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  - 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  - 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  - Yan, Wan
A1  - Rudolph, Tobias
A1  - Nöchel, Ulrich
A1  - Gould, Oliver E. C.
A1  - Behl, Marc
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Reversible actuation of thermoplastic multiblock copolymers with overlapping thermal transitions of crystalline and glassy domains
JF  - Macromolecules : a publication of the American Chemical Society
N2  - Polymeric materials possessing specific features like programmability, high deformability, and easy processability are highly desirable for creating modern actuating systems. In this study, thermoplastic shape-memory polymer actuators obtained by combining crystallizable poly(epsilon-caprolactone) (PCL) and poly(3S-isobutylmorpholin-2,5-dione) (PIBMD) segments in multiblock copolymers are described. We designed these materials according to our hypothesis that the confinement of glassy PIBMD domains present at the upper actuation temperature contribute to the stability of the actuator skeleton, especially at large programming strains. The copolymers have a phase-segregated morphology, indicated by the well-separated melting and glass transition temperatures for PIBMD and PCL, but possess a partially overlapping T-m of PCL and T-g of PIBMD in the temperature interval from 40 to 60 degrees C. Crystalline PIBMD hard domains act as strong physical netpoints in the PIBMD-PCL bulk material enabling high deformability (up to 2000%) and good elastic recoverability (up to 80% at 50 degrees C above T-m,T-PCL). In the programmed thermoplastic actuators a high content of crystallizable PCL actuation domains ensures pronounced thermoreversible shape changes upon repetitive cooling and heating. The programmed actuator skeleton, composed of PCL crystals present at the upper actuation temperature T-high and the remaining glassy PIBMD domains, enabled oriented crystallization upon cooling. The actuation performance of PIBMD-PCL could be tailored by balancing the interplay between actuation and skeleton, but also by varying the quantity of crystalline PIBMD hard domains via the copolymer composition, the applied programming strain, and the choice of T-high. The actuator with 17 mol% PIBMD showed the highest reversible elongation of 11.4% when programmed to a strain of 900% at 50 degrees C. It is anticipated that the presented thermoplastic actuator materials can be applied as modern compression textiles.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.macromol.8b00322
SN  - 0024-9297
SN  - 1520-5835
VL  - 51
IS  - 12
SP  - 4624
EP  - 4632
PB  - American Chemical Society
CY  - Washington
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 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  - 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  - 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  - 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  - Wang, Weiwei
A1  - Kratz, Karl
A1  - Behl, Marc
A1  - Yan, Wan
A1  - Liu, Yue
A1  - Xu, Xun
A1  - Baudis, Stefan
A1  - Li, Zhengdong
A1  - Kurtz, Andreas
A1  - Lendlein, Andreas
A1  - Ma, Nan
T1  - The interaction of adipose-derived human mesenchymal stem cells and polyether ether ketone
JF  - Clinical hemorheology and microcirculation : blood flow and vessels
N2  - Polyether ether ketone (PEEK) as a high-performance, thermoplastic implant material entered the field of medical applications due to its structural function and commercial availability. In bone tissue engineering, the combination of mesenchymal stem cells (MSCs) with PEEK implants may accelerate the bone formation and promote the osseointegration between the implant and the adjacent bone tissue. In this concept the question how PEEK influences the behaviour and functions of MSCs is of great interest. Here the cellular response of human adipose-derived MSCs to PEEK was evaluated and compared to tissue culture plate (TCP) as the reference material. Viability and morphology of cells were not altered when cultured on the PEEK film. The cells on PEEK presented a high proliferation activity in spite of a relatively lower initial cell adhesion rate. There was no significant difference on cell apoptosis and senescence between the cells on PEEK and TCP. The inflammatory cytokines and VEGF secreted by the cells on these two surfaces were at similar levels. The cells on PEEK showed up-regulated BMP2 and down-regulated BMP4 and BMP6 gene expression, whereas no conspicuous differences were observed in the committed osteoblast markers (BGLAP, COL1A1 and Runx2). With osteoinduction the cells on PEEK and TCP exhibited a similar osteogenic differentiation potential. Our results demonstrate the biofunctionality of PEEK for human MSC cultivation and differentiation. Its clinical benefits in bone tissue engineering may be achieved by combining MSCs with PEEK implants. These data may also provide useful information for further modification of PEEK with chemical or physical methods to regulate the cellular processes of MSCs and to consequently improve the efficacy of MSC-PEEK based therapies.
