Animated Particles dip into mesh (collision physics activated)

Dear Blender cracks!

This is my first post - but not the first time I read threads in this forum. So thanks to all, first of all, for the tons of useful tips I am finding here!

Now my question: I have been following a tutorial on making a blood vessel with animated red blood cells using a particle system and collision physics. This worked quite well, but I encountered one problem:

The red blood cells do collide with the mesh and stay inside the blood vessel (made up of a bezier circle extruded along a bezier curve), but some of them dip into the mesh half way and then float along inside the mesh.

To explain myself better, I am inserting a test render:

Any ideas how to solve this? I was already thinking of duplicating the vessel mesh, scaling to fit into the vessel and setting collision with this mesh. But there has to be a better solution, I guess…

thanx guys,

No ideas? Anybody?

Try checking Size Deflect. You can find it under the Physics tab on your emitter.

o.k. thanks, I will give it a try…