C2sm25928a 3556..3559

Toroidal-spiral (TS) particles, with large surface-to-volume ratio and well-defined internal channels, were recently generated by a novel process of flash solidification of polymeric droplets during their sedimentation in a miscible solution. TS particles have an overall doughnut or toroidal shape and a thin spiral-shaped channel near the surfaces (Fig. 1a). Entrainment of the bulk solution within the spiralshaped channel offered a mechanism for encapsulating active agents under benign flow conditions (low shear with only an aqueous phase). Thus, TS particles may have significant potential applications for tissue engineering and drug delivery. Previously generated toroidal or doughnut-shaped particles offer advantages compared to the spherical beads because of their larger surface to volume ratio and closer proximity of all points in the interior to the surface.However, without the feature of internal channels, drug release from the doughnut-shaped particles occurs by the same processes as for spherical beads: hindered diffusion through the polymeric matrix and/or degradation of the matrix. Both of these mechanisms are challenging to tune for different drugs and especially for multiple drugs with separate release schedules. By contrast, release through the well-defined nanoand micro-channels of TS particles can be much more easily predicted and controlled. Themain advance of this paper beyond our previous, single-drop generation of TS particles is to harness the interaction of two or more sedimenting drops to produce the intricate liquid-phase structures that are subsequently solidified. Multiple drops potentially offer the flexibility to encapsulate multiple active agents without concern for their mutual compatibility in one solution. Furthermore, the amount of encapsulation can be precisely controlled with the known volume of the drop and concentration of the active compounds. Additionally, understanding drop interaction