TY - JOUR A1 - Liu, Yue A1 - Gould, Oliver E. C. A1 - Rudolph, Tobias A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Polymeric microcuboids programmable for temperature-memory JF - Macromolecular materials and engineering N2 - Microobjects with programmable mechanical functionality are highly desirable for the creation of flexible electronics, sensors, and microfluidic systems, where fabrication/programming and quantification methods are required to fully control and implement dynamic physical behavior. Here, programmable microcuboids with defined geometries are prepared by a template-based method from crosslinked poly[ethylene-co-(vinyl acetate)] elastomers. These microobjects could be programmed to exhibit a temperature-memory effect or a shape-memory polymer actuation capability. Switching temperaturesT(sw)during shape recovery of 55 +/- 2, 68 +/- 2, 80 +/- 2, and 86 +/- 2 degrees C are achieved by tuning programming temperatures to 55, 70, 85, and 100 degrees C, respectively. Actuation is achieved with a reversible strain of 2.9 +/- 0.2% to 6.7 +/- 0.1%, whereby greater compression ratios and higher separation temperatures induce a more pronounced actuation. Micro-geometry change is quantified using optical microscopy and atomic force microscopy. The realization and quantification of microparticles, capable of a tunable temperature responsive shape-change or reversible actuation, represent a key development in the creation of soft microscale devices for drug delivery or microrobotics. KW - actuation KW - atomic force microscopy KW - biomaterials KW - microparticles KW - shape-memory polymers Y1 - 2020 U6 - https://doi.org/10.1002/mame.202000333 SN - 1438-7492 SN - 1439-2054 VL - 305 IS - 10 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Liu, Yue A1 - Razzaq, Muhammad Yasar A1 - Rudolph, Tobias A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Two-Level Shape Changes of Polymeric Microcuboids Prepared from Crystallizable Copolymer Networks JF - Macromolecules : a publication of the American Chemical Society N2 - 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 mu m and a height of 10 mu m 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,R-micro), while at the. nanolevel, the recovery ratio of the nanoroughness (R-r,R-nano) was measured. The values of R-r,R-micro,,micro could be tailored in a range from 42 +/- 1% to 102 +/- 1% and Rr,nano from 89 +/- 6% to 136 +/- 21% depending on the applied compression ratio and the amount of vinyl acetate content in the cPEVA microcuboids. Y1 - 2017 U6 - https://doi.org/10.1021/acs.macromol.6b02237 SN - 0024-9297 SN - 1520-5835 VL - 50 SP - 2518 EP - 2527 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yan, Wan A1 - Fang, Liang A1 - Nöchel, Ulrich A1 - Gould, Oliver E. C. A1 - Behl, Marc A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Investigating the roles of crystallizable and glassy switching segments within multiblock copolymer shape-memory materials JF - MRS Advances N2 - The variation of the molecular architecture of multiblock copolymers has enabled the introduction of functional behaviour and the control of key mechanical properties. In the current study, we explore the synergistic relationship of two structural components in a shape-memory material formed of a multiblock copolymer with crystallizable poly(epsilon-caprolactone) and crystallizable polyfoligo(3S-iso-butylmorpholine-2,5-dione) segments (PCL-PIBMD). The thermal and structural properties of PCL-PIBMD films were compared with PCI.-PU and PMMD-PU investigated by means of DSC, SAXS and WARS measurements. The shape-memory properties were quantified by cyclic, thermomechanical tensile tests, where deformation strains up to 900% were applied for programming PCL-PIBMD films at 50 degrees C. Toluene vapor treatment experiments demonstrated that the temporary shape was fixed mainly by glassy PIBMD domains at strains lower than 600% with the PCL contribution to fixation increasing to 42 +/- 2% at programming strains of 900% This study into the shape-memory mechanism of PCL-PIBMD provides insight into the structure function relation in multiblock copolymers with both crystallizable and glassy switching segments. Y1 - 2018 U6 - https://doi.org/10.1557/adv.2018.590 SN - 2059-8521 VL - 3 IS - 63 SP - 3741 EP - 3749 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Krüger-Genge, Anne A1 - Dietze, Stefanie A1 - Yan, Wan A1 - Liu, Yue A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas A1 - Jung, Friedrich T1 - Endothelial cell migration, adhesion and proliferation on different polymeric substrates JF - Clinical hemorheology and microcirculation : blood flow and vessels N2 - BACKGROUND: The formation of a functionally-confluent endothelial cell (EC) monolayer affords proliferation of EC, which only happens in case of appropriate migratory activity. AIM OF THE STUDY: The migratory pathway of human umbilical endothelial cells (HUVEC) was investigated on different polymeric substrates. MATERIAL AND METHODS: Surface characterization of the polymers was performed by contact angle measurements and atomic force microscopy under wet conditions. 