Algodoo

in this scene, we have modified a Xok's DNA to make it able to grow by frequeny colliding
but i intented for the Xok to only grow on the material "Agar" but it grew anyway on any surface it touched
is there a way to make it continusly grow or able to only grow with touching the "Agar" material
the agar in this peri dish is engineered to grow xoks much faster

help and suggestions are accepted