*2.5. Quantification of Nifedipine eEncapsulation in Liposomes*

To quantify the nifedipine encapsulation efficiency of the liposomes, we dispersed the samples in the SGF and phosphate buffer and prepared them as described previously in Section 2.4. The total dissolved nifedipine in the supernatants was measured with HPLC. To separate the free drug from the liposomal-bound drug, we centrifuged the samples in 30 kDa cutoff Amicon Ultra Centrifugal Filter Units (Merck Millipore, Merck KGaA, Darmstadt, Germany) for 10 min at 4000 RCF at room temperature. The amount of the free drug and the encapsulated drug were measured by HPLC from the filtrate and the retentate, respectively, and the encapsulation efficiency of the liposomes in every formulation was calculated.
