I hope the word “natural” in rubber doesn’t cause the illusion that it is safe.
Natural rubber is pretty bad if you are allergic to it, and repeated exposure increases risk of developing allergy.
But that’s minor anyway. The process used to create/extract the material and create the product can add toxicants for both rubber and silicone.
Then check for degradability. Anything that degrades develops cracks and pores, i.e. bacteria breeding grounds.
Make sure you pick “food grade” or “cosmetic grade”, and either pick should be perfectly safe.
Part of the answer is that the UI is “designed first” and coded to follow the design. If changes are seen as necessary when coding the UI, the design is updated first then the code made to follow.
So any UI behavior will already have a lot of accurate design and animation resources for them to work with.