You generally have two options. You can either get a native mesh with “Springs.ToolkitMeshToMesh”(faster) and then create a directshape, or extract the triangles, make a unified polysurface and create a “FamilyInstance.ByGeometry”:
If you go with the native mesh route, keep in mind that if your mesh is too complex ( ie it’s a group of meshes or has many voids/openings), the conversion might fail because Dynamo’s native meshes are very limited.
Attempting to make a solid out of a mesh with many triangles is usually not a good idea.