5.9. In Vitro Release Kinetics of Dexamethasone from Nanogels

In vitro drug release experiments were conducted in a multi-compartment rotating cell, comprising a donor chamber separated by a cellulose membrane (Spectrapore, cut-off = 12,000 Da) from a receiving chamber. One milliliter of dexamethasone-loaded nanogels was placed in the donor chamber. The receiving compartment contained 1 mL of phosphate-buffered saline (PBS) at pH 7.4 with 0.1% sodium dodecyl sulfate (SDS) to assure drug solubility. The receiving phase was withdrawn at regular intervals and completely replaced with the same amount of fresh solution, to maintain sink conditions. The concentration of dexamethasone in the withdrawn samples was detected by HPLC.

For the dexamethasone quantitative determination an HPLC analysis was performed using a Perkin Elmer pump (Perkin Elmer PUMP 250B, Waltham, MA, USA) equipped with a spectrophotometer detector (Flexar UV/Vis LC spectrophotometer detector, Perkin Elmer, Waltham, MA, USA). A reversed phase Agilent TC C18 column (150 cm × 4.6 mm, pore size 5 μm; Agilent Technologies, Santa Clara, CA, USA) was used. A mixture of acetonitrile −25 mM phosphate buffer pH 3 (27:73, v/v) was used as the mobile phase at a flow rate of 1.0 mL/min and the effluent monitored by measuring absorbance at 246 nm. HPLC chromatograms of dexamethasone are reported in Supplementary Material (Figure S1).