A free acid form of a polysaccharide is produced from its alkali-metal
salt. In one example, free-form hyaluronic acid is produced by preparing
a solution of an alkali-metal salt of hyaluronic acid, dispersing into
the solution a strong acid, enclosing the dispersion within a
semi-permeable membrane, dialyzing the dispersion in water, and
harvesting the product from within the membrane. The strong acid can be
hydrochloric acid, sulfuric acid, nitric acid, orthophosphoric acid, or
oxalic acid, for example. The semi-permeable membrane is non-ionic, and
has a molecular weight cut-off large enough to pass the strong acid, and
preferably much larger. The invention provides a simple and economical
way to produce a product which is not commercially available.
