Stabilization and X-ray Attenuation of PEGylated Cholesterol/Polycaprolactone-Based Perfluorooctyl Bromide Nanocapsules for CT Imaging

Contrast-enhanced X-ray computed tomography plays an important role in cancer imaging and disease progression monitoring. Imaging using radiopaque nanoparticle platforms can provide insights on the likelihood of nanoparticle accumulation and can enable image-guided therapies. Perfluorooctyl bromide (PFOB)-loaded nanocapsules designed for this purpose were stabilized using an in-house synthesized PEGylated polycaprolactone-based copolymer (PEG-b-PCL(Ch)) and compared with commercial polycaprolactone employing a Quality-by-Design approach. PFOB is a dense liquid, weakly polarizable, and immiscible in organic and aqueous solvents; thus, carefully designed formulations for optimal colloidal stabilization to overcome settling-associated instability are required. PFOB-loaded nanocapsules exhibited high PFOB loading due to the intrinsic properties of PEG-b-PCL(Ch). Settling and caking are major sources of instability for PFOB formulations. However, the PEG-b-PCL(Ch) copolymer conferred the nanocapsules enough steric impediment and polymer shell elasticity to settle without significant caking, increasing the overall colloidal stability of the formulation. Furthermore, a clear relationship between nanocapsule physical properties and X-ray attenuation was established. Nanocapsules were able to enhance the X-ray contrast in vitro as a function of PFOB loading. This nanocapsule-based platform is promising for future translational studies and image-guided tumor therapy due to its enhanced contrastability and optimal colloidal stability.