A computer-controlled method for forming a composition-controlled product using 3D printing includes disposing two or more liquid reactant compositions in respective two or more reservoirs； and mixing the two or more liquid reactant compositions, which in turn includes controlling by the computer a mass ratio of the mixed two or more liquid reactant compositions. The computer-controlled method further includes scanning, under control of the computer, a mixed liquid reactants nozzle over a substrate； depositing the mixed liquid reactant compositions onto the substrate； and operating, under control of the computer, a light source to polymerize the deposited mixed liquid reactant compositions.
