Anionically charged chitosan

A method of therapeutic treatment for osteoarthritis or repairing a cartilage defect, said method comprising administering a carboxyalkyl chitosan to a subject in need thereof, wherein said carboxyalkyl chitosan is administered via injection into the synovial fluid or via implantation in the cartilage, wherein said carboxyalkyl chitosan comprises glucosamine units, N-acetyl-glucosamine units, and glucosamine units substituted by a carboxyalkyl group, wherein the carboxyalkyl chitosan is N,O-carboxyalkyl chitosan and has:

• a zeta potential, measured at pH 7.5, that is lower than or equal to −18 mV;
• a degree of acetylation in a range of about 40% to about 80%, expressed at the number of moles of N-acetyl-glucosamine units relative to the number of moles of total units;
• and
• a degree of substitution by the carboxyalkyl group that is greater than 70% expressed as the number of moles of the substituent carboxyalkyl group relative to the number of moles of total units, and
• wherein the carboxyalkyl chitosan is water-soluble at a pH less than 3.5 and at a physiological pH and is sufficiently pure and suitable for providing a non-opalescent aqueous solution for injection, implantation, or instillation to a human or animal subject.