30,000 HUVEC per well were seeded on polytetrafluoroethylene (PTFE) (theta(adv) = 119 degrees +/- 2 degrees), on low-attachment plate LAP (theta(adv) = 28 degrees +/- 2 degrees) and on polystyrene based tissue culture plates (TCP, theta(adv) = 22 degrees +/- 1 degrees). HUVEC tracks (trajectories) were recorded by time lapse microscopy and the euclidean distance (straight line between starting and end point), the total distance and the velocities of HUVEC not leaving the vision field were determined. RESULTS: On PTFE, 42 HUVEC were in the vision field directly after seeding. The mean length of single migration steps (SML) was 6.1 +/- 5.2 mu m, the mean velocity (MV) 0.40 +/- 0.3 mu m.min(-1) and the complete length of the trajectory (LT) was 710 +/- 440 mu m. On TCP 82 HUVEC were in the vision field subsequent to seeding. The LT was 840 +/- 550 mu m, the SML 6.1 +/- 5.2 mu m and the MV 0.44 +/- 0.3 mu m.min(-1). The trajectories on LAP differed significantly in respect to SML (2.4 +/- 3.9 mu m, p <0.05), the MV (0.16 +/- 0.3 mu m.min(-1), p <0.05) and the LT (410 +/- 300 mu m, p <0.05), compared to PTFE and TCP. Solely on TCP a nearly confluent EC monolayer developed after three days. While on TCP diffuse signals of vinculin were found over the whole basal cell surface organizing the binding of the cells by focal adhesions, on PTFE vinculin was merely arranged at the cell rims, and on the hydrophilic material (LAP) no focal adhesions were found. CONCLUSION: The study revealed that the wettability of polymers affected not only the initial adherence but also the migration of EC, which is of importance for the proliferation and ultimately the endothelialization of polymer-based biomaterials. KW - Endothelial cells KW - migration KW - polymer-based biomaterials KW - cytokine release Y1 - 2019 U6 - https://doi.org/10.3233/CH-189317 SN - 1386-0291 SN - 1875-8622 VL - 70 IS - 4 SP - 511 EP - 529 PB - IOS Press CY - Amsterdam ER - TY - JOUR A1 - Fang, Liang A1 - Gould, Oliver E. C. A1 - Lysyakova, Liudmila A1 - Jiang, Yi A1 - Sauter, Tilman A1 - Frank, Oliver A1 - Becker, Tino A1 - Schossig, Michael A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Implementing and quantifying the shape-memory effect of single polymeric micro/nanowires with an atomic force microscope JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - The implementation of shape-memory effects (SME) in polymeric micro- or nano-objects currently relies on the application of indirect macroscopic manipulation techniques, for example, stretchable molds or phantoms, to ensembles of small objects. Here, we introduce a method capable of the controlled manipulation and SME quantification of individual micro- and nano-objects in analogy to macroscopic thermomechanical test procedures. An atomic force microscope was utilized to address individual electro-spun poly(ether urethane) (PEU) micro- or nanowires freely suspended between two micropillars on a micro-structured silicon substrate. In this way, programming strains of 10 +/- 1% or 21 +/- 1% were realized, which could be successfully fixed. An almost complete restoration of the original free-suspended shape during heating confirmed the excellent shape-memory performance of the PEU wires. Apparent recovery stresses of sigma(max,app)=1.2 +/- 0.1 and 33.3 +/- 0.1MPa were obtained for a single microwire and nanowire, respectively. The universal AFM test platform described here enables the implementation and quantification of a thermomechanically induced function for individual polymeric micro- and nanosystems. KW - cyclic thermomechanical testing KW - atomic force microscopy KW - soft matter micro- and nanowires KW - shape-memory effect KW - materials science Y1 - 2018 U6 - https://doi.org/10.1002/cphc.201701362 SN - 1439-4235 SN - 1439-7641 VL - 19 IS - 16 SP - 2078 EP - 2084 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Jiang, Yi A1 - Mansfeld, Ulrich A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Temperature-induced