Shape-Memory Actuation of Individual Micro-/Nanofibers
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.276
Shape-Memory Actuation of Individual Micro-/Nanofibers Yue Liu1,2, Oliver E. C. Gould1, Karl Kratz1, Andreas Lendlein1,2 1
Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Kantstr. 55, 14513 Teltow, Germany
2
Institute of Chemistry, University of Potsdam, 14476 Potsdam, Germany
*Correspondence to: Prof. Andreas Lendlein [email protected]
ABSTRACT
Advances in the fabrication and characterization of polymeric nanomaterials has greatly advanced the miniaturization of soft actuators, creating materials capable of replicating the functional physical behavior previously limited to the macroscale. Here, we demonstrate how a reversible shape-memory polymer actuation can be generated in a single micro/nano object, where the shape change during actuation of an individual fiber can be dictated by programming using an AFM-based method. Electrospinning was used to prepare poly(ε-caprolactone) micro-/nanofibers, which were fixed and crosslinked on a structured silicon wafer. The programming as well as the observation of recovery and reversible displacement of the fiber were performed by vertical three point bending, using an AFM testing platform introduced here. A plateau tip was utilized to improve the stability of the fiber contact and working distance, enabling larger deformations and greater rbSMPA performance. Values for the reversible elongation of ε rev = 3.4 ± 0.1% and 10.5 ± 0.1% were obtained for a single micro (d = 1.0 ± 0.2 µm) and nanofiber (d = 300 ± 100 nm) in cyclic testing between the temperatures 10 and 60 °C. The reversible actuation of the nanofiber was successfully characterized for 10 cycles. The demonstration and characterization of individual shape-memory nano and microfiber 1
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actuators represents an important step in the creation of miniaturized robotic devices capable of performing complex physical functions at the length scale of cells and structural component of the extracellular matrix.
INTRODUCTION: Micro-/nanoscale polymeric devices capable of stimuli-responsive actuation are highly sought after for applications in sensors [1], medicine [2, 3], and microfluidics [4], where the ability to sense and reversibly react to changes in the external environment is important for achieving autonomous functional behavior [5]. Among the wide variety of previously demonstrated micro-/nanoscale morphologies [6, 7], the highly scalable nature of fiber production has made polymeric fibers capable of dynamic shape change popular for the creation of artificial muscles, biosensors, and wearable devices [8, 9]. The implementation of a shape-memory effect has enabled one-way programmable shape change without the presence of a solvent, and the exertion of stresses in the order of megapascals
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