In order to use MICP during the additive deposition process, we need to maintain and monitor ideal conditions for the bacteria. To do so we are thinking of making a diy bioreactor that supplies the bacteria to one of the inputs in the auger system through a push to connect tube fitting.
A bioreactor is a system that supports a biologically active environment. For S. Pasteurii we would need to monitor temperature and pH. pH is particularly important since a range of 9-10 will let us know that the bacteria is alive and active. We are also considering mixing the bacteria with the cementation solution in the same tank. This requires the incorporation of a hydrofoil impeller to ensure that any crystals in the solution are fully incorporated.
Another key part of the system is the integration of a peristaltic pump to control flow. The pump can be controlled with a NEMA 17 stepper motor to ensure accurate measurements at the scale of ml/min.
The first step in constructing this component will be to build and test the peristaltic pump design.
A peristaltic pump is a type of displacement pump that can be used with a variety of fluids and in our case the flow of bacteria. The system works through rotary motion and a series of rollers that compress the flexible tube as it rotates. The portion of the tube under compression closes, forcing the fluid to move through the tube. The advantages of using this pump system is that we limit the probability of contamination since the motor/ pump system does not come into contact with the bacteria. We can also control the precise amount of liquid flow since a fixed amount of liquid is pumped per rotation.
Our thoughts are to build the pump out of 3d printed parts, 6 ball bearings, and a NEMA 17 stepper motor in order to keep cost down since a peristaltic pump with the capacity to move fluid at high rate (100ml/min) can cost $75 and up. The first version is based on the tutorial and open source model shown HERE.
parts of the peristaltic pump and diagram of mechanism
PERISTALTIC PUMP
BIOREACTOR
The other main component of the MICP bioreactor is the axial flow hydrofoil impeller. There are different types of flow impellers: axial flow and radial flow. Axial flow impellers create liquid flows parallel to the axis around which the impeller rotates. They typically pump the liquid in the tank downward allowing content at the top and bottom of the tank to mix. I wasn't able to find a 3d model of a hydrofoil online, but I think it could be an interesting side project to design/optimize the geometry of one and run a fluid flow COMSOL analysis.
HYDROFOIL IMPELLER
Left: Bioreactor section showing current position and design of impeller Top Right: Axial vs radial flow, Paul Mueller Company Engineering Bottom Right: low viscosity hydrofoil impeller, spx flow
References:
Paul Mueller Company Engineering. “How to Choose the Right Impeller.” Paul Mueller Company, 2018, de.paulmueller.com/akademie/how-to-choose-the-right-impeller.
Verder. “How Do Peristaltic Hose and Tube Pumps Work?” Verder Liquids, 3 Sept. 2020, www.verderliquids.com/us/en/how-do-peristaltic-pumps-work/.