evolution of microstructures on poly[ethylene-co-(vinyl acetate)] substrates switches their underwater wettability JF - Materials & design N2 - Material surfaces with tailored aerophobicity are crucial for applications where gas bubble wettability has to be controlled, e.g., gas storage and transport, electrodes, bioreactors or medical devices. Here, we present switchable underwater aerophobicity of hydrophobic polymeric substrates, which respond to heat with multilevel micro-and nanotopographical changes. The cross-linked poly[ethylene-co-(vinyl acetate)] substrates possess arrays of microcylinders with a nanorough top surface. It is hypothesized that the specific micro-/nanotopography of the surface allows trapping of a water film at the micro interspace and in this way generates the aerophobic behavior. The structured substrates were programmed to a temporarily stable, nanoscale flat substrate showing aerophilic behavior. Upon heating, the topographical changes caused a switch in contact angle from aerophilic to aerophobic for approaching air bubbles. In this way, the initial adhesion of air bubbles to the programmed flat substrate could be turned into repellence for the recovered substrate surface. The temperature at which the repellence of air bubbles starts can be adjusted from 58 +/- 3 degrees C to 73 +/- 3 degrees C by varying the deformation temperature applied during the temperature-memory programming procedure. The presented actively switching polymeric substrates are attractive candidates for applications, where an on-demand gas bubble repellence is advantageous. (c) 2018 Helmholtz-Zentrum Geesthacht, Zentrum fur Material- und Kustenforschung. Published by Elsevier Ltd. KW - Aerophobicity KW - Temperature-memory effect KW - Switchable wettability KW - Air bubble repellence KW - Thermo-responsive polymer Y1 - 2018 U6 - https://doi.org/10.1016/j.matdes.2018.12.002 SN - 0264-1275 SN - 1873-4197 VL - 163 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Yan, Wan A1 - Fang, Liang A1 - Weigel, Thomas A1 - Behl, Marc A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - The influence of thermal treatment on the morphology in differently prepared films of a oligodepsipeptide based multiblock copolymer JF - Polymers for advanced technologies N2 - Degradable multiblock copolymers prepared from equal weight amounts of poly(epsilon-caprolactone)-diol (PCL-diol) and poly[oligo(3S-iso-butylmorpholine-2,5-dione)]-diol (PIBMD-diol), named PCL-PIBMD, provide a phase-segregated morphology. It exhibits a low melting temperature from PCL domains (T-m,T-PCL) of 382 degrees C and a high T-m,T-PIBMD of 170 +/- 2 degrees C with a glass transition temperature (T-g,T-PIBMD) at 42 +/- 2 degrees C from PIBMD domains. In this study, we explored the influence of applying different thermal treatments on the resulting morphologies of solution-cast and spin-coated PCL-PIBMD thin films, which showed different initial surface morphologies. Differential scanning calorimetry results and atomic force microscopy images after different thermal treatments indicated that PCL and PIBMD domains showed similar crystallization behaviors in 270 +/- 30 mu m thick solution-cast films as well as in 30 +/- 2 and 8 +/- 1nm thick spin-coated PCL-PIBMD films. Existing PIBMD crystalline domains highly restricted the generation of PCL crystalline domains during cooling when the sample was annealed at 180 degrees C. By annealing the sample above 120 degrees C, the PIBMD domains crystallized sufficiently and covered the free surface, which restricted the crystallization of PCL domains during cooling. The PCL domains can crystallize by hindering the crystallization of PIBMD domains via the fast vitrification of PIBMD domains when the sample was cooled/quenched in liquid nitrogen after annealing at 180 degrees C. These findings contribute to a better fundamental understanding of the crystallization mechanism of multi-block copolymers containing two crystallizable domains whereby the T-g of the higher melting domain type is in the same temperature range as the T-m of the lower melting domain type. Copyright (c) 2016 John Wiley & Sons, Ltd. KW - multiblock copolymer KW - oligodepsipeptides KW - phase morphology KW - thermal treatments KW - crystallization behavior Y1 - 2017 U6 - https://doi.org/10.1002/pat.3953 SN - 1042-7147 SN - 1099-1581 VL - 28 SP - 1339 EP - 1345 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Yan, Wan A1 - Fang, Liang A1 - Nöchel, Ulrich A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Influence