Two-Level Shape Changes of Polymeric Microcuboids Prepared from Crystallizable Copolymer Networks

Polymeric microdevices bearing features like nonspherical shapes or spatially segregated surface properties are of increasing importance in biological and medical analysis, drug delivery, and bioimaging or microfluidic systems as well as in micromechanics, sensors, information storage, or data carrier devices. Here, a method to fabricate programmable microcuboids with shape-memory capability and the quantification of their recovery at different levels is reported. The method uses the soft lithographic technique to create microcuboids with well-defined sizes and surface properties. Microcuboids having an edge length of 25 μm and a height of 10 μm were prepared from cross-linked poly[ethylene-co-(vinyl acetate)] (cPEVA) with different vinyl acetate contents and were programmed by compression with various deformation degrees at elevated temperatures. The microlevel shape-recovery of the cuboidal geometry during heating was monitored by optical microscopy (OM) and atomic force microscopy (AFM) studying the related changes in the projected area (PA) or height, while the nanolevel changes of the nanosurface roughness were investigated by in situ AFM. The shape-memory effect at the microlevel was quantified by the recovery ratio of cuboids (R_r,micro), while at the nanolevel, the recovery ratio of the nanoroughness (R_r,nano) was measured. The values of R_r,micro could be tailored in a range from 42 ± 1% to 102 ± 1% and R_r,nano from 89 ± 6% to 136 ± 21% depending on the applied compression ratio and the amount of vinyl acetate content in the cPEVA microcuboids.