🌪️Stirring

Description

The eVOLVER platform features tunable and independent stir rate control across culture vials. Stirring in eVOLVER is actuated by 12V brushless DC motors with attached neodymium magnets. The fastened magnets spin a stir bar (20 mm x 3 mm, PTFE coated) within an autoclaved glass vial (28 mm x 95 mm, borosilicate). The stirring module utilizes a single SA slot on the Motherboard; in the particular configuration described in this study, we utilized SA slot 1 (Supplementary Fig. 4). The two leads of the motor (12V & GND) are connected to a screw terminal on the component mount board, from which a ribbon cable connects the smart sleeve to the Motherboard. The PWM board (plugged into the SA slot) can control each motor independently to achieve different stir rates across eVOLVER vials. Briefly, the 16-channel PWM board amplifies a 3.3V signal from the Arduino microcontroller to a 12V signal to actuate Nature Biotechnology: doi:10.1038/nbt.4151 12 the motor. Arduino 1, which manages SA slot 1, was programmed to take in serial inputs from the Raspberry Pi and translate the serial values to different stir rates, determined by pulsing the motor ON and OFF at different ratios (Supplementary Fig. 4).

Individually controllable stirring utilizing DIY parts. (a) Photographs of eVOLVER stirring components. A 30 mm x 30 mm computer fan affixed with neodymium magnets actuates stirring in the eVOLVER smart sleeve (left). Two 1/8” acrylic sheets are used to space the magnets from the glass vial. The 3D printed part and CMB are fastened with screws (center, right). Electric leads are connected to the CMB with a screw terminal. (b) Schematic of system design for eVOLVER stirring module. The computer fan spins a stir bar (20 mm x 3 mm, PTFE coated) within a glass vial (28mm x 95 mm, borosilicate) (left). The Arduino interprets the serial command from the Raspberry Pi, amplifies the signal with the PWM board, and applies a 12V signal to the motor (right). The stir rate is determined by the ratio of pulsing the fan ON and OFF. (c) Stir rates can be roughly calibrated by using a smartphone camera recording at ≥240 frames per second. Calibration curve shown is for a single Smart Sleeve. Stir rate was calculated multiple times in a five second window, with error bars depiction standard deviation of these measurements. Rotations per minute varies with different types of Nature Biotechnology: doi:10.1038/nbt.4151 13 stir bars and volume of liquid in the vessel due to drag. Stir rates remain stable after 3 weeks of continuous use.

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