction.”

This finding was, I think, inevitable in the light of the evidence of Mr Woodings to which I have referred and upon which the case was based. In my judgment, the judge was entitled to conclude, as he did at [116], that it had not been established that 2-3 grams of liquid per gram of fibre was a relevant, as opposed to a measurable, difference such as it could be said that the CES comprised two different types of fibre. Further, I agree with the defendants that there is a further reason why claim 3 is not infringed and that is because, upon its correct construction, it requires the wound contacting surface to “consist” of the blend of gel forming fibres. The presence of Tencel means that it does not consist of this blend.

Two issues arise: first, whether the judge fell into error in holding that if ConvaTec had established infringement of claim 3 by Durafiber then it would have been invalid over Bahia; second, whether the judge fell into error in finding that claim 3 is valid over Qin. The first issue arises on the appeal and the second on the cross-appeal. I will address them in turn.

ConvaTec maintained that claim 1 of the Patent was valid over Bahia but did not contend that claim 3 was independently valid over this publication. It was therefore sufficient for the judge to deal with the validity of claim 3 over Bahia simply by reference to claim 1.

Bahia is a PCT application which was published on 4 August 1994. It discloses “Wound Dressings” comprising CMC fibres in the wound contacting surface.

The defendants relied upon Example 1 which describes a solvent based system for making CMC fibres which involves preparing an aqueous alcoholic solution containing a mixture of sodium hydroxide, sodium monochloroacetic acid and industrial methylated spirits; adding this solution to dried solvent-spun cellulose filaments in a reaction vessel which is heated to 50˚C for 180 minutes; and then washing the resulting CMC tow in a solution containing industrial methylated spirits, water, acetic acid and citric acid.

ConvaTec accepted this process would typically be carried out in a kier and that it was perfectly obvious to blend separate batches of the CMC so produced. They also accepted that, when making derivatized cellulose in kiers, whether CMC or CES, there will always be some variation in the degree of substitution of the fibres both within a batch and between batches.

In these circumstances the defendants argued before the judge, and maintained on appeal, that if, contrary to their primary case, wound dressings made using their CES fibres fall within the scope of the Patent as a result of the variability in the absorbency properties of those fibres, then so also must wound dressings made in accordance with the teaching of Bahia and accordingly claims 1 and 3 must be invalid.

The judge accepted this submission. He held at [170] – [171]:

“170.

On the basis of my findings on the infringement side of the case, that ConvaTec has not established that the CES product of the defendants falls within the claim on their construction of it, plainly there is no basis for finding that the product of example 1 of 746 [Bahia] would fall within the claim. However I am far from convinced that a credible case has been made out that would save the claims from invalidity if in fact Durafiber did infringe. In other words I have grave doubts whether there is anything patentably distinct between ‘746 and the defendants’ actions which are alleged to infringe. My reasons are in summary:

i)

When making derivatized cellulose in kiers (whether CMC or CES), variation in degree of substitution to some degree will always exist.

ii)

‘746 discloses a process of making a wound dressing using modified cellulose made from a mixture of fibres from a single kier and renders obvious a process of making a wound dressing using modified cellulose made from a mixture of fibres from different batches made in separate kier runs.

iii)

ConvaTec say that you infringe the claim if you have a mixture of fibres which have different absorbency figures, when the differences are more than trivial.

iv)

Considering ‘746, it is accepted that some variability in the CMC will exist, it is just that ConvaTec point out there is no evidence how big that variation is and therefore no evidence it passes some threshold between trivial and not-trivial.

v)

However, the point that there is a lack of evidence showing that the variation which is accepted to exist in ‘746 is large enough to pass the threshold is really the same as the position as regards the defendants’ CES process.

vi)

As regards the defendants’ process, there is no evidence before me that the variation seen in the batch averages reflects variation in underlying qualities of CES product rather than variation in the test.

vii)

So in truth the position is the same as for ‘746. In both cases there is no doubt that some variation exists, but there is in fact no sufficient evidence on which to base a finding as to the magnitude of the actual variation in the underlying properties of the fibres. Accordingly there can be no evidence of the significance of any variation which does exist.

viii)

If this sort of evidential position is enough to say that the defendants’ modified cellulose product made from running a kier based process falls within the claim then the modified cellulose product made from running a kier based process based on what is obvious over 746 must also fall within the claim. That is a Gillette defence of the purest kind. In my judgment neither falls within the claims of the ‘013 patent but if one does so must the other.

