I will present the "D-material universe", a model of a brane world propagating in a higher-dimensional bulk populated by collections of D-particle stringy defects. I will discuss how D-particle recoil velocity excitations as a result of the interactions of the defects with stringy matter and radiation on the brane world, lead to a vector field that can assist the growth of large-scale structure. I will then analyse the circumstances under which the D-particle recoil velocity fluid may "mimic" dark matter in galaxies. Finally, I will discuss a cosmic evolution for the D-material universe by analysing the conditions under which the late eras of this universe associated with large-scale structure are connected to early epochs, where inflation takes place. I will show that inflation can be induced by dense populations of D-particles in the early universe, with the role of the inflaton field played by the condensate of the D-particle recoil-velocity fields under their interaction with relativistic stringy matter, only for sufficiently large brane tensions and low string mass scales compared to the Hubble scale. For large string scales, where the recoil-velocity condensate fields are weak, inflation may be driven by dilaton (or other moduli) fields in the underlying string theory.
