A method of assembling composite structures from objects in fluid includes providing a plurality of objects, each having a preselected size, shape, and spatial distribution of surface structural features characterizing a surface roughness; dispersing the objects into the fluid; and introducing a depletion agent. The depletion agent includes a plurality of particles having a size distribution preselected causing an attractive force arising from a depletion attraction between at least a first object and second object of the plurality in at least one relative position and orientation based on the preselected spatial distribution of surface structural features on the first and second objects, and the depletion attraction between the first and second objects forms at least one rigid bond or slippery bond at or proximate to respective surface portions based on the preselected spatial distribution of surface structural features on the first and second objects to form a two-object composite structure.