Smolin used these preons to bring matter into Loop Gravity. It looks like we need to learn about Bilson-Thompson type preons. there is this march 2005 paper http://arxiv.org/hep-ph/0503213 A topological model of composite preons Sundance O.Bilson-Thompson 9 pages, 3 figures, submitted to Phys. Lett. B Arivero started a thread about preons in "Particles" forum and Ohwilleke brought up this paper of B-T and discussed it some, along with earlier work that it derives from. Here is Ohwilleke's post https://www.physicsforums.com/showpost.php?p=581108&postcount=7 the basic ideas is since we know that protons and neutrons are composite each being made of 3 quarks (which really exist even tho hard to pull apart) that perhaps now it is time to discover that QUARKS ARE COMPOSITE AND each quark is made of 3 preons (which are even harder to pull apart) and furthermore NOT ONLY do you get all the different type quarks by combining preons YOU ALSO GET LEPTONS AND BOSONS by combining these same old preons. so you can get not only quarks (to make your protons with) but you can also get neutrinos and electrons and photons-----the idea is to get all the stuff in the Standard Muddle by tasteful combinations of a small number of preons. the reason that we need to know about preons in context of QUANTUM GRAVITY is that Smolin found that you could imagine preons as long (sometimes twisted or braided) strands of CONFETTI and that a good way to combine the GRAVITY-states of spin networks with the MATTER-states of the Standard Muddle would simply be to make the spin networks out of that type of confetti so that the network that described a quantum state of gravity would have its LINKAGE CORDS MADE OUT OF PRION RIBBON The point is that people have been wanting for a long time to have a quantum theory of spacetime geometry that would also explain the Standard Muddle and hopefully simplify both---and string ideas have not been working out very well----so this could be something to investigate as a way to combine gravity with matter.