Every rigid body is just a cloud of particles. If they are bonded together, they are bonded together with other particles like photons. Or gravity. Or strong nuclear force, as quarks in protons and neutrons.
Also the strong nuclear force is responsible for bounding atomic nucleus together. The force just doesn’t stop at the “edge of a proton”.
But why do you think they “must be bonded together” in the first place?
A bunch of particles not bound to each other by anything is not rigid in any reasonable sense I can think of, so what’s your point?
Every rigid body is just a cloud of particles. If they are bonded together, they are bonded together with other particles like photons. Or gravity. Or strong nuclear force, as quarks in protons and neutrons.
Also the strong nuclear force is responsible for bounding atomic nucleus together. The force just doesn’t stop at the “edge of a proton”.
But why do you think they “must be bonded together” in the first place?