KW  - Polyether ether ketone
KW  - mesenchymal stem cells
KW  - biocompatibility
KW  - cell-material interaction
KW  - osteogenic differentiation
Y1  - 2015
U6  - https://doi.org/10.3233/CH-152001
SN  - 1386-0291
SN  - 1875-8622
VL  - 61
IS  - 2
SP  - 301
EP  - 321
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Wang, Li
A1  - Razzaq, Muhammad Yasar
A1  - Rudolph, Tobias
A1  - Heuchel, Matthias
A1  - Nöchel, Ulrich
A1  - Mansfeld, Ulrich
A1  - Jiang, Yi
A1  - Gould, Oliver E. C.
A1  - Behl, Marc
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Reprogrammable, magnetically controlled polymeric nanocomposite actuators
JF  - Material horizons
N2  - Soft robots and devices with the advanced capability to perform adaptive motions similar to that of human beings often have stimuli-sensitive polymeric materials as the key actuating component. The external signals triggering the smart polymers’ actuations can be transmitted either via a direct physical connection between actuator and controlling unit (tethered) or remotely without a connecting wire. However, the vast majority of such polymeric actuator materials are limited to one specific type of motion as their geometrical information is chemically fixed. Here, we present magnetically driven nanocomposite actuators, which can be reversibly reprogrammed to different actuation geometries by a solely physical procedure. Our approach is based on nanocomposite materials comprising spatially segregated crystallizable actuation and geometry determining units. Upon exposure to a specific magnetic field strength the actuators’ geometric memory is erased by the melting of the geometry determining units allowing the implementation of a new actuator shape. The actuation performance of the nanocomposites can be tuned and the technical significance was demonstrated in a multi-cyclic experiment with several hundreds of repetitive free-standing shape shifts without losing performance.
Y1  - 2018
U6  - https://doi.org/10.1039/c8mh00266e
SN  - 2051-6347
SN  - 2051-6355
VL  - 5
IS  - 5
SP  - 861
EP  - 867
PB  - Royal Society of Chemistry
CY  - Cambridge
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  - 
TY  - JOUR
A1  - Wang, Li
A1  - Baudis, Stefan
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization
JF  - Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry
N2  - A versatile strategy to integrate multiple functions in a polymer based material is the formation of polymer networks with defined nanostructures. Here, we present synthesis and comprehensive characterization of covalently surface functionalized magnetic nanoparticles (MNPs) comprising a bi-layer oligomeric shell, using Sn(Oct)(2) as catalyst for a two-step functionalization. These hydroxy-terminated precursors for degradable magneto-and thermo-sensitive polymer networks were prepared via two subsequent surfaceinitiated ring-opening polymerizations (ROPs) with omega-pentadecalactone and e-caprolactone. A two-step mass loss obtained in thermogravimetric analysis and two distinct melting transitions around 50 and 85 degrees C observed in differential scanning calorimetry experiments, which are attributed to the melting of OPDL and OCL crystallites, confirmed a successful preparation of the modified MNPs. The oligomeric coating of the nanoparticles could be visualized by transmission electron microscopy. The investigation of degrafted oligomeric coatings by gel permeation chromatography and H-1-NMR spectroscopy showed an increase in number average molecular weight as well as the presence of signals related to both of oligo(omega-pentadecalactone) (OPDL) and oligo(e-caprolactone) (OCL) after the second ROP. A more detailed analysis of the NMR results revealed that only a few.-pentadecalactone repeating units are present in the degrafted oligomeric bi-layers, whereby a considerable degree of transesterification could be observed when OPDL was polymerized in the 2nd ROP step. These findings are supported by a low degree of crystallinity for OPDL in the degrafted oligomeric bi-layers obtained in wide angle X-ray scattering experiments. Based on these findings it can be concluded that Sn(Oct)(2) was suitable as catalyst for the preparation of nanosized bi-layered coated MNP precursors by a two-step ROP.
KW  - degradable polyester
KW  - magnetic nanoparticles
KW  - nanoparticle characterization
KW  - NICE-2014
KW  - ring opening polymerization
KW  - surface functionalization
Y1  - 2015
U6  - https://doi.org/10.1515/pac-2015-0607
SN  - 0033-4545
SN  - 1365-3075
VL  - 87
IS  - 11-12
SP  - 1085
EP  - 1097
PB  - De Gruyter
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Tung, Wing Tai
A1  - Maring, Janita A.
A1  - Xu, Xun
A1  - Liu, Yue
A1  - Becker, Matthias
A1  - Somesh, Dipthi Bachamanda
A1  - Klose, Kristin
A1  - Wang, Weiwei
A1  - Sun, Xianlei
A1  - Ullah, Imran
A1  - Kratz, Karl
A1  - Neffe, Axel T.
