The particles were dissolved in 1,4-dioxane to determine the encapsulation efficiency (EE%). The absorbance spectra of the prepared solutions were measured by a Jasco V-630 double-beam spectrophotometer. The spectra were registered in the range of 400-200 nm using a 1 cm quartz cuvette at room temperature. The characteristic absorbance band of the α-TP appeared at 294 nm. The concentration of the encapsulated drug was calculated based on the calibration curve. The data of the EE% was calculated from the mass of the PBA-DLA NPs following the equation ( ):