  We prove the existence and uniqueness of a strong solution of a stochastic
differential equation with normal reflection representing the random motion of
finitely many globules. Each globule is a sphere with time-dependent random
radius and a center moving according to a diffusion process. The spheres are
hard, hence non-intersecting, which induces in the equation a reflection term
with a local (collision-)time. A smooth interaction is considered too and, in
the particular case of a gradient system, the reversible measure of the
dynamics is given. In the proofs, we analyze geometrical properties of the
boundary of the set in which the process takes its values, in particular the
so-called Uniform Exterior Sphere and Uniform Normal Cone properties. These
techniques extend to other hard core models of objects with a time-dependent
random characteristic: we present here an application to the random motion of a
chain-like molecule.
