Hyaluronic acid, in its natural form, is characterized by a very fast turn-over: it is rapidly degraded by specific enzymes, the hyaluronidases, so its half-life, if introduced into the dermis from the outside, is extremely short. 

In order to extend its life, are used several techniques of chemical or physical-chemical esterification, getting a network between the polymer chains (crosslinking) that will change the physical and mechanical properties of materials: elasticity, hardness, strength, viscosity, etc..