@article{YanFangNoecheletal.2015,
  author    = {Yan, Wan and Fang, Liang and N{\"o}chel, Ulrich and Kratz, Karl and Lendlein, Andreas},
  title     = {Influence of deformation temperature on structural variation and shape-memory effect of a thermoplastic semi-crystalline multiblock copolymer},
  series = {eXPRESS polymer letters},
  volume    = {9},
  journal   = {eXPRESS polymer letters},
  number    = {7},
  publisher = {Budapest University of Technology and Economics, Department of Polymer Engineering},
  address   = {Budapest},
  issn      = {1788-618X},
  doi       = {10.3144/expresspolymlett.2015.58},
  pages     = {624 -- 635},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{SchoeneRichauKratzetal.2015,
  author    = {Sch{\"o}ne, Anne-Christin and Richau, Klaus and Kratz, Karl and Schulz, Burkhard and Lendlein, Andreas},
  title     = {Influence of Diurethane Linkers on the Langmuir Layer Behavior of Oligo[(rac-lactide)-co-glycolide]-based Polyesterurethanes},
  series = {Macromolecular rapid communications},
  volume    = {36},
  journal   = {Macromolecular rapid communications},
  number    = {21},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1022-1336},
  doi       = {10.1002/marc.201500316},
  pages     = {1910 -- 1915},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{WangBaudisKratzetal.2015,
  author    = {Wang, Li and Baudis, Stefan and Kratz, Karl and Lendlein, Andreas},
  title     = {Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization},
  series = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry},
  volume    = {87},
  journal   = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry},
  number    = {11-12},
  publisher = {De Gruyter},
  address   = {Berlin},
  issn      = {0033-4545},
  doi       = {10.1515/pac-2015-0607},
  pages     = {1085 -- 1097},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{RochKratzMaetal.2015,
  author    = {Roch, Toralf and Kratz, Karl and Ma, Nan and Lendlein, Andreas},
  title     = {Polymeric inserts differing in their chemical composition as substrates for dendritic cell cultivation},
  series = {Clinical hemorheology and microcirculation : blood flow and vessels},
  volume    = {61},
  journal   = {Clinical hemorheology and microcirculation : blood flow and vessels},
  number    = {2},
  publisher = {IOS Press},
  address   = {Amsterdam},
  issn      = {1386-0291},
  doi       = {10.3233/CH-152004},
  pages     = {347 -- 357},
  year      = {2015},
  abstract  = {Dendritic cells (DC) contribute to immunity by presenting antigens to T cells and shape the immune response by the secretion of cytokines. Due to their immune stimulatory potential DC-based therapies are promising approaches to overcome tolerance e.g. against tumors. In order to enforce the immunogenicity of DCs, they have to be matured and activated in vitro, which requires an appropriate cell culture substrate, supporting their survival expansion and activation. Since most cell culture devices are not optimized for DC growth, it is hypothesized that polymers with certain physicochemical properties can positively influence the DC cultures. With the aim to evaluate the effects that polymers with different chemical compositions have on the survival, the activation status, and the cytokine/chemokine secretion profile of DC, their interaction with polystyrene (PS), polycarbonate (PC), poly(ether imide) (PEI), and poly(styrene-co-acrylonitrile) (PSAN)-based cell culture inserts was investigated. By using this insert system, which fits exactly into 24 well cell culture plates, effects induced from the culture dish material can be excluded. The viability of untreated DC after incubation with the different inserts was not influenced by the different inserts, whereas LPS-activatedDCshowed an increased survival after cultivation on PC, PS, and PSAN compared to tissue culture polystyrene (TCP). The activation status of DC estimated by the expression of CD40, CD80, CD83, CD86 and HLA-DR expression was not altered by the different inserts in untreated DC but slightly reduced when LPS-activated DC were cultivated on PC, PS, PSAN, and PEI compared to TCP. For each polymeric cell culture insert a distinct cytokine profile could be observed. Since inserts with different chemical compositions of the inserts did not substantially alter the behavior of DC all insert systems could be considered as alternative substrate. The observed increased survival on some polymers, which showed in contrast to TCP a hydrophobic surface, could be beneficial for certain applications such as T cell expansion and activation.},
  language  = {en}
}
@misc{NoechelReddyWangetal.2015,
  author    = {N{\"o}chel, Ulrich and Reddy, Chaganti Srinivasa and Wang, Ke and Cui, Jing and Zizak, Ivo and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-81124},
  pages     = {8284 -- 8293},
  year      = {2015},
  abstract  = {Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.},
  language  = {en}
}
@article{NoechelReddyWangetal.2015,
  author    = {N{\"o}chel, Ulrich and Reddy, Chaganti Srinivasa and Wang, Ke and Cui, Jing and Zizak, Ivo and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers},
  series = {Journal of Materials Chemistry A, Materials for energy and sustainability},
  volume    = {16},
  journal   = {Journal of Materials Chemistry A, Materials for energy and sustainability},
  number    = {3},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7488},
  doi       = {10.1039/c4ta06586g},
  pages     = {8284 -- 8293},
  year      = {2015},
  abstract  = {Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.},
  language  = {en}
}
@article{WangKratzBehletal.2015,
  author    = {Wang, Weiwei and Kratz, Karl and Behl, Marc and Yan, Wan and Liu, Yue and Xu, Xun and Baudis, Stefan and Li, Zhengdong and Kurtz, Andreas and Lendlein, Andreas and Ma, Nan},
  title     = {The interaction of adipose-derived human mesenchymal stem cells and polyether ether ketone},
  series = {Clinical hemorheology and microcirculation : blood flow and vessels},
  volume    = {61},
  journal   = {Clinical hemorheology and microcirculation : blood flow and vessels},
  number    = {2},
  publisher = {IOS Press},
  address   = {Amsterdam},
  issn      = {1386-0291},
  doi       = {10.3233/CH-152001},
  pages     = {301 -- 321},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{NoechelReddyWangetal.2015,
  author    = {N{\"o}chel, Ulrich and Reddy, Chaganti Srinivasa and Wang, Ke and Cui, Jing and Zizak, Ivo and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers},
  series = {Journal of materials chemistry : A, Materials for energy and sustainability},
  volume    = {3},
  journal   = {Journal of materials chemistry : A, Materials for energy and sustainability},
  number    = {16},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7488},
  doi       = {10.1039/c4ta06586g},
  pages     = {8284 -- 8293},
  year      = {2015},
  abstract  = {Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 degrees C related to a broad melting transition (similar to 100 degrees C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (T-deform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 degrees C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low T-deform (<50 degrees C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.},
  language  = {en}
}
@article{ZhangSauterFangetal.2015,
  author    = {Zhang, Quanchao and Sauter, Tilman and Fang, Liang and Kratz, Karl and Lendlein, Andreas},
  title     = {Shape-Memory Capability of Copolyetheresterurethane Microparticles Prepared via Electrospraying},
  series = {Macromolecular materials and engineering},
  volume    = {300},
  journal   = {Macromolecular materials and engineering},
  number    = {5},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1438-7492},
  doi       = {10.1002/mame.201400267},
  pages     = {522 -- 530},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}