Smith & Nephew Plc v Convatec Technologies Inc

This is an action for revocation of European Patent (UK) No. 1,343,510 entitled “Light Stabilized Antimicrobial Materials”. The patent is concerned with methods of making a wound dressing which uses silver as an antimicrobial agent and which is photostable. The defendant, Convatec is the patentee. The claimant, Smith & Nephew, applies to revoke the patent on various grounds.

James Mellor QC leading Charlotte May appear for Smith & Nephew instructed by Bristows. Piers Acland QC leading Geoffrey Pritchard appear for Convatec instructed by Bird & Bird.

In the course of the proceedings Convatec conceded that the unamended patent is invalid and applied to amend. Convatec maintains that claim 1 in its amended form is valid. Convatec does not contend that the dependent claims are independently valid.

Smith & Nephew submits that the amendments sought to claim 1 are not allowable. The other issues (assuming the claim is amended) relate to the validity of claim 1 in its amended form. The issues are obviousness over two items of prior art (Gibbins and Kreidl) and an insufficiency argument. There was a third item of prior art relied on (US 2,396,515, also known as Kreidl 2) but it was not pressed.

Although there was a priority point pleaded, by the opening of the trial Convatec had accepted that the amended claim was not entitled to claim priority from the cited priority document. Accordingly the relevant date for consideration of this patent is the filing date, which is 29^th November 2001.

Wound dressings have advanced over the years and in the 1990s wound dressings were developed which were intended to keep the wound surface moist. One method of achieving this aim was to use materials which formed a gel. One class of gelling wound dressing used alginate materials. Another kind used carboxymethyl cellulose (CMC).

Infection is a problem associated with wounds and consequently there is a need to both prevent and treat infection resulting from wounds. Antimicrobial agents can be used topically to achieve this result. A dry wound environment was not conducive to bacterial, fungal or viral growth. However, as gel dressings became more popular the problem of bacterial growth became more apparent. One antimicrobial agent known for many years is silver. Silver has a number of advantages for topical application including low toxicity. However there is a practical problem associated with the use of silver in wound dressings. It is light stability. This sensitivity is well known. For example the light sensitive nature of silver salts was used in photography for many years.

The patent relates to a method of preparing a light stabilized antimicrobial material for use in wound dressings and medical devices. Essentially the method is one whereby a wound dressing material can be made which comprises silver as an antimicrobial agent but which is stable in the presence of light.

I heard evidence from two witnesses, Professor Burrell for Smith & Nephew and Professor Kennedy for Convatec.

Prof Burrell is Professor of Chemicals and Materials Engineering at the University of Alberta, Canada. He has worked in the field of wound dressings since 1991. A particular focus of his work has been the use of silver in wound management. Prof Burrell graduated from the University of Guelph, Ontario in 1976 with a BSc in Zoology, then worked in the field of environmental Biology and completed his PhD in Biology at the University of Waterloo, Ontario in 1983. Between 1986 and 1991 Prof Burrell worked at Alcan. While at Alcan he first began to investigate wound dressings and the use of silver. He joined Westaim Corporation in 1991 and there specialised in silver dressings from 1991 to 2002. During his time at Westaim Prof Burrell worked on a product now known as Acticoat. He moved to the University of Alberta in 2002.

Acticoat has been a major advance in wound care. It is a wound dressing which incorporates silver as an antimicrobial agent. Prof Burrell has been recognised personally for the outstanding contribution to science and medicine which his Acticoat work represents. He has won a number of awards for that work including the Jonas Salk Award in 2010.

Today the Acticoat product is owned, manufactured and marketed by Smith & Nephew and as a result Prof Burrell has links to Smith & Nephew. I have no doubt that these links did not colour Prof Burrell’s evidence at all.

Convatec submitted that Prof Burrell was not a good witness and that his approach was so flawed that in certain respects little or no weight can be given to his evidence. This was for two main reasons.

The first related to the Professor’s evidence about ionic binding of silver to NaCMC to form AgCMC and the subsequent removal of the silver to form AgCl. This removal was sometimes called stripping. Convatec submitted that the theory was absent from Prof Burrell’s first report and developed from his second through to his fourth report. It included a detailed issue concerning the solubility of AgCMC. These expert reports did not mention the Professor’s own paper published in 2003 which, submitted Convatec, contained data adverse to the point the Professor was making. The submission was that Prof Burrell had no reasonable basis for not referring to the 2003 paper.

I am not convinced that from Prof Burrell’s personal standpoint, it was clear that the 2003 paper was contrary to the opinion which he was advancing. The paper can certainly be read in a way which is adverse to the Professor’s position on AgCMC solubility. However in my judgment the Professor’s re-examination showed that from his point of view the matter was not clear cut. The Professor had obtained the data from Convatec. The paper describes the relevant material as “AgCMC” but the material may in fact have contained AgCl complexes. If so then the data reported in the paper does not relate to the solubility of AgCMC although the paper states that it does.

The re-examination showed that Prof Burrell was clearly well aware of the paper. It should have been referred to and explained in his expert report(s). However I reject the attack on the Professor as a witness based on the failure. It is clear that the reason Prof Burrell did not refer to it in evidence is because he thought he should stick to material available before the priority date. That is not right but it is an understandable error. Since the validity of patents is strictly concerned with information available at the priority date, post published material has to be treated with caution. However the point here was concerned with a simple scientific fact (the solubility of AgCMC). In order to establish a fact like that, any evidence which bears on the point is relevant regardless of when it is published. The fact the paper was post-published was not a good reason not to refer to it.

The second point related to calculations Prof Burrell had put forward as part of the obviousness case. Convatec submitted that he had taken an inconsistent approach. He did not take into account the presence of water in a silver nitrate stock solution. He had not missed the point, he had decided to ignore it because he thought it would make little difference. However Prof Burrell had taken into account other factors of a similar magnitude and in fact the silver nitrate / water point, if accepted, undermines the argument that a salt concentration within claim 1 is reached. There was a similar argument about his calculations of molar ratios. Convatec submitted that all this showed a lack of independence on the part of the witness. That goes too far in my judgment. I think the Professor should not have simply neglected the silver nitrate / water point. Since he thought of it, he should have referred to it and explained why he regarded it as irrelevant. However I regard this as a small point and reject Convatec’s attempt to magnify it to this extent.

The defendant called Professor Kennedy. He obtained his BSc in Chemistry from the University of Birmingham in 1964, his PhD there in 1967 and worked as a lecturer at that institution from 1969 to 1987 and a senior lecturer from 1987 to 2001. He was director of the University of Birmingham Carbohydrate and Protein Technology Group and Director of the University of Birmingham Research Park Chembiotech Laboratories from 1987 to 2008, honorary Professor of Applied Chemistry at Glyndwr University from 1984 to the present and a director of Chembiotech Ltd. His work has included a focus on carbohydrates both monomolecular and macromolecular for many years.

Prof Kennedy’s position in this case was an unusual and difficult one. These proceedings were due to come on to trial in November 2011 and at that stage Convatec’s expert was Prof Qin. At the very last moment Prof Qin was taken ill and could not give evidence. The trial had to be adjourned and Convatec had to find a new expert in very short order. They did so and Prof Kennedy was instructed. He formed his opinions on the prior art first, then the patent. Then he was shown Prof Qin’s first reports (Qin 1 and Qin 2). Prof Kennedy commented on them line by line. He was then provided with Prof Burrell’s evidence in chief and asked for comments. Then he was provided with Prof Qin’s reply report and finally Prof Burrell’s reply evidence. Prof Kennedy’s evidence in the case consisted of annotated versions of Qin 1, 2 and 3 and relatively short reports in his own words.

This approach was adopted because at the time of the adjournment it seemed appropriate to require the new expert to adopt Convatec’s existing evidence to the extent that he wished to do so. Although this was an understandable approach and it probably did mean a shorter adjournment was possible, since it would inevitably have taken longer for Prof Kennedy to write full reports from scratch, it had the inevitable result that the written expert evidence was unwieldy.

Smith & Nephew submitted that Prof Kennedy demonstrated a reluctance to assist the court by failing to answer questions directly or by giving evasive answers. I entirely reject that. I listened carefully to Prof Kennedy’s testimony. In my judgment he was always seeking to assist the court and was not evasive at all.

He was also criticised for refusing to accept that the teaching of one of the cited items of prior art (Kreidl) was the same for all the materials mentioned (in particular clays and cotton). However Prof Kennedy clearly thought there was not enough detailed data in Kreidl to resolve that point. It is not a fair criticism of him. He was also criticised for viewing Kreidl at its publication date (1946) rather than the priority date (2001). However I understood the Professor’s point to be that reading the document in 2001 he would consider what people writing in 1946 must have meant. I reject that criticism also.

Smith & Nephew suggested that when it suited him to do so, Prof Kennedy tried to distance himself from the evidence of Prof Qin that he (Kennedy) had adopted as his own. I did not think he did that but in any case I think the point is unreal. Prof Kennedy had clearly done his best to adopt as much of Prof Qin’s evidence as he could (the vast majority of it) but adopting the words of another is never the same as formulating words yourself.

In cross-examination Mr Mellor took Prof Kennedy to task about his opinion regarding the teaching (or lack of it) in Gibbins concerning silver complexes. I will deal with this issue on its merits below. I did not regard Prof Kennedy’s testimony on the issue as unreasonable or open to criticism.

I am grateful to both witnesses for their assistance in this case. Each side attacked the other’s expert as a witness but in my judgment neither attack was well founded. I am sure both Prof Burrell and Prof Kennedy gave their evidence fairly.

Smith & Nephew emphasised that Prof Kennedy’s experience of the use of silver in wound dressings was limited to one project. The Professor also accepted that he had not worked on silver chemistry and was not working on incorporating silver into wound dressings at the priority date. I agree that Prof Burrell has much more experience with silver in wound dressings than Prof Kennedy. However that on its own is not a reason to prefer Prof Burrell’s evidence to that of Prof Kennedy.

At the end I found that in general I preferred Prof Kennedy’s evidence to that of Prof Burrell. This was not the case on every point of detail but as a generalisation I thought Prof Kennedy’s views about what a skilled person would do or think were more convincing than Prof Burrell’s. Prof Burrell is clearly a man of exceptional innovative talent. Convatec submitted that this meant his views about what was obvious had to be treated with caution. That is going too far, however listening to Prof Burrell give his evidence, it was clear that he is a problem solver who will persist in pursuing a hypothesis even in the teeth of negative experimental results. I think his evidence, perhaps inevitably, attributed too much of that persistence to the skilled person. On the other hand I found Prof Kennedy’s evidence generally to be straightforward and plausible.

