Bridging membrane fluidity studies with a predictive model of drug encapsulation to address industrial challenges of liposomal injectables manufacturing.

Industrial manufacturing of liposomal drugs, often involves high-temperature processes, resulting in increased energy consumption, prolonged process times, and elevated costs, while posing risks of phospholipid and drug degradation. The current study addresses these challenges by exploring remote loading of doxorubicin into liposomes, at temperatures below the phase transition temperature (PTT) of the primary phospholipid (DSPC, 55 °C). Drug loading efficiencies exceeding 90% at 45 °C were achieved, while efficiencies dropped significantly (6-fold and 23-fold) at 37 °C and 25 °C, respectively. This prompted the hypothesis that efficient drug loading might be attained below the PTT, when a minimal threshold for liposomal membrane fluidity is overcome. Using design of experiments (DoE), key factors influencing fluidity were identified: temperature, cholesterol content and surface tension (dependent on the isotonic agent). A full factorial DoE confirmed that membrane fluidity increased with lower surface tension, and high cholesterol content. A predictive model was also generated establishing a correlation between drug loading efficiency, membrane fluidity, and drug partitioning coefficient (logP). This model revealed that doxorubicin (logP = 1.5) requires a fluidity threshold of 4.41 for efficient loading (≥ 90%), whereas daunorubicin (logP = 2.32) needs a lower threshold of 3.85, suggesting that drugs with higher logP values demand lower fluidity thresholds for effective loading. The model's applicability was validated across various lipid formulations, enabling effective drug loading at temperatures as low as 25 °C, potentially reducing degradation risks and energy costs. Overall, these findings highlight the relevance of liposomal membrane fluidity studies as a potential tool for enabling more effective industrial processes.