Crosslinked butyrate or butyrate-formate derivatives of hyaluronic acid and the crosslinking thereof

A process for preparing crosslinked hyaluronic acid butyrate or crosslinked hyaluronic acid butyrate-formate or an acceptable salt thereof, the process comprising:

• crosslinking hyaluronic acid butyrate or hyaluronic acid butyrate-formate or a pharmaceutically acceptable salt thereof in an organic solvent with a carboxyl group activating reagent and a base forming a reaction mixture,
• buffering said reaction mixture to a pH of 7.2;
• and
• obtaining said crosslinked hyaluronic acid butyrate or said crosslinked hyaluronic acid butyrate-formate or said acceptable salt thereof,
• wherein the hyaluronic acid butyrate or hyaluronic acid butyrate-formate or a pharmaceutically acceptable salt thereof is a mixture of a high molecular weight polysaccharide having a weight average molecular weight ranging between 1000 kDa and 10000 kDa and a low molecular weight polysaccharide having a weight average molecular weight ranging between 1 kDa and 900 kDa, and
• wherein the process comprises sterilizing in an autoclave at 121° C. for 15 minutes.