However I remind myself of the following. Expert witnesses are usually highly skilled individuals. The function of an expert witness is not simply to represent the skilled person. Calling an expert in a patent case is not an exercise in conducting an experiment to see what a notional skilled person thinks with the expert presented as an exemplar. As has been said repeatedly in patent cases, what matters are the reasons given by an expert why a step may or may not be obvious, rather than the existence of their opinion itself.

Patents are addressed to those likely to have a practical interest in the subject matter of the invention (per Lord Diplock in Catnic v Hill & Smith [1982] RPC 183 at 242-243). In many cases such as this one the skilled person is in fact a team comprising individuals with different skills and knowledge. In this case there was no substantial argument about the identity of the skilled team. Given the nature of the technology, the skilled team will have a number of members. It will comprise a biomedical engineer, a chemist and a materials scientist. The biomedical engineer will have an undergraduate engineering degree with a biomedical elective and a PhD in biomedical engineering, with practical experience of wound dressing development. The chemist would have particular knowledge of and interest in silver chemistry, although all the members of the team would understand it as it is at an undergraduate level. The materials scientist (or physicist) would have knowledge and experience of dressing structures and components, and physical materials issues such as shelf life and light stability. In addition the team might also comprise (or consult with) a life scientist with an understanding of microbial organisms and experience of antimicrobial testing and biocompatibility.

In this judgment I will use the expression “skilled person” even though in fact in this case the skilled person is a team.

The matters of background in paragraphs 6 and 7 above are part of the common general knowledge. One area of common general knowledge is wound dressings. Traditional wound dressings were made of cotton. As to that:

Cotton is approximately 95% cellulose.

The remaining material comprises waxes, fats and resins – these reduce cotton’s ability to absorb water.

Cotton fibres consist of a single long tubular cell.

The cell wall is rather thin and the lumen occupies two thirds of the entire breadth of the fibre.

The absorption of water by cotton is accounted for by the lumen and the amorphous regions.

The filling of the lumen accounts for much of the water absorbing capacity of cotton.

Cotton dressings were used to keep the wound dry by absorbing exudate (fluid) from the wound. In the 1960s George Winter showed that wounds heal much better if they are kept moist but a problem with moist wounds is that they encourage infection. One way to avoid infection in a moist setting is to provide a dressing with antimicrobial activity. Ionic silver possesses antimicrobial activity. There were commercial products using silver ions as antimicrobial agents on the market at the priority date including Actisorb and Acticoat.

By the priority date wound dressings existed in a number of different forms commonly comprising natural, modified natural and synthetic polymers with known desirable characteristics. In particular gel forming dressings such as hydrogels, alginates, and other gel forming fibres were well established and commonly used because they can absorb exudate whilst keeping the wound moist. A well known commercial example of a gel forming fibre was Aquacel. Aquacel is comprised of sodium carboxymethyl cellulose (NaCMC). It is a Convatec product.

Part of the common general knowledge included interactions known as absorption and adsorption. Adsorption is a gathering of a substance on the surface of a material whereas absorption is the uptake of substances into a material. Adsorption can be by electrostatic binding caused by the interaction of oppositely charged dipoles on molecules (Van der Waals forces). Professor Burrell called this “physisorption”. Another form of interaction is as follows. If NaCMC is treated with silver nitrate (AgNO₃) then AgCMC will be formed. This is a form of ion exchange. The sodium ion in NaCMC has come off and been replaced by the silver ion from the silver nitrate. This kind of ionic binding was referred to by Professor Burrell as “chemisorption”.

Another area of common general knowledge is silver chemistry. There was at one stage a debate about the level of the skilled team’s knowledge of silver chemistry. I find that the team (and in particular the chemist in the team) would know about ion complexes and co-ordination chemistry in general and silver complexes in particular. In summary the common general knowledge included the following:

Metallic silver (Ag⁰) is a stable metal. It may be ionised to form silver ions. Normally the ion formed has one positive charge (Ag⁺), although silver can also exist in ionised states with higher charges (Ag²⁺) and Ag³⁺).

Ionised silver is highly reactive. In particular, 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, although due to the dynamic equilibrium there will always be a small proportion of silver ions in solution. Le Chatelier’s principle, whereby adding an excess of a species on one side of an equilibrium reaction pushes the equilibrium in the opposite direction to maintain the balance, means that adding an excess of chloride will favour the formation of AgCl in this equilibrium.

In the presence of a large excess of chloride ions, coordination complexes can be formed. These are species in which the central silver ion is bound to more than one chloride ion. The chloride ions are said to coordinate to the silver ion. A silver chloride complex with two chloride ions would be [AgCl₂]^-. Silver chloride complexes were known to be more soluble than silver chloride (AgCl) itself albeit that they are still largely insoluble.

The terms “photostable” and “light-stable” were not terms of art with a precise meaning or meanings.

As regards the light stability of particular materials: AgCl was known not to be stable to light. However it was not common general knowledge that silver chloride coordination complexes were light-stable (or more light-stable than AgCl itself).

It was common ground in this case that part of the common general knowledge was that AgCMC was light unstable, albeit it was more light-stable than AgCl. I must say I had my doubts since there was little evidence that anyone had given detailed consideration to the properties of AgCMC by the priority date or published their findings but since it was common ground I accept it.

The patent explains that the invention relates to light stabilised antimicrobial materials and methods of preparing antimicrobial polymers for use in wound dressings. The background section deals with the problem of infection in wounds, the use of silver as an antimicrobial agent and the difficulty that silver containing materials are typically sensitive to light. The light causes uncontrolled discoloration of the silver containing material. Numerous efforts have been made to render such materials photostable but there is still a need to enhance the photostabilization of silver in certain polymers, especially when those polymers are used in medical devices. Various prior art proposals are discussed and the background section ends by indicating that the present invention is a novel method for the preparation of light stabilised silver containing hydrophilic, amphoteric and anionic polymers. The methods are simple and inexpensive ways of preparing such polymers which provide effective and non-toxic antimicrobial activity in a water swellable material.

The summary of the invention section describes the method in general terms. A solution is prepared comprising an organic solvent and a source of silver. Typically the solution is formed by initially dissolving the silver in water and mixing the water with the organic solvent. Next the polymer is subjected to the solution for a sufficient time to incorporate the silver. During or after that period the polymer is subjected to an agent which is to facilitate the binding of the silver and the polymer together. Later the patent refers to the agents as “facilitating agents” (e.g. paragraph 29) and I will adopt that expression.

Once the facilitating agent has done its work, the resultant material is substantially photostable on drying. However the material will dissociate to release the silver if it is rehydrated.

A detailed description follows. It starts with a statement that the inventors have found it possible to stabilise silver in polymers used in medical related materials. The material is particularly useful for wound dressings that create a moist wound healing environment. The detailed description goes on to address topics such as suitable polymers, the quantity of silver, suitable facilitating agents and the quantity of agents to be used. There is a definition of “photostable” which I will address below.

Finally at the end of the description is a single example. This involves treating an Aquacel wound dressing with a solution of silver nitrate in IMS/water. IMS is an organic solvent. After the silver treatment, sodium chloride is added to the IMS/silver nitrate bath. At paragraph 37 the patent states that Aquacel wound dressings having between 1% and 5% silver have been found to be photostable and possess excellent antimicrobial activity. Irradiation does not adversely affect the silver dressings.

In its form as granted claim 1 is invalid. The sole relevant claim is claim 1 as proposed to be amended. The amendments sought by Convatec varied somewhat during the course of these proceedings. By the trial the amendments sought were in the form shown below:

The legal approach to patent construction is well established and there was no dispute on it before me. The leading authority is Kirin Amgen v TKT [2005] RPC 9. The key point is that construction is concerned with what a skilled person would understand the author to be using the words to mean. Guidelines on the general approach were given by the Court of Appeal in Virgin Atlantic v Premium Aircraft [2010] FSR 10. I remind myself that claims are not construed alone or in the abstract but in their context in the specification; that purposive construction is vital (there may be several purposes and several embodiments) and that one is in the end concerned with the meaning of the language used. Meticulous verbal analysis is eschewed.

The main point on construction was the meaning of the term photostable in the claim. I will deal with it below. Before doing so there are some lesser points on construction to mention.

First, the claim refers to subjecting the polymer to the facilitating agent “during or after” the silver loading step (b). By the closing it was common ground that this meant that the material should be subjected to the silver solution first, and then to the facilitating agent either in the same bath or in a separate one.

Second, the facilitating agent has to be present in a concentration of between 1% and 25% of the total volume of treatment. This expression (total volume of treatment) is not defined in the patent. It was common ground that this refers to the concentration of the agent in the total volume of solution present when the polymer is subjected to the agent.

Third, there is an issue about the words “material which includes gel-forming fibres containing one or more hydrophilic, amphoteric or anionic polymers”. I will address that in the section on amendment.

Fourth, is a question about scientific mechanisms. The patent does not propose a mechanism to explain why the invention works. It is not obliged to do so. Smith & Nephew submitted it was plain that the patented process worked by creating silver complexes. So in the example silver chloride complexes are formed by using an excess of sodium chloride as the facilitating agent. Curiously enough, although the patent does not mention complexes, its priority document makes it clear that complexing the silver is the key. It seems to me that the method of the patent must be based on forming silver complexes. Whether this has a bearing on the issues I have to decide remains to be seen.

Claim 1 relates to a method of preparing a light stabilized material. In the patent light stable and photostable are used interchangeably and nothing turns on that difference. At the end of claim 1 step (c) requires that the material is “substantially photostable upon drying”. Paragraph 33 of the specification provides that:

It seems to me that the meaning of claim 1 is clear enough. The claim does not mean the product has to be white or stay white. The claim means that once the method is finished and upon drying the material, the colour change is minimal. When drying the material can undergo a controlled colour change provided this change stops at a desired colour. No doubt a change to black would not be regarded as sensible but a material which was white during the manufacturing process but became purple on drying and stayed purple thereafter would be within the claim. It seems to me the words of the claim, referring to being photostable “upon drying”, coupled with the definition in the patent referring to a controlled colour change, mean that the controlled colour change happens as part of the drying process.

