Design of poly-epsilon-caprolactone nanospheres coated with bioadhesive hyaluronic acid for ocular delivery.

This study was performed to design a new ocular drug delivery system based on poly-epsilon-caprolactone (PCL) biodegradable nanospheres (NS) coated with a bioadhesive polymer, hyaluronic acid (HA), in order to combine ophthalmic prolonged action with the ease of application. The aim of this work was to investigate three strategies to attach HA on NS surface: (1) coating the core by chain entanglement with HA; (2) coating NS by HA adsorption; (3) coating NS by electrostatic interactions between negatively charged HA and a cationic surfactant (stearylamine, SA, or benzalkonium chloride, BKC). A radioimmunoassay technique, usually used for HA quantification in serum, was transposed to determine the amount of HA on the NS. The results show that HA is strongly attached on NS positively charged by cationic surfactant. This system is stable and not influenced by dilution. These results show the possibility of using cationic surfactants to obtain a HA coating by electrostatic interactions. BKC, approved for ophthalmic administration, was retained because it was more firmly anchored within the PCL matrix and the amount of HA attached was high (41.6 microg HA/mg PCL). Moreover, the yield of fixation reached 50%. Therefore, by using a simple preparation method, it was possible to obtain stable HA and intact HA-coated NS.