Tunable Nanoscale Channels in Diblock Copolymer Films for Biomolecule Organization

Abstract

We describe an approach to create nanoscale, functionalized channels in block copolymer films and demonstrate their use as templates for attaching filamentous actin (F-actin). Topographic and chemical patterns on the surface are created and controlled by exposure to UV-ozone (UVO) and reacting with an amine-terminated silane, respectively. Continuous UVO exposure degrades polymer domains by an autocatalytic reaction, and thus, film thickness decreases in a sigmoidal manner. Utilizing the differential etching rates of each domain, nanoscale channels with tunable depth and width are created by varying UVO exposure time and block copolymer molecular weight, respectively. For a perpendicular lamellar morphology poly(styrene-b-methyl methacrylate), P(S-b-MMA), films (65 nm), initially exhibiting higher MMA domains, undergo a height inversion after 3 min of UVO because MMA domains etch twice as fast as S domains. The maximum height difference between domains is approximately 16 nm after approximately 10 min of UVO. Similar behavior is observed for UVO etching of a parallel cylinder morphology. UVO exposure also produces reactive polar groups on the surfaces of poly(styrene) and poly(methyl methacrylate) as well as their corresponding domains in P(S-b-MMA). By exposing UVO-treated films to 3-aminopropyltriethoxysilane (APTES), P(S-b-MMA) surface becomes enriched with amine groups which act as binding sites for biomolecules. Under physiological conditions (pH approximately 7.4), these positively charged nanostructures attract negatively charged F-actin by an electrostatic interaction.