A rotaxane is a mechanically interlocked structure comprising a
dumbbell-shaped molecule threaded through a cyclic
macromolecule. The name comes from the Latin for wheel (rota)
and axle (axis). Polyrotaxanes (joined-up rotaxanes) have been
little studied for drug-delivery applications but they offer
great promise in this field because of their unique properties,
which include the fact that they are rigid and biocompatible.
To make drug-delivery capsules, Henk Dam and Frank Caruso began
by assembling polyrotaxanes on the surface of silica particle
templates. The researchers then cross-linked the polyrotaxanes
and removed the silica cores. The resulting spheres are equipped
with alkynes, a chemical group that can be specifically reacted
with a variety of molecules – such as those with so-called
“stealth” properties that minimize unwanted adhesion of other
substances.  The same functionalization strategy might also be
used to attach antibodies to the surface of the capsules that
could then specifically target d