Shape memory polymers have the unique ability to memorize and recover their permanent shapes after being programmed to hold high strain levels up to a few hundred percent. While studies have traditionally focused on utilizing shape memory effects for macro-scale applications such as surgical stents and sutures, as well as temperature sensors, recent work highlighted the potential of polymers to memorize and recover sub-micrometer surface patterns. On the other hand, polymeric micro- and nano-particles, ranging from structurally homogeneous, to core-shell, to Janus-particles, already enjoy wide interest in their uses in drug delivery, electronic packaging, optical bio- sensors, and test-beds for the mechanosensitivity of cells. Incorporating shape memory effect, i.e. the ability to change shape upon external stimuli, into these current polymer-particle-based technological platforms could potentially lead to a host of new engineering applications. However, the ability of micro and nano-particles to successfully fix large 3-dimensional strains and recover their permanent shapes has not yet been investigated. Here we demonstrate the successful programming of large compressive engineering strains in crosslinked polymer microparticles via nanoimprint lithography (NIL). The recovery of these particles is shown to be strongly dependent on the constraints of substrates and superstrates, the latter of which is shown to generate a series of rosette-like smart Janus particles.
Citation: Advanced Materials
Pub Type: Journals
Shape Memory Polymer, Nanoimprint Lithography, Atomic Force Microscopy