Size effects of discoidal PLGA nanoconstructs in Pickering emulsion stabilization

Solid particle stabilized emulsions, using unique shape defined particles, are receiving increasing research interest due to ease of formulation and interesting physiochemical characteristics. There is, however, a need to systematically investigate the effect of anisotropic discoidal microparticles, realized with top-down fabrication approaches, in emulsion stabilization. Here, the effect of poly(d,l-lactide-co-glycolide) (PLGA) discoidal polymeric nanoconstruct (DPN) size on the formation and stability of oil-in-water emulsions is studied. Particles with a diameter of 1, 2, and 5 mu m are fabricated with a lithographic templating technique, and used to stabilize medium chain triglyceride (MCT) oil emulsions. Three phase contact angles decreased from 85 degrees +/- 7 degrees to 68 degrees +/- 12 degrees moving from 1 to 5 mu m DPN stabilized emulsions, showing a particle "hydrophilicity" increase with size. Microscopy imaging showed that the mean droplet diameter and dispersity increased with particle size, and that DPNs were present at the oil-water interface. DPN based emulsions were stable for about 24 h or less in the case of 1 and 2 mu m DPNs. Emulsion stability was shorter than 12 h in case of 5 mu m DPNs. Finally, calculations of DPN detachment free energies Delta G(dw) and excess surface coverages C-excess demonstrated that, despite the significantly high adhesion energy of the discoidal DPN, emulsion stability was mostly affected by gravitational forces for DPN sizes above 2 mu m. The use of PLGA and MCT oil in this study is relevant for future use of Pickering emulsions in pharmaceutical and drug delivery applications.