Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

Delivery of therapeutic agents to posterior segment of the eyes is challenging due to the anatomy and physiology of ocular barriers and thus long-acting implantable formulations are much desired. In this study, a thermogelling system composed of two poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers was developed as an injectable matrix for intravitreal drug delivery. The thermogel was prepared by mixing a sol and a precipitate of PLGA-PEG-PLGA triblock copolymers with different block ratios, among which a hydrophobic glucocorticoid, dexamethasone (DEX), was incorporated. The DEX-loaded thermogel was a low-viscous liquid at low temperature and formed a non-flowing gel at body temperature. The in vitro release rate of DEX from the thermogel could be conveniently modulated by varying the mixing ratio of the two copolymers. The long-lasting intraocular residence of the thermogel was demonstrated by intravitreal injection of a fluorescence-labeled thermogel to rabbits. Compared with a DEX suspension, the intravitreal retention time of DEX increased from a dozen hours to over 1week when being loaded in the thermogel. Additionally, intravitreal administration of the thermogel did not impair the morphology of retina and cornea. This study reveals that the injectable PLGA-PEG-PLGA thermogel is a biocompatible carrier for sustained delivery of bioactive agents into the eyes, and provides an alternative approach for treatment of posterior segment diseases.