This thesis presents the project conducted with the French enterprise SYMATESE, located in the west of Lyon, specialized in biopolymers extraction and transformation for the development of medical devices. The objective of the project is to create a new product for the viscosupplementation characterized by the combination between the hyaluronic acid gel and an active substance. The final product should achieve some characteristics that are requested by the client: • defined pH; • defined buffer composition: no presence of phosphates; • osmolarity compatible with human body; • viscoelastic solid behavior of the gel (G’>G”) with a defined G’ value; • defined value of injection force; • maintenance of elastic properties and pH after accelerated ageing test.