Fig. 1. Conceptual overview of magnetically controlled micropropellers for convection-enhanced NP transport.

(A) Conceptual schematic depicting a single microrobot, the ABF, enhancing mass transport of NPs at the vessel-tissue interface (left), and swarms of MTB generating convective flow to improve mass transport (right). ECM, extracellular matrix. (B) Schematic of magnetofluidic platform for NP mass transport studies using magnetically induced convection. The microfluidic chip is placed between the objective lens of an inverted optical microscope and the electromagnets (left). A schematic depicts the chip, consisting of an upper channel filled with NPs (red) and a lower water channel (blue) that both border a collagen matrix (gray) along restricting trapezoidal posts made of PDMS. NPs can passively diffuse into the collagen matrix along their concentration gradient toward the water channel.