171.

In conclusion on ‘746, the claims are not invalid over this reference. However ConvaTec are on the horns of a dilemma. If the evidence did establish that the defendants’ product infringes the relevant claims (construed as per ConvaTec’s case) then that can only be on the basis that a mixture of fibres with some unspecified level of variation falls within the claim. On that basis the claims would be invalid as being obvious over ‘746.”

ConvaTec submitted that the judge fell into error in making this finding because although the CES fibres used in Durafiber dressings are made in a kier, the reaction conditions and the underlying chemistry are not the same as those used in Example 1 of Bahia. Further, they continued, there was direct evidence before the court as to the magnitude of the variation in absorbency between different batches of CES made by Speciality Fibres, and that such variability would be regarded as material. By contrast, there was no evidence as to the magnitude of any inter-batch variability in the CMC process described in Example 1 of Bahia.

In my judgment the fallacy in ConvaTec’s submission lies in the assertion that the variability in absorbency between different batches of CES made by Speciality Fibres is material from the point of view of wound dressing behaviour. This was not something the judge was persuaded about and, indeed, he formed the impression that Mr Woodings doubted that it was. So much is clear from the paragraphs of the judgment to which I have referred at [50] above. I believe the judge was therefore entitled to find, as he did at [171], there was no evidence before him of the significance of any variation which existed between the batches or within a batch of CES fibres. It followed that if the claims of the Patent are sufficiently broad to encompass dressings made from Speciality Fibres’ CES fibres then they must also be sufficiently broad to encompass dressings made from the CMC fibres the subject of Example 1 of Bahia, and the judge was right to so hold.

Qin is a PCT application which was published on 9 May 1996. It describes a two layer dressing with (i) a wound contact layer designed to provide a positive action in assisting healing of the wound, and (ii) a second layer of greater hydrophilicity than the first layer. It is accepted that the judge correctly summarised the disclosure of Qin at [130] – [133] of his judgment:

“130.

The idea is to have a generally relatively thin wound contacting layer (i) designed to provide positive action in assisting healing of the wound while layer (ii) has greater hydrophilicity than layer (i) so that exudate present in layer (i) may pass into layer (ii) so as to increase the time before layer (i) is saturated. So layer (i) might assist healing by providing clotting via agglutination of red blood cells or might debride the wound or deliver components to the wound like ions, drugs or antimicrobial agents. Examples of materials to be used in layer (i) are given. They include calcium alginate to provide calcium ions for haemostasis, chitosan for haemoglutination, pectin for stimulating autolysis and wound debridement. (Autolysis is a form of self destruction of cells.) Layer (i) may be provided as a woven, non-woven or knitted material or as a gel.

131.

One example given for layer (i) is to use “pectin/carboxymethyl cellulose/alginate”. While this might sound like a blend similar to the claimed invention in the ‘013 patent it is in fact a reference to a co-spun material, as Mr Woodings accepted.

132.

Layer (ii) is preferably a woven, non-woven or knitted fibrous material, e.g. a felt. The examples for what it may comprise include a sodium alginate/calcium alginate felt, a CMC felt and importantly “an alginate/CMC felt”. A particular example of a wound dressing taught by Qin is chitosan as layer (i) and an alginate or alginate/CMC felt as layer (ii) (page 4 line 8).

133.

It is the disclosure of an alginate/CMC felt for layer (ii) which invalidates claim 1 of the ‘013 patent on any view. It is a blend of discrete modified cellulose gel forming fibres (CMC) with at least one other type of discrete gel forming fibres (alginate).”

The defendants put their case on obviousness in two ways. First, they argued that instead of using a co-spun pectin/CMC/alginate material as the wound contacting layer (i), it would have been obvious to make the same sort of mixture as a felt or in some other similar manner. That would fall within the scope of claim 3, being a blend of discrete fibres. Alternatively, it was obvious to use the CMC/alginate felt of layer (ii) as the wound contacting layer (i).

The judge rejected both arguments. First, he explained that Qin discloses a two layer arrangement and that the two layers have distinct functions:

“138.

