Development of new delivery systems of hyaluronic acid based on silica hydrogels: In vitro kinetics of release and enzymatic degradation of the drug

• HA was encapsulated into silica hydrogels using sol-gel technology • Silica matrix modification affects kinetics of HA degradation and release • Kinetics of HA degradation and release depends on HA amount and molecular weight • Release of encapsulated HA is controlled by delayed Fickian diffusion • Silica hydrogels slow down enzymatic degradation of HA Hyaluronic acid (HA) is a well-known anti-inflammatory drug that is widely used clinically to treat various diseases and as a component in cosmetic products. However some properties of HA (rapid release and enzymatic degradation) significantly reduce its functioning in the body and, consequently, its therapeutic effect. To develop new soft delivery system of HA with improved functional properties, the drug was encapsulated into silica hydrogels with various surface chemistry of silica matrix. The hydrogels of silica modified with aminopropyl and mercaptopropyl groups, as well as unmodified silica were studied as HA carriers. The effects of silica matrix modification, average molecular weight and concentration HA on the kinetics of its release from the formed composite hydrogels, as well as enzymatic degradation were revealed in vitro. It was found that the encapsulation of HA into silica hydrogels significantly slows down release process of the acid and, in most cases, its enzyme-induced degradation. The release controlled by delayed (pseudo-Fickian) diffusion as well as the protective effect of the silica hydrogel matrixes on the enzymatic degradation showed that the silica hydrogels are promising materials for creation of new soft formulations of HA.