Direct laser writing (DLW) is a three-dimensional (3D) manufacturing technology that offers significant geometric versatility at submicron length scales. Although these characteristics hold promise for fields including organ modeling and microfluidic processing, difficulties associated with facilitating the macro-to-micro interfaces required for fluid delivery have limited the utility of DLW for such applications. To overcome this issue, here we report an
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Abstract in-situ DLW (is DLW) strategy for creating 3D nanostructured features directly inside of—and notably, fully sealed to—sol-gel-coated elastomeric microchannels. In particular, we investigate the role of microchannel geometry (e.g ., cross-sectional shape and size) in the sealing performance ofis DLW-printed structures. Experiments revealed that increasing the outward tapering of microchannel sidewalls improved fluidic sealing integrity for channel heights ranging from 10μ m to 100μ m, which suggests that conventional microchannel fabrication approaches are poorly suited foris DLW. As a demonstrative example, we employedis DLW to 3D print a microfluidic helical coil spring diode and observed improved flow rectification performance at higher pressures—an indication of effective structure-to-channel sealing. We envision that the ability to readily integrate 3D nanostructured fluidic motifs with the entire luminal surface of elastomeric channels will open new avenues for emerging applications in areas such as soft microrobotics and biofluidic microsystems. -
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.more » « less
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Deterministic lateral displacement (DLD) is a microfluidic micro/nanopost array-based technique for size-based particle separations. A key challenge in scaling DLD for handling smaller particles is that creating such “nanoDLD” arrays can be cost-intensive with substantial technical hurdles. To circumvent such issues, here we explore a new “hexagonally arranged triangles (HAT)” DLD geometry that is based on patterns associated with nanosphere lithography (NSL). Finite element simulations and preliminary experiments with 0.86 μm and 4.7 μm particles suggest effective separation capabilities of the HAT-DLD approach, marking an important first step toward new classes of nanoDLD arrays fabricated through bottom-up, self-assembly-based NSL.more » « less
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Nanosphere lithography (NSL) is a bottom‐up, self‐assembly approach that enables rapid, low‐cost patterning of nanoscale features. The practical application and scalability of NSL relies on the ability to achieve defect‐free nanosphere self‐assembly over large substrate areas. Self‐assembly methods for single‐layer nanosphere templates are typically evaluated using scanning electron microscopy (SEM) imaging, with literature reports focusing on maximum area of continuous nanosphere coverage. An alternative performance metric—namely, the percentage of nanospheres exhibiting perfect hexagonal close‐packing (%HCP)—is uniquely critical to NSL precision and repeatability. To enhance current methods of evaluating nanosphere self‐assembly, this work presents an SEM image analysis approach for rapidly quantifying packing defects in single‐layer nanospheres to determine %HCP. The method uses variations in SEM edge effect brightness to distinguish spheres with perfect packing from those in defect configurations or along edges. Comparison of image analysis program results with manual counting of nanospheres indicates that the program has a high degree of accuracy, with a mean error on the %HCP metric of +8.6% (absolute error). The results suggest that the present strategy offers a promising pathway to rapid evaluation of nanosphere self‐assembly for high‐precision NSL applications such as surface‐enhanced Raman scattering, photovoltaic cells, and nanogap electrodes.
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In situ direct laser writing ( is DLW) strategies that facilitate the printing of three-dimensional (3D) nanostructured components directly inside of, and fully sealed to, enclosed microchannels are uniquely suited for manufacturing geometrically complex microfluidic technologies. Recent efforts have demonstrated the benefits of using micromolding and bonding protocols for is DLW; however, the reliance on polydimethylsiloxane (PDMS) leads to limited fluidic sealing ( e.g. , operational pressures <50–75 kPa) and poor compatibility with standard organic solvent-based developers. To bypass these issues, here we explore the use of cyclic olefin polymer (COP) as an enabling microchannel material for is DLW by investigating three fundamental classes of microfluidic systems corresponding to increasing degrees of sophistication: (i) “2.5D” functionally static fluidic barriers (10–100 μm in height), which supported uncompromised structure-to-channel sealing under applied input pressures of up to 500 kPa; (ii) 3D static interwoven microvessel-inspired structures (inner diameters < 10 μm) that exhibited effective isolation of distinct fluorescently labelled microfluidic flow streams; and (iii) 3D dynamically actuated microfluidic transistors, which comprised bellowed sealing elements (wall thickness = 500 nm) that could be actively deformed via an applied gate pressure to fully obstruct source-to-drain fluid flow. In combination, these results suggest that COP-based is DLW offers a promising pathway to wide-ranging fluidic applications that demand significant architectural versatility at submicron scales with invariable sealing integrity, such as for biomimetic organ-on-a-chip systems and integrated microfluidic circuits.more » « less
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Direct laser writing (DLW) is a three-dimensional (3D) manufacturing technology that offers vast architectural control at submicron scales, yet remains limited in cases that demand microstructures comprising more than one material. Here we present an accessible microfluidic multi-material DLW (μFMM-DLW) strategy that enables 3D nanostructured components to be printed with average material registration accuracies of 100 ± 70 nm (Δ X ) and 190 ± 170 nm (Δ Y ) – a significant improvement versus conventional multi-material DLW methods. Results for printing 3D microstructures with up to five materials suggest that μFMM-DLW can be utilized in applications that demand geometrically complex, multi-material microsystems, such as for photonics, meta-materials, and 3D cell biology.more » « less