Every good calibration starts with a pile of new materials, a daunting task, a ridiculous timeline, and our favorite ingredient…caffeine.
How many of these ingredients are for the tester and how many for the printer? The gummy worms, sour straws and energy drinks were for the Humans. The jello, alginate, bone meal, laxatives, joint support powder, mystery tub, and ABS plastic were for the Bots. It seemed like a fair balance.
The task at hand was to come up with a reasonable recipe and calibration for a bone gelatin hybrid.
Equal parts by weight
Bone Meal (extra fine)
PolyEthyleneGlycol (PEG) aka smoothLAX (coarse)
Jello (fine)… yes unfortunately you have to by the little packets. Royal (extra coarse)
Why the little packets?… because bulk pack Gelatin is a coarse grind, not a fine grind. You can either ball mill the stuff down to size or simply purchase the smaller more expensive name brand stuff.
Print resolution is dictated by the coarsest material in a batch. Variance in grain size can cause continuous failures in the print resolution as the layers perpetuate upwards. Long story short, try to get ingredients that are the same mesh size, or ball mill them all together until there is a homogenous consistency [Seen below].
If calibration seems close, the next step is to test scalability. Then do some more intensive troubleshooting.
Remember gelatin is a protein. Proteins take advantage of water to do some ridiculous tricks like folding, coiling, cross-linking, and hydrogen bonding. Normally we are used to seeing this happen in a warm pot of water…100 degrees C warm. The printer is unfortunately not that warm. In order to get to that kinetically favorable part of the jello [ie structural jello-y goodness] we must apply heat. Hence there is a take and bake aspect to the recipe.
After parts have been depowdered they are put into an oven. The oven is set at the lowest temperature possible, which measured by thermocouple was ~180-194F or ~82-90C. Then parts were baked for 15 minute per inch or 25mm of thickness. Unfortunately nothing we print in real life is uniform in thickness… so as always… use your best judgement.
After the prints have been baked there will be a diffusion gradient. A level where the prints absorbed some water but not enough to achieve full strength. This outer casing should flake/crumble off fairly quickly when compressed or picked. If the parts have been over cooked they will be darker, blistered, and it may not be possible for the casing to be removed.
The prints after desiccation will be rock hard, but will solvate in water, because 2/3 of the ingredients are gel-like substance.
What are the applications for printing in jello? This is the cheap way to test bone hybrids for tissue engineering. Jello, basic gelatin, and collagen have similar printing behavior but maintain different levels of biocompatibility. When it comes down cellular science the biocompatible materials are very expensive. The more preparation that can be done with ingredients that are similar, cheap, and readily available… the more real science can be done with the expensive materials.
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