Once the product is dry, is any change in colour permitted? The claim does not demand perfection. The change in colour afterwards should be “minimal” and the claim itself only requires the material to be “substantially” photostable. These are words of degree but I do not regard them as so vague as to render the claim hopelessly ambiguous. Some colour change is permitted after drying but not much.

There was a debate about whether the meaning of photostable in the patent would or would not accord with the meaning a skilled person would give the term from his or her common general knowledge in any event. I do not see that that is relevant here since it seems to me the skilled reader of the patent would have no difficulty understanding what the draughtsman intended on this point.

By section 75 of the 1977 Act the court has power to permit amendments to granted patents in proceedings of this kind, subject to section 76. The relevant part of s76 in this case is s76(3)(a) which provides (so far as material) that no amendment of the specification of a patent shall be allowed under s75 if it results in the specification disclosing additional matter. The issue is whether additional matter is disclosed in the amended specification as compared to the application for the patent as it was filed.

The law on added matter is well settled. The correct approach was explained in European Central Bank v DSS [2008] EWCA Civ 192 (Jacob and Lloyd LJJ and Sir John Chadwick). In paragraph 12 of the judgment of the court Jacob LJ said:

This passage focuses on comparing the application to the granted patent because it is concerned with added matter as a ground of invalidity. The same approach applies in relation to post grant amendments. In that case the patent as proposed to be amended must be compared with the application as filed.

Smith & Nephew submits that the amendments here are an example of intermediate generalisation. This was described by the Court of Appeal in Vector v Glatt [2008] RPC 10 (Smith, Jacob and Wall LJJ) as follows:

Finally I remind myself that it is important to distinguish between the disclosure of subject matter and the scope of the claim. This point arose in AC Edwards v Acme Signs [1992] RPC 131 and was recently reaffirmed in Gedeon Richter v Bayer Pharma [2012] EWCA Civ 235 (see paragraph 17).

The form of claim 1 as proposed to be amended is set out above. The point of the amendment in section (b) of claim 1 is clear enough. By limiting the claim to methods applied to materials including gel forming fibres, the claim is novel over Kreidl. No gel forming fibres are disclosed in Kreidl. The section (b) amendment does not confer novelty over Gibbins since the relevant examples in Gibbins relate to Aquacel material. Aquacel is a gel forming fibre.

The amendment in section (b) involves a change in language which can confuse the issue and may or may not be significant. Step (b) of claim 1 is the place in which the thing to be treated is defined. The treatment is to subject that thing to the organic solvent/silver solution for a time sufficient to incorporate the desired silver concentration into the polymer. The thing to be treated is the object of the verb “to subject”. As a matter of grammar, in granted claim 1 the thing was “a polymer” whereas in amended claim 1 it is “a material”.

The amendment in section (b) of claim 1 is opposed and I will deal with it below.

The amendment in section (c) of claim 1 is not opposed. It limits the method claimed to one in which the concentration of the facilitating agent has to fall within a certain range of the total volume of treatment. Smith & Nephew did not dispute that this amendment was supported by the application but it did argue that the claim as amended would lack priority given that the concentration feature was not disclosed in the priority document. In the end Convatec abandoned the claim to priority and so that issue did not fall to be decided. The point of the amendment is that the concentration feature makes claim 1 as amended novel over Gibbins.

Smith & Nephew contends that the amendment to part (b) of claim 1 would constitute added matter and is contrary to s76(3) of the 1977 Act. The manner in which Smith & Nephew pleaded its case and the way in which it was put in argument were a little different in form but not in substance. The argument is that as amended the claim discloses added matter.

The first submission is that the only mention of gel forming fibres in the application was in relation to two specific materials, Aquacel and Versiva. The gel forming fibres they both contain are made of sodium CMC. In other words the only gel forming fibre referred to in the application is sodium CMC and so amended claim 1, which refers to gel forming fibres generally, represents added matter. Smith & Nephew contends that what Convatec is trying to do is take the disclosure of the only gel forming fibre disclosed in the application (sodium CMC) and combine it with references to the lists in the application as filed (the list “one or more hydrophilic, amphoteric or anionic polymers” and/or the list of polysaccharides, modified polysaccharides etc.) in order to create an intermediate, generalised class of materials which was not disclosed before.

The second submission is about the word “containing”. The application as filed only concerns a polymer containing gel forming fibres whereas the claim now relates to gel forming fibres containing a polymer (or rather containing one or more hydrophilic, amphoteric or anionic polymers). Smith & Nephew argues that the two concepts are different, the latter is new and represents added matter.

The third submission is that there is nothing in the application as filed to teach the skilled reader that a material which includes gel forming fibres (or gel forming fibres containing one or more hydrophilic, amphoteric or anionic polymers) is necessary to obtain the advantages of the invention or is in any way central to or relevant to the invention. As disclosed in the application, the invention is not limited to the use of gel forming fibres. So, it is said, the application teaches that the nature of the material is not central to the invention whereas the amended patent would do and that represents added matter.

Following Bonzel, the first step is to decide what is disclosed by the application as filed.

The application is entitled “Light Stabilized Antimicrobial Materials”. The sentence under the title “Field of the Invention” indicates that it relates to light stabilized antimicrobial materials and to methods of preparing antimicrobial polymers for use in wound dressings and medical devices (p1 ln 6-7). Looking ahead to one of the arguments which arises, I note that the words “materials” and “polymer” appear here. In my judgment the skilled reader would not think any subtle distinction was being drawn. “Materials” is a more generalised word to use than “polymer” but in any case it is clear that the point of all this is to make them light-stable and antimicrobial. Perhaps, if he thought about it at all, the skilled reader would consider that “materials” refers to wound dressings and medical devices whereas polymer refers to the stuff they are made of but I doubt the reader would analyse the language in that level of detail.

I have mentioned the “Background of the Invention” section in the granted patent already. This part of the application is the same in all material respects.

The “Summary of the Invention” section (p3 ln 24 to p4 ln17) starts with the statement that the present invention is directed to methods of preparing a material which contains one or more hydrophilic, amphoteric or anionic polymers, where the material has antimicrobial activity. The summary section continues, making the point that also included in the invention are polymers and materials prepared by the methods described. The method is summarised on page 4 (ln1 -17) as the preparation of an organic solvent/ silver solution, treatment of the polymer with the solution and treatment with an agent which facilitates binding of the silver and polymer together (a facilitating agent). The section ends with the statement that the resultant material is substantially photostable upon drying of the material.

The detailed description starts at p4 with a statement that the inventors have found it is possible to stabilize silver in polymers used in medical related materials and goes on to give examples such as wound dressings. At p4 ln 28 an important paragraph begins with the statement that the invention provides methods of preparing a material which contains one or more hydrophilic, amphoteric or anionic polymers, where the polymers have antimicrobial activity, refers to the use of the material in medical devices and continues:

The next paragraph (p5 ln 11-18) continues :

The document then goes on to discuss the preparation of the silver solution and various reaction conditions. This includes different silver salts, times, temperatures, different facilitating agents and silver concentrations. After defining certain terms (including photostable) the description ends with the Aquacel example (p8 ln 5-18).

The claims follow. Claim 1 as filed has the same structure as claim 1 as granted with steps (a) (b) and (c). The major differences are first that as filed the facilitating agents are defined by their function and not limited to the classes in granted claim 1, and second that as filed the polymer is defined by reference to the list of properties (hydrophilic, amphoteric or anionic) whereas as granted the polymer is defined by reference to the list of chemical types (polysaccharide or modified polysaccharide, polyvinylpyrrolidone, etc.).

Of the 11 dependent claims as filed only claim 10 calls for comment. It defines the polymer by reference to the list of chemical types.

The argument about intermediate generalisation involves considering whether a new combination of features or lists of features has been created by the amendment which was not present in the application as filed. To approach this one needs to see whether the features combined in the amended claim were disclosed as a combination in the application. The features are aspects of the definition of the material which is to be treated. The three features are: first, gel forming fibres; second, the definition of polymers by reference to properties (hydrophilic, amphoteric or anionic); and third, the definition of polymers by reference to chemical types (polysaccharide or modified polysaccharide, polyvinylpyrrolidone (etc.)).

Claim 10 in the application, dependent on claim 1, is an express disclosure (if one were needed) of the combination of the list of properties and the list of chemical types as definitions of the polymer to be treated. I believe the same conclusion would be reached by a skilled reader reading the description itself (in particular p4 ln38-30 and then p5 ln11-18) but claim 10 puts the matter beyond doubt. In other words the application discloses the idea of preparing a material which contains one or more hydrophilic, amphoteric or anionic polymer and in which the polymer comprises a polysaccharide or modified polysaccharide, a polyvinylpyrrolidone (etc.).

The idea of gel forming fibres is expressly disclosed in combination with the properties list (see p4 ln28 to p5 ln2 of the application). Additional support for that (if it were needed) comes from the fact that the polymer definition in claim 1 in the application is based on the list of properties and the sole example in the application is a gel forming fibre. No skilled reader would read the application and think the example was outside the claim. The example would be understood to be an example of practising claim 1.

In my judgment the gel forming fibre idea is also clearly and unambiguously disclosed in combination with the list of polymers defined by their chemistry. The list at p5 ln11-14 is the only place in the document in which a list of chemical types of polymer is given. Moreover the skilled person would know that the gel forming fibre the subject of the sole example (Aquacel) was a polysaccharide and therefore was within the listed chemical types. Indeed the application makes essentially the same point at p5 ln14-18 in giving sodium CMC gel forming fibres as a preferred embodiment.

Smith & Nephew argues that the only gel forming fibre disclosed in the application is sodium CMC, which is either mentioned by name or by reference to other products which contain it – Aquacel and Versiva. It contends that no other kind of gel forming fibre is mentioned. Convatec did not dispute that no gel forming fibre apart from sodium CMC is mentioned by name or could be said to be disclosed by necessary implication. By “necessary implication” Convatec meant for example because it was in a commercial product which was mentioned by name.

The issue is whether the skilled person would read the application as a whole as disclosing gel forming fibres generally and sodium CMC simply as an example (Convatec’s case) or as disclosing only sodium CMC gel forming fibres (Smith & Nephew’s case).

The phrase “gel forming fibres” only appears a few times in the document. Smith & Nephew’s best point is the argument that when the gel forming fibres idea is introduced at the top of p5 of the application the language would be understood as a disclosure not that any gel forming fibres would do and Aquacel was simply an example but that the gel forming fibres being discussed are those like Aquacel. That, says Smith & Nephew, is what the document means by words like “gel forming fibres such as Aquacel”. It is reinforced by the text “or those described in WO 00/01425 […]”, which are also sodium CMC and at line 4 the reference to similar gel forming fibres means sodium CMC not least because the product mentioned, Versiva, uses sodium CMC.

