In simple words the beads have to be large enough to be trapped by the polymer mesh and small enough to disturb the mesh.

Thank you. Are there any software programs to calculate the size based on the properties of the gel?

HI Aragon, I think Josef is right. Bead size should be larger than mesh size otherwise there will be pocket diffusion if bead size is smaller and you will get wrong information. Recently, we studied extensively on microrheology of liquid crystal (Langmuir 2011, 27, 6171). You can also check Langmuir 2005, 21, 3084. They explained the effects of bead surface on microrheology. Microrheology is my interested topic.