Testing 30-70 wt% earth sand conditions with 850 µm particle size using methodology from Bioink Composition Testing. Observing whether the gel can be easily extruded from a syringe and maintain its layers after crosslinking.
Materials & Methods
1L Glass Bottle for CaCl2 solution
Small glass bottle for alginate solution
Plastic containers for
sieved sand
mixing the gel
Magnetic stirrer
Spatula
distilled water
10 mL syringe
Petri dish
Reagent
Amount Used
Alginate
1.65 g
CMC
0.9 g
Sand
3.05 g, 4g, 5g, 6g, 7g
Calcium Chloride (anhydrous)
4.44 g
Made 3% (wt.) alginate solution for 55mL of DI water
use a magnetic stirrer + hotplate to help dissolve (was very thick and hard to dissolve)
For next time: add alginate slowly into the water while spinning
Made 400 mL of 100mM calcium chloride bath
use a magnetic stirrer
Mixed CMC with sand together (dry mix)
sieved sand using the 850 µm sieve
Dry mix added into 10 mL of alginate solution ---> mixed with spatula
Scooped mixture into 10 mL syringe
Extruded a straight line into calcium chloride bath on petri dish
Extruded a rectangle with three layers
Crosslinked for 10 mins
Results
Figure 1. Particle size of 850 µm. Extruded using a straight line (left) then a box with three layers stacked (right) on a 10 mL syringe.
Observations
With increasing sand %, the mixture got thicker, did not seem to affect extrusion as much as particle size
3wt% alginate was very thick, required heat to dissolve
may not be homogenously mixed
40-70wt% sand particles got clogged in the syringe and extrusion was not uniform
30-40wt% layers could not hold on top of each other
60-70wt% can see clear three layers
For layering, calcium chloride solution was added after extrusion onto a petri dish
Straight line was extruded directly into CaCl2 bath ---> could not form layers into bath (became solid right away and layers could not stick together)
Rectangle + line was drawn and traced for each condition to maintain consistent shapes
Summary
Need to find a quicker / more efficient way of making alginate solution
maybe try less concentrated, 2wt%?
Bioprinter design consideration: crosslinking solution needs to be added after ink has been extruded or layers will not stack on each other to create a 3D structure
Two nozzles (one for bioink, one for crosslinking) or soak the ink in solution after
Need to optimize for best timing
The gel is thick enough to maintain its structure without crosslinking, but will collapse with time
Sand wt% did not play a significant role in ease of extrusion
850 µm is too large of a particle size / sieve ---> sand will clog the syringe
Hand off
Materials and reagents kept:
4 plastic cups (labelled for measuring sand, CMC, and mixing solutions)
Sodium alginate (in a resealable bag)
Fig 1. gel samples
1 empty small glass bottle (100mL?) for making alginate solution
