Would it be possible to design a TPU mold with a part that supplies extra material, print it, fill both the mold and reservoir with chocolate chips, and microwave the mold? Would the end result be foodsafe?
It would not be.
Another idea would be to 3d print parts to be used to create molds from food safe silicone.
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I would add that nothing in 3D printing can be inherently food-safe given that the product cannot be sealed. One would have to use a food-grade sealant to make it truly food-safe.
Having said that, many filament makers claim “USDA food-grade,” but if you read the fine print, that only applies to the raw material meeting USDA safety standards for microbial contact. 3D printing by its nature has open pores where bacteria can accumulate and be retained.
Here’s a good writeup that sums up the do’s and don’ts, how’s and why’s.
Just in case you’re interested there was a discussion on this topic a while back that may lend additional insights.
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Printers that can print food safe cost a small fortune, same for the filaments.
And no matter what you print at home it won’t be suited for holding food, especially not warm or microwaved.
Do it the other way around:
Print the shapes you like or carve them our out of wax.
Use FOOD safe 2 part silicone for mould making after creating you two part box or whatever required for the chocolate…
Benefit is that you not only can heat this up to about 160 degrees celsius but that nothing will get into the food inside.
Sure you have to fill, sand or do whatever to get a smooth finish for your positives but once done and the mould is ready it lasts for a very long time.
While its tough to call something “food safe” and I would never sell a printed object or upload a model as food safe, I think that for personal use it also depends a lot on how it’s used. I’ve seen star awarded restaurants that used basic 3d printed forms to cut out / shape their expensive creations on the plates to make it look fancy - similar to cookie cutters. Do they throw it away after a few hours and use a new one to avoid bacteria? Much likely.
One thing to be aware of is that any “texture” is also a good place for .bacteria, but so does kitchen boards with cut marks can be. Downside of many 3d printed parts is that we can’t clean them as effective. You also don’t want any brittle stuff in your food.
But depending on the use case you can also wrap kitchen plastic foil around the 3d printed part or do similar tricks to make use of the part, but avoid direct contact to the food.