On the other hand Convatec argues that the words “such as” Aquacel show that the disclosure is not limited to Aquacel but includes other gel forming fibres made from other polymers such as the ones listed in the list of chemical types a few lines further on. It also make the point that the skilled person would know from his common general knowledge that gel forming fibres could be made from other polymers in that list such as polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl ether and polyurethane.

Smith & Nephew’s argument on this point is a strong one and I recognise both that the test for added matter is strict and that if the document is unclear on the point then Smith & Nephew succeed. After all the policy underlying the rule against extension of subject matter is to prevent the patentee from gaining an unwarranted advantage. However it seems to me that Convatec’s submission about common general knowledge is the decisive point.

If you read the language of the application simply as a matter of words then there is force in Smith & Nephew’s argument. However when I consider how a skilled person would read this in the knowledge that sodium CMC is by no means the only type of gel forming fibre known and that other polymers can also be made as gel forming fibres as well, it seems to me that the reader would see that the document is simply using sodium CMC/Aquacel as an example. The reader would know that when “gel forming fibres” are mentioned at p5 ln2 the concept is general. The important thing about the fibres is that they are gel forming. Their chemical make up does not matter. The term “such as Aquacel” is simply an indication of an example of a gel forming fibre to make sure the reader knows the kind of thing being talked about. It would not be read as a limitation that the only gel forming fibres contemplated had to be based on sodium CMC because a skilled reader with their common general knowledge would expect, and be entitled to expect, a firmer statement than that if the draughtsman really did intend to mean that the only gel forming fibres to be used were sodium CMC for some reason.

Furthermore it seems to me that the list of chemical types (polysaccharide etc.) assists Convatec. That is the place in the document in which there is a teaching about the chemical make up of the polymers. The skilled reader would know in reading the list that gel forming fibres can be made from many (if not all) of the chemical classes listed. Again the reader would think the list was odd if the inventor really did intend gel forming fibres to be limited to sodium CMC fibres. The fact that the document goes on to refer to embodiments with gel forming fibres comprising sodium CMC does not undermine that view. The inventor clearly regards sodium CMC as an exemplary gel forming fibre but that does not mean the inventor intended to be limited to sodium CMC.

A separate argument is that even if the application can be said to include a disclosure of using a gel forming fibre generally, it does not imbue the idea with inventive significance. I reject that. It seems to me that the application discloses the idea of using gel forming fibres in the method generally and that is sufficient from the point of view of the added matter test. Although the words of Pumfrey J in Palmaz and approved in Vector v Glatt refer to features not being disclosed “as having any inventive significance”, I do not understand that to mean that only features expressly asserted as being inventive in the specification may be added to a claim by amendment. A patentee does not have to repeatedly assert, with every line of the disclosure, that he thinks each point is or may be inventive. On the other hand of course, the context is crucial and a patentee cannot extract features disclosed in one context and introduce them into a claim stripped of their context. That is what I understand the principle to be.

I find that the application as filed discloses the idea of using gel forming fibres generally and not just sodium CMC gel forming fibres and I also find that the application discloses the combination of all three ideas of gel forming fibres, the list of polymer properties and the list of polymer chemical types.

I will now turn to the disclosure of the patent as proposed to be amended. The first point is that the disclosure set out in the description is to all intents and purposes the same as that in the application as filed. There is no need to repeat it. The issue concerns the text of claim 1 as proposed to be amended.

As I read step (b) of claim 1 in its amended form, the material to be subjected to the organic solvent/silver solution is defined in three ways. The material must include “gel forming fibres”. The gel forming fibres must contain “one or more hydrophilic, amphoteric or anionic polymers”. The polymer(s) in question, i.e. the ones contained in the gel forming fibres, must comprise “a polysaccharide or modified polysaccharide, a polyvinylpyrrolidone, a polyvinyl alcohol, a polyvinyl ether, a polyurethane, a polyacrylate, a polyacrylamide, collagen, or gelatin or mixtures thereof”. All three criteria must be satisfied and they are cumulative. That is what the claim as amended discloses. One clear aspect of the disclosure is that the gel forming fibres need not consist of sodium CMC. In my judgment this is not a case in which one could say merely that other gel forming fibres are covered by the claim but not disclosed (c.f. A. C. Edwards v Acme). The claim teaches that the gel forming fibres may consist of substances which are not sodium CMC.

At times I thought Smith & Nephew was arguing that the features were not completely cumulative so that a material would satisfy the definition if it included gel forming fibres of any kind provided it also contained one or more polymers of the relevant sort (that is to say hydrophilic, amphoteric or anionic and included in the list at the end of step (b)). In other words it did not matter what the gel forming fibres were made of provided some gel forming fibres were present and as long as a relevant kind of polymer was also present. The fibres and the polymer may or may not be the same thing. I reject that interpretation. It seems to me that the claim would be understood as a series of cumulative requirements.

Accordingly since I have found that the application as filed discloses a cumulative combination of all three ideas and is not limited to sodium CMC gel forming fibres, I reject the first and third grounds of Smith & Nephew’s added matter attack.

The remaining issue is the “contains” point. The argument focussed upon a difference in meaning between two phrases “a polymer containing a gel forming fibre” and “a gel forming fibre containing a polymer”. The former phrase appears in the application as filed at p5 ln17 while the latter is a paraphrase of the relevant part of the amendment to claim 1.

Professor Burrell explained his view that the phrases “a polymer containing a gel forming fibre” and “a gel forming fibre containing a polymer” describe different groups of materials, the main difference being the ratio of polymer to gel forming fibre. He said that “a polymer containing a gel forming fibre” would have a greater proportion of polymer to gel forming fibres whereas “a gel forming fibre containing a polymer” would have a greater proportion of gel forming fibre. They would only coincide for a material with 50% polymer and 50% gel forming fibre. On this basis Smith & Nephew argued that since the two phrases had different meanings, the appearance of “a gel forming fibre containing a polymer” in amended claim 1 is added matter over the only basis for it in the application as filed namely the phrase “a polymer containing a gel forming fibre”.

Professor Kennedy did not agree with Professor Burrell. His evidence (in fact Prof Qin’s evidence which he adopted) was that the phrase “a polymer containing a gel forming fibre” did not make technical sense. The phrase appears at p5 ln17-18 of the application as filed and paragraph 19 of the granted patent. It reads:

Professor Kennedy thought the skilled person would understand the inventor to be saying in a somewhat muddled way that sodium CMC can be made into gel forming fibres which can be incorporated into wound dressings.

Whether or not it is a matter of evidence, I agree with and accept Professor Kennedy’s point. It seems to me that the application here would be understood as Professor Kennedy suggests simply as a teaching to make gel forming fibres from sodium CMC and using them in a wound dressing.

In any event I do not believe this argument about the phrasing of that passage in the application has much to do with the question of added matter. The question is whether the amendments give rise to added matter. In step (b) the amended claim refers to “a material which includes gel-forming fibres containing one or more hydrophilic, amphoteric or anionic polymers … wherein said polymer comprises a polysaccharide (etc.)”. In my judgment all this discloses is a material which has within it gel forming fibres, those gel forming fibres containing within them polymers which satisfy both lists of properties. That is disclosed in the application as filed. There is no added matter.

Accordingly I reject the attack of added matter. The amendments are allowable.

Section 3 of the 1977 Act provides that an invention shall be taken to involve an inventive step if it is not obvious to a person skilled in the art having regard to any matter which forms part of the state of the art by virtue of s2(2) of the 1977 Act. A structured approach to the assessment of obviousness was set out by the Court of Appeal in Windsurfing International Inc v Tabur Marine [1985] RPC 59 and was adjusted somewhat by Jacob LJ in Pozzoli v BDMO [2007] EWCA Civ 588, [2007] FSR 37. It is:

In Conor v Angiotech [2008] UKHL 49, [2008] RPC 28 the House of Lords considered the issue of obviousness. There Lord Hoffmann (with whom the others of their lordships agreed) approved the following statement of Kitchin J made in Generics v Lundbeck [2007] RPC 32:

Since Kreidl was published in 1946 and the patent in this case was filed in 2001, the question of the age of a piece of prior art arises. In the joint judgment of Kitchin LJ and Sir Robin Jacob given in Gedeon Richter v Bayer (supra) at paragraph 61, their lordships observed that it was trite law that dates matter when considering obviousness and that the older a piece of prior art said to render a patent obvious, the harder it is to show obviousness. I understand their lordships to mean that the point of law is that dates matter. The observation about it being harder to show obviousness over an old citation is a reflection of long experience in patent cases and common sense. It is not a legal principle. Mr Mellor reminded me of the fuller analysis of this point in Brugger v Medicaid [1996] RPC 635 at 653-655. He also reminded me of the conclusion on this point in Terrell (17^th Ed.) which attempts to sum up Brugger as follows “In short there may be many reasons why something was not done before, and one cannot simply conclude that everything that is not anticipated is not obvious”. I will bear this in mind.

The person skilled in the art, and the common general knowledge, have been identified above. In terms of inventive concept, although rather wordy, amended claim 1 speaks for itself. The invention is a method of preparing a light stabilized antimicrobial material. There are three steps. First a solution comprising an organic solvent and a sufficient source of silver is prepared. This aspect will be satisfied by silver nitrate (AgNO₃) in ethanol/water (EtOH/H₂O). Second the polymer material is subjected to the solution for a sufficient time. The polymer material is defined in the claim and it is common ground that Aquacel satisfies the criterion. Third the polymer material must be subjected to a facilitating agent defined in the claim. Using sodium chloride (NaCl) will satisfy this aspect of the claim. There are two further relevant aspects of the claim which bear emphasis. The facilitating agent must be added during or after the second step and the agent must be present in a concentration between 1% and 25% of the total volume of treatment.

Finally the claim provides that the product is substantially photostable on drying and will dissociate in appropriate circumstances. I regard the patent as teaching that if the skilled person follows the steps of the method as claimed fairly the result will be a product which satisfies these criteria. By “fairly” I mean the skilled person has to approach the matter with a will to make it work. The significance of this is that it means that if it is obvious to employ conditions which fall within the method steps with a view to making a light stable antimicrobial dressing, the claim will be invalid. There is no need to go on and separately consider whether those steps would in fact produce a photostable dressing because the patent’s teaching is that that is what will happen.

