EPI was dissolved in double-distilled water at a concentration of 1 mg/mL. The same mass of mMWCNTs was then mixed into EPI solution by sonication for 30 minutes. mMWCNTs-EPI were produced and then purified via external magnets. Briefly, the suspension of mMWCNTs-EPI and free EPI was placed on a magnetic rack (Solarbio Life Sciences, Beijing, China) for 10 minutes. mMWCNTs-EPI were then held tightly to the flask wall by magnetic forces. The free EPI was aspirated and measured on a Shimadzu SCL-10AVP series HPLC system coupled with ultraviolet detection set at 480 nm and C18 analytical column (150×4.6 mm, 5 µm particle size) (Beckman Coulter). The binary mobile phase was sodium dihydrogen phosphate (68%) and acetonitrile (32%) delivered at 1.0 mL/min. The loading efficiency of EPI was calculated:22 (link)
mMWCNTs-EPI were then dispersed in PBS (pH 6) on a shaking table. Every 2 hours, the released solution was collected with external magnets and PBS refreshed (mimicking physiological condition of urine). The EPI release ratio from mMWCNTs-EPI was determined according to the change in concentration. Areas under concentration–time curves for EPI were calculated.
mMWCNTs-EPI were then dispersed in PBS (pH 6) on a shaking table. Every 2 hours, the released solution was collected with external magnets and PBS refreshed (mimicking physiological condition of urine). The EPI release ratio from mMWCNTs-EPI was determined according to the change in concentration. Areas under concentration–time curves for EPI were calculated.