MicroPET

From Development and flight-testing of a modular autonomous cultivation system for biological plastics upcycling aboard the International Space Station

Xin Liu1,, Pat Pataranutaporn1,, Benjamin Fram2, Allison Z. Werner3,*, Sunanda Sharma5, Nicholas P. Gauthier4, Erika Erickson3, Patrick Chwalek1, Kelsey J. Ramirez3, Morgan A. Ingraham3, Natasha P. Murphy3, Krista A Ryon6, Braden T Tierney6, Gregg T. Beckham3, Christopher E. Mason7, Ariel Ekblaw1

[1] MIT Media Lab , Massachusetts Institute of Technology, Cambridge, MA [2] Harvard Medical School, Department of Systems Biology, Boston, MA [3] Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, CO [4] Department of Data Sciences, Dana-Farber Cancer Institute, Boston, MA [5] Space Exploration Initiative, Massachusetts Institute of Technology, Cambridge, MA [6] Weill Cornell Medical College, Cornell University, New York, NY [7] Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY

Correspondence: xxxxxxin@mit.edu, patpat@mit.edu, allison.werner@nrel.gov

Abstract

Cultivation of microorganisms in space has enormous potential to enable in-situ resource utilization (ISRU), but spaceflight infrastructure for growing microorganisms without resource-intensive astronaut support is lacking. Here, we develop and validate an autonomous payload, termed the Modular Open Biological Platform (MOBP), for enzymatic reactions and microbial cultivation with fully programmable serial passaging and sample preservation. The MOBP is a compact, modular bioreactor system that allows for automatic media transfers and precise data monitoring from integrated sensors. The payload enables serial sample collection and storage for terrestrial analysis, including RNA and DNA sequencing and proteomics. We designed two experiments for validation of the MOBP aboard the International Space Station (ISS) with the application of upcycling the ubiquitous plastic poly(ethylene terephthalate) (PET). In the enzymatic experiment, PET is depolymerized by the enzyme PETase to terephthalate (TPA), which can then be polymerized back into virgin quality PET. In the cell-based experiment, TPA is converted to β-ketoadipate (βKA) by an engineered Pseudomonas putida KT2440 bacterium. βKA can be polymerized into a nylon-6,6 analog with improved properties for use in the production of a variety of materials, including high-performance textiles and molded parts including air intake manifolds, electro-insulation elements and hinges, thus demonstrating plastics upcycling. We posit our modular open system will enable increased realization of synthetic biology experiments and applications in spaceflight that will ultimately enable ISRU and plastics upcycling during space travel.

Keywords

In-situ resource utilization, plastics upcycling, biomanufacturing

Repository

• Teensy Launch Code: Teensyduino code to operate MicroPET payload
• Simulation: simulating liquid operation for MicroPET payload

Teensy Launch Code

Base Board Connection

The base board connections are as follows:

• E1VA + E1PA - J10
• E1VB + E1PB - J09
• E2VA + E2PA - J12
• E2VB + E2PB - J11
• The valve board connector J1-6 are the same on the base board

Dependencies

The code depends on the following libraries:

• TimeLib.h
• TimeAlarms.h
• Wire.h
• SPI.h
• Adafruit_Sensor.h
• Adafruit_BME280.h
• Adafruit_AS726x.h
• Adafruit_MCP23X17.h
• RTClib.h
• SD.h

Experiment Prototypes

The code defines the following experiment prototypes:

• day_1()
• day_2()
• day_3()
• day_4()
• ...
• day_26()

The experiment functions are stored in an array called experimentArray, which is of size TOTAL_EXPERIMENTS.

Global Variables

• rtc: RTC_PCF8523 object to interface with the RTC module.
• experimentIndex: uint16_t variable to keep track of the current experiment index.
• delayTime: unsigned long variable to store the delay time between experiments.
• sensorValues: uint16_t array to store the sensor values read from the AS726x sensor.
• myFile: File object to store data in a file.
• expLogFile: File object to store experimental log data in a file.
• systemStateStructVar: systemStateStruct object to store the system state.

Main Functions

• setup(): Initializes the program by initializing variables, setting up the RTC, SD card, and IO ports, and setting the first alarm.
• loop(): Loops indefinitely, checking for a start command via serial communication and executing the corresponding experiment.
• rtcInit(): Initializes the RTC module by checking for RTC availability, adjusting the time if necessary, and calibrating the RTC.
• grabStateFromSD(): Reads the system state from the SD card if it exists, and returns true if successful.
• saveStateToSD(): Saves the system state to the SD card.
• checkForStartSerialCommand(): Checks for a start command via serial communication and returns true if it is received.
• recoverSystemStart(): Resumes system operation after an unscheduled power loss by checking for hard faults and setting up timers.
• setNextAlarm(): Sets the next alarm based on the current experiment index.
• moveLiquid(): Moves liquid from one location to another based on the experiment, origin, target, and liquid volume.
• switchCollection(): Switches the collection bag for a particular experiment.
• Taking_Sensor_Data(): Takes sensor data by reading temperature and spectral values from the BME280 and AS726x sensors.
• saveExperimentalLog(): Saves an experimental log message to the experiment log file.
• init_card(): Initializes the SD card by checking for availability, opening the save file, and writing the header if necessary.
• initExpLogFile(): Initializes the experiment log file by opening it and writing the header.
• motorSensorBrdCtrl(): Controls the motors on the sensor board based on the motor number and direction.

Helper Functions

• digitalClockDisplay(): Displays the current time on the serial monitor.
• printDigits(): Prints digits with leading zeroes if necessary.
• tmConvert_t(): Converts a specified date and time to a time_t format.