Method for attaching microspheres to a substrate

A method of manufacturing an article having a plurality of layers of microspheres, including the steps of:

• reacting a surface of the solid substrate with a first ligand to covalently bond the first ligand to the surface of the substrate to form a ligand-bonded substrate;
• and
• contacting the ligand-bonded substrate with a dispersion of first microspheres, that contain intrinsic reactive functions, in a liquid carrier, for a time sufficient to covalently bond the first microspheres to the ligand;
• reacting the first microspheres with another ligand disposed farthest from the substrate, said another ligand being the same as or different from the first ligand, to covalently bond the first microspheres to said another ligand;
• and
• contacting said another ligand with another dispersion of microspheres, that contain intrinsic reactive functions, said another microspheres disposed farthest from the substrate, for a time sufficient to covalently bond said another microspheres to the second ligand, said another microspheres being the same or different from said first microspheres;
• and
• wherein after formation of microsphere/ligand covalent bonds, residual unreacted intrinsic reactive functions remain in the microspheres;
• said article being further characterized by the fact that said microspheres are bound to said substrate by means consisting of said first ligand.