@article{MazurekBudzyńskaBehlRazzaqetal.2019, author = {Mazurek-Budzyńska, Magdalena and Behl, Marc and Razzaq, Muhammad Yasar and N{\"o}chel, Ulrich and Rokicki, Gabriel and Lendlein, Andreas}, title = {Hydrolytic stability of aliphatic poly(carbonate-urea-urethane)s: Influence of hydrocarbon chain length in soft segment}, series = {Polymer Degradation and Stability}, volume = {161}, journal = {Polymer Degradation and Stability}, publisher = {Elsevier}, address = {Oxford}, issn = {0141-3910}, pages = {283 -- 297}, year = {2019}, abstract = {Poly(carbonate-urethane)s (PCUs) exhibit improved resistance to hydrolytic degradation and in vivo stress cracking compared to poly(ester-urethane)s and their degradation leads to lower inflammation of the surrounding tissues. Therefore, PCUs are promising implant materials and are considered for devices such as artificial heart or spine implants. In this work, the hydrolytic stability of different poly(carbonate-urethane-urea)s (PCUUs) was studied under variation of the length of hydrocarbon chain (6, 9, 10, and 12 methylene units) between the carbonate linkages in the precursors. PCUUs were synthesized from isophorone diisocyanate and oligo(alkylene carbonate) diols using the moisture-cure method. The changes of sample weight, thermal and mechanical properties, morphology, as well as the degradation products after immersion in a buffer solution (PBS, pH = 7.4) for up to 10 weeks at 37 degrees C were monitored and analyzed. In addition, mechanical properties after 20 weeks (in PBS, 37 degrees C) were investigated. The gel content was determined based on swelling experiments in chloroform. Based on the DSC analysis, slight increases of melting transitions of PCUUs were observed, which were attributed to structure reorganization related to annealing at 37 degrees C rather than to the degradation of the PCUU. Tensile strength after 20 weeks of all investigated samples remained in the range of 29-39 MPa, whereas the elongation at break e(m) decreased only slightly and remained in the range between 670 and 800\%. Based on the characterization of degradation products after up to 10 weeks of immersion it was assessed that oligomers are mainly consisting of hard segments containing urea linkages, which could be assigned to hindered-urea dissociation mechanism. The investigations confirmed good resistance of PCUUs to hydrolysis. Only minor changes in the crystallinity, as well as thermal and mechanical properties were observed and depended on hydrocarbon chain length in soft segment of PCUUs. (C) 2019 Published by Elsevier Ltd.}, language = {en} } @article{RazzaqBehlLendlein2019, author = {Razzaq, Muhammad Yasar and Behl, Marc and Lendlein, Andreas}, title = {Magneto-Mechanical Actuators with Reversible Stretching and Torsional Actuation Capabilities}, series = {MRS Advances}, volume = {4}, journal = {MRS Advances}, number = {19}, publisher = {Cambridge Univ. Press}, address = {New York}, issn = {2059-8521}, doi = {10.1557/adv.2019.123}, pages = {1057 -- 1065}, year = {2019}, abstract = {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.}, language = {en} } @article{RazzaqBehlHeucheletal.2019, author = {Razzaq, Muhammad Yasar and Behl, Marc and Heuchel, Matthias and Lendlein, Andreas}, title = {Matching magnetic heating and thermal actuation for sequential coupling in hybrid composites by design}, series = {Macromolecular rapid communications}, volume = {41}, journal = {Macromolecular rapid communications}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201900440}, pages = {7}, year = {2019}, abstract = {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.}, language = {en} } @article{RazzaqBehlFranketal.2012, author = {Razzaq, Muhammad Yasar and Behl, Marc and Frank, Ute and Koetz, Joachim and Szczerba, Wojciech and Lendlein, Andreas}, title = {Oligo(omega-pentadecalactone) decorated magnetic nanoparticles}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {18}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c2jm16146j}, pages = {9237 -- 9243}, year = {2012}, abstract = {Hybrid magnetic nanoparticles (mgNP) with a magnetite core diameter of 10 +/- 1 nm surface functionalized with oligo(omega-pentadecalactone) (OPDL) oligomers with M-n between 1300 and 3300 g mol(-1) could be successfully prepared having OPDL grafted from 200 mg g(-1) to 2170 mg g(-1). The particles are dispersible in chloroform resulting in stable suspensions. Magnetic response against an external magnetic field proved the superparamagnetic nature of the particles with a low coercivity (B-c) value of 297 mu T. The combination of the advantageous superparamagnetism of the mgNP with the exceptional stability of OPDL makes these novel hybrid mgNP promising candidates as multifunctional building blocks for magnetic nanocomposites with tunable physical properties.