Replication of high aspect ratio pillar array structures in biocompatible polymers for tissue engineering applications

We developed a simple two-step replication method to transfer arrays of high aspect ratio nanopillars into films of poly(l-d,l-lactic acid) (PLLA). Such structures are promising model surfaces for tissue engineering applications. From arrays of 1 μm high and 200 nm wide pillars produced with e-beam lithography and reactive ion etching negative replicas were first formed by polydimethylsiloxane (PDMS) casting. The final replicates were produced by solvent casting from 1% to 4% solutions of PLLA in chlorinated solvents on the PDMS templates. The silicon masters provide excellent stability and reusability, whereas the flexibility and low surface energy of the PDMS are necessary for the separation of the casts made with PLLA, a brittle material which is difficult to handle. AFM and SEM characterizations confirmed a high fidelity reproduction of the structures with aspect ratios of 1:5. In vitro tests using mouse neural stem cells seeded on nanopillars showed that the cells sense the nano-sized topography and respond accordingly by orienting themselves.