On 12^th April 2001 International Application PCT/US00/26890 was published as WO 01/24839 (“Gibbins”). The application is entitled “Silver-Containing Compositions, Devices and Methods for Making”. The first sentence of the abstract states that “the present invention comprises methods and compositions for making a silver-containing antimicrobial hydrophilic material.”

The background section of Gibbins runs from p1 ln27 to p9 ln5. This discusses wound healing and the need to maintain an optimum level of moisture over the wound bed. Examples of wound dressings are referred to and the delivery of active agents is discussed. At p5 ln20 Gibbins states that silver has long been recognised for its broad spectrum of anti-microbial activity and compatibility with mammalian tissues. The drawbacks of using silver are mentioned including light mediated discoloration. At p5 ln29 Gibbins states:

A similar passage about silver is repeated at p6 and Gibbins moves on to a more detailed discussion of silver’s mode of action and means of incorporation into medical inventions. Again the problem of light stability is referred to and the discussion turns to previous proposals describing the stabilisation of silver (p8). The background section ends by stating the need for compositions and methods for silver incorporation into medical devices such as moisture containing wound dressings and other things. In terms of its objectives, Gibbins is concerned with the same problem as the patent in this case: how to make light-stable, silver containing, wound dressings.

In terms of solutions to the problem, Gibbins contains a broad discussion but focuses on two particular areas, acrylamide matrices and hydrophilic fibres, in particular Aquacel.

With the acrylamide matrix, the silver is incorporated before polymerisation takes place. The acrylamide matrix is the subject of all the examples from 1 to 23. Those examples relate to various aspects of the formation, absorption and construction of the acrylamide matrices and the incorporation of substances into them together with their antimicrobial activity, light stability and sustained release of silver characteristics. This topic represents the bulk of the disclosure of Gibbins.

Gibbins certainly teaches that copper (Cu) or iron (Fe) are preferred in order to achieve the photostability of these silver containing acrylamide dressings. However Smith & Nephew submitted that although these ions were preferred, the teaching of Gibbins was not that they were essential. Convatec disagreed, submitting that Prof Burrell had accepted in cross-examination that Gibbins taught that without ferric or copper ions the silver in the acrylamide matrix was not photostable. I agree with Convatec. Prof Burrell did accept this and it seems to me that a skilled person reading Gibbins would understand that Cu or Fe ions were needed for light stability of silver in the acrylamide matrix (see e.g. Examples 8 and 16). They are a key part of the solution to the problem taught by Gibbins when the document is considering the acrylamide matrix.

Examples 24 to 28 are concerned with the second area of focus, mainly Aquacel. The point of these Examples is to impregnate hydrophilic fibres with silver in order to make a light-stable antimicrobial product. The fibres used are usually Aquacel (Examples 24-26 and 28). Broadly the process involves using a silver salt like silver nitrate (AgNO₃) and a source of chloride ions such as sodium chloride (NaCl) to precipitate AgCl in a water:alcohol solution. Gibbins recognises that precipitating AgCl using water as the solvent is impractical because water will cause gelling of the Aquacel material. These examples would plainly be of interest to a skilled person.

In Example 24 various samples of silver impregnated materials are made and tested in various ways. The example ends with a light stability test on dry material and material after wetting with water. The results are:

Ag-Aquacel means Aquacel with silver incorporated in it, Hi Ag-Aquacel has twice the amount of silver as Ag Aquacel. I believe Aquacel C has no silver and is a control. The example concludes with the statement that silver was incorporated into hydrophilic fibres in amounts that allowed for sustained release and that ethanol is the preferred solvent when using sodium chloride in the impregnation process. The final statement is “The resulting materials possess antimicrobial activity and do not appreciably discolor in the presence of light.”

Example 25 takes 2 x 2 inch samples of Aquacel and treats them in different ways in order to impregnate colour stable antimicrobial silver. The example consists of 15 tests of various combinations of reagents and orders of addition. The tests are designated a, b, c, etc. up to test “o” although the label “o” has gone missing and the last labelled test is “n”. The tests use varying mixtures of sodium chloride (NaCl), water (H₂O), ethanol (EtOH), copper (Cu) and silver nitrate (AgNO₃). The Example concludes as follows:

Example 26 tests different approaches to nucleating silver chloride and seeks to see if the solution could be reused. Example 27 is not concerned with Aquacel and nothing turns on that.

Example 28 concerns the effects on silver treated Aquacel of using an electron beam irradiation sterilisation technique. Convatec submitted that this example showed that products produced using the methods of Example 25 (j), (k) and (l) turned dark on longer exposure to light and therefore could not be regarded as photostable whatever definition of that term was used. I will address photostability next.

A major dispute was about whether the teaching of Gibbins was that the Aquacel materials being made there were photostable. It was clear that Prof Kennedy did not regard the references to “eventually purplish” and “purple, specks” (Gibbins Example 24) as an indication that the products were stable in the presence of light. However in my judgment he was applying his own (entirely genuine) view about what constituted photostability which is different from that called for by the patent. Essentially if a dressing was coloured he did not regard that as light-stable.

Convatec submitted that the results shown in Example 24 were not photostable because “White, good, eventually purplish” in the “dry” column meant that the colour was white once it was dry but then changed later to purplish. Smith & Nephew emphasised the words at the end of Example 24 that the material did not appreciably discolour in the presence of light. In my judgment this material is within the photostability criterion of claim 1. It is undeniable that “eventually purplish” means that there was a small degree of colour change after the white colour the material had on drying, but the change stops when the material is “purplish”. The statement that the materials “do not appreciably discolour” means that the change to purplish after drying was minimal and was regarded as such by Gibbins. Or in other words the material was substantially photostable within the terms of claim 1.

Example 25 is a different matter. Gibbins is not specific about exactly what happened in which tests. All that is said is that the example was designed to develop a colour stable material, that the samples with higher silver concentrations discoloured more quickly in light and that most samples eventually turned a purplish colour. Moreover in Example 28 three samples made following parts of Example 25 turned dark on prolonged exposure to light. I am not satisfied that as written in Example 25, Gibbins discloses that all the samples in that example were photostable materials within claim 1. The reference to “eventually turning a purplish colour” may mean that most samples behaved in the same way as the Ag Aquacel in Example 24 but it is not clear. Nor is it clear which samples behaved in what way. It may be that every sample in Example 25 was photostable within the meaning of the patent but I find that Gibbins’ words in Example 25 do not allow one to draw that conclusion. Furthermore I did not understand Smith & Nephew to have an answer to the point arising from the results of the light exposure tests in Example 28, save to point out that the materials had been electron beam tested. But there was no reason given why that would matter.

I bear in mind that Gibbins regarded antimicrobial activity as important in itself. In other words it may not matter to Gibbins whether light has reduced some of the silver, rendering it inactive and turning the dressing a dark colour, provided there is still sufficient silver available as an antimicrobial agent in the material when it is used. Gibbins tested antimicrobial activity after irradiation in Example 28 and concluded that the samples retained their activity.

Smith & Nephew’s obviousness case over Gibbins is that if it is read fairly and understood properly then the only difference between Gibbins and claim 1 lies in the % concentration of facilitating agent (sodium chloride). The concentration used in the examples is too low to satisfy the claim but Smith & Nephew submits it would have been obvious to increase it for various reasons and if one did so, the result would fall within the claim. Smith & Nephew also says that once the point about photostability is resolved, there is a clear expectation of success.

This case was expressed primarily in paragraphs 239 to 244 of Prof Burrell’s first report, as follows:

Claim 1 requires a facilitating agent concentration of between 1 % and 25%. A calculation (in Annex 2 to Prof Burrell’s report) shows that the concentration of NaCl in Example 14 of Gibbins is 1%.

It would be obvious to a skilled person that he could change the concentration of NaCl in Gibbins. Changing NaCl concentrations would be much cheaper than changing AgNO₃ concentrations and risk wasting silver containing material.

It would be obvious to increase the NaCl concentration because it was well known that silver could form complex halides, that the complexes had increased solubility compared to simple metal halide and that excess halide favoured the formation of complexes.

The skilled person would know they could increase the halide concentration but there would be an upper limit somewhere where they would be limited by the solubility of the halide or complex. Gibbins gives guidance on this in that a wide variety of molar ratios of chloride:silver are taught resulting in light stability. In Example 14 the Cl:Ag molar ratio is 0.5693:0.0033 or 172.5:1. In Example 25 the ratio varies from 11.5:1 to 47.62:1. These differ by a factor of 3.62 (because 172.5/47.62 = 3.62). Thus the skilled person would know that in following Example 25 you could increase the concentration of chloride by a factor of 3.62 times and still have a Cl:Ag ratio which was demonstrated to work. If for example the skilled team followed Example 25(b) where the NaCl molar concentration was 30 x 10^-4 and knew they could multiply this by 3.62, they would get a molar concentration of 0.01086M. That is 0.6353g of NaCl which, in the 55ml total volume of treatment in Example 25(b) gives a percentage of 1.2%.

That is within claim 1 and so the claim is obvious.

It seems to me that in a case like this it is important to be clear about the starting point. Gibbins consists of a general disclosure and some specific examples. Almost all of Gibbins’ disclosure is outside claim 1. All the acrylamide examples and many of the Aquacel examples do not satisfy the claim on any view. Moreover although Gibbins teaches that some of the Aquacel examples are photostable within the meaning of claim 1 (Example 24) the teaching about others is different (Example 25) . Another reason why many of the Aquacel examples are not within claim 1 is because they involve a different sequence of steps. Thus it is not correct to say that simply increasing the chloride concentration in Gibbins falls within claim 1. It depends which example you start from.

The examples on which attention was focussed were tests in Example 25, in particular Examples 25(b) and 25(m). Like all the tests in Example 25, these two use salt concentrations which are outside claim 1 because they are too low. However Example 25(b) also differs from claim 1 in terms of method steps. Example 25(b) consists of making a composition of sodium chloride in ethanol/water, then adding the dressing and then adding silver nitrate. That is not within claim 1. No amount of increasing the salt concentration in this example will produce a process within claim 1.

