@article{MazurekBudzyńskaBehlNeumannetal.2022,
  author    = {Mazurek-Budzyńska, Magdalena and Behl, Marc and Neumann, Richard and Lendlein, Andreas},
  title     = {4D-actuators by 3D-printing combined with water-based curing},
  series = {Materials today. Communications},
  volume    = {30},
  journal   = {Materials today. Communications},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2352-4928},
  doi       = {10.1016/j.mtcomm.2021.102966},
  pages     = {7},
  year      = {2022},
  abstract  = {The shape and the actuation capability of state of the art robotic devices typically relies on multimaterial systems from a combination of geometry determining materials and actuation components. Here, we present multifunctional 4D-actuators processable by 3D-printing, in which the actuator functionality is integrated into the shaped body. The materials are based on crosslinked poly(carbonate-urea-urethane) networks (PCUU), synthesized in an integrated process, applying reactive extrusion and subsequent water-based curing. Actuation capability could be added to the PCUU, prepared from aliphatic oligocarbonate diol, isophorone diisocyanate (IPDI) and water, in a thermomechanical programming process. When programmed with a strain of epsilon(prog) = 1400\% the PCUU networks exhibited actuation apparent by reversible elongation epsilon'(rev) of up to 22\%. In a gripper a reversible bending epsilon'(rev)((be)(nd)()) in the range of 37-60\% was achieved when the actuation temperature (T-high) was varied between 45 degrees C and 49 degrees C. The integration of actuation and shape formation could be impressively demonstrated in two PCUU-based reversible fastening systems, which were able to hold weights of up to 1.1 kg. In this way, the multifunctional materials are interesting candidate materials for robotic applications where a freedom in shape design and actuation is required as well as for sustainable fastening systems.},
  language  = {en}
}
@article{BalkBehlLendlein2020,
  author    = {Balk, Maria and Behl, Marc and Lendlein, Andreas},
  title     = {Actuators based on oligo[(epsilon-caprolactone)-co-glycolide] with accelerated hydrolytic degradation},
  series = {MRS advances : a journal of the Materials Research Society (MRS)},
  volume    = {5},
  journal   = {MRS advances : a journal of the Materials Research Society (MRS)},
  number    = {12-13},
  publisher = {Cambridge University Press},
  address   = {New York, NY},
  issn      = {2059-8521},
  doi       = {10.1557/adv.2019.447},
  pages     = {655 -- 666},
  year      = {2020},
  abstract  = {Polyester-based shape-memory polymer actuators are multifunctional materials providing reversible macroscopic shape shifts as well as hydrolytic degradability. Here, the function-function interdependencies (between shape shifts and degradation behaviour) will determine actuation performance and its life time. In this work, glycolide units were incorporated in poly(epsilon-caprolactone) based actuator materials in order to achieve an accelerated hydrolytic degradation and to explore the function-function relationship. Three different oligo[(epsilon-caprolactone)-co-glycolide] copolymers (OCGs) with similar molecular weights (10.5 +/- 0.5 kg center dot mol(-1)) including a glycolide content of 8, 16, and 26 mol\% (ratio 1:1:1 wt\%) terminated with methacrylated moieties were crosslinked. The obtained actuators provided a broad melting transition in the range from 27 to 44 degrees C. The hydrolytic degradation of programmed OCG actuators (200\% of elongation) resulted in a reduction of sample mass to 51 wt\% within 21 days at pH = 7.4 and 40 degrees C. Degradation results in a decrease of T-m associated to the actuating units and increasing T-m associated to the skeleton forming units. The actuation capability decreased almost linear as function of time. After 11 days of hydrolytic degradation the shape-memory functionality was lost. Accordingly, a fast degradation behaviour as required, e.g., for actuator materials intended as implant material can be realized.},
  language  = {en}
}
@article{TartivelBlockiBrauneetal.2022,
  author    = {Tartivel, Lucile and Blocki, Anna M. and Braune, Steffen and Jung, Friedrich and Behl, Marc and Lendlein, Andreas},
  title     = {An Inverse shape-memory hydrogel scaffold switching upon cooling in a tissue-tolerated temperature range},
  series = {Advanced materials interfaces},
  volume    = {9},
  journal   = {Advanced materials interfaces},
  number    = {6},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {2196-7350},
  doi       = {10.1002/admi.202101588},
  pages     = {9},
  year      = {2022},
  abstract  = {Tissue reconstruction has an unmet need for soft active scaffolds that enable gentle loading with regeneration-directing bioactive components by soaking up but also provide macroscopic dimensional stability. Here microporous hydrogels capable of an inverse shape-memory effect (iSME) are described, which in contrast to classical shape-memory polymers (SMPs) recover their permanent shape upon cooling. These hydrogels are designed as covalently photo cross-linked polymer networks with oligo(ethylene glycol)-oligo(propylene glycol)-oligo(ethylene glycol) (OEG-OPG-OEG) segments. When heated after deformation, the OEG-OPG-OEG segments form micelles fixing the temporary shape. Upon cooling, the micelles dissociate again, the deformation is reversed and the permanent shape is obtained. Applicability of this iSME is demonstrated by the gentle loading of platelet-rich plasma (PRP) without causing any platelet activation during this process. PRP is highly bioactive and is widely acknowledged for its regenerative effects. Hence, the microporous inverse shape-memory hydrogel (iSMH) with a cooling induced pore-size effect represents a promising candidate scaffold for tissue regeneration for potential usage in minimally invasive surgery applications.},
  language  = {en}
}
@article{ZhangBehlPengetal.2019,
  author    = {Zhang, Pengfei and Behl, Marc and Peng, Xingzhou and Balk, Maria and Lendlein, Andreas},
  title     = {Chemoresponsive Shape-Memory Effect of Rhodium-Phosphine Coordination Polymer Networks},
  series = {Chemistry of materