TY  - JOUR
A1  - Zhang, Quanchao
A1  - Rudolph, Tobias
A1  - Benitez, Alejandro J.
A1  - Gould, Oliver E. C.
A1  - Behl, Marc
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Temperature-controlled reversible pore size change of electrospun fibrous shape-memory polymer actuator based meshes
JF  - Smart materials and structures
N2  - Fibrous membranes capable of dynamically responding to external stimuli are highly desirable in textiles and biomedical materials, where adaptive behavior is required to accommodate complex environmental changes. For example, the creation of fabrics with temperature-dependent moisture permeability or self-regulating membranes for air filtration is dependent on the development of materials that exhibit a reversible stimuli-responsive pore size change. Here, by imbuing covalently crosslinked poly(ε-caprolactone) (cPCL) fibrous meshes with a reversible bidirectional shape-memory polymer actuation (rbSMPA) we create a material capable of temperature-controlled changes in porosity. Cyclic thermomechanical testing was used to characterize the mechanical properties of the meshes, which were composed of randomly arranged microfibers with diameters of 2.3 ± 0.6 μm giving an average pore size of approx. 10 μm. When subjected to programming strains of εm = 300% and 100% reversible strain changes of εʹrev = 22% ± 1% and 6% ± 1% were measured, with switching temperature ranges of 10 °C–30 °C and 45 °C–60 °C for heating and cooling, respectively. The rbSMPA of cPCL fibrous meshes generated a microscale reversible pore size change of 11% ± 3% (an average of 1.5 ± 0.6 μm), as measured by scanning electron microscopy. The incorporation of a two-way shape-memory actuation capability into fibrous meshes is anticipated to advance the development and application of smart membrane materials, creating commercially viable textiles and devices with enhanced performance and novel functionality.
KW  - reversible shape-memory effect
KW  - fiber meshes
KW  - electrospinning
Y1  - 2019
U6  - https://doi.org/10.1088/1361-665X/ab10a1
SN  - 0964-1726
SN  - 1361-665X
VL  - 28
IS  - 5
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Zhang, Pengfei
A1  - Behl, Marc
A1  - Peng, Xingzhou
A1  - Balk, Maria
A1  - Lendlein, Andreas
T1  - Chemoresponsive Shape-Memory Effect of Rhodium-Phosphine Coordination Polymer Networks
JF  - Chemistry of materials : a publication of the American Chemical Society
N2  - Chemoresponsive polymers are of technological significance for smart sensors or systems capable of molecular recognition. An important key requirement for these applications is the material’s structural integrity after stimulation. We explored whether covalently cross-linked metal ion–phosphine coordination polymers (MPN) can be shaped into any temporary shape and are capable of recovering from this upon chemoresponsive exposure to triphenylphosphine (Ph3P) ligands, whereas the MPN provide structural integrity. Depending on the metal-ion concentration used during synthesis of the MPN, the degree of swelling of the coordination polymer networks could be adjusted. Once the MPN was immersed into Ph3P solution, the reversible ligand-exchange reaction between the metal ions and the free Ph3P in solution causes a decrease of the coordination cross-link density in MPN again. The Ph3P-treated MPN was able to maintain its original shape, indicating a certain stability of shape even after stimulation. In this way, chemoresponsive control of the elastic properties (increase in volume and decrease of mechanical strength) of the MPN was demonstrated. This remarkable behavior motivated us to explore whether the MPN are capable of a chemoresponsive shape-memory effect. In initial experiments, shape fixity of around 60% and shape recovery of almost 90% were achieved when the MPN was exposed to Ph3P in case of rhodium. Potential applications for chemoresponsive shape-memory systems could be shapable semiconductors, e.g., for lighting or catalysts, which provide catalytic activity on demand.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.chemmater.9b00363
SN  - 0897-4756
SN  - 1520-5002
VL  - 31
IS  - 15
SP  - 5402
EP  - 5407
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Yuan, Jinkai
A1  - Neri, Wilfrid
A1  - Zakri, Cecile
A1  - Merzeau, Pascal
A1  - Kratz, Karl
A1  - Lendlein, Andreas
A1  - Poulin, Philippe
T1  - Shape memory nanocomposite fibers for untethered high-energy microengines
JF  - Science
N2  - Classic rotating engines are powerful and broadly used but are of complex design and difficult to miniaturize. It has long remained challenging to make large-stroke, high-speed, high-energy microengines that are simple and robust. We show that torsionally stiffened shape memory nanocomposite fibers can be transformed upon insertion of twist to store and provide fast and high-energy rotations. The twisted shape memory nanocomposite fibers combine high torque with large angles of rotation, delivering a gravimetric work capacity that is 60 times higher than that of natural skeletal muscles. The temperature that triggers fiber rotation can be tuned. This temperature memory effect provides an additional advantage over conventional engines by allowing for the tunability of the operation temperature and a stepwise release of stored energy.
Y1  - 2019
U6  - https://doi.org/10.1126/science.aaw3722
SN  - 0036-8075
SN  - 1095-9203
VL  - 365
IS  - 6449
SP  - 155
EP  - 158
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Weiwei
A1  - Xu, Xun
A1  - Li, Zhengdong
A1  - Kratz, Karl
A1  - Ma, Nan
A1  - Lendlein, Andreas
T1  - Modulating human mesenchymal stem cells using poly(n-butyl acrylate) networks in vitro with elasticity matching human arteries
JF  - Clinical hemorheology and microcirculation : blood flow and vessels
N2  - Non-swelling hydrophobic poly(n-butyl acrylate) network (cPnBA) is a candidate material for synthetic vascular grafts owing to its low toxicity and tailorable mechanical properties. Mesenchymal stem cells (MSCs) are an attractive cell type for accelerating endothelialization because of their superior anti-thrombosis and immune modulatory function. Further, they can differentiate into smooth muscle cells or endothelial-like cells and secret pro-angiogenic factors such as vascular endothelial growth factor (VEGF). MSCs are sensitive to the substrate mechanical properties, with the alteration of their major cellular behavior and functions as a response to substrate elasticity. Here, we cultured human adipose-derived mesenchymal stem cells (hADSCs) on cPnBAs with different mechanical properties (cPnBA250, Young’s modulus (E) = 250 kPa; cPnBA1100, E = 1100 kPa) matching the elasticity of native arteries, and investigated their cellular response to the materials including cell attachment, proliferation, viability, apoptosis, senescence and secretion. The cPnBA allowed high cell attachment and showed negligible cytotoxicity. F-actin assembly of hADSCs decreased on cPnBA films compared to classical tissue culture plate. The difference of cPnBA elasticity did not show dramatic effects on cell attachment, morphology, cytoskeleton assembly, apoptosis and senescence. Cells on cPnBA250, with lower proliferation rate, had significantly higher VEGF secretion activity. These results demonstrated that tuning polymer elasticity to regulate human stem cells might be a potential strategy for constructing stem cell-based artificial blood vessels.
KW  - Poly(n-butyl acrylate)
KW  - mechanical property
KW  - vascular graft
KW  - mesenchymal stem cells
KW  - VEGF
Y1  - 2019
U6  - https://doi.org/10.3233/CH-189418
SN  - 1386-0291
SN  - 1875-8622
VL  - 71
IS  - 2
SP  - 277
EP  - 289
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Tarazona, Natalia A.
A1  - Machatschek, Rainhard Gabriel
A1  - Schulz, Burkhard
A1  - Auxiliadora Prieto Jiménez, M.
A1  - Lendlein, Andreas
T1  - Molecular Insights into the Physical Adsorption of Amphiphilic Protein PhaF onto Copolyester Surfaces
JF  - Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences
N2  - Phasins are amphiphilic proteins located at the polymer-cytoplasm interface of bacterial polyhydroxyalkanoates (PHA). The immobilization of phasins on biomaterial surfaces is a promising way to enhance the hydrophilicity and supply cell- directing elements in bioinstructing processes. Optimizing the physical adsorption of phasins requires deep insights into molecular processes during polymer-protein interactions to preserve their structural conformation while optimizing surface coverage. Here, the assembly, organization, and stability of phasin PhaF from Pseudomonas putida at interfaces is disclosed. The Langmuir technique, combined with in situ microscopy and spectroscopic methods, revealed that PhaF forms stable and robust monolayers at different temperatures, with an almost flat orientation of its alpha-helix at the air-water interface. PhaF adsorption onto preformed monolayers of poly[(3-R-hydroxyoctanoate)-co-(3-R-hydroxyhexanoate)] (PHOHHx), yields stable mixed layers below pi = similar to 15.7 mN/m. Further insertion induces a molecular reorganization. PHOHHx with strong surface hydrophobicity is a more adequate substrate for PhaF adsorption than the less hydrophobic poly[(rac-lactide)-co-glycolide] (PLGA). The observed orientation of the main axis of the protein in relation to copolyester interfaces ensures the best exposure of the hydrophobic residues, providing a suitable coating strategy for polymer functionalization.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.biomac.9b00069
SN  - 1525-7797
SN  - 1526-4602
VL  - 20
IS  - 9
SP  - 3242
EP  - 3252
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Tarazona, Natalia A.
A1  - Machatschek, Rainhard Gabriel
A1  - Lendlein, Andreas
T1  - Unraveling the interplay between abiotic hydrolytic degradation and crystallization of bacterial polyesters comprising short and medium side-chain-length Polyhydroxyalkanoates
JF  - Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences
N2  - Polyhydroxyalkanoates (PHAs) have attracted attention as degradable (co)polyesters which can be produced by microorganisms with variations in the side chain. This structural variation influences not only the thermomechanical properties of the material but also its degradation behavior. Here, we used Langmuir monolayers at the air-water (A-W) interface as suitable models for evaluating the abiotic degradation of two PHAs with different side-chain lengths and crystallinity. By controlling the polymer state (semi crystalline, amorphous), the packing density, the pH, and the degradation mechanism, we could draw several significant conclusions. (i) The maximum degree of crystallinity for a PHA film to be efficiently degraded up to pH = 12.3 is 40%. (ii) PHA made of repeating units with shorter side-chain length are more easily hydrolyzed under alkaline conditions. The efficiency of alkaline hydrolysis decreased by about 65% when the polymer was 40% crystalline. (iii) In PHA films with a relatively high initial crystallinity, abiotic degradation initiated a chemicrystallization phenomenon, detected as an increase in the storage modulus (E'). This could translate into an increase in brittleness and reduction in the material degradability. Finally, we demonstrate the stability of the measurement system for long-term experiments, which allows degradation conditions for polymers that could closely simulate real-time degradation.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.biomac.9b01458
SN  - 1525-7797
SN  - 1526-4602
VL  - 21
IS  - 2
SP  - 761
EP  - 771
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Saretia, Shivam
A1  - Machatschek, Rainhard Gabriel
A1  - Schulz, Burkhard
A1  - Lendlein, Andreas
T1  - Reversible 2D networks of oligo(epsilon-caprolactone) at the air-water interface
JF  - Biomedical Materials
N2  - Hydroxyl terminated oligo(epsilon-caprolactone) (OCL) monolayers were reversibly cross-linked forming two dimensional networks (2D) at the air-water interface. The equilibrium reaction with glyoxal as the cross-linker is pH-sensitive. Pronounced contraction in the area of the prepared 2DOCL films in dependence of surface pressure and time revealed the process of the reaction. Cross-linking inhibited crystallization and retarded enzymatic degradation of the OCLfilm. Altering the subphase pH led to a cleavage of the covalent acetal cross-links. The reversibility of the covalent acetal cross-links was proved by observing an identical isotherm as non-cross-linked sample. Besides as model systems, these customizable reversible OCL2D networks are intended for use as pHresponsive drug delivery systems or functionalized cell culture substrates.
KW  - poly(epsilon-caprolactone)
KW  - langmuir monolayer
KW  - two dimensional network
KW  - crystallization
KW  - cross-linking
Y1  - 2019
U6  - https://doi.org/10.1088/1748-605X/ab0cef
SN  - 1748-6041
SN  - 1748-605X
VL  - 14
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Reinthaler, Markus
A1  - Johansson, Johan Backemo
A1  - Braune, Steffen
A1  - Al-Hindwan, Haitham Saleh Ali
A1  - Lendlein, Andreas
A1  - Jung, Friedrich
T1  - Shear-induced platelet adherence and activation in an in-vitro dynamic multiwell-plate system
JF  - Clinical hemorheology and microcirculation : blood flow and vessels
N2  - Circulating blood cells are prone to varying flow conditions when contacting cardiovascular devices. For a profound understanding of the complex interplay between the blood components/cells and cardiovascular implant surfaces, testing under varying shear conditions is required. Here, we study the influence of arterial and venous shear conditions on the in vitro evaluation of the thrombogenicity of polymer-based implant materials. Medical grade poly(dimethyl siloxane) (PDMS), polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE) films were included as reference materials. The polymers were exposed to whole blood from healthy humans. Blood was agitated orbitally at low (venous shear stress: 2.8 dyne. cm(-2)) and high (arterial shear stress: 22.2 dyne .cm(-2)) agitation speeds in a well-plate based test system. Numbers of non-adherent platelets, platelet activation (P-Selectin positive platelets), platelet function (PFA100 closure times) and platelet adhesion (laser scanning microscopy (LSM)) were determined. Microscopic data and counting of the circulating cells revealed increasing numbers of material-surface adherent platelets with increasing agitation speed. Also, activation of the platelets was substantially increased when tested under the high shear conditions (P-Selectin levels, PFA-100 closure times). At low agitation speed, the platelet densities did not differ between the three materials. Tested at the high agitation speed, lowest platelet densities were observed on PDMS, intermediate levels on PET and highest on PTFE. While activation of the circulating platelets was affected by the implant surfaces in a similar manner, PFA closure times did not reflect this trend. Differences in the thrombogenicity of the studied polymers were more pronounced when tested at high agitation speed due to the induced shear stresses. Testing under varying shear stresses, thus, led to a different evaluation of the implant thrombogenicity, which emphasizes the need for testing under various flow conditions. Our data further confirmed earlier findings where the same reference implants were tested under static (and not dynamic) conditions and with fresh human platelet rich plasma instead of whole blood. This supports that the application of common reference materials may improve inter-study comparisons, even under varying test conditions.
Y1  - 2019
U6  - https://doi.org/10.3233/CH-189410
SN  - 1386-0291
SN  - 1875-8622
VL  - 71
IS  - 2
SP  - 183
EP  - 191
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Razzaq, Muhammad Yasar
A1  - Behl, Marc
A1  - Lendlein, Andreas
T1  - Magneto-Mechanical Actuators with Reversible Stretching and Torsional Actuation Capabilities
JF  - MRS Advances
N2  - Composite actuators consisting of magnetic nanoparticles dispersed in a crystallizable multiphase polymer system can be remotely controlled by alternating magnetic fields (AMF). These actuators contain spatially segregated crystalline domains with chemically different compositions. Here, the crystalline domain associated to low melting transition range is responsible for actuation while the crystalline domain associated to the higher melting transition range determines the geometry of the shape change. This paper reports magnetomechanical actuators which are based on a single crystalline domain of oligo(omega-pentadecalactone) (OPDL) along with covalently integrated iron(III) oxide nanoparticles (ioNPs). Different geometrical modes of actuation such as a reversible change in length or twisting were implemented by a magneto-mechanical programming procedure. For an individual actuation mode, the degree of actuation could be tailored by variation of the magnetic field strengths. This material design can be easily extended to other composites containing other magnetic nanoparticles, e.g. with a high magnetic susceptibility.
Y1  - 2019
U6  - https://doi.org/10.1557/adv.2019.123
SN  - 2059-8521
VL  - 4
IS  - 19
SP  - 1057
EP  - 1065
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Razzaq, Muhammad Yasar
A1  - Behl, Marc
A1  - Heuchel, Matthias
A1  - Lendlein, Andreas
T1  - Matching magnetic heating and thermal actuation for sequential coupling in hybrid composites by design
JF  - Macromolecular rapid communications
N2  - Sequentially coupling two material functions requires matching the output from the first with the input of the second function. Here, magnetic heating controls thermal actuation of a hybrid composite in a challenging system environment causing an elevated level of heat loss. The concept is a hierarchical design consisting of an inner actuator of nanocomposite material, which can be remotely heated by exposure to an alternating magnetic field (AMF) and outer layers of a porous composite system with a closed pore morphology. These porous layers act as heat insulators and as barriers to the surrounding water. By exposure to the AMF, a local bulk temperature of 71 degrees C enables the magnetic actuation of the device, while the temperature of the surrounding water is kept below 50 degrees C. Interestingly, the heat loss during magnetic heating leads to an increase of the water phase (small volume) temperature. The temperature increase is able to sequentially trigger an adjacent thermal actuator attached to the actuator composite. In this way it could be demonstrated how the AMF is able to initiate two kinds of independent actuations, which might be interesting for robotics operating in aqueous environments.
KW  - artificial muscles
KW  - magnetosensitivity
KW  - nanocomposites
KW  - soft actuators
Y1  - 2019
U6  - https://doi.org/10.1002/marc.201900440
SN  - 1022-1336
SN  - 1521-3927
VL  - 41
IS  - 1
PB  - Wiley-VCH
CY  - Weinheim
ER  -