The ability to fabricate surfaces possessing chemical gradients has been pursued for a variety of applications. Some applications include: cellular and tissue growth, biomimetic responses, combinatorial surface studies, and advanced assays. Although several methods of making such substrates exist, their product(s) lack some critical aspects. Current methods of fabrication rely on microfluidic environments, thus limiting their applicability. Changes in composition are usually made of discrete steps rather than a continuous transition. Also, these methods of fabrication are limited to specific substrates and chemistries.

To close these technological gaps, chemical vapor deposition (CVD) technology was used to copolymerize two reactive monomers, 4-aminomethyl-[2.2]paracyclophane and 4-trifluoroacetyl-[2.2]paracyclophane, in a custom-built CVD polymerisation system. Both monomers are fed into the chamber separately but simultaneously, in a manner that deposits a gradient of monomer functionality. The ratio of functional groups changes along the gradient. FTIR spectroscopy verifies the change in monomer ratio with respect to the position of the substrate(s). XPS also confirms the gradual changes in amine and trifluoroacetyl groups. The composition changes at relatively small intervals, showing that the composition change is continuous and not discrete. Two fluorescent ligands, each possessing selective reactivity towards the PPX functionalities,[1] were reacted onto the copolymer gradients, as verified by fluorescence scanning. Fluorescence ratios of both ligands changed in accordance with the composition along the gradient. These results have broader applications in biomaterials engineering, microfluidics, and diagnostic testing. Not only do CVD gradients deposit over non-confined surfaces, but the paracyclophane monomers can be modified with a wide variety of functional groups.[2]

[1] Y. Elkasabi, H.Y. Chen, J. Lahann. Adv. Mater. 2006 18(12) 1521-1526 [2] J. Lahann, R. Langer. Macromol. 2002 35(11) 4380-4386.