[barnabee]

3D printing (additive manufacturing) usually involves layers that tend to be a weak point.

If you want something truly long lasting you might find substractive manufacturing techniques like CNC milling better. Indeed there are solutions from companies like Cryptotag for punching cryptographic seed data into plates / blocks of titanium. Something like this could be automated with a CNC router to store a bunch more data.

[Intralexical]

Titanium gets hype, but is it actually the best option considering chemical and fatigue properties? I find it implausible that tensile strength-to-weight would be the weakest part even for good old fashioned stainless steel.