An article of manufacture comprising: (a) a body at least a portion of which is a multi-phase material (MPM) defining a traction surface; (b) the MPM comprising at least first and second zones comprising first and second materials, M1, M2, respectively, at or near the traction surface, the M1 and M2 having first and second Young moduli respectively, the first and second moduli differing by at least a factor of 3; and (c) wherein each of the second zones has a center, and wherein the second zones have a center-to-center radial distribution function having a peak at between 10 μm and 10 mm.