@inproceedings{BehlKratzNoecheletal.2014, author = {Behl, Marc and Kratz, Karl and N{\"o}chel, Ulrich and Sauter, Tilman and Lendlein, Andreas}, title = {Polymer networks capable of reversible shape-memory-effects}, series = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, volume = {248}, booktitle = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, publisher = {American Chemical Society}, address = {Washington}, issn = {0065-7727}, pages = {1}, year = {2014}, language = {en} } @article{SauterKratzHeucheletal.2021, author = {Sauter, Tilman and Kratz, Karl and Heuchel, Matthias and Lendlein, Andreas}, title = {Fiber diameter as design parameter for tailoring the macroscopic shape-memory performance of electrospun meshes}, series = {Materials and design}, volume = {202}, journal = {Materials and design}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, issn = {1873-4197}, doi = {10.1016/j.matdes.2021.109546}, pages = {10}, year = {2021}, abstract = {Fibrous shape-memory polymer (SMP) scaffolds were investigated considering the fiber as basic microstructural feature. By reduction of the fiber diameter in randomly oriented electrospun polyetherurethane (PEU) meshes from the micro-to the nano-scale, we observed changes in the molecular orientation within the fibers and its impact on the structural and shape-memory performance. It was assumed that a spatial restriction by reduction of the fiber diameter increases molecular orientation along the orientation of the fiber. The stress-strain relation of random PEU scaffolds is initially determined by the 3D arrangement of the fibers and thus is independent of the molecular orientation. Increasing the molecular orientation with decreasing single fiber diameter in scaffolds composed of randomly arranged fibers did not alter the initial stiffness and peak stress but strongly influenced the elongation at break and the stress increase above the Yield point. Reduction of the single fiber diameter also distinctly improved the shape-memory performance of the scaffolds. Fibers with nanoscale diameters (< 100 nm) possessed an almost complete shape recovery, high recovery stresses and fast relaxation kinetics, while the shape fixity was found to decrease with decreasing fiber diameter. Hence, the fiber diameter is a relevant design parameter for SMP.}, language = {en} } @article{SauterKratzLendlein2013, author = {Sauter, Tilman and Kratz, Karl and Lendlein, Andreas}, title = {Pore-size distribution controls shape-memory properties on the macro- and microscale of polymeric foams}, series = {Macromolecular chemistry and physics}, volume = {214}, journal = {Macromolecular chemistry and physics}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201300062}, pages = {1184 -- 1188}, year = {2013}, abstract = {Open porous foams with identical foam density but different pore-size distributions (bimodal or monomodal) are prepared from a shape-memory polyetherurethane (PEU) by thermally induced phase separation. The shape-memory effect of the two PEU foams is explored by cyclic thermomechanical compression tests and microstructural analysis. The obtained results reveal that the PEU foam with a bimodal pore-size distribution exhibits an increased shape-recovery under stress-free conditions, both on the macro- (foam level) as well as the microscale (pore level). While bimodal pore-size distributions induce microscale bending during compression, buckling occurs in foams with monomodal pore-size distributions, leading to both a reduced and delayed shape recovery.}, language = {en} } @article{HaaseKrostSauteretal.2017, author = {Haase, Tobias and Krost, Annalena and Sauter, Tilman and Kratz, Karl and Peter, Jan and Kamann, Stefanie and Jung, Friedrich and Lendlein, Andreas and Zohlnh{\"o}fer, Dietlind and R{\"u}der, Constantin}, title = {In vivo biocompatibility assessment of poly (ether imide) electrospun scaffolds}, series = {Journal of Tissue Engineering and Regenerative Medicine}, volume = {11}, journal = {Journal of Tissue Engineering and Regenerative Medicine}, number = {4}, publisher = {Wiley}, address = {Hoboken}, issn = {1932-6254}, doi = {10.1002/term.2002}, pages = {1034 -- 1044}, year = {2017}, abstract = {Poly(ether imide) (PEI), which can be chemically functionalized with biologically active ligands, has emerged as a potential biomaterial for medical implants. Electrospun PEI scaffolds have shown advantageous properties, such as enhanced endothelial cell adherence, proliferation and low platelet adhesion in in vitro experiments. In this study, the in vivo behaviour of electrospun PEI scaffolds and PEI films was examined in a murine subcutaneous implantation model. Electrospun PEI scaffolds and films were surgically implanted subcutaneously in the dorsae of mice. The surrounding subcutaneous tissue response was examined via histopathological examination at 7 and 28days after implantation. No serious adverse events were observed for both types of PEI implants. The presence of macrophages or foreign body giant cells in the vicinity of the implants and the formation of a fibrous capsule indicated a normal foreign body reaction towards PEI films and scaffolds. Capsule thickness and inflammatory infiltration cells significantly decreased for PEI scaffolds during days 7-28 while remaining unchanged for PEI films. The infiltration of cells into the implant was observed for PEI scaffolds 7days after implantation and remained stable until 28days of implantation. Additionally some, but not all, PEI scaffold implants induced the formation of functional blood vessels in the vicinity of the implants. Conclusively, this study demonstrates the in vivo biocompatibility of PEI implants, with favourable properties of electrospun PEI scaffolds regarding tissue integration and wound healing.