DSC for evaluating the encapsulation efficiency of lidocaine-loaded liposomes compared to the ultracentrifugation method

This study reports the investigation of liposomal formulations of lidocaine in the form of a free base (LID). LID was encapsulated into large multilamellar vesicles composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Samples of a mass ratio of LID with respect to DMPC ranging from 1 to 10% were investigated. The effects of the increasing LID concentration on the bilayer membrane were determined in terms of size, polydispersity index, zeta potential, encapsulation efficiency (EE %) and partition coefficient. Furthermore, differential scanning calorimetry (DSC) studies were also carried out to analyze the effect of LID on the liposome phase transition temperature and to calculate the EE % with an unfrequented method. The EE % results obtained by different experimental procedures were quite ambiguous, but the DSC measurements confirmed the ultracentrifugation direct method. The calculated partition coefficients of these two methods were in good agreement, too. Our research revealed a less known application field of DSC, as a fast and reliable tool to determine EE%.