Proof of Concept
Our concept
Our project CosMIC – Microorganisms in Space - offers a big opportunity to have more independence on future space missions. It contains a 3D Bioprinter, which only must be installed once, the chosen bacteria Azotobacter vinelandii, media for the bacteria and a light source. To achieve our goal of a usable bioink, the bacteria A. vinelandii must overexpress alginate. Alginate turns out to be a very popular polysaccharide often used as a bioink. In addition to that, alginate is a biodegradable polymer and therefore can potentially be reused. Also, to complete the ink we need to add genes into the bacteria, which are responsible for cellulose expression. Cellulose is important for the strengthening of the material. It is possible to create new tools in less time and within an only one-step production. To learn more, take a look at our project description.
To confirm the concept of 3D-bioprinting in space we made a few experiments for the used bioink (alginate and cellulose).
In the beginning, we combined several different concentrations of alginate and cellulose, starting with a base of 4% alginate.
| Alginate | Alginate - Cellulose | Alginate - Cellulose | Alginate - Cellulose | Alginate - Cellulose | |
|---|---|---|---|---|---|
| c | 4% | 4%-/ 1% | 4% / 2% | 4% / 3% | 4% / 4% |
| Alginate | 0,4 g | 0,4 g | 0,4 g | 0,4 g | 0,4 g |
| H2O | 9,6 g | 9,5 g | 9,4 g | 9,3 g | 9,2 g |
| Cellulose | / | 0,1 g | 0,2 g | 0,3 g | 0,4 g |
During the mixing process, we noticed how the strength of the product changed as more cellulose was added.
To test this, we carried out a filament drop test, which we adapted to our printer and developed ourselves based on
For this, we made the printer print a certain file with a distance to the printing bed of 8cm. The flow was 100 and the speed.
We used a 3 ml syringe as the vessel for the bioink. The test was carried out ten times for each concentration. The number of drops that dripped onto the plate during printing was counted.
Graphic 1: Different quantity of drops per round in relation to their relative composition (alginate / cellulose)
The second experiment was a filament collapse test.
For this, 1 ml of each concentration was injected over different lengths and it was evaluated whether they collapsed, sagged or held.
We chose lengths of 0.5 cm, 1 cm, 2 cm and 3 cm.
We used a scientific paper on the 3D printability of alginate-carboxymethyl cellulose hydrogel by Ahasan Habib et al. as a template.1
The following graph shows the results of the test:
Graphic 2: Different states of the filament in relation to alginate / cellulose concentration and to their length
After both attempts we decided to use 4% alginate and 4% cellulose. since this showed the best results in the filament collapse test.
As the last experiment we printed the bioink upside-down onto a petri dish to create anti gravity conditions.
We applied the ink multilayer and let it stand over three days overhead.
It turned out that not a single drop fell onto the opposite side.
The result showed that it is possible to use the bioink even under anti gravity conditions. It sticks to the surface and does not run despite several layers, but remains in place.
Conclusion
From the results of our experiments, it can be summarized that the combination of alginate and cellulose turned out to be most suitable with a 1:1 concentration. It is generally possible to work with the ink and form a resistant material. Experiments one and two prove that it is possible to use alginate and cellulose as bioink. Especially experiment number three shows that it would be possible to use the printer in space.
- Habib, Ahasan, Venkatachalem Sathish, Sanku Mallik, and Bashir Khoda. 2018. "3D Printability of Alginate-Carboxymethyl Cellulose Hydrogel" Materials 11, no. 3: 454.https://doi.org/10.3390/ma11030454