On the other hand it is common ground that the steps in Example 25(m) are within claim 1 but of course the salt concentration is too low. However Example 25(m) also has half the salt concentration of Example 25(b). As a result Mr Acland submitted, and Mr Mellor did not dispute, that if the mathematical logic based on molar ratios, which was applied to produce a salt concentration of 1.2% in Example 25(b), was applied to increase the salt concentration of Example 25(m), the end result would still be too low for claim 1. (I note that in that respect there was a typographical error in Smith & Nephew’s closing submissions whereby paragraph 122(b) should have referred to Example 25(b) and not 25(m) as written.)

This seems to me to illustrate the importance of carefully identifying the differences between the prior art concerned and the claim as part of the proper consideration of obviousness. It is not accurate to say that the only difference is salt concentration.

The correct way to characterise the differences between Gibbins and claim 1 is as follows. Gibbins is clearly directed at the same objective as the patent in general terms, i.e. the production of light-stable antimicrobial wound dressing materials. In terms of features of claim 1: Gibbins clearly discloses methods directed to trying to make light-stable antimicrobial Aquacel material which incorporates silver. These methods use solvents within claim 1 (ethanol/water) and the same reagents (AgNO₃ and NaCl). Some of the Aquacel examples involve the use of copper but some do not. Some of the Aquacel examples are outside claim 1 in terms of the sequences of steps but there is disclosure of sequences of steps within claim 1 (Example 25(m)). None of the Aquacel examples as described have a salt concentration within claim 1.

Although it is important analytically to be clear what the differences are between Gibbins and the claim, it also seems to me that one should not lose sight of the similarities. Smith & Nephew submits that Gibbins and the Convatec patent are based on precisely the same basic chemistry. That is the creation of silver chloride complexes by means of an excess of chloride in order to create a photostable Aquacel wound dressing incorporating silver. It submits that the key difference, which is the 1% - 25% salt concentration feature added by amendment to claim 1, is in truth a largely arbitrary matter. That is because the range of salt concentrations in the claim is unconnected to any concentration of silver whereas what really matters is the relative amounts of salt and silver.

Convatec submits that the invention is not obvious over Gibbins. It makes the following general points:

Smith & Nephew’s argument starts from Example 25. But Convatec submits the skilled person would not believe that the example had worked and produced a photostable product. A key part of Gibbins’ technique which worked for acrylamide (copper or ferric ions) has no stabilising effect with Aquacel. Gibbins tested copper in Example 25 but it did not make a difference. The natural conclusion is that the teaching is not applicable to Aquacel. The lack of photostability would also be consistent with the common general knowledge because the skilled person would think Gibbins was concerned with precipitating silver chloride and that it was known to be highly light unstable.

The argument that the skilled person would be motivated to increase halide concentration was wrong because it is based on the incorrect argument that Gibbins teaches silver chloride complex formation.

The argument that a skilled person would vary the concentrations of sodium chloride by reference to Example 14 is wrong. For one thing the best sample in Example 25 is 25(n) which had no chloride. Next Example 14 is an illogical starting point. In any event using the numbers based on Example 14 does not get within the range of the claims. Convatec submits that in an attempt to salvage this point Prof Kennedy was cross-examined on a new point that it was obvious to use a lot more silver (and hence a lot more halide). Mr Acland called this a lawyer’s point and not one advanced by Prof Burrell. In any event the “Hi Ag” Example 24 produced more instability.

In order to decide the issue I need to address the following points:

Complexes in Gibbins

Photostability in Gibbins

The applicability of Example 14

Order of steps

Increasing silver

What does Gibbins teach the skilled reader about silver chloride complex formation? Smith & Nephew contends Gibbins teaches complexes and that this would motivate the skilled person to use increasing amounts of halide – to favour complex formation. Convatec contends Gibbins does not teach complexes. Moreover the fact that silver chloride complexes are relatively photostable (compared to silver chloride) was not common general knowledge and so there was no motivation to the skilled person to favour complex formation anyway. It says the teaching of Gibbins relates to silver chloride (AgCl) and not to silver chloride complexes.

The word “complex” does indeed appear in Gibbins but the idea that silver chloride complexes are the key to photostability hardly jumps off the page. I will deal with the document below after addressing the opinions of the experts. Prof Kennedy’s view was that Gibbins related to silver chloride rather than silver chloride complexes. That is how he read it from the start. He was cross-examined at length on the topic but maintained his view.

Prof Burrell’s view was that the document taught silver chloride complex formation. Mr Acland submitted that although this was a conclusion in the Professor’s fourth report, it was not in his first or second report and indeed the second report appears to draw a distinction between Gibbins and Kreidl on that basis. This opinion was not as clearly expressed in his earlier reports as it might have been but it can be said that the significance of the point developed during the exchanges of reports in this case. I have no doubt that it is Professor Burrell’s genuinely held opinion that Gibbins envisages that silver halide complexes can be created and that Gibbins intentionally uses the term complex. However it seemed to me that Prof Burrell had a particular understanding of and interest in complexes, which did not reflect the position of the skilled person in this case, as a result of his scientific experience in environmental biology and toxicology. This point by no means undermines Prof Burrell’s opinion entirely but it is a factor which goes to weight.

What of the document itself? Gibbins discusses the formation of the weakly soluble salt silver chloride in a passage starting at p20 ln 30. This discusses fully dispersing silver chloride throughout the matrix. It is written in terms of what I have referred to above as the acrylamide matrix. Gibbins also contains a clear teaching at p21 ln15-30 to use excess chloride ions to favour association rather than disassociation. This is reference to the equilibrium between AgCl (association) and Ag⁺ and Cl^- (disassociation) and would be understood by the skilled reader as a reference to Le Chatelier’s principle. The section continues at p21 ln30 with a discussion of the details of light instability and how ionic copper or iron helps to stabilise the silver.

At p21 ln22 the following sentence appears:

This sentence immediately follows one dealing with the disclosure of a prior US patent which describes the formation of a silver chloride colloidal precipitate in the context of incorporating antimicrobial silver into materials. As I read the sentence at line 22 referring to the “silver complex”, Gibbins is still discussing what is disclosed in the US patent. However even if that is so, I accept that a skilled reader would see here a teaching about silver chloride complexes.

A few lines further on is another reference:

Although this also has echoes of the earlier US patent, since it starts with the words “Therefore this invention also comprises …” I think it would be a clear reference to Gibbins’ own invention.

Finally in Example 14 (one of the key acrylamide Examples) at line 13 there is a clear statement that a finely dispersed silver complex is formed. The formation takes place after silver nitrate has been added to a batch of the precursor material (containing sodium chloride) which will later be polymerised to make a polyacrylate hydratable matrix.

These citations are a slender foundation for Smith & Nephew’s argument. I find as follows. I am not surprised Prof Kennedy did not regard Gibbins as teaching silver chloride complexes. I reject the idea that Gibbins can be simplified down to a clear, firm teaching that the key to everything is the production of silver chloride complexes. Apart from anything else it was not common general knowledge that such complexes were more photostable than silver chloride itself and Gibbins does not say that they are. So the skilled reader has no reason to latch onto these rather stray phrases as being the heart of the disclosure. However I believe it is undeniable that, read very carefully, there is a teaching about silver chloride complex formation in Gibbins.

It seems to me that the real issue is the extent to which the skilled person would be motivated to increase the halide concentration and by how much. As to this there are clear statements in Gibbins which teach the use of an excess of chloride over silver. The passage on page 21 is one example. However the skilled person would not understand page 21 as a teaching to set out to make complexes but as a teaching to use Le Chatelier’s principle to favour association (AgCl) rather than disassociation (Ag⁺ and Cl^-). Page 23 line 21 refers specifically to an excess of chloride to stabilise the silver complex but I note it also refers to copper.

In my judgment as a general point it would not have been inventive for a skilled person reading Gibbins to think they could tinker with the chloride concentration, and increase it somewhat in order to favour association rather than disassociation. That is what Gibbins teaches. Indeed they would know from their chemical common general knowledge that this would be so. The skilled person would also know from their common general knowledge that a large excess of chloride favoured the formation of complexes. However I think that the suggestion that the skilled person would latch onto the references to complexes in Gibbins and think they should set out to increase chloride concentrations with complex formation and photostability in mind is a point imbued with hindsight. It is clear now that Gibbins and the patent in suit probably provide photostability (to the extent they do) by means of the formation of silver chloride complexes. However the skilled person reading Gibbins does not know that and the document does not teach him or her that it is the case.

Gibbins clearly teaches that a photostable acrylamide matrix containing antimicrobial silver can be made. As regards Aquacel, I have held that Example 24 is photostable but I am not satisfied there is a disclosure that all the samples in Example 25 are photostable within the meaning of claim 1.

The important question is about the motivation of the skilled person. Prof Kennedy’s view was that Gibbins did not provide a light-stable product and so a skilled person would not start from there and would not know how to move forward. I do not accept that. I bear in mind that at least Example 24 satisfied the claimed requirement for photostability. In my judgment there is a sufficient teaching in Gibbins about stability to light to mean this is not a case in which the skilled person would simply put the document aside. They would see that a degree of light stability was achieved. The skilled person is not concerned with worrying about whether the materials do or do not fall inside the Convatec patent claim. There is enough in Gibbins to motivate the skilled person to take its disclosure seriously and consider how to make further improvements to the method with a view to aiming to make dressings which are stable to light. Stability in the presence of light is a goal worth pursuing and Gibbins provides a clear motivation to take it forward with that in mind.

There are three important points about the teaching of Example 14.

First Example 14 is clearly concerned with acrylamide. In that context Gibbins had much more success in relation to light stability. Example 16, in which the products of Example 14 were exposed to light, simply states that the relevant samples “did not show discolorization”. There is no equivocation in Gibbins on the point and the skilled reader would see the contrast between this and the results achieved for Aquacel. Regardless of whether the Aquacel light stability results in Gibbins are within the claim or not, they are less clear cut than those reported for acrylamide.

Second it is clear that Example 14 includes the use of copper or iron. Using those reagents is what Gibbins calls “stabilization chemistry”. A skilled reader starting at Example 25 would see that copper did not have the same effect with Aquacel as it had with the acrylamide matrix. The stabilization chemistry in Example 14 does not work with Aquacel.

Third, in Example 14 the finely dispersed silver complex is formed in the precursor mixture before polymerisation. This is a different technique from adding silver to existing Aquacel fibres.

For these reasons I reject the argument that a skilled person would look at the quantities in Example 14 and use them as a basis to make changes to the quantities in Example 25. It would not be obvious that any parameters in Example 14 could be lifted and used with Aquacel.

