Microemulsions as Lipid Nanosystems Loaded into Thermoresponsive In Situ Microgels for Local Ocular Delivery of Prednisolone.

This study aimed to develop and evaluate thermoresponsive in situ microgels for the local ocular delivery of prednisolone (PRD) (PRD microgels) to improve drug bioavailability and prolong ocular drug residence time. Lipid nanosystems of PRD microemulsions (PRD-MEs) were prepared and evaluated at a drug concentration of 0.25-0.75%. PRD microgels were prepared by incorporating PRD-MEs into 10 and 12% Pluronic® F127 (F127) or combinations of 12% F127 and 1-10% Kolliphor®P188 (F68). PRD microgels were characterized for physicochemical, rheological, and mucoadhesive properties, eye irritation, and stability. Results showed that PRD-MEs were clear, miscible, thermodynamically stable, and spherical with droplet size (16.4 ± 2.2 nm), polydispersity index (0.24 ± 0.01), and zeta potential (-21.03 ± 1.24 mV). The PRD microgels were clear with pH (5.37-5.81), surface tension (30.96-38.90 mN/m), size, and zeta potential of mixed polymeric micelles (20.1-23.9 nm and -1.34 to -10.25 mV, respectively), phase transition temperature (25.3-36 °C), and gelation time (1.44-2.47 min). The FTIR spectra revealed chemical compatibility between PRD and microgel components. PRD microgels showed pseudoplastic flow, viscoelastic and mucoadhesive properties, absence of eye irritation, and drug content (99.3 to 106.3%) with a sustained drug release for 16-24 h. Microgels were physicochemically and rheologically stable for three to six months. Therefore, PRD microgels possess potential vehicles for local ocular delivery.

Concentration of a microemulsion influences the mechanical properties of ibuprofen in situ microgels.

The aim of this study was to develop an ibuprofen microemulsion (IBU-ME) incorporated into in situ gels (microgels) for local delivery into periodontal pockets. The IBU-ME was prepared at a concentration of 1% w/v IBU. Various concentrations of the thermosensitive Pluronic® F127 (P127) solution and a series of combinations of the P127 solution and IBU-ME at a 1:1 ratio were initially developed and tested to determine their sol-gel transition temperatures (Tsol→gel). Based on these studies, a constant concentration of P127 (11.1% w/v) and variable concentrations of IBU-ME were used to prepare the microgels. The mechanical properties (Tsol→gel, gelling time (Tgel), viscosity, and viscoelastic properties) of the microgels were evaluated. The release of IBU from the microgels was determined in vitro. Rheological stability studies were performed to investigate the mechanical properties of the microgels after one month. The transition behavior studies demonstrated that the microgels are thermosensitive systems with pseudoplastic flow and their viscoelastic properties indicated that the elastic property was greater than the viscous property (G' > G″). The results showed that the mechanical properties of the microgels depend on the concentration of IBU-ME. In addition, rheological stability studies demonstrated that Tgel and Tsol→gel are increased after one month, whereas the viscosity and viscoelastic properties are decreased after one month. Owing to the rigid structure of the microgels, the release of IBU from the microgels followed a controlled-release pattern.