*2.4. Liposomal Size Measurement*

Simulated gastric fluid without enzyme (SGF), pH 1.2, and phosphate buffer, pH 6.8, were produced as per United States Pharmacopeia and the National Formulary (USP-NF) [44]. The hydrodynamic size of the liposomes in SGF and phosphate buffer was measured by dynamic light scattering (DLS) using a Malvern Zetasizer Nano (Malvern Instruments, United Kingdom). For this measurement, aliquots of the powder formulations were added to the medium to result in a 5 mg/L concentration of nifedipine in the solution. The samples were stirred at 37 ◦C for 10 min to allow release of liposomes. The dispersions were then centrifuged at a 1000 relative centrifugal field (RCF) for 10 min at room temperature to separate FCC particles and undissolved drug from the liposomal dispersion. The DLS measurements were made on the supernatants for 10 measurement cycles.
