A method of making a coating solution includes the steps of polymerising an initial monomer feed comprising an N-vinyl pyrrolidone and an acrylate, preferably methacrylate, salt in water to synthesise a copolymer thereof, acidifying the resulting copolymer-water mixture to give free carboxylic acid groups along the copolymer backbone, diluting the aqueous solution down with alcohol, and adding a cross-linking agent which is capable of reacting with the carboxylic acid groups and curing the copolymer at a later stage after the coating solution has been applied to a substrate and the copolymer coated thereon. Also disclosed are a coating solution in storage, a method of coating a substrate which is on, or is part of, a medical device or other article, a substrate, article or medical device having a coating so applied, and a coated medical device packaged in a hydration solution. The aqueous-alcoholic coating solution may be stored for an extended period, suitably for at least one month and desirably for substantially longer, without deteriorating.