Furthermore and separately I am not satisfied that the sort of calculation Prof Burrell performed in order to derive the silver concentration and the molar ratios and apply them to Example 25 is something the skilled person would do. It is plainly something a skilled person could do. Such calculations of molar ratios and the like are common general knowledge. However unless the skilled person was actually thinking they wished specifically to make complexes (which I have rejected, albeit I accept complexes are mentioned in Example 14) there is no reason to seek to calculate such values from the example. There were points of detail about the calculations themselves but I do not find it necessary to resolve them.

It is clear that Gibbins discloses different ways of carrying out the relevant processes. Mr Acland submitted the main teaching as far as Aquacel was concerned was a “two step two bath” procedure which involved immersing the fibres in an alcohol/water chloride solution, removing the fibres and then immersing the fibres in an alcohol/water containing silver ions (and copper or iron). This would not be within the claim. Smith & Nephew submitted that the skilled person would pick up on the statement in Gibbins that steps could be reversed and Convatec replied arguing that what was disclosed in that respect by Example 26 indicated that reversal produced a less satisfactory result. I am not satisfied that the skilled person would regard the reversal of the steps of a given method as a trivial matter. It is another factor to take into account.

It seems to me that, irrespective of reversal, an important point is that the order of steps in Example 25(m) is within the claim. It cannot be said that the skilled person could not have employed the order of steps in Example 25 (m) in taking the teaching of Gibbins forward. On the other hand I am not aware of any reason why Example 25(m), in terms of its order of steps, would be favoured as opposed to other parts of Example 25.

There was a suggestion that the skilled person would increase the silver concentration. The effect of this would be that the chloride concentration would obviously go up as well. Thus if the silver concentration was raised high enough, a chloride level inside the claim would be reached. Mr Acland submitted that Prof Burrell had not advanced this suggestion at any stage and that this argument only arose during the trial when Smith & Nephew realised there was a problem with the mathematical argument that numbers based on Example 14 produced a result within the claim. I accept Mr Acland’s first submission. As to the second I am not concerned with Smith & Nephew’s motives. In any event I am not satisfied it was obvious to increase the silver concentration, at least not sufficiently to lead to a result inside the claim.

The disclosure of Gibbins is complex and it is not clear to me how a skilled person, without knowledge of the invention, could be said to arrive at a process within the Convatec claim by nothing more than an obvious step or steps. I accept that the skilled person would not simply dismiss Gibbins out of hand. There is a sufficient disclosure of light stable silver containing Aquacel to be worth taking seriously and moving forwards. It is true that increasing the chloride concentration of Example 25(m) to a certain point produces a result inside claim 1 but I am not satisfied the skilled person would select Example 25(m) as the place to start. Example 25(n) produces the best result as far as light stability is concerned. Even leaving aside the oddity that 25(n), which was probably intended as a control, produced a better result than 25(a) to (m), there is no reason to alight on 25(m) without hindsight. But to arrive at claim 1 the person has to use the method steps in the order provided for in 25(m) rather than for example 25(b).

I accept that increasing chloride concentration somewhat was not inventive but I am not satisfied the skilled person would go far enough to arrive inside claim 1 without hindsight. If I had accepted Smith & Nephew’s argument about Example 14 then that would have removed the hindsight element in this respect but I reject the reliance on Example 14. If I had accepted Smith & Nephew’s argument that complexes would be the driver for the skilled person then that might have helped but I reject that too. Moreover I am not convinced the silver complex point alone, even if Smith & Nephew were right that the skilled person would see complexes as the route to photostability (or better photostability), goes far enough to lead to a chloride concentration which would take the skilled person inside claim 1. It is too vague for that.

There is also a relationship between the Example 14 argument and the selection of Example 25(m) as a starting point since even if Prof Burrell’s calculations based on Example 14 are applied to the salt level in Example 25(m), as opposed to Example 25(b), the end result is not within the claim. To reach the claim from Example 25(b) instead of 25(m) one needs to increase the salt concentration to the right degree and also to reverse the steps. But again there is no reason to do that without hindsight.

Mr Mellor submitted that “hindsight” had not been put to Prof Burrell. That is true but I do not regard the point as significant. Prof Burrell’s opinion was clearly not based on hindsight from his point of view. He derived figures from Example 14 and saw the complexes in Gibbins as the motivation to increase the salt concentration to the relevant extent. However I have not accepted those points and it seems to me that without them the argument would be based on hindsight.

I find that claim 1 is not obvious over Gibbins.

US Patent 2,396,514 (Kreidl) was published in 1946 and is entitled “Sterilizing materials and methods for making the same”. At one stage Smith & Nephew pleaded a second Kreidl patent (so called Kreidl 2) and submitted they should be read together. By the closing no mention was made of Kreidl 2 and I do not need to address it.

Kreidl relates to disinfectant products which contain silver in combination with a halogen and methods for making them. In the preamble, the document notes that the specific action of silver and particularly its antiseptic and disinfectant action are well known in the art but there is a drawback. Most of the known silver preparations “are difficult to prepare, have an undesirable dark colour and are none too stable with respect to organic matter and light” (p1 LH side ln14-17).

Kreidl’s stated purposes are set out in the third paragraph. The first sentence reads “an object of this invention is a disinfectant product having silver halide in a stabilized form as the effective agent.” Further on (p1 LH side ln39-44) Kreidl states that the invention is “based on the discovery that disinfectant silver halide preparations of an increased stability, more particularly with respect towards the action of light, may be obtained by having the silver halide protected by an excess of halide.”

The document explains that whilst the theory of action of the excess halide is not quite understood “it may be assumed that the silver halide products according to the invention owe their increased stability to a complex formation of the simple silver halide (AgCl, AgBr, AgI) with other halides. It appears that in this protected state, the silver is more tightly bound to the halogen and thus not readily reduced by the solarising influence of light.”

The emphasis on silver halide complex formation in Kreidl is clear. Just as an example, one element of Kreidl’s disclosure relates to stable solutions of silver halides for use as disinfectant solutions. In that context at p2 RH side ln15-18 it states “without restricting this invention to any theory it may be assumed that the stability of such solutions may be due to the formation of complex silver halide compounds as described above”.

At page 3 the document addresses solid disinfectant silver halide preparations and at line 42 of the left hand column states:

Kreidl explains that the impregnation may be carried out in two stages, preferably first with the silver salt and then with the halide type compound or else the impregnation may be a one stage process using the solution of silver halide product described in Kreidl 2 (p3 RH side ln25-26). The two stage impregnation process is described (p3 RH side from ln37) as soaking a bandage gauze in a silver nitrate solution, drying and then dipping the material into sodium chloride solution. After the reaction is completed the gauze has to be washed so as to remove any non-adsorbed salts regardless of whether they are soluble or precipitated. The point of washing off non-adsorbed silver halide compounds which just adhere to the fibres is that they will not be stable to light (passage bridging p3 and p4). They have to be washed off carefully.

Kreidl includes thirteen worked examples. In Example 5 a bandage gauze is dipped into 1% AgNO₃ solution, wrung out, dried and immersed in cold 20% NaCl solution for one hour and washed carefully. Kreidl states “The gauze does not discolor when exposed to light.”

At the end of the description, before the claims, the point is made that in some cases mixed solvents such as diluted alcohol and so forth may be desirable.

Kreidl is a clear teaching of a method of preparing a light stabilised antimicrobial material for use in wound dressings with the same basic steps as the Convatec invention. Consider Kreidl Example 5. A solution of silver is prepared (1% AgNO₃). That corresponds to step (a) of claim 1. A wound dressing material (bandage gauze, i.e. cotton) is dipped in it. That corresponds to step (b). Afterwards the material is subjected to a 20% sodium chloride solution. That corresponds to step (c) and, unlike Gibbins, the salt concentration is squarely within the claim. The result is a light-stable product. Example 6 is in a similar vein but uses a salt concentration of 5%. A light-stable cotton gauze is produced.

However there are important differences too. The key difference is that the claim is concerned with gel forming fibres such as Aquacel. They are not mentioned in Kreidl, indeed they had not been invented yet. Cotton gauze is not a gel forming fibre. Also Example 5 takes place in water whereas the claim requires an organic solvent. However Kreidl clearly teaches that diluted alcohol can be used and that would satisfy the claim. Finally Kreidl teaches that a washing step is important at the end of the process. That may or may not be significant.

Although Kreidl was published in 1946, it was common ground that the correct approach is to consider the situation at the filing date of 29^th November 2001. The question is: was the invention obvious to a skilled person at the filing date?

There is no doubt Aquacel was common general knowledge in 2001. Prof Burrell’s opinion was that it was obvious for the skilled person to apply the teaching of Kreidl to more modern materials including gel forming fibres such as Aquacel. His reasons were in summary (i) that Kreidl’s method expressly applies to a range of different materials and there is no teaching to suggest that it could not be used with others, (ii) that it can be applied to water soluble or water swellable materials using organic solvents that will avoid premature gelling, (iii) that the skilled person would appreciate that the chemistry of the method could be applied equally to more modern materials, and (iv) there was a general motivation to use modern materials because they were readily available and had their own advantages (including keeping the wound moist).

On the face of it these are good reasons why it would be obvious to a skilled person in 2001 reading Kreidl to use its method, for example with the concentrations in Example 5 albeit now using an organic solvent, and dip a piece of Aquacel material in 1% silver nitrate and then in 20% sodium chloride. This would be a method within claim 1.

Prof Kennedy’s opinion was to the contrary. Convatec emphasised that his view was formed before reading the patent or the reports of Prof Qin or Prof Burrell. In summary his first reaction was that Kreidl was about sterilising solutions based on silver and ways of making them. The application of such solutions was only a minor feature of Kreidl. He said:

Prof Kennedy’s view was that Kreidl taught a way of physically trapping AgCl within the cotton fibre and not on its surface. The entrapment gives rise to physical shielding of the AgCl and hence light stability. That is also why careful washing is required, to wash AgCl from the surface of the cotton because it is not light-stable there. In other words in Kreidl the AgCl is kept in the dark inside the cotton fibre. However, as Prof Kennedy pointed out, unlike cotton, CMC (the material in Aquacel) has no relevant capillaries or amorphous areas and there can be no physical shielding. Furthermore if the method of Kreidl is applied to CMC, light unstable AgCMC will be formed.

On the face of it these are good reasons why it would not be obvious to embark on applying Kreidl to a modern “high tech” dressing material such as Aquacel.

At trial both experts were cross-examined by highly skilled counsel.

