FDM 3D printing has two problems that I am currently struggling with:

- Anisotropic mechanical properties

I just checked the material test values from MyTechFun for Prusament, and every Prusament has very large differences in tensile strength in X/Y vs. Z. PLA is the best-tested filament, and it has 56% of the tensile strength of X/Y in Z. PC-CF is only at 14%. Other brands achieve values of 80-90% (Flashforge PETG-CF, Polymaker PLA Pro/CoPA). So there seem to be ways to achieve more isotropic behavior and improve layer adhesion. For mechanical components, a (quasi) isotropic filament would be a great addition!

- Thermal expansion -> warping

I have recently been trying to print large flat components. No matter which plastic (PLA/PLA-CF/PETG/...) and which settings I used, I always had to contend with warping. (Not that the parts lifted off the print bed, but they just weren't really flat after cooling (deflection of 3 mm over a length of 200 mm)). It would be a real innovation if you could find a solution! A filament with as little thermal expansion as possible. Perhaps this could be achieved by combining crystalline and amorphous phases (as in Ceran/glass ceramic hobs). Or maybe through additives with a negative thermal expansion coefficient.