Multiple colloids or hydrogels may each have a different chemical composition. A printer may extrude the colloids or hydrogels to form a physical object, in such a way that which hydrogel or colloid is deposited—or the amount of each hydrogel or colloid that is deposited—varies as a function of spatial position. Thus, the material composition and material properties of the physical object may vary at different locations. In some cases, physical properties of the structure being fabricated, such as surface roughness and hydrophilicity, are directly related to relative proportions of the materials being deposited and their fabrication processes. In some cases, cells, microorganisms, nutrients or other bioactive materials are embedded in or introduced to the fabricated structure. In some cases, the different materials in different spatial positions in the fabricated object may have different abilities to immobilize, localize, and stabilize specific nutrients and chemical signals.