Structures ignore each other upn contact

Hi,

I'm new to comsol, just started using it few weeks ago. I'm building a model of capillaries and white blood cells. I tried to fit a sphere inside a tube and make the sphere expand due to internal pressure, and then stretches the tube upon impact. Unfortunately the sphere extend beyond the tube as if the tube was not there.

I tried using contact pairs and have the geometries as union, but I neither solved the problem.

I would really appreciate someone give me some help as soon as possible.