A1  - Stamm, Christof
A1  - Ma, Nan
A1  - Lendlein, Andreas
T1  - In vivo performance of a cell and factor free multifunctional fiber mesh modulating postinfarct myocardial remodeling
JF  - Advanced Functional Materials
N2  - Guidance of postinfarct myocardial remodeling processes by an epicardial patch system may alleviate the consequences of ischemic heart disease. As macrophages are highly relevant in balancing immune response and regenerative processes their suitable instruction would ensure therapeutic success. A polymeric mesh capable of attracting and instructing monocytes by purely physical cues and accelerating implant degradation at the cell/implant interface is designed. In a murine model for myocardial infarction the meshes are compared to those either coated with extracellular matrix or loaded with induced cardiomyocyte progenitor cells. All implants promote macrophage infiltration and polarization in the epicardium, which is verified by in vitro experiments. 6 weeks post-MI, especially the implantation of the mesh attenuates left ventricular adverse remodeling processes as shown by reduced infarct size (14.7% vs 28-32%) and increased wall thickness (854 mu m vs 400-600 mu m), enhanced angiogenesis/arteriogenesis (more than 50% increase compared to controls and other groups), and improved heart function (ejection fraction = 36.8% compared to 12.7-31.3%). Upscaling as well as process controls is comprehensively considered in the presented mesh fabrication scheme to warrant further progression from bench to bedside.
KW  - bioinstructive materials
KW  - cardiac regeneration
KW  - function by structure;
KW  - modulation of in vivo regeneration
KW  - multifunctional biomaterials
Y1  - 2022
U6  - https://doi.org/10.1002/adfm.202110179
SN  - 1616-301X
SN  - 1616-3028
VL  - 32
IS  - 31
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Tetali, Sarada D.
A1  - Jankowski, Vera
A1  - Luetzow, Karola
A1  - Kratz, Karl
A1  - Lendlein, Andreas
A1  - Jankowski, Joachim
T1  - Adsorption capacity of poly(ether imide) microparticles to uremic toxins
JF  - Clinical hemorheology and microcirculation : blood flow and vessels
N2  - Uremia is a phenomenon caused by retention of uremic toxins in the plasma due to functional impairment of kidneys in the elimination of urinary waste products. Uremia is presently treated by dialysis techniques like hemofiltration, dialysis or hemodiafiltration. However, these techniques in use are more favorable towards removing hydrophilic than hydrophobic uremic toxins. Hydrophobic uremic toxins, such as hydroxy hipuric acid (OH-HPA), phenylacetic acid (PAA), indoxyl sulfate (IDS) and p-cresylsulfate (pCRS), contribute substantially to the progression of chronic kidney disease (CKD) and cardiovascular disease. Therefore, objective of the present study is to test adsorption capacity of highly porous microparticles prepared from poly(ether imide) (PEI) as an alternative technique for the removal of uremic toxins. Two types of nanoporous, spherically shaped microparticles were prepared from PEI by a spraying/coagulation process. PEI particles were packed into a preparative HPLC column to which a mixture of the four types of uremic toxins was injected and eluted with ethanol. Eluted toxins were quantified by analytical HPLC. PEI particles were able to adsorb all four toxins, with the highest affinity for PAA and pCR. IDS and OH-HPA showed a partially non-reversible binding. In summary, PEI particles are interesting candidates to be explored for future application in CKD.
KW  - Adsorption of uremic toxins
KW  - chronic kidney disease (CKD)
KW  - hydrophobic uremic toxins
KW  - poly(ether imide)
KW  - microparticles
KW  - uremia
Y1  - 2016
U6  - https://doi.org/10.3233/CH-152026
SN  - 1386-0291
SN  - 1875-8622
VL  - 61
SP  - 657
EP  - 665
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Schöne, Anne-Christin
A1  - Schulz, Burkhard
A1  - Richau, Klaus
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Characterization of Langmuir films prepared from copolyesterurethanes based on oligo(omega-pentadecalactone) and oligo(epsilon-caprolactone)segments
JF  - Macromolecular chemistry and physics
N2  - A series of multiblock copolymers (PDLCL) synthesized from oligo(omega-pentadecalactone) diol (OPDL) and oligo(epsilon-caprolactone) diol (OCL), which are linked by 2,2(4), 4-trimethyl-hexamethylene diisocyanate (TMDI), is investigated by the Langmuir monolayer technique at the air-water interface. Brewster angle microscopy (BAM) and spectroscopic ellipsometry are employed to characterize the polymer film morphologies in situ. PDLCL containing >= 40 wt% OCL segments form homogeneous Langmuir monofilms after spreading. The film elasticity modulus decreases with increasing amounts of OPDL segments in the copolymer. In contrast, the OCL-free polyesterurethane OPDL-TMDI cannot be spread to monomolecular films on the water surface properly, and movable slabs are observed by BAM even at low surface pressures. The results of the in situ morphological characterization clearly show that essential information concerning the reliability of Langmuir monolayer degradation (LMD) experiments cannot be obtained from the evaluation of the pi-A isotherms only. Consequently, in situ morphological characterization turns out to be indispensable for characterization of Langmuir layers before LMD experiments.