}, language = {en} } @article{BehlRazzaqMazurekBudzynskaetal.2020, author = {Behl, Marc and Razzaq, Muhammad Yasar and Mazurek-Budzynska, Magdalena and Lendlein, Andreas}, title = {Polyetheresterurethane based porous scaffolds with tailorable architectures by supercritical CO2 foaming}, series = {MRS advances}, volume = {5}, journal = {MRS advances}, number = {45}, publisher = {Cambridge University Press}, address = {New York, NY}, issn = {2059-8521}, doi = {10.1557/adv.2020.345}, pages = {2317 -- 2330}, year = {2020}, abstract = {Porous three-dimensional (3D) scaffolds are promising treatment options in regenerative medicine. Supercritical and dense-phase fluid technologies provide an attractive alternative to solvent-based scaffold fabrication methods. In this work, we report on the fabrication of poly-etheresterurethane (PPDO-PCL) based porous scaffolds with tailorable pore size, porosity, and pore interconnectivity by using supercritical CO2(scCO(2)) fluid-foaming. The influence of the processing parameters such as soaking time, soaking temperature and depressurization on porosity, pore size, and interconnectivity of the foams were investigated. The average pore diameter could be varied between 100-800 mu m along with a porosity in the range from (19 +/- 3 to 61 +/- 6)\% and interconnectivity of up to 82\%. To demonstrate their applicability as scaffold materials, selected foams were sterilized via ethylene oxide sterilization. They showed negligible cytotoxicity in tests according to DIN EN ISO 10993-5 and 10993-12 using L929 cells. The study demonstrated that the pore size, porosity and the interconnectivity of this multi-phase semicrystalline polymer could be tailored by careful control of the processing parameters during the scCO(2)foaming process. In this way, PPDO-PCL scaffolds with high porosity and interconnectivity are potential candidate materials for regenerative treatment options.}, language = {en} } @article{WangRazzaqRudolphetal.2018, author = {Wang, Li and Razzaq, Muhammad Yasar and Rudolph, Tobias and Heuchel, Matthias and N{\"o}chel, Ulrich and Mansfeld, Ulrich and Jiang, Yi and Gould, Oliver E. C. and Behl, Marc and Kratz, Karl and Lendlein, Andreas}, title = {Reprogrammable, magnetically controlled polymeric nanocomposite actuators}, series = {Material horizons}, volume = {5}, journal = {Material horizons}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2051-6347}, doi = {10.1039/c8mh00266e}, pages = {861 -- 867}, year = {2018}, abstract = {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.}, language = {en} } @article{MazurekBudzynskaRazzaqBehletal.2019, author = {Mazurek-Budzynska, Magdalena and Razzaq, Muhammad Yasar and Behl, Marc and Lendlein, Andreas}, title = {Shape-Memory Polymers}, series = {Functional Polymers}, journal = {Functional Polymers}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-95987-0}, issn = {2510-3458}, doi = {10.1007/978-3-319-95987-0_18}, pages = {605 -- 663}, year = {2019}, abstract = {Shape-memory polymers (SMPs) are stimuli-sensitive materials capable of changing their shape on demand. A shape-memory function is a result of the polymer architecture together with the application of a specific programming procedure. Various possible mechanisms to induce the shape-memory effect (SME) can be realized, which can be based on thermal transitions of switching domains or on reversible molecular switches (e.g., supramolecular interactions, reversible covalent bonds). Netpoints, which connect the switching domains and determine the permanent shape, can be either provided by covalent bonds or by physical intermolecular interactions, such as hydrogen bonds or crystallites. This chapter reviews different ways of implementing the phenomenon of programmable changes in the polymer shape, including the one-way shape-memory effect (1-W SME), triple-and multi-shape effects (TSE/ MSE), the temperature-memory effect (TME), and reversible shape-memory effects, which can be realized in constant stress conditions (rSME), or in stress-free conditions (reversible bidirectional shape-memory effect (rbSME)). Furthermore, magnetically actuated SMPs and shape-memory hydrogels (SMHs) are described to show the potential of the SMP technology in biomedical applications and multifunctional approaches.}, language = {en} } @article{RazzaqBehlLendlein2018, author = {Razzaq, Muhammad Yasar and Behl, Marc and Lendlein, Andreas}, title = {Thermally-induced actuation of magnetic nanocomposites based on Oligo(ω-pentadecalactone) and covalently integrated magnetic nanoparticles}, series = {MRS advances: a journal of the Materials Research Society (MRS)}, volume = {3}, journal = {MRS advances: a journal of the Materials Research Society (MRS)}, number = {63}, publisher = {Cambridge University Press}, address = {New York}, issn = {2059-8521}, doi = {10.1557/adv.2018.613}, pages = {3783 -- 3791}, year = {2018}, abstract = {The incorporation of inorganic particles in a polymer matrix has been established as a method to adjust the mechanical performance of composite materials. We report on the influence of covalent