Medical Applications of Hyaluronan and its Derivatives

Hyaluronan (hyaluronic acid) is a natural polyanionic polysaccharide (glycosaminoglycan) present in the intercellular matrix of most vertebrate connective tissues. The unique properties of hyaluronan result in a molecular network which, in highly hydrated conditions (>99% water content), is extremely elastoviscous and pseudoplastic. These rheological properties are responsible for the biological function of hyaluronan and its medical applications. During the last decade, a highly purified fraction of hyaluronan was introduced in human and veterinary medicine as a therapeutic device for arthritis and eye surgery. The use of elastoviscous hyaluronan solutions in surgery was called viscosurgery. The medical use of viscous hyaluronan solutions for the treatment of arthritis is called viscosupplementation. The use of the natural, highly purified, high molecular size hyaluronan did not fulfill all the medical needs for elastoviscous fluids. Therefore, in the mid-1980s the development of crosslinked derivatives of hyaluronan began. Fluids, gels and solids were made from the native high molecular mass hyaluronan by creating permanent attachment between the polysaccharide chains. These crosslinked derivatives of hyaluronan are called hylans (generic name). Hylans have the same tissue compatibility as native hyaluronan. They, however, have a considerably longer residence time in tissues, which offers a major advantage in their medical efficacy compared to hyaluronan. Most importantly, hylan fluids and gels have enhanced rheological (elastic, viscous, pseudoplastic) properties and therefore more suitable for viscosurgery use and for viscosupplementation.