Rational design of microfluidic liposome formulations: Integrating flow control with multi-analytical...

Liposomes are vesicular structures consisting of one or more lipid bilayers that enclose an aqueous inner core, allowing the encapsulation of both hydrophilic compounds in the inner compartment and lipophilic and amphiphilic molecules within the lipid bilayer. In recent years, microfluidic-based manufacturing techniques have emerged as a highly attractive approach for liposome production, as they allow precise control over fluid dynamics at the micrometer scale, thereby enabling reproducible and scalable fabrication of nanocarriers with narrow size distributions. Since even minor variations in liposomal formulations can markedly influence their critical features, a well-defined manufacturing process and stringent process control are essential to ensure that the final product consistently meets the required quality standards. The selection of the organic solvent plays a critical role in governing lipid solubilization, solvent-antisolvent mixing, and lipid self-assembly kinetics, ultimately affecting vesicle nucleation, growth, and bilayer organization. Likewise, microfluidic operating parameters critically influence the physicochemical characteristics of the resulting liposomes, including particle size, polydispersity index, surface charge, lamellarity, and colloidal stability. Within a rational formulation-development approach, a comprehensive understanding of the relationships between critical material attributes (e.g., lipid composition and solvent properties) and critical process parameters (e.g., Reynolds number; flow rate ratio, FRR; total flow rate, TFR; and mixing efficiency) is essential for rational process optimization. Specifically, this work highlights how lipid composition, organic solvent selection, microfluidic operating conditions, and purification methods collectively influence the structural and functional behavior of liposomes, thereby supporting the development of robust and well-controlled microfluidic manufacturing processes.