Problem reading STL files in netgen

Dear Netgen/NGSolve community

I am trying to mesh the SARS-Cov-2 replication/transcription/error checking machinery from a cryo-EM density map.

I have prepared 2D meshes in stl format using meshlab and meshmixer that I am quite happy with (example attached). However, when I read them into netgen, the triangles are not recognised, and there are issues with numbers of neighbours and orientation. Stldoctor can't fix this, because the file is not recognised as an stl. How do I solve this please?

I have been able to read this stl into gmsh and successfully create and optimise a 3D volumetric mesh. However, I can only output this in .msh format (example attached) which my simulation software does not read. I have tried reading into netgen using the python shell under "solve" and the command:

from ngsolve import *
from netgen.read_gmsh import ReadGmsh
# import the Gmsh file to a Netgen mesh object
mesh = ReadGmsh('mesh.msh')

but unfortunately the file is not read properly. Please could you explain what I am doing wrong?

Please note that because we are simulating very small objects (protein complexes!) we have a strict lower limit on the resolution of our meshes imposed by the physics, so please don't be surprised that they look very coarse!

Many thanks for your help and advice
#Sarah#