Injectable in situ forming microgels of hyaluronic acid-g-polylactic acid for methylprednisolone release

A hydrophobic derivative of hyaluronic acid (HA), obtained by grafting polylactic acid (PLA) to the polysaccharide, has been exploited to produce injectable in situ forming microgels. First of all, self assembling properties of HA-g-PLA copolymer have been evaluated by determining the critical aggregation concentration (CAC) value, then this copolymer has been dissolved in a mixture water/NMP 5:2 v/v with a concentration greater than CAC. When solutions at 1% or 2% w/v were injected into Dulbecco phosphate buffer solution (DPBS) pH 7.4, microgels promptly are formed. Their stability in DPBS pH 7.4 in the absence or in the presence of hyaluronidase and cell compatibility have been evaluated, as well as the ability to entrap a hydrophobic drug and to prolong its release. At this aim it has been chosen methylprednisolone, a drug employed for the treatment of osteoarthritis. Obtained results suggest the potential use of these in situ forming microgels for the intraarticular administration of antiinflammatory drugs.