The key matters arising in Prof Burrell’s cross-examination were the following:

He accepted that shielding would occur to the skilled person as possible in Kreidl but did not accept that shielding was the only rational explanation.

Although the skilled person would understand that Kreidl will be producing silver complexes, it was not common general knowledge that complexes were light-stable. Prof Burrell’s view was that the reader may believe that it is the adsorbed form of complex which gives stability. This probably involved Van der Waals forces acting on complexes but the effect of this was not known to the skilled person.

Convatec submitted that Professor Burrell accepted that a skilled person in 2001 would say that the adsorption theory cannot be right. I do not accept that. Although one can derive that conclusion from passages in his cross-examination, in my judgment listening to the Professor’s evidence as a whole he did not accept that the skilled person in 2001 would reject the adsorption explanation which Kreidl itself teaches. The Professor’s view was that the skilled person would consider there to be two possible mechanisms, surface adsorption and shielding.

The upshot of Prof Burrell’s cross-examination was that he accepted that it would not be obvious to try Kreidl’s method on Aquacel if physical shielding was the way Kreidl’s method worked. However he did not accept the premise and maintained his view that Aquacel was an obvious material to try if the skilled person accepted Kreidl’s teaching that adsorption provided stability.

The key matters arising in Prof Kennedy’s cross examination were:

He maintained his view that he would have put Kreidl aside.

He accepted that the key teaching of Kreidl was to create silver halide preparations with an excess of halide to bring about light stability and that the stability of such halides could be further increased by having them truly adsorbed on the material.

He accepted that the teaching of Kreidl was not limited to cotton. Clays are offered as alternatives.

He accepted that Kreidl forms silver chloride complexes and they will be adsorbed onto cotton by Van der Waals forces.

He did not accept that the term “adsorption” used in Kreidl would be understood by a skilled person in 2001 in its normal technical meaning.

The upshot of Prof Kennedy’s cross examination was that he maintained his view that shielding from light explained the light stability of the cotton product in Kreidl but he accepted that clay was in Kreidl and there was no possibility of shielding with clay. He maintained that it was not obvious to try Kreidl’s teaching on a modern gel forming material.

There are a number of points which I can deal with initially.

First, I do not accept that the skilled person would simply put Kreidl aside. In law the skilled person reads the document with interest. In my judgment if a skilled person read Kreidl in 2001 in that way they would not dismiss it out of hand. Irrespective of questions of chemical mechanism, the document contains a clear disclosure showing that a photostable silver impregnated wound dressing made of cotton gauze was made in a simple process (examples 5 and 6).

Second, this is not a case in which the age of Kreidl in and of itself gives rise to an inference of non-obviousness. I am not satisfied that the forensic question “if it was obvious over Kreidl why was it not done before?” helps Convatec. Mr Mellor submitted that in the 1940s penicillin was the wonder drug and everybody has been searching for antibiotics over many decades. It was only with the more recent increase in antibiotic resistance that interest in silver has returned. The silver dressings that came along were in the 1990s and mostly in the late 1990s. I did not have my attention drawn to any evidence to gainsay that point.

However the forensic question “if it was obvious over Kreidl why was it not done before?” is not the only issue. I am quite sure a skilled person reading the document in 2001 would notice that it dated from 1946 and would take that into account.

Third however, although the skilled person would take into account that Kreidl dated from the 1940s, I do not accept that the skilled person reading it in 2001 would think the document was using the word “adsorption” in an unusual way. In my judgment the document used “adsorption” in 1946 in the same way it would be understood by a skilled person in 2001 and the skilled reader in 2001 would not think otherwise. I listened carefully to Prof Kennedy’s evidence to the contrary but I was not convinced.

Fourth, there is nothing in the nature of the solvent. Convatec did not suggest that there was but it bears recording that in this case, if the skilled person decided to test Aquacel using Kreidl’s method, they would plainly use an organic solvent.

Fifth, I think the washing step is not relevant. Convatec argued that one reason the skilled person would not think Kreidl’s method would work would be because the washing step would wash away all the silver chloride (or all silver chloride complexes). In my judgment the point stands or falls with the shielding / lumen argument in the debate between shielding and adsorption. A skilled person who accepted the surface adsorption idea would think that the washing was not intended to be so vigorous as to wash off the adsorbed material on the surfaces (wherever they were). Whereas a skilled person who accepted the shielding theory that the light-stable silver is stable because it is shaded inside the lumen may well think the washing step washed away all the other material.

Sixth, in my judgment this is not a case in which the skilled person would simply try it and see. In some factual situations it might be obvious to a skilled person to have a go with an experiment even though they have no opinion about whether it will actually work. It may be obvious to test 10 different reagents in parallel with a reasonable expectation that one is likely work albeit the skilled person does not know which one. That is not this case. Having heard both Professors, it seems to me that in this art the skilled person will not perform a test without thinking about the rationale for what they are doing. The skilled person in this field will consider how and why the test they are considering may or may not work before they carry it out.

Seventh, however, the process of thinking about the rationale for an experiment can be taken too far. I am not persuaded that what I will call the AgCMC / stripping point makes a significant difference to the obviousness argument over Kreidl. This requires some explanation. Aquacel is made of NaCMC. Convatec submitted that a skilled person would think that when AgNO₃ is added to NaCMC, an ion exchange reaction takes place to form AgCMC. In other words the sodium ions which were bound by an ionic bond to the CMC molecule are replaced by the silver ions. It was common ground that AgCMC was not light-stable and that this was a matter of common general knowledge. Therefore Convatec argued that the skilled person would think that the Kreidl method would not work for NaCMC materials. There was then a lively debate about “stripping”. This was concerned with whether the Ag ions would be stripped off the AgCMC by the subsequent treatment with NaCl to produce NaCMC and AgCl. It also involved considering the solubility of AgCMC. Convatec said that stripping was Prof Burrell’s idea but that Prof Kennedy did not agree and the point had never been put to Prof Kennedy. Smith & Nephew’s answer to this was to point to the mechanism of the patent, which I can take it plainly works in practice. Smith & Nephew submitted that when excess chloride ions are added, the silver ions react with the chloride ions to form AgCl complexes which are light-stable and so the argument falls away.

While I believe a skilled person will consider the rationale for Kreidl’s results (in other words how they come to arise) and will think about the implications of this for a putative test on Aquacel, I do not believe they would descend into the level of scientific theory and detail exemplified by this AgCMC/stripping argument. I am not convinced a fear that they might simply form AgCMC would put off the skilled person nor was I convinced by the counter theory concerned with stripping and the solubility of AgCMC vs AgCl. I am not satisfied these considerations would play a material role in the approach of the skilled person.

Looking at the matter overall, it seems to me that three things will stand out to a skilled person reading Kreidl in 2001. First, the strong positive aspect is that here is a simple teaching which reports clear, successful results producing a light-stable silver impregnated wound dressing made of cotton gauze. Second however, I think the skilled person would be faced with a puzzle. He or she will certainly consider what is going on in Kreidl and see its teaching about complexes. There is nothing in his or her common general knowledge which supports Kreidl’s idea that surface adsorption of complexes is the key to it. I find that the skilled person would also consider that shielding may well be the much simpler explanation. The fact that Kreidl teaches that clay can be used is clear support for the surface adsorption theory but in the end the skilled person is not interested in stabilising silver on clay, he or she is interested in stabilising silver in wound dressings. Third, the date of the document will stand out to a reader in 2001. Gel forming dressings such as Aquacel were a relatively recent invention in 2001 and did not exist in 1946. The skilled person would be aware of that. In terms of dressing materials, Kreidl focuses on cotton gauze and does not purport to refer to the modern gel forming dressing materials. The explanation why they are not referred to is obvious enough (they did not exist) but the fact remains that this is a document from the 1940s which is not concerned with modern materials.

I bear in mind the policy of the law in this respect is to prevent the state of the art being patented again and to prevent patents from monopolising the results of taking obvious steps from any matter which has been made available to the public. Kreidl’s teaching is publicly available and the public are entitled to do obvious things with it, without fear of patents. On the other hand it is all too easy to see things as obvious steps when looking back at them after the event and knowing what the step to be taken is.

I have no doubt that the skilled person would consider whether to test Aquacel in Kreidl’s conditions (using an organic solvent) but the problem is the existence of alternative explanations for Kreidl’s results. If surface adsorption of complexes is the explanation, the test on Aquacel has a prospect of achieving success. It might work. Nevertheless Aquacel is different from cotton gauze. It is one of the modern gel forming dressing materials and is not referred to in Kreidl. The skilled person would have no certainty that the test would work. It might or might not.

However if shielding is the explanation for Kreidl’s cotton results then the method has no prospect of working with Aquacel at all. There are no places for the silver to be shielded in Aquacel. It may also be that both mechanisms are relevant in which case the skilled person will know that shielding will not provide any help with Aquacel.

I think the key to the problem is that it would not be obvious to the skilled person which theory was right. Plainly the test could be done very simply but that is not enough. To run the test and see if the Kreidl conditions work for Aquacel, when the skilled person knows that the simpler explanation for Kreidl’s results is one which will lead to certain failure and the other explanation by no means guarantees success, is not the act of an unimaginative person. I think it is the act of an inventive person. The obviousness case over Kreidl is a powerful and simple one but I am not persuaded that Convatec’s claim lacks an inventive step. I find that the claim is valid over Kreidl.

I can deal with the insufficiency argument shortly. It was relied on by Smith & Nephew as a squeeze over Gibbins in relation to photostability. Smith & Nephew’s pleaded case is:

Smith & Nephew referred to Prof Kennedy’s view that a material which had purple specks when dry would not fall within the definition in the patent. It argued that if a material that is purple with specks when dry, i.e. at the end of the manufacturing process, is not a material which has undergone a controlled colour change within the meaning of the patent then the patent must be insufficient. I do not have to resolve that question because I have found that Example 24 (the material that is purple with specks when dry) is within the claim.

The fact that I am not satisfied that as written, Gibbins discloses that all the samples in Example 25 were photostable materials within claim 1, has no bearing on insufficiency. It does not show any ambiguity about the definition.

There is nothing before me to suggest that the skilled person would not know what “substantially photostable” in the patent means. Nor is there anything to suggest that the skilled person would have difficulty knowing whether any given method fell within the claim or determining how to perform a method in a way which meets the criterion. I reject the insufficiency argument.

I will allow the amendment. As amended the patent is valid.