Density-Controlled Freestanding Biodegradable Nanopillar Arrays Patterned via Block Copolymer Micelle Lithography

Vertically aligned polymer nanopillar arrays on substrates are receiving increasing interest as functional surfaces for a broad range of applications. However, methods for preparing polymeric nanopillar arrays have poor controllability of dimensional parameters and are limited to few polymers. Here, a new method to prepare freestanding biodegradable nanopillar arrays on different substrates, including flexible sheets, by plasma etching with polystyrene-blockpoly( acrylic acid) (PS-PAA) block copolymer (BCP) micelles encapsulating Au nanoparticles (AuNP@PS-PAA) is reported. The adsorption density of the AuNP@PS-PAA micelles is controlled by the pH of the micelle solutions, affecting electrostatic interaction with the polyelectrolyte layers formed on a poly(lactic-co-glycolic acid) (PLGA) film coated on the substrates; thus, density-controlled PLGA nanopillar arrays are prepared using the micelle array as an etching mask during plasma etching. The height of the PLGA nanopillars is controlled by adjusting the plasma etching time, achieving high aspect ratios (>10) on inch-sized substrates. This new platform combining bottom-up (controlling absorption of BCP micelles used as etching mask) and top-down (plasma etching for nanopillar formation) approaches can be applied to prepare nanopillar arrays on substrates using different soft materials including biodegradable polymers.