Enhanced stability of liposomes against solidification stress during freeze-drying and spray-drying by coating with calcium alginate

Abstract

This study aimed to investigate the effect of exterior calcium alginate coating on physical stability of liposomes against solidification stress caused by freeze-drying and spray-drying. Uncoated liposomes (ULs) were prepared by a thin-film dispersion method, and exterior coating was achieved through crosslinking by dispersing calcium ions-loaded liposomes into bulk sodium alginate solution. Calcium alginate-coated liposomes (CALs) prepared under optimum conditions showed a particle size of 354.21 ± 5.4 nm and entrapment efficiency of 81.12 ± 2.5% using paclitaxel as a model drug. CALs showed better structural integrity in simulated gastric and intestinal fluids than ULs. Both CALs and ULs were solidified by freeze-drying and spray-drying, and their ability to withstand the processing stress was evaluated. CALs showed better performance in maintaining structural stability and keeping drug from leakage than ULs. The entrapment efficiency of CALs was 67.5 ± 2.5%, which was much higher than that of 36.4% of ULs after reconstitution from freeze-drying samples; similarly, the entrapment efficiency of spray-dried CALs was 58.6 ± 3.3%, but 47.8 ± 2.8% for ULs. Particle size and morphology observation by transmission electron microscopy also proved better preservation of CALs than ULs. Taken together, calcium alginate coating could significantly enhance physical stability of liposomes against the processing stress of solidification by freeze-drying and spray-drying.