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1. 3d Nanoprinted External Microfluidic Structures Via Ex Situ Direct Laser Writing

   https://doi.org/10.1109/MEMS51782.2021.9375347  

   Acevedo, Ruben; Wen, Ziteng; Rosenthal, Ian B.; Freeman, Emmett Z.; Restaino, Michael; Gonzalez, Noemi; Sochol, Ryan D. (January 2021, 2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS))

   null (Ed.)

   Additive manufacturing (or "three-dimensional (3D) printing") technologies offer unique means to expand the architectural versatility with which microfluidic systems can be designed and constructed. In particular, "direct laser writing (DLW)" supports submicron-scale 3D printing via two-photon (or multi-photon) polymerization; however, such high resolutions are poorly suited for fabricating the macro-to-micro interfaces (i.e., fluidic access ports) critical to microfluidic applications. To bypass this issue, here we present a novel strategy for using DLW to 3D print architecturally complex microfluidic structures directly onto-and notably, fully integrated with-macroscale fused silica tubes. Fabrication and experimental results for this "ex situ DLW (esDLW)" approach revealed effective structure-to-tube sealing, with fluidic integrity maintained during fluid transport from macroscale tubing, into and through demonstrative 3D printed microfluidic structures, and then out of designed outlets. These results suggest that the presented DLW-based printing approach for externally coupling microfluidic structures to macroscale fluidic systems holds promise for emerging applications spanning chemical, biomedical, and soft robotics fields. 

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2. Programmable Switching of Fluids via Pre-Twisting

   https://doi.org/10.1109/RoboSoft60065.2024.10522006  

   Wu, Yijia; Nemitz, Markus P (April 2024, IEEE)

   Manipulating airflow is important for controlling pneumatically actuated soft robots, however, current switching techniques suffer from leakage under high pressure (>200 kPa) or require a complex fabrication process. We propose a new method for reliably and repeatably cutting off airflow by harnessing pre-loaded torsional forces applied to our tubing. The switching distance and hysteresis of our pre-twisted tubing are programmable by varying the tube length and the twisting angle. Our experiments demonstrate the use of pretwisted tubing to implement CMOS equivalent fluidic switches configured as NOT-, AND-, and OR-gates, and a distance sensor for feedback control for the oscillation of a PneuNet. Our approach of pre-loading tubes with a torsional force allows for simplicity, integrated functionality, and the capability of manipulating high-pressure, fluidic signals mainly at the cost of tubing. 

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3. Tube-Balloon Logic for the Exploration of Fluidic Control Elements

   https://doi.org/10.1109/LRA.2022.3156174  

   Tracz, Jovanna A.; Wille, Lukas; Pathiraja, Dylan; Kendre, Savita V.; Pfisterer, Ron; Turett, Ethan; Abrahamsson, Christoffer K.; Root, Samuel E.; Lee, Won-Kyu; Preston, Daniel J.; et al (April 2022, IEEE Robotics and Automation Letters)

   The control of pneumatically driven soft robots typically requires electronics. Microcontrollers are connected to power electronics that switch valves and pumps on and off. As a recent alternative, fluidic control methods have been introduced, in which soft digital logic gates permit multiple actuation states to be achieved in soft systems. Such systems have demonstrated autonomous behaviors without the use of electronics. However, fluidic controllers have required complex fabrication processes. To democratize the exploration of fluidic controllers, we developed tube-balloon logic circuitry, which consists of logic gates made from straws and balloons. Each tube-balloon logic device takes a novice five minutes to fabricate and costs $0.45. Tube-balloon logic devices can also operate at pressures of up to 200 kPa and oscillate at frequencies of up to 15 Hz. We configure the tube-balloon logic device as NOT-, NAND-, and NOR-gates and assemble them into a three-ring oscillator to demonstrate a vibrating sieve that separates sugar from rice. Because tube-balloon logic devices are low-cost, easy to fabricate, and their operating principle is simple, they are well suited for exploring fundamental concepts of fluidic control schemes while encouraging design inquiry for pneumatically driven soft robots. 

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4. Geometrical Modifications for Reliable 3D Printing of Microvalves in Multi-Plane Microfluidic Devices

   https://doi.org/10.31224/4274  

   Nguyen, Huu_Anh Minh; Goz, Abigail; Voronov, Roman (January 2025, engrxiv)

   Three-dimensional (3D) printing has emerged as a transformative technology for fabricating complex microfluidic devices, enabling features that were previously unattainable with traditional layer-by-layer soft lithography. One key challenge in advancing 3D-printed microfluidics is the integration of functional microvalves across multiple spatial orientations. This study explores the design, simulation, and experimental realization of novel microvalve configurations to overcome the limitations of conventional, single-plane valves. We hypothesize that non-traditional valve orientations, such as those with vertically printed membranes or perpendicular control channels, present unique fabrication and operational challenges, including membrane delamination and stress-induced failure. To address these issues, we developed optimized geometries and fabrication techniques, supported by computational fluid dynamics (CFD) simulations to predict and mitigate stress concentrations. Our results demonstrate successful implementation of previously unreported valve configurations, validated through pressure testing and flow control experiments. These advancements expand the versatility of 3D-printed microfluidic systems, paving the way for more robust and adaptable devices in biomedical, chemical, and environmental applications. 

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5. The Soft Compiler: A Web-Based Tool for the Design of Modular Pneumatic Circuits for Soft Robots

   https://doi.org/10.1109/LRA.2022.3159858  

   Kendre, Savita V.; Whiteside, Lauryn; Fan, Tian Y.; Tracz, Jovanna A.; Teran, Gus T.; Underwood, Thomas C.; Sayed, Mohammed E.; Jiang, Haihui J.; Stokes, Adam A.; Preston, Daniel J.; et al (July 2022, IEEE Robotics and Automation Letters)

   Developing soft circuits from individual soft logic gates poses a unique challenge: with increasing numbers of logic gates, the design and implementation of circuits lead to inefficiencies due to mathematically unoptimized circuits and wiring mistakes during assembly. It is therefore practically important to introduce design tools that support the development of soft circuits. We developed a web-based graphical user interface, the Soft Compiler , that accepts a user-defined robot behavior as a truth table to generate a mathematically optimized circuit diagram that guides the assembly of a soft fluidic circuit. We describe the design and experimental verification of three soft circuits of increasing complexity, using the Soft Compiler as a design tool and a novel pneumatic glove as an input interface. In one example, we reduce the size of a soft circuit from the original 11 logic gates to 4 logic gates while maintaining circuit functionality. The Soft Compiler is a web-based design tool for fluidic, soft circuits and published under an open-source MIT License. 

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