Biological materials such as vaccines can be stabilised in certain glassy materials, soluble in water. It has been proposed to form these glassy materials as a powder suspended in a non-aqueous liquid for injection into a patient. There is a problem in maintaining the suspension because the particles tend to sink to the bottom. The problem is solved by adding a blowing agent into a solution for which the glass is formed. The blowing agent decomposes as the solution evaporates thereby forming cavities in the resulting glass structure, reducing its density to match that of the liquid in which it is to be suspended. Other uses for the invention are in compositions intended for inhalation and for rapid dissolution in aqueous solutions immediately before use.