KW  - brewster angle microscopy
KW  - ellipsometry
KW  - Langmuir layers
KW  - morphology
KW  - polyesterurethanes
Y1  - 2014
U6  - https://doi.org/10.1002/macp.201400377
SN  - 1022-1352
SN  - 1521-3935
VL  - 215
IS  - 24
SP  - 2437
EP  - 2445
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schöne, Anne-Christin
A1  - Richau, Klaus
A1  - Kratz, Karl
A1  - Schulz, Burkhard
A1  - Lendlein, Andreas
T1  - Influence of Diurethane Linkers on the Langmuir Layer Behavior of Oligo[(rac-lactide)-co-glycolide]-based Polyesterurethanes
JF  - Macromolecular rapid communications
N2  - Three oligo[(rac-lactide)-co-glycolide] based polyesterurethanes (OLGA-PUs) containing different diurethane linkers are investigated by the Langmuir monolayer technique and compared to poly[(rac-lactide)-co-glycolide] (PLGA) to elucidate the influence of the diurethane junction units on hydrophilicity and packing motifs of these polymers at the air-water interface. The presence of diurethane linkers does not manifest itself in the Langmuir layer behavior both in compression and expansion experiments when monomolecular films of OLGA-PUs are spread on the water surface. However, the linker retard the evolution of morphological structures at intermediate compression level under isobaric conditions (with a surface pressure greater than 11 mN m(-1)) compared to the PLGA, independent on the chemical structure of the diurethane moiety. The layer thicknesses of both OLGA-PU and PLGA films decrease in the high compression state with decreasing surface pressure, as deduced from ellipsometric data. All films must be described with the effective medium approximation as water swollen layers.
KW  - Brewster angle microscopy
KW  - Langmuir monolayer
KW  - poly[(rac-lactide)-co-glycolide]
KW  - polyesterurethanes
KW  - spectroscopic ellipsometry
Y1  - 2015
U6  - https://doi.org/10.1002/marc.201500316
SN  - 1022-1336
SN  - 1521-3927
VL  - 36
IS  - 21
SP  - 1910
EP  - 1915
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schöne, Anne-Christin
A1  - Kratz, Karl
A1  - Schulz, Burkhard
A1  - Lendlein, Andreas
T1  - The relevance of hydrophobic segments in multiblock copolyesterurethanes for their enzymatic degradation at the air-water interface
JF  - Polymer : the international journal for the science and technology of polymers
N2  - The interplay of an enzyme with a multiblock copolymer PDLCL containing two segments of different hydrophilicity and degradability is explored in thin films at the air-water interface. The enzymatic degradation was studied in homogenous Langmuir monolayers, which are formed when containing more than 40 wt% oligo(epsilon-caprolactone) (OCL). Enzymatic degradation rates were significantly reduced with increasing content of hydrophobic oligo(omega-pentadecalactone) (OPDL). The apparent deceleration of the enzymatic process is caused by smaller portion of water-soluble degradation fragments formed from degradable OCL fragments. Beside the film degradation, a second competing process occurs after adding lipase from Pseudomonas cepacia into the subphase, namely the enrichment of the lipase molecules in the polymeric monolayer. The incorporation of the lipase into the Langmuir film is experimentally revealed by concurrent surface area enlargement and by Brewster angle microscopy (BAM). Aside from the ability to provide information about the degradation behavior of polymers, the Langmuir monolayer degradation (LMD) approach enables to investigate polymer-enzyme interactions for non-degradable polymers. (C) 2016 Elsevier Ltd. All rights reserved.
