preventing my printer nozzle from getting too dull, from nothing but PLA filament
Your extruder nozzle will wear from the inside out if you are using abrasive filaments, which include carbon fiber, wood type filaments, glow-in-the-dark and many other types.
Because they are abrasive, removing material from the inside also thins the cone shape of the outside (point) of the nozzle.
The solution is to not use abrasive filaments, or to use a hardened nozzle specifically manufactured for abrasive filaments, or to change the nozzle frequently.
If this is a 3D printing pen as your post suggests, please clarify, as the answer is likely to change but only slightly. If this is a nozzle for a 3D printer, consider to edit your question to reflect thusly.