Validating the bioprinter involved the completed and optimized bioink to produce basic geometric structures and testing their strengths. We will be testing its capabilities by printing at slow speeds in 2D and 3D squares, comparing the results to experiments conducted by the bioink team as a control.
Goals
Our minimal goals with bioprinter validation is to ensure that it can produce bricks consisting of our bioink consistently. We will be using geometries tested in the lab by the biomaterials team such as the rectangular wall and grid formation shown in their pages. 3 materials will be tested: alginate, earth sand alginate gel, and martian regolith (MGS-1) alginate gel.
Experimental Approach
The first validation tests we will do is manual extrusion using the printer’s extrusion mechanism to ensure that the extrusion of the material is consistent and controlled. One major concern for materials that have different viscosities is the potential of leaking out of the nozzle. To test this, we will use alginate, the least viscous material, to determine whether there would be leaking for other materials. Presumably, the least viscous material would be at the highest risk of leaking. The next issue we would test is the layering of the material and ensuring CaCl2 solidifies the material and creates layers we can stack upon. This will also be done manually with 100 mMCaCl2 sprayed directly onto the plate. Typically, without spraying, the layers would not solidify and stack causing them to droop and blend into one larger layer, decreasing resolution. Another test that we would do is automating the brick extrusion and geometry. This would involve using the TronXY printer’s native firmware and adjusting it for printing. This will be primarily tested using martian regolith.
Results
Test 1: Alginate Gel Manual Extrusion
We extruded a single layer of a square and grid shape shown in Figure 1. As expected, 3 weight % alginate gel could not solidify and stack quick enough between layers with the addition of calcium chloride. However, no leaking was observed and extrusion was smooth and easily controllable.
Figure 1. A single layer of 3 weight % alginate gel being extruded from the printer. 3 sprays of 100 mM calcium chloride was added right after extrusion. The image on the right shows the crosslinked alginate gel after 10 minutes in calcium chloride.
Test 2: Earth Sand Alginate Gel Manual Extrusion
We extruded a grid shape and a 3D structure with multiple layers as shown in Figure 2. In the solid structure with no visible layers, the calcium chloride was sprayed onto the earth sand alginate gel after the structure was extruded. In the hollow structure with visible layers, the calcium chloride was sprayed twice per layer and then extruded right after. This method allowed layers to form and a taller structure to be formed. We confirmed that no leaking was observed with the earth sand alginate gel and that the ink was uniformly extruded.
Figure 2. 30 wt% earth sand, 9 wt% CMC, and 3 wt% alginate extruded (in layers) by the printer. On the top image, calcium chloride was sprayed after extruded all layers on the left structure and calcium chloride was sprayed between each layer on the right structure.
Test 3: MGS-1 Alginate Gel Manual Extrusion
We printed a grid and square shape as shown in the sped-up video below using the MGS-1 alginate gel. The video shows controlled and precise extrusion using the TronXY printer. We extruded a single layer as shown in Figure 3. We confirmed that no leaking was observed with the MGS-1 alginate gel and that the ink was uniformly extruded.
Figure 3. 20 wt% MGS-1, 3.5 wt% CMC, and 3 wt% alginate extruded by the printer.
Next step involves creating CADs of 3D structures and utilize the TronXY printer’s native firmware to print and extrude automatically.
