Fabrication of Poly(L-lactide)-block- Poly(ethylene glycol)-block-Poly(L-lactide) Triblock Copolymer Thin Films with Nanochannels: An AFM Study Sung-Wook Choi, Yongwoo Kim, In Woo Cheong, Jung-Hyun Kim * Introduction Block copolymers are fascinating materials in the fabrica- tion of nano-sized periodic patterns by an easy and simple procedure. [1,2] Various surface structures can be generated, such as dot-like, worm-like, striped, furrowed, and porous nanopatterns by controlling the chemical structure, block length, solvent, and processing conditions. [3–6] These well- defined nanostructures have applications in many fields [4] and, in particular, can be used as drug-delivery devices (such as in drug-loaded patches) and cell-patterning templates [7] in biomedicine. However, most work on patternable block copolymers has been based on poly- styrene (PS) because its molecular weight can be accurately controlled by living polymerizations. [8,9] For biomedical applications, patternable block copolymers are limited by the material and domain size, because PS is not bio- compatible and its micro-domains are generally less than 100 nm in size. It is also difficult to expand the micro- domain size to 100 nm by controlling only the block length. Therefore, solvent-induced microphase separation has been suggested and studied as an easier procedure to Communication S.-W. Choi, Y. Kim, J.-H. Kim Nanosphere Process & Technology Laboratory, Department of Chemical Engineering, Yonsei University, 134 Shinchon-dong, Sudaemoon-ku, Seoul 120-749, Korea E-mail: jayhkim@yonsei.ac.kr I. W. Cheong College of Engineering, Kyungpook National University, 1370 Sankyuk-3-dong, Buk-gu, Daegu 702-701, Korea This paper aims to report the fabrication of biodegradable thin films with micro-domains of cylindrical nanochannels through the solvent-induced microphase separation of poly(L-lactide)-block-poly(ethylene glycol)-block-poly(L-lactide) (PLA-b-PEG-b-PLA) triblock copolymers with different block ratios. In our experimental scope, an increase in each of the block lengths of the PLA and PEG blocks led to both a variation in the average number density (146 to 32 per 100 mm 2 ) and the size of the micro-domains (140 to 427 nm). Analyses by atomic force microscopy (AFM) and fluorescence microscopy indicated that the hydro- philic PEG nanochannels were dispersed in the PLA matrix of the PLA-b-PEG-b-PLA films. We demonstrated that the micro-domain morphology could be controlled not only by the block length of PEG, but also by the solvent evaporation conditions. Macromol. Rapid Commun. 2008, 29, 175–180 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.200700564 175