(200h) Experiments and Multi-Scale Models to Understand Liposome Processing Using a Turbulent Jet in Co-Flow

The continuous processing administers considerable advantages over batch manufacturing to improve scalability, automated control and incorporation of process analytical technology (PAT). Conventional methods to form liposomes do not provide for precise control of the particle size and particle size distribution both of which can directly impact encapsulation efficiency, cellular uptake and biodistribution. The continuous manufacturing platform provides precise control over liposome formation including monitoring of particle size and size distribution. The present study focuses on coaxial turbulent jet flow design to control liposome properties and quantify them as a function of the flow conditions (velocity, temperature, Reynold’s number). Computational Fluid Dynamics (CFD) based models have been developed to verify the dynamics of the micro-environment at site of liposome formation. Molecular Dynamics (MD) simulation being further performed to analyze the lipid-lipid interactions and lipid-salt interactions at the liposomal formation site.

METHODS

Liposomes were formed using an ethanol injection method with a custom-built continuous processing system that is controlled using a program developed using National Instruments LabVIEW. Briefly, the continuous processing system consists of multiple tanks that contain lipid dissolved in ethanol and another set of tanks for the aqueous components (e.g.DI water or buffer salts) along with at-line particle size measurements using a Malvern Zetasizer Nano. Fluid flow profiles (i.e. Flow Velocity ratio (FVR) vs Reynolds number (Re) were related to the liposomal size distribution (i.e.Z-Average particle size and PDI). CFD geometry similar to the continuous liposome manufacturing unit was developed using ANSYS 19.0. Species Transport Equations were implemented to predict the fluidic microenvironment at the site of liposome formation and was validated with experimental data by image analysis and fluid flow dimensions (FVR and Re) of the co-axial jet formed from ethanol water mixture.

RESULTS

The continuous processing system at UConn can form monodispersed liposomes. Process parameters can be controlled to regulate the velocity, density, and viscosity at the co-axial jet. The CFD studies have successfully be used to predict the experimental flow properties observed at the co-axial jet. Based on the FVR and Re, the model provides insight on the alteration of the micro-environment at the liposome formation site. The liposome mean particle size can also be controlled and has dependence on the Reynolds number of the mixed fluid. In addition, MD modeling can be used to understand the differences in liposome formation based on factors such as type of lipid and aqueous phase additives.

CONCLUSION

The liposome size and PDI can be systematically controlled using a co-axial turbulent jet in co-flow. The non-linear increment of the ethanol-water mixture viscosity at the site of liposome formation (predicted from the CFD studies), plays a significant role to alter the fluid properties and can be directly related to the liposome dimensions and distribution. MD simulations are being performed to predict the mechanism of liposome formation due to variability of fluid flow properties and physical properties of the formulation.

ACKNOWLEDGEMENTS

This work was supported by the FDA (1U01FD005773-01).

DISCLAIMER

This article reflects the views of the authors and should not be construed to represent FDA’s views or policies.