Abstract
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 in-situ DLW (isDLW) 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 of isDLW-printed structures. Experiments revealed that increasing the outward tapering of microchannel sidewalls improved fluidic sealing integrity for channel heights ranging from 10 μm to 100 μm, which suggests that conventional microchannel fabrication approaches are poorly suited for isDLW. As a demonstrative example, we employed isDLW 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.
Highlights
Recent advances in the capabilities of additive manufacturing or “three-dimensional (3D) printing” technologies have dramatically expanded the degree of architectural freedom with which researchers can design and manufacture systems at micron-to-submicron scales[1,2]
Other groups have developed PDMS-photoresist-glass sandwich-chip approaches in which 3D structures are first printed in unenclosed photoresist-on-glass channels, and a PDMS slab is sealed atop the photoresist to form enclosed microchannels[27,28,29]
For the oil-immersion mode-based In-situ DLW (isDLW) step, we utilized a “ceiling-to-floor” direct laser writing (DLW) strategy in which structures were printed starting at the tallest point of the sol-gel-coated PDMS microchannel (Fig. 1g–left)
Summary
Recent advances in the capabilities of additive manufacturing or “three-dimensional (3D) printing” technologies have dramatically expanded the degree of architectural freedom with which researchers can design and manufacture systems at micron-to-submicron scales[1,2]. Challenges associated with nozzle-material interactions and controls have typically restricted the utility of extrusion-based methods to structures with feature sizes of approximately 10 μm or larger[8]. For micron- and submicron-scale fluidic applications, this resolution results in an inherent trade-off that limits or prevents the incorporation of the macro-to-micro interfaces that are critical for delivering fluid volumes (e.g., chemicals, reagents, wash buffers, particle suspensions, etc.) into enclosed DLW-manufactured systems[12,13]. In-situ DLW (isDLW) encompasses a variety of approaches that involve first manufacturing a microfluidic channel using alternative fabrication processes (e.g., micromolding or laser ablation), inputting a photocurable material into the microfluidic channel, and lastly, using DLW to print structures directly inside of the channel[21]. Fully glass microchips can be used for isDLW30–33; the methods for manufacturing glass microdevices (e.g., wet etching and laser ablation) can be exceedingly time, labor, and cost-intensive, while necessitating access to advanced fabrication facilities[34]
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