KW  - Multiblock copolymer
KW  - Enzymatic polymer degradation
KW  - Oligo(omega-pentadecalactone)
KW  - Oligo(epsilon-caprolactone)
KW  - Langmuir monolayer degradation technique
Y1  - 2016
U6  - https://doi.org/10.1016/j.polymer.2016.09.001
SN  - 0032-3861
SN  - 1873-2291
VL  - 102
SP  - 92
EP  - 98
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Schöne, Anne-Christin
A1  - Kratz, Karl
A1  - Schulz, Burkhard
A1  - Lendlein, Andreas
T1  - Polymer architecture versus chemical structure as adjusting tools for the enzymatic degradation of oligo(epsilon-caprolactone) based films at the air-water interface
JF  - Polymer Degradation and Stability
N2  - The enzymatic degradation of oligo(epsilon-caprolactone) (OCL) based films at the air-water interface is investigated by Langmuir monolayer degradation (LMD) experiments to elucidate the influence of the molecular architecture and of the chemical structure on the chain scission process. For that purpose, the interactions of 2D monolayers of two star-shaped poly(epsilon-caprolactone)s (PCLs) and three linear OCL based copolyesterurethanes (P(OCL-U)) with the lipase from Pseudomonas cepacia are evaluated in comparison to linear OCL. While the architecture of star-shaped PCL Langmuir layers slightly influences their degradability compared to OCL films, significantly retarded degradations are observed for P(OCL-U) films containing urethane junction units derived from 2, 2 (4), 4-trimethyl hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HDI) or lysine ethyl ester diisocyanate (LDI). The enzymatic degradation of the OCL based 2D structures is related to the presence of hydrophilic groups within the macromolecules rather than to the packing density of the film or to the molecular weight. The results reveal that the LMD technique allows the parallel analysis of both the film/enzyme interactions and the degradation process on the molecular level. (C) 2016 Elsevier Ltd. All rights reserved.
KW  - Langmuir technique
KW  - Oligo(epsilon-caprolactone)
KW  - Enzymatic degradation
KW  - Polymer architecture
Y1  - 2016
U6  - https://doi.org/10.1016/j.polymdegradstab.2016.07.010
SN  - 0141-3910
SN  - 1873-2321
VL  - 131
SP  - 114
EP  - 121
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Schneider, Tobias
A1  - Kohl, Benjamin
A1  - Sauter, Tilman
A1  - Kratz, Karl
A1  - Lendlein, Andreas
A1  - Ertel, Wolfgang
A1  - Schulze-Tanzil, Gundula
T1  - Influence of fiber orientation in electrospun polymer scaffolds on viability, adhesion and differentiation of articular chondrocytes
JF  - Clinical hemorheology and microcirculation : blood flow and vessels
N2  - Degradable polymers with a tailorable degradation rate might be promising candidate materials for biomaterial-based cartilage repair. In view of the poor intrinsic healing capability of cartilage, implantation of autologous chondrocytes seeded on a biocompatible slow degrading polymer might be an encouraging approach to improve cartilage repair in the future. This study was undertaken to test if the fiber orientation (random versus aligned) of two different degradable polymers and a polymer intended for long term applications could influence primary articular chondrocytes growth and ultrastructure.
 A degradable copoly(ether) esterurethane (PDC) was synthesized via co-condensation of poly(p-dioxanone) diol and poly(epsilon-caprolactone) diol using an aliphatic diisocyanate as linker. Poly(p-dioxanone) (PPDO) was applied as commercially available degradable polymer, while polyetherimide (PEI) was chosen as biomaterial enabling surface functionalization. The fibrous scaffolds of PDC and PPDO were obtained by electrospinning using 1,1,1,3,3,3 hexafluoro-2-propanol (HFP), while for PEI dimethyl acetamide (DMAc) was applied as solvent. Primary porcine articular chondrocytes were seeded at different cell densities on the fibrous polymer scaffolds and analyzed for viability (fluorescein diacetate/ethidiumbromide staining), for type II collagen synthesis (immunolabelling), ultrastructure and orientation on the fibers (SEM: scanning electron microscopy).
 Vital chondrocytes adhered on all electrospun scaffolds irrespective of random and aligned topologies. In addition, the chondrocytes produced the cartilage-specific type II collagen on all tested polymer topologies suggesting their differentiated functions. SEM revealed an almost flattened chondrocytes shape on scaffolds with random fiber orientation: whereby chondrocytes growth remained mainly restricted to the scaffold surface. On aligned fibers the chondrocytes exhibited a more spindle-shaped morphology with rougher cell surfaces but only a minority of the cells aligned according to the fibers. As a next step the reduction of the fiber diameter of electrospun scaffolds should be addressed as an important parameter to mimic cartilage ECM structure.
KW  - Chondrocytes
KW  - electrospinning
KW  - scaffold
KW  - differentiation
KW  - multiblock copolymer
Y1  - 2012
U6  - https://doi.org/10.3233/CH-2012-1608
SN  - 1386-0291
VL  - 52
IS  - 2-4
SP  - 325
EP  - 336
PB  - IOS Press
CY  - Amsterdam
ER  -