integration of magnetic nanoparticles (MNP) on the actuation behavior and mechanical performance of hybrid nanocomposite (H-NC) based shape-memory polymer actuators (SMPA). The H-NC were synthesized by reacting two types of oligo(ω-pentadecalactone) (OPDL) based precursors with terminal hydroxy groups, a three arm OPDL (3 AOPDL, Mn = 6000 g mol•1-1 ) and an OPDL (Mn =3300 g • mol-1 ) coated magnetite nanoparticle ({\O} = 10 ± 2 nm), with a diisocyanate. These H-NC were compared to the homopolymer network regarding the actuation performance, contractual stress (σcontr) as well as thermal and mechanical properties. The melting range of the OPDL crystals (ΔTm,OPDL) was shifted in homo polymer networks from 36 ºC - 76 ºC to 41ºC - 81 °C for H-NC with 9 wt\% of MNP content. The actuators were explored by variation of separating temperature (Tsep), which splits the OPDL crystalline domain into actuating and geometry determining segments. Tsep was varied in the melting range of the nanocomposites and the actuation capability and contractual stress (σcontr) of the nanocomposite actuators could be adjusted. The reversible strain (εrev) was decreased from 11 ± 0.3\% for homo polymer network to 3.2±0.3\% for H-NC9 with 9 wt\% of MNP indicating a restraining effect of the MNP on chain mobility. The results show that the performance of H-NCs in terms of thermal and elastic properties can be tailored by MNP content, however for higher reversible actuation, lower MNP contents are preferable.}, language = {en} } @article{LiuRazzaqRudolphetal.2017, author = {Liu, Yue and Razzaq, Muhammad Yasar and Rudolph, Tobias and Fang, Liang and Kratz, Karl and Lendlein, Andreas}, title = {Two-Level Shape Changes of Polymeric Microcuboids Prepared from Crystallizable Copolymer Networks}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {50}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.6b02237}, pages = {2518 -- 2527}, year = {2017}, abstract = {Polymeric microdevices bearing features like nonspherical shapes or spatially segregated surface properties are of increasing importance in biological and medical analysis, drug delivery, and bioimaging or microfluidic systems as well as in micromechanics, sensors, information storage, or data carrier devices. Here, a method to fabricate programmable microcuboids with shape-memory capability and the quantification of their recovery at different levels is reported. The method uses the soft lithographic technique to create microcuboids with well-defined sizes and surface properties. Microcuboids having an edge length of 25 mu m and a height of 10 mu m were prepared from cross-linked poly[ethylene-co-(vinyl acetate)] (cPEVA) with different vinyl acetate contents and were programmed by compression with various deformation degrees at elevated temperatures. The microlevel shape-recovery of the cuboidal geometry during heating was monitored by optical microscopy (OM) and atomic force microscopy (AFM) studying the related changes in the projected area (PA) or height, while the nanolevel changes of the nanosurface roughness were investigated by in situ AFM. The shape-memory effect at the microlevel was quantified by the recovery ratio of cuboids (R-r,R-micro), while at the. nanolevel, the recovery ratio of the nanoroughness (R-r,R-nano) was measured. The values of R-r,R-micro,,micro could be tailored in a range from 42 +/- 1\% to 102 +/- 1\% and Rr,nano from 89 +/- 6\% to 136 +/- 21\% depending on the applied compression ratio and the amount of vinyl acetate content in the cPEVA microcuboids.}, language = {en} } @article{ZhangBehlPengetal.2016, author = {Zhang, Pengfei and Behl, Marc and Peng, Xingzhou and Razzaq, Muhammad Yasar and Lendlein, Andreas}, title = {Ultrasonic Cavitation Induced Shape-Memory Effect in Porous Polymer Networks}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201600439}, pages = {1897 -- 1903}, year = {2016}, abstract = {Inspired by the application of ultrasonic cavitation based mechanical force (CMF) to open small channels in natural soft materials (skin or tissue), it is explored whether an artificial polymer network can be created, in which shape-changes can be induced by CMF. This concept comprises an interconnected macroporous rhodium-phosphine (Rh-P) coordination polymer network, in which a CMF can reversibly dissociate the Rh-P microphases. In this way, the ligand exchange of Rh-P coordination bonds in the polymer network is accelerated, resulting in a topological rearrangement of molecular switches. This rearrangement of molecular switches enables the polymer network to release internal tension under ultrasound exposure, resulting in a CMF-induced shape-memory capability. The interconnected macroporous structure with thin pore walls is essential for allowing the CMF to effectively permeate throughout the polymer network. Potential applications of this CMF-induced shape-memory polymer can be mechanosensors or ultrasound controlled switches.}, language = {en} }