It is important to appreciate that Qin is a two layer arrangement and that these two layers have distinct functions. The purpose of wound contacting layer (i) is to have a positive effect on healing, so for example the alginate would have that effect by promoting haemostasis. To employ a layer at the wound contacting surface which did not have a positive effect on healing would be to go flatly against Qin’s proposal and would not be an obvious way forward over Qin.

139.

Qin does employ a material which includes (inter alia) a combination of CMC and alginate at layer (i) but it is a co-spun alloy fibre (pectin/CMC/alginate). Mr Bishop explained that alloys like this did not necessarily provide the benefit of both properties of alginate and pectin. One property may predominate depending on how it was made.”

The judge then considered the evidence before him in assessing whether it was obvious to take the step from Qin to the invention of claim 3. As for Mr Woodings, he accepted that before making a dressing from a blend of CMC and alginate, he would consult with the wound care scientist or clinician members of the team. The defendants did not call such a witness and so the judge was left with the evidence of Mr Bishop. He summarised that evidence and the conclusions he drew from it at [140] – [142]:

“140.

The contention that a felt was an obvious alternative to an alloy like the co-spun material was put to Mr Bishop. His evidence was that the skilled person would be concerned about knowing what the properties of the combined layer would be. Would the CMC predominate or the alginate? He was concerned that the CMC could disrupt the haemostatic potential of the alginate. So 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. This seems to me to provide prima facie evidence that it would not be obvious over Qin to employ such a felt as the layer (i) wound contacting surface. Moreover that applies whether one is looking at an alternative to the pectin/CMC/alginate co-spun layer (i) or to employing the CMC/alginate of layer (ii) as wound contacting layer (i).

141.

Dr Turner submitted that Mr Bishop’s evidence in this respect was not really that mixing was not obvious, he was in effect accepting that a felt was one obvious way forward among a number of other obvious alternatives such as having the CMC on top of the alginate, which would be irrelevant in principle. If that is all that Mr Bishop’s evidence amounted to then I would accept it was irrelevant but it seems to me that Mr Bishop’s concern about interfering with alginate haemostasis means that he did not regard the alternatives as all equally obvious. His concern was about CMC at the wound contacting surface along with alginate and he made the point despite having the pectin/CMC/alginate alloy fibre (which can be said to include such a combination albeit in a different form) being put to him.

142.

In another case such a point might have been debated between wound care experts but I have Mr Bishop alone. It seems to me that I do not have a basis to reject his concern as fanciful. These are the concerns of the wound care scientist and in my judgment it does not matter how obvious the material itself would be to a cellulose chemist. This invention is a wound dressing and the claim will only be obvious it if is obvious to the relevant team as a whole.”

He therefore rejected the allegation of obviousness.

On this appeal the defendants only pursued the case that it was obvious to use the CMC/alginate felt of layer (ii) as the wound contacting layer (i). They submitted the judge fell into error in reaching his conclusion in that first, he failed to have regard to Mr Woodings’ evidence and second, he wrongly assumed the skilled person was only interested in a haemostatic dressing. Further, Mr Bishop was not a clinician and was in no better position to discuss the desirability of haemostasis than Mr Woodings. As to whether the skilled person might be concerned that CMC combined with alginate would exhibit different properties, this was as much a matter for Mr Woodings as it was for Mr Bishop.

I am unable to accept these submissions. During the course of the appeal we were taken through all of the evidence given by Mr Woodings and Mr Bishop on this issue. As for Mr Woodings, I am entirely satisfied that he believed that before making a dressing comprising alginate and CMC in the wound contact layer, he would consult with the wound care scientist or clinician members of the team. Further, there is nothing in Mr Woodings’ report to suggest that he was purporting to give evidence other than from the perspective of a cellulose fibre chemist.

As for Mr Bishop, he was asked during the course of his cross-examination whether there were any technical reasons why the skilled person would not consider using CMC and alginate in a wound-contacting layer. He responded that the CMC might interfere with the haemostatic properties of the alginate. The judge clearly had this evidence in mind in reaching his conclusion. The judge had the benefit of seeing and hearing the witness and his assessment is not one with which this court should interfere without good reason. None has been shown. No other route to claim 3 from Qin was ever suggested and the judge therefore had no evidential basis upon which to find it obvious.

For all these reasons I would dismiss the appeal and the cross-appeal.

I agree.

I also agree.