Co-encapsulating hydrophobic payloads and hydrophobic ion pairs in polymeric nanocarriers affects liquid crystalline mesophase packing and formation kinetics.

Liquid crystalline (LC) mesophases contain both polar and non-polar domains that enable co-loading of therapeutics with different physicochemical preparties into a single delivery vehicle. Understanding the relationship between formulation parameters, LC structure, and drug release is necessary to inform the rational design of these materials. This work interrogates the time scales over which LC phases assemble in polymeric nanocarrier cores as a function of composition. Nanocarrier formulations containing co-encapsulated hydrophilic (polymyxin B) and hydrophobic (vitamin E acetate, cholesterol, methyl oleate, or polycaprolactone) payloads were developed using Flash NanoPrecipitation with hydrophobic ion pairing using a confined impinging jets mixer. The mixer was integrated into a synchrotron small-angle X-ray scattering beamline to obtain spatiotemporally resolved kinetic data for the formation of internal liquid crystalline mesophases. The physical chemistries and concentrations of the hydrophobic counterion and the co-loaded hydrophobic molecule were found to significantly influence the assembly time of LC phases. For instance, in the presence of hydrophobic species such as vitamin E acetate or cholesterol, the time required for resolvable LC phase assembly was extended from seconds (for the case of only polymyxin B and a hydrophobic counterion) to several minutes. These time scales increased with increasing weight fraction of the hydrophobic molecule, suggesting physical interference during diffusion-mediated self-assembly of the LC phases. Our findings highlight how formulation composition plays a critical role in both the assembly timeline and the characteristics of the final product, which are essential to ensuring that the liquid crystal-mediated drug delivery system contains the intended critical quality attributes.