Smith & Nephew plc v Convatec Technologies Inc

The patent relates to a method of preparing a wound dressing that comprises the known antimicrobial agent silver but which is stable in the presence of light. The defendant proposed an amendment that included adding to claim 1 the feature of:

A material which includes gel-forming fibres containing one or more hydrophilic, amphoteric or anionic polymers.

Claim 1 went on to specify that the polymer was selected from a list of chemical types or mixtures thereof.

The patent only contained a few mentions of the phrase ‘gel-forming fibres’, these included statements that:

Materials which are particularly adapted for the inventive method include gel-forming fibres such as AquacelTM…or those described in WO 00/01425…wound dressings containing similar gel-forming fibres behind or overlying a non-continuous or perforated skin-contact layer such as VersivaTM.

AquacelTM is a commercially available material that contains sodium carboxymethyl cellulose.

The claimant argued that the amendment involved an intermediate generalisation and that there was no general disclosure of ‘gel-forming fibres’. In particular, the issue arose of whether a skilled person would read the application as a whole as disclosing gel-forming fibres generally and sodium carboxymethyl cellulose as an example (as argued by the defendant) or as disclosing only sodium carboxymethyl cellulose gel-forming fibres (as argued by the claimant).

The claimant’s argument was strengthened by the fact that the only gel-forming fibre disclosed in the application was sodium carboxymethyl cellulose or products that contain this fibre. In particular, the claimant argued that when gel-forming fibres are introduced in the application the language would be understood as a disclosure that the gel-forming fibres being discussed are those like AquacelTM. The claimant pointed out that alternatives mentioned such as the disclosures in WO 00/01425 and the product VersivaTM also disclose or contain sodium carboxymethyl cellulose.

The defendant argued that the words “such as” AquacelTM show that the disclosure is not limited to this product but includes other gel-forming fibres made from other polymers such as those mentioned in claim 1. It was pointed out that a skilled person would know from his common general knowledge that gel-forming fibres could be made from the other polymers in the list.

The judge commented that the claimant’s argument was a strong one on the basis of the words of the patent specification alone. However, the judge considered the argument regarding the common general knowledge to be the decisive one. The judge considered that a skilled person would read the disclosures in the knowledge that sodium carboxymethyl cellulose is by no means the only type of gel-forming fibre known and that other polymers can be made as gel-forming fibres as well. Hence, a skilled person would see that sodium carboxymethyl cellulose was being used as an example only. The amendment was therefore held allowable. The amended patent was also held to be valid.

This decision highlights that the issue of what is considered common general knowledge can be a key factor in the interpretation of the disclosure of the patent specification and in determining whether an amendment adds subject matter.