TY  - JOUR
A1  - Sauter, Tilman
A1  - Kratz, Karl
A1  - Heuchel, Matthias
A1  - Lendlein, Andreas
T1  - Fiber diameter as design parameter for tailoring the macroscopic shape-memory performance of electrospun meshes
JF  - Materials and design
N2  - Fibrous shape-memory polymer (SMP) scaffolds were investigated considering the fiber as basic microstructural feature. By reduction of the fiber diameter in randomly oriented electrospun polyetherurethane (PEU) meshes from the micro-to the nano-scale, we observed changes in the molecular orientation within the fibers and its impact on the structural and shape-memory performance. It was assumed that a spatial restriction by reduction of the fiber diameter increases molecular orientation along the orientation of the fiber. The stress-strain relation of random PEU scaffolds is initially determined by the 3D arrangement of the fibers and thus is independent of the molecular orientation. Increasing the molecular orientation with decreasing single fiber diameter in scaffolds composed of randomly arranged fibers did not alter the initial stiffness and peak stress but strongly influenced the elongation at break and the stress increase above the Yield point. Reduction of the single fiber diameter also distinctly improved the shape-memory performance of the scaffolds. Fibers with nanoscale diameters (< 100 nm) possessed an almost complete shape recovery, high recovery stresses and fast relaxation kinetics, while the shape fixity was found to decrease with decreasing fiber diameter. Hence, the fiber diameter is a relevant design parameter for SMP.
KW  - Nanofiber
KW  - Shape-memory polymer
KW  - Electrospinning
KW  - Function by design
KW  - Molecular orientation
Y1  - 2021
U6  - https://doi.org/10.1016/j.matdes.2021.109546
SN  - 1873-4197
VL  - 202
PB  - Elsevier
CY  - Amsterdam [u.a.]
ER  - 
TY  - JOUR
A1  - Farhan, Muhammad
A1  - Behl, Marc
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Origami hand for soft robotics driven by thermally controlled polymeric fiber actuators
JF  - MRS communications / a publication of the Materials Research Society
N2  - Active fibers can serve as artificial muscles in robotics or components of smart textiles. Here, we present an origami hand robot, where single fibers control the reversible movement of the fingers. A recovery/contracting force of 0.2 N with a work capacity of 0.175 kJ kg(-1) was observed in crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) fibers, which could enable the bending movement of the fingers by contraction upon heating. The reversible opening of the fingers was attributed to a combination of elastic recovery force of the origami structure and crystallization-induced elongation of the fibers upon cooling.
KW  - Robotics
KW  - Polymer
KW  - Fiber
KW  - Actuation
KW  - Shape-memory
Y1  - 2021
U6  - https://doi.org/10.1557/s43579-021-00058-4
SN  - 2159-6859
SN  - 2159-6867
VL  - 11
IS  - 4
SP  - 476
EP  - 482
PB  - Springer
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Izraylit, Victor
A1  - Heuchel, Matthias
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Non-woven shape-memory polymer blend actuators
JF  - MRS advances : a journal of the Materials Research Society (MRS)
N2  - The hierarchical design approach provides various opportunities to adjust the structural performance of polymer materials. Electrospinning processing techniques give access to molecular orientation as a design parameter, which we consider here in view of the shape-memory actuation performance. The aim of this work is to investigate how the reversible strain epsilon'(rev) can be affected by a morphology change from a bulk material to an electrospun mesh. epsilon'(rev) could be increased from 5.5 +/- 0.5% to 15 +/- 1.8% for a blend from a multiblock copolymer with poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA) segments with oligo(D-lactide) (ODLA). This study demonstrates an effective design approach for enhancing soft actuator performance, which can be broadly applied in soft robotics and medicine.
Y1  - 2021
U6  - https://doi.org/10.1557/s43580-021-00063-8
SN  - 2059-8521
VL  - 6
IS  - 33
SP  - 781
EP  - 785
PB  - Springer Nature Switzerland AG
CY  - Cham
ER  -