Octobots

The Octobot is a 3-D printed, fully autonomous microfluidic robot. The robot is made completely out of soft materials such as polydimethylsiloxane (PDMS) and Pluronic F127, SE 1700, and Sylgard 184, which are soft, silicone-based materials. In place of a rigid control center, the octobot is powered by a microfluidic logic circuit alongside a decomposition reaction that generates gas

Several different fabrication techniques are used to produce the Octobot:

Soft controller fabrication

The soft controllers are fabricated from PDMS using traditional soft lithography molding and bonding techniques. Upper and lower molds for the controller are first fabricated using SU-8 3050 negative photoresist. PDMS is then poured into the molds and cured. After punching inlet and outlet holes, the upper and lower PDMS layers are then exposed to oxygen plasma so that they can be bonded to an intermediate thin film.

Mould fabrication

Negative moulds (molds for US English speakers) for the octobot are designed in SolidWorks (a CAD software), then fabricated from acetal blocks using CNC milling. Holes are then drilled for 1mm dowel pins to use for controller placement in the mould.

Soft robot assembly

A multi-material, embedded 3D printing (EMB3D) technique is used to pattern the pneumatic actuator networks, on-board fuel reservoirs, and catalytic reaction chambers the octobot uses to power movement. Before EMB3D printing, Ecoflex 30 is poured into what will become the arms of the octobot, degassed, and cured. After excess material is removed, the soft controller is loaded onto the pins that have been placed in the mold. The fuel matrix material is then loaded, degassed, and cured. Following this, the body matrix material is loaded and degassed. Once this is done, the fugitive and catalytic inks are deposited using EMB3D printing. Finally, the entire assembly is cured two times to crosslink the inks and the matrix materials, and the octobot is release-cut using a CO2 laser.

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  Figure 3:The 3-D printing process of the Octobot a-b The arms of the mold are filled with PDMS. c-f The soft controller is pre-made and placed into the mold, which is filled with matrix material. g-h The chambers and actuators are printed using EMB3-D. i-k The Octobot is then removed from the mold..

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  Figure 4:EMB3D printing shown with fluorescent dye markers.

Actuation

Figure 5: Microfluidic system of the octobot

In microfluidic devices, pressure generation can be used to create a pneumatic battery to replace the use of electrical energy and the constraints that come with it as an actuator. One approach to creating a pressure-based actuator is to use chemical reactions to generate gas in a system. This gas can build up to increase pressure and power the microfluidic device.

The octobot is controlled fully through such a microfluidic system, without the need of any rigid control systems. A soft, microfluidic controller sits at the center of the Octobot. The controller regulates fluid flow and the catalytic decomposition of the monopropellant fuel inside the robot.

The controller system is divided into four sections: upstream for liquid fuel storage, oscillator for liquid fuel regulation, reaction chamber for the decomposition into pressurized gas, and downstream for gas distribution for actuation and venting. In the upstream section, the fuel reservoirs are filled using a syringe pump. Backflow into the fuel inlets is prevented using check valves. The networks downstream from the reaction are inflated from the gas produced from the fuel decomposition. The inflation causes parts of the Octobot to move.

The decomposition of aqueous hydrogen peroxide powers the robot:

[math]\displaystyle{ 2H_2O_2 (l) \to 2H_2O (l,g) + O_2 (g) }[/math]

This reaction results in a 240-fold volumetric expansion. The controller is designed to operate at fuel flow rates of 40 μl min^-1, with a fuel capacity of 1 mL, resulting in a theoretical run time of 12.5 minutes

Figure 5:Octobot top view