[semion]

Hello,
I'm working with an STL file of a blood vessel, I need to modify the geometry and build a robust mesh. The imported geometry is very irregular and I managed to trim out most of the little vessels attached to the main one. After these (probably badly performed) operations the build topology tool can't seem to fix much and the geometry I'm left with is full of errors, holes and imperfections.
1)Is there a way to smooth out my geometry so it can be meshed better?
2)If I import the STL file as mesh the inlet and outlet surfaces are badly meshed; how can I modify the mesh on just a selected surface?

Thank you to whomever will reply!