Introduction
Last year, we built 2 microgravity simulators and developed one space bioreactor concept. Here we will discuss one of our experimental devices in-depth. The 3D clinostat is part of our engineering group�s undergraduate final year project. It was purposefully built for iGEM Concordia to run microgravity synthetic biology experiments.
Recently, we developed our experiment protocol. Our device is verifying our experiment methodologies and testing our hypothesis. We conducted a series of pilot experiments which demonstrated the effectiveness of our devices. For more information about the result of the pilot experiment, please see our genetics team page.
We learned a lot from our last years project. We started the design phase by following this engineering flowchart:
Design
We have implemented an iterative design approach during our design phase. The design process was lengthy in order to obtain the most optimized version of the 3D clinostat. Several aspects, such as manufacturing, budget, and feasibility of the design, were our main concerns. This design validation diagram summarises our process visually:
First Design Iteration
Cons & Revisions:
- Bioreactor size & geometry could cause a large moment of inertia
- Aluminum extrusions of the outer frame would cause poor wire management
- Large aluminum base frames would be expensive, heavy and hard to manufacture/source.
Second Design Iteration
Cons & Revisions:
- Large aluminum base frames would be expensive, heavy and hard to manufacture/source.
- Spherical bioreactor is not viable from a manufacturing standpoint as the two spherical halves of the bioreactor would be welded yielding a high stress concentration possibly leading to failure.
Final Design
Revisions & Improvements:
- Aluminum extrusions for the base frame to support the motors & payload.
- Hollow sheet metal outer frame for easier wire management
- Rectangular shaped bioreactor made from acrylic
Build
With our final design in hand and feasibility verified, we moved on to the next stage. The finalized design components (including the electronics) are listed as:
During the building phase, we have revisioned our design in 2 parts to increase device stability and reduce cost. We implemented the laser cutting process, which is an easy-to-use process as it substitutes the more conventional cutting processes due to its economic and technical benefits. We have also revisioned our frame assembly manufacturing process. This minor revision reduces manufacturing difficulties. Our outer frame assembly was welded together and assembled to the whole construct.
The total engineering cost for our 3D clinostat was 800$ CAD, excluding operational costs.
Test
In order to validate our design, we had to test all aspects extensively, as shown in the testing diagram below.
However, despite some minor tweaks to facilitate the assembly and quick modifications to the electronics, namely the stepper motors and drivers, to enhance the performance of the device, the 3D clinostat does achieve its function!
Finally, we collected data from the accelerometer placed in the center of rotation of the bioreactor to evaluate the different components of acceleration in the x, y, and z directions. Here are the resulting plots after 5 minutes of rotation.
From the data collected from the ADXL 345 accelerometer after a sampling time of 360s, we can conclude that the rotation of the 3D Clinostat for an extended testing time of around 24h in a laboratory environment would most definitely showcase the damping or convergence of the sum of the acceleration in the x, y & z to 10^(-3) g, so as to achieve the simulation of microgravity due to its slow rotation as well as the constant dispersion of the gravity vector, as discussed given the relatively low values of acceleration in the y and z axes.
Learn
After we moved the clinostat to our iGEM lab, several issues were exposed. Those issues include excess vibration, installation error, false wiring connections, and overheating. Those issues are relatively minor issues and simple to solve.
However, the effect of vibration will be amplified on a cellular level which is much harder to solve.
Improve
We attached several support pieces which were 3D printed. Those pieces drastically improved our device stability.
Friction is an inevitable factor when it comes to machines. Due to excess friction and vibration of the outer frame, we upgraded our stepper motor. The new motor provides more torque to sustain the unsupervised run.
We have also learned due to the nature of the stepping motor, vibration from the motor was conducted to our inner bioreactor box. When vibration from the stepping motor reaches the resonance frequency of the inner box, it will create an oscillating motion. Thus, we have used