of programming strain rates on the shape-memory performance of semicrystalline multiblock copolymers JF - Journal of polymer science : B, Polymer physics N2 - Multiblock copolymers named PCL-PIBMD consisting of crystallizable poly(epsilon-caprolactone) segments and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape-memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL-PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL-PIBMD. Programming was conducted at 50 degrees C by elongation to epsilon(m)=50% with strain rates of 1 or 10 or 50 mmmin(-1). The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X-ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain-induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape-memory polymers with designed recovery forces. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1935-1943 KW - atomic force microscopy (AFM) KW - crystal structures KW - crystallization KW - multiblock copolymer KW - stimuli-sensitive polymers KW - SAXS KW - shape-memory effect KW - WAXS KW - X-ray scattering Y1 - 2016 U6 - https://doi.org/10.1002/polb.24097 SN - 0887-6266 SN - 1099-0488 VL - 54 SP - 1935 EP - 1943 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Fang, Liang A1 - Yan, Wan A1 - Nöchel, Ulrich A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Programming structural functions in phase-segregated polymers by implementing a defined thermomechanical history JF - Polymer : the international journal for the science and technology of polymers N2 - Unwanted shrinkage behaviors or failure in structural functions such as mechanical strength or deformability of polymeric products related to their thermomechanical history are a major challenge in production of plastics. Here, we address the question whether we can turn this challenge into an opportunity by creating defined thermomechanical histories in polymers, represented by a specific morphology and nanostructure, to equip polymeric shaped bodies with desired functions, e.g. a temperature-memory, by hot, warm or cold deformation into multiblock copolymers having two partially overlapping melting transitions. A copolyesterurethane named PDLCL, consisting of poly(epsilon-caprolactone) (PCL) and poly(omega-pentadecalactone) (PPDL) crystalline domains, exhibiting a pronounced phase-segregated morphology and partially overlapping melting transitions was selected for this study. Different types of PCL and PPDL crystals as well as distinct degrees of orientation in both amorphous and crystalline domains were obtained after deformation at 20 or 40 degrees C and to a lower extent at 60 degrees C. The generated non-isotropic structures were stable at ambient temperature and represent the different stresses stored. Stress-free heating experiments showed that the relaxation in both amorphous and crystalline phases occurred predominantly with melting of PCL crystals. When the switching temperature, which was similar to the applied deformation temperature (temperature-memory), was exceeded in stress-free heating experiments, the implemented thermomechanical history could be reversed. In contrast, during constant-strain heating to 60 degrees C the generated structural features remained almost unchanged. These findings provide insights about the structure function relation in multiblock copolymers with two crystalline phases exhibiting a temperature-memory effect by implementation of specific thermomechanical histories, which might be a general principle for tailoring other functions like mechanical strength or deformability in polymers. (C) 2016 Elsevier Ltd. All rights reserved. KW - Temperature-memory effect KW - Phase morphology KW - Thermomechanical history Y1 - 2016 U6 - https://doi.org/10.1016/j.polymer.2016.08.105 SN - 0032-3861 SN - 1873-2291 VL - 102 SP - 54 EP - 62 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Zhang, Quanchao A1 - Sauter, Tilman A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Shape-Memory Capability of Copolyetheresterurethane Microparticles Prepared via Electrospraying JF - Macromolecular materials and engineering N2 - Multifunctional thermo-responsive and degradable microparticles exhibiting a shapememory effect (SME) have attracted widespread interest in biomedicine as switchable delivery vehicles or microactuators. In this work almost spherical solid microparticles with an average diameter of 3.9 +/- 0.9 mm are prepared via electrospraying of a copolyetheresterurethane named PDC, which is composed of crystallizable oligo(p-dioxanone) (OPDO) hard and oligo(e-caprolactone) (OCL) switching segments. The PDC microparticles are programmed via compression at different pressures and their shapememory capability is explored by off-line and online heating experiments. When a low programming pressure of 0.2 MPa is applied a pronounced thermally-induced shape-memory effect is achieved with a shape recovery ratio about 80%, while a high programming pressure of 100 MPa resulted in a weak shape-memory performance. Finally, it is demonstrated that an array of PDC microparticles deposited on a polypropylene (PP) substrate can be successfully programmed into a smart temporary film, which disintegrates upon heating to 60 degrees C. KW - biomaterials KW - microparticles KW - processing KW - stimuli-sensitive polymers KW - shape-memory effect Y1 - 2015 U6 - https://doi.org/10.1002/mame.201400267 SN - 1438-7492 SN - 1439-2054 VL - 300 IS - 5 SP - 522 EP - 530 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yan, Wan A1 - Fang, Liang A1 - Nöchel, Ulrich A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Influence of deformation temperature on structural variation and shape-memory effect of a thermoplastic semi-crystalline multiblock copolymer JF - eXPRESS polymer letters N2 - A multiblock copolymer termed as PCL-PIBMD, consisting of crystallizable poly(epsilon-caprolactone) (PCL) segments and crystallizable poly(3S-isobutyl-morpholine-2,5-dione) (PIBMD) segments, has been reported as a material showing a thermally-induced shape-memory effect. While PIBMD crystalline domains act as netpoints to determine the permanent shape, both PCL crystalline domains and PIBMD amorphous domains, which have similar transition temperatures (T-trans) can act as switching domains. In this work, the influence of the deformation temperature (T-deform = 50 or 20 degrees C), which was above or below T-trans, on the structural changes of PCL-PIBMD during uniaxial deformation and the shapememory properties were investigated. Furthermore, the relative contribution of crystalline PCL and PIBMD amorphous phases to the fixation of the temporary shape were distinguished by a toluene vapor treatment approach. The results indicated that at 50 degrees C, both PCL and PIBMD amorphous phases can be orientated during deformation, resulting in thermally-induced crystals of PCL domains and joint contribution to the switching domains. In contrast at 20 degrees C, the temporary shape was mainly fixed by PCL crystals generated via strain-induced crystallization. KW - biodegradable polymers KW - shape-memory polymer KW - multiblock copolymer KW - polydepsipeptide Y1 - 2015 U6 - https://doi.org/10.3144/expresspolymlett.2015.58 SN - 1788-618X VL - 9 IS - 7 SP - 624 EP - 635 PB - Budapest University of Technology and Economics, Department of Polymer Engineering CY - Budapest ER - TY - JOUR A1 - Wang, Li A1 - Heuchel, Matthias A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Influence of a polyester coating of magnetic nanoparticles on magnetic heating behavior of shape-memory polymer-based composites JF - Journal of applied biomaterials & functional materials N2 - Background: Magnetic composites of thermosensitive shape-memory polymers (SMPs) and magnetite nanoparticles (MNPs) allow noncontact actuation of the shape-memory effect in an alternating magnetic field. In this study, we investigated whether the magnetic heating capability of cross-linked poly(epsilon-caprolactone)/MNP composites (cPCLC) could be improved by covalent coating of MNPs with oligo(epsilon-caprolactone) (OCL). Methods: Two different types of cPCLC containing uncoated and OCL-coated MNP with identical magnetite weight content were prepared by thermally induced polymerization of poly(epsilon-caprolactone) diisocyanatoethyl methacrylate. Both cPCLCs exhibited a melting transition at T-m = 48 degrees C, which could be used as switching transition. Results: The dispersion of the embedded nanoparticles within the polymer matrix could be substantially improved, when the OCL-coated MNPs were used, as visualized by scanning electron microscopy. We could further demonstrate that in this way the maximal achievable bulk temperature (T-bulk) obtained within the cPCLC test specimen in magnetic heating experiments at a magnetic field strength of H = 30 kA.m(-1) could be increased from T bulk = 48 degrees C to T bulk = 74 degrees C. KW - Magnetic composites KW - Magnetite nanoparticles KW - Polymer networks KW - Shape-memory effect Y1 - 2012 U6 - https://doi.org/10.5301/JABFM.2012.10293 SN - 2280-8000 VL - 10 IS - 3 SP - 203 EP - 209 PB - Wichtig CY - Milano ER -