}, language = {en} } @article{RuederSauterKratzetal.2013, author = {R{\"u}der, Constantin and Sauter, Tilman and Kratz, Karl and Haase, Tobias and Peter, Jan and Jung, Friedrich and Lendlein, Andreas and Zohlnh{\"o}fer, Dietlind}, title = {Influence of fibre diameter and orientation of electrospun copolyetheresterurethanes on smooth muscle and endothelial cell behaviour}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {55}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, number = {4}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-131787}, pages = {513 -- 522}, year = {2013}, abstract = {Polymers exhibiting cell-selective effects represent an extensive research field with high relevance for biomedical applications e.g. in the cardiovascular field supporting re-endothelialization while suppressing smooth muscle cell overgrowth. Such an endothelial cell-selective effect could be recently demonstrated for a copolyetheresterurethane (PDC) containing biodegradable poly(p-dioxanone) and poly(epsilon-caprolactone) segments, which selectively enhanced the adhesion of human umbilical vein endothelial cells (HUVEC) while suppressing the attachment of smooth muscle cells (SMC). In this study we investigated the influence of the fibre orientation (random and aligned) and fibre diameter (2 mu m and 500 nm) of electrospun PDC scaffolds on the adhesion, proliferation and apoptosis of HUVEC and SMC. Adhesion, viability and proliferation of HUVEC was diminished when the fibre diameter was reduced to a submicron scale, while the orientation of the microfibres did only slightly influence the cellular behaviour. In contrast, a submicron fibre diameter improved SMC viability. In conclusion, PDC scaffolds with micron-sized single fibres could be promising candidate materials for cell-selective stent coatings.}, language = {en} } @article{SauterLuetzowSchossigetal.2012, author = {Sauter, Tilman and L{\"u}tzow, Karola and Schossig, Michael and Kosmella, Hans and Weigel, Thomas and Kratz, Karl and Lendlein, Andreas}, title = {Shape-memory properties of polyetherurethane foams prepared by thermally induced phase separation}, series = {Advanced engineering materials}, volume = {14}, journal = {Advanced engineering materials}, number = {9}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1438-1656}, doi = {10.1002/adem.201200127}, pages = {818 -- 824}, year = {2012}, abstract = {In this study, we report the preparation of two structurally different shape-memory polymer foams by thermally induced phase separation (TIPS) from amorphous polyetherurethanes. Foams with either a homogeneous, monomodal, or with a hierarchically structured, bimodal, pore size distribution are obtained by adoption of the cooling protocol. The shape-memory properties have been investigated for both foam structures by cyclic, thermomechanical experiments, while the morphological changes on the micro scale (pore level) have been compared to the macro scale by an in situ micro compression device experiment. The results show that the hierarchically structured foam achieves higher shape-recovery rates and a higher total recovery as compared to the homogeneous foam, which is due to an increased energy storage capability by micro scale bending of the hierarchically structured foam compared to pure compression of the homogeneous foam.}, language = {en} } @article{LendleinSauter2013, author = {Lendlein, Andreas and Sauter, Tilman}, title = {Shape-memory effect in polymers}, series = {Macromolecular chemistry and physics}, volume = {214}, journal = {Macromolecular chemistry and physics}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201300098}, pages = {1175 -- 1177}, year = {2013}, language = {en} } @article{SchneiderKohlSauteretal.2012, author = {Schneider, Tobias and Kohl, Benjamin and Sauter, Tilman and Kratz, Karl and Lendlein, Andreas and Ertel, Wolfgang and Schulze-Tanzil, Gundula}, title = {Influence of fiber orientation in electrospun polymer scaffolds on viability, adhesion and differentiation of articular chondrocytes}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {52}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, number = {2-4}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-2012-1608}, pages = {325 -- 336}, year = {2012}, abstract = {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.}, language = {en} } @article{SauterGeigerKratzetal.2015, author = {Sauter, Tilman and Geiger, Brett and Kratz, Karl and Lendlein, Andreas}, title = {Encasement of metallic cardiovascular stents with endothelial cell-selective copolyetheresterurethane microfibers}, series = {Polymers for advanced technologies}, volume = {26}, journal = {Polymers for advanced technologies}, number = {10}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1042-7147}, doi = {10.1002/pat.3583}, pages = {1209 -- 1216}, year = {2015}, abstract = {Cardiovascular metallic stents established in clinical application are typically coated by a thin polymeric layer on the stent struts to improve hemocompatibility, whereby often a drug is added to the coating to inhibit neointimal hyperplasia. Besides such thin film coatings recently nano/microfiber coated stents are investigated, whereby the fibrous coating was applied circumferential on stents. Here, we explored whether a thin fibrous encasement of metallic stents with preferentially longitudinal aligned fibers and different local fiber densities can be achieved by electrospinning. An elastic degradable copolyetheresterurethane, which is reported to selectively enhance the adhesion of endothelial cells, while simultaneously rejecting smooth muscle cells, was utilized for stent coating. The fibrous stent encasements were microscopically assessed regarding their single fiber diameters, fiber covered area and fiber alignment at three characteristic stent regions before and after stent expansion. Stent coatings with thicknesses in the range from 30 to 50 mu m were achieved via electrospinning with 1,1,1,3,3,3-hexafluoro-2-propanol (HFP)-based polymer solution, while a mixture of HFP and formic acid as solvent resulted in encasements with a thickness below 5 mu m comprising submicron sized single fibers. All polymeric encasements were mechanically stable during expansion, whereby the fibers deposited on the struts remained their position. The observed changes in fiber density and diameter indicated diverse local deformation mechanisms of the microfibers at the different regions between the struts. Based on these results it can be anticipated that the presented fibrous encasement of stents might be a promising alternative to stents with polymeric strut coatings releasing anti-proliferative drugs. Copyright (c) 2015 John Wiley \& Sons, Ltd.}, 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} }