Summary
Our hardware project consists of three parts: the microgravity-optimized bioreactor AstroYeast Microfarm, 3D clinostat, and high aspect ratio vessel (HARV). To support the development of our microgravity-resistant yeast strain or AstroYeast, we built two microgravity simulators based on different principles. We will use them as screening tools to introduce microgravity stress and conduct directed evolution experiments.
We also conceptualized a microgravity-optimized bioreactor, the AstroYeast Microfarm, to conduct bioproduction operations in space and on other planets using our AstroYeast. The idea is to conceptualize a device that could support the expansion of our engineered yeast strains (AstroYeast) in space. It should be noted that the proposed bioreactor was designed for the iGEM 2021 competition as well as for the Canadian Space Agency’s Deep Space Food Challenge.
Our hardware project will discuss the difficulties of conducting medium-scale to large-scale bioproduction in space. We hope we could support the use of synthetic biology tools in space through an all-in-one solution. We envision our studies will support future deep space missions, such as colonization on other planets as well as provide an alternative sustainable food source for communities on Earth.
Due to constraints of our content length, it is impossible to discuss every detail. Instead, we will focus on the engineering and modeling of the 3D clinostat instead. For more information about our 3D clinostat, please check out our engineering section and our modeling section.
Bioreactor Design
Introduction
The first part of our project is a space-optimized bioreactor concept: the AstroYeast Microfarm. It is a nutrient and flavour factory, a bioreactor tailored specifically to our AstroYeast growth.
The Microfarm is designed to be sustainable, plug-and-play, and easy-to-use for the operator. The bioreactor will be divided into six components: The control area, the pistons, nutrition area, the mixer, the incubator, and the sensor suite. The component materials were chosen based on these criteria: outgassing, thermal properties, toughness, and weight.
This system is a compact and easy-to-use system which cultures a renewable source of food. We can input AstroYeast as freeze-dried pallets or frozen cell stock. The Microfarm operates at the optimal conditions for yeast growth to maximize output. The crew would seed the Microfarm with AstroYeast and grow the yeast over the period of a week in the bioreactor. The products are then harvested and transformed into a yeast spread for not only a safe, but also a nutritious and delicious food source.
The AstroYeast Microfarm concept is therefore a novel, sustainable, and innovative way of meeting the nutritional needs of a space-faring crew on their long voyage.
Control Area
The control area is used to monitor and control the operation of the bioreactor when necessary. A control panel with a display is used to interact with the onboard computer. The electronics unit comprising the onboard computer as well as the sensor and control system interfaces is located behind this panel. The unit is kept cool using passive air cooling with the help of fans and heat sinks.. We will be using a computer of the Raspberry Pi family which allows for remote control and sensor integration.
In addition, it simplifies debugging and is built upon an open-source ecosystem.
Figure 1: Control Area
Pistons
The bioreactor tank is split into two syringe-like containers. Each one has a piston acting as the agitators. By pushing the biological media from one container to the other, a mixing action occurs. This is necessary in a microgravity environment since we cannot rely on gravity to assist in the mixing process as many conventional systems do. The pistons are water-tight and made from resistant materials to increase the operational lifespan since they will be subject to a great amount of mechanical wear. The containers are made of a clear plastic to allow for visual monitoring of the media. They are connected using tubing, which also serve as the feeding/monitoring port.
Figure 2: Pistons
Mixer
The external mixer is used to mix the final product collected in the filtered container to ensure all the product is well incorporated.
Figure 3: Mixer
Incubator
The incubator is a sealed chamber making up most of the bioreactor volume. It is located next to the control area and contains the two bioreactor chambers and the piston motors. The incubator will maintain a constant temperature with the help of a heating element and fans. A clear cover allows the monitoring of the system without needing to open it.
Figure 4: Incubator
Nutrition
Between the two bioreactor chambers is the feeding and oxygenation area. The feeding will happen in-line when necessary. The oxygenation process uses a hollow fibre membrane. An air compressor will ensure adequate gas pressure, and the pumping action will provide the necessary flow for the media across the membrane. This area also contains the loading and unloading valves for cleaning between batches.
Figure 5: Nutrition
Sensors/Actuators
The control system consists of multiple temperature probes, fans, and heaters for temperature regulation, motors for moving the pistons and opening/closing valves automatically, and a light sensor for determining biological growth using optical density.
Figure 6: Bioreactor
Microgravity Simulators
3D Clinostat
Why do we need it?
The purpose of the 3D clinostat is to simulate a microgravity environment in laboratory settings on Earth. We could screen and grow microgravity resistant yeast strains. By rotating the samples located about the center of rotation of the bioreactor in two axes at an optimised velocity, we can potentially achieve what is known as time-averaged simulated microgravity. The microgravity resistant strains, namely Astroyeast, can now become a suitable nutritious food source for astronauts on a three year space mission.
Figure 7: Clinostat
What does it do
A 3D Clinostat or also called Random Positioning Machine (RPM) is a device which negates the effects of gravity and simulates microgravity by means of rotations. In order to achieve a microgravity environment with the RPM which “provides a continuous random change in orientation� and does not allow the object that is being tested upon to respond quicker than the effects on gravity [1], the 3D clinostat operates by having two frames rotate about their respective axes at specific velocities such that the bioreactor, located at the center, is in constant rotation and subjected to minimal gravitational force. [1] The bioreactor containing the yeast samples must be maintained at a temperature of 30-35C for optimal growth conditions using a heating element and temperature sensor to regulate it.
Simulations
In order to determine the velocities at which the inner and outer frame rotate to achieve microgravity, the kinematic equations of the device had to be determined and subsequently used to simulate the distribution of the gravity vector across a spherical plane. We based the kinematic model of the 3D clinostat on the model presented in “An Experimental and Theoretical Approach to Optimize a Three-Dimensional Clinostat for Life Science Experiments� [2]. In fact, the 3D Clinostat consists of two frames that rotate on axes orthogonal to each other at a given angular velocity for each rotational axis. The principle of the kinematic model is to assume there is an arbitrary vector � at the origin of the global frame. This vector rotates with an angular velocity �⃗. The details of the kinematic model will be explored further in the Modelling section. Furthermore, we determined that the optimal rotational velocities for the inner and outer frame are 4.5 and 10 rpm, respectively.
We also performed simulations for the vibrational, stress and heat transfer analysis in order to optimise the design of the 3D clinostat.
Potential Impacts
The 3D clinostat design is environmentally friendly since the base and the outer frame are constructed with aluminum. Aluminum can be melted down and recycled or can be repurposed for other uses. The acrylic (Plexiglas) used for the bioreactor can also be recycled through a more stringent process, however it would serve better for other applications. Moreover, all the electronic components can be reused if they are still functional. The 3D clinostat will help study the effects of microgravity on yeast growth, giving us more insight into the behavior of organisms in space, which will positively impact human knowledge and future space explorations by allowing us to explore deeper into space.
Figure 8: Clinostat
HARV
The HARV (High Aspect-Ratio Vessel) is one of the existing designs of a Rotating Wall Vessel (RWV), designed to emulate micro-gravity conditions similar to those experience in orbital spaceflights. The design consists mainly of a rotating cylindrical polycarbonate vessel, a motor, and an Arduino-based control and monitoring system. This allows for fine control over the vessel’s rotational speed, which is displayed (in RPM) by a small LCD screen attached to its Electric Box.
Figure 9: Harv Diagram
The objective of the design is to cancel out the gravity vector acting upon cells in the interior of the polycarbonate chamber. These cells are suspended in liquid media, and their natural tendency to fall gets countered by the added acceleration created by their rotating medium.
The HARV has been fully developed and seamlessly utilized in the running of several experiments related to the research of yeast in microgravity conditions.
Figure 10: Harv
Figure 11: Harv Arduino
In future, we hope we could utilize the nature of this device to conduct directed evolution experiment. We hypothesis through intercellular evolution. We could use population genetics method combined with our stress reporter constructs to track cellular population change and choose our adapted AstroYeast strains.
Sources
[1] Wuest, S., Richard, S., Kopp, S., Grimm, D. and Egli, M., 2015. Simulated Microgravity: Critical Review On The Use Of Random Positioning Machines For Mammalian Cell Culture. [online] https://www.researchgate.net/. Available at: <https://www.researchgate.net/publication/272352738_Simulated_Microgravity_Critical_Revie w_on_the_Use_of_Random_Positioning_Machines_for_Mammalian_Cell_Culture> [Accessed 12 October 2020].
[2] S. M. Kim et al., “An Experimental and Theoretical Approach to Optimize a Three- Dimensional Clinostat for Life Science Experiments,� Microgravity Sci. Technol., vol. 29, no. 1, pp. 97–106, Feb. 2017, doi: 10.1007/s12217-016-9529-2