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Multi-stage fluidic reaction schemes for suspended particles (e.g., micro/nanospheres, cells, bacterial species, and extracellular vesicles) underly a diversity of chemical and biological applications. Conventional methods for executing such protocols can be exceedingly time, labor, and/or cost intensive. Microfluidic strategies can address these drawbacks; however, such technologies typically rely on clean room-based microfabrication that suffer from similar deficits for manufacturing the chips. To simultaneously overcome these challenges, here we explore the use of the submicron-scale additive manufacturing approach, “Two-Photon Direct Laser Writing (DLW)”, as a means for fabricating micro-fluidic “Deterministic Lateral Displacement (DLD)” arrays capable of passively guiding suspended particles across discrete, adjacent flow streams—the fundamental capability of continuous-flow multi-stage particle microreactors. Experimental results from microfluidic experimentation with 5 μm-in-diameter fluorescent particles revealed effective particle transport across flow streams, with 87.5% of fluorescent peaks detected in the designated, opposing outlet following the DLD array. These results suggest utility of the presented approach for micro- and nanoparticle-based microfluidic reactors targeting wide-ranging chemical and biological applications. 

Microinjection protocols are ubiquitous throughout biomedical fields, with hollow microneedle arrays (MNAs) offering distinctive benefits in both research and clinical settings. Unfortunately, manufacturing‐associated barriers remain a critical impediment to emerging applications that demand high‐density arrays of hollow, high‐aspect‐ratio microneedles. To address such challenges, here, a hybrid additive manufacturing approach that combines digital light processing (DLP) 3D printing with “ex situ direct laser writing (esDLW)” is presented to enable new classes of MNAs for fluidic microinjections. Experimental results foresDLW‐based 3D printing of arrays of high‐aspect‐ratio microneedles—with 30 µm inner diameters, 50 µm outer diameters, and 550 µm heights, and arrayed with 100 µm needle‐to‐needle spacing—directly onto DLP‐printed capillaries reveal uncompromised fluidic integrity at the MNA‐capillary interface during microfluidic cyclic burst‐pressure testing for input pressures in excess of 250 kPa (n = 100 cycles). Ex vivo experiments perform using excised mouse brains reveal that the MNAs not only physically withstand penetration into and retraction from brain tissue but also yield effective and distributed microinjection of surrogate fluids and nanoparticle suspensions directly into the brains. In combination, the results suggest that the presented strategy for fabricating high‐aspect‐ratio, high‐density, hollow MNAs could hold unique promise for biomedical microinjection applications.