2.3.4. Measurement of Drug Entrapment Efficiency (%EE) and Drug Release Study

The supernatant collected after the centrifugation processes (mentioned in Section 2.2), was measured using ultraviolet spectrophotometry to determine the amount of excess EPI. The concentration of EPI entrapped in the NPs was measured from the precipitated NPs by dissolving a known amount of the NPs in DMSO to release the drug, then determining the absorbance. The %EE was calculated according to the following equation:

For the release study, 4 mg of the EPI-NPs resuspended in 1.5 mL pbs inserted into a dialysis tube (W 25 mm) made from cellulose membrane, Mwt cut off = 14,000 (Sigma–Aldrich, Co., MO, USA). The sample-containing tube was immersed in 14 mL of PBS in a small dark glass bottle containing magnet. The bottle was then closed and placed on a magnetic stirrer at a speed of 4 rpm and temperature of 37 °C. To determine the amount of the released EPI, UV absorbance was measured; each time, 1 mL of the sample was taken for measurement and replaced by PBS to maintain sink conditions. The data were obtained through SoftMax Pro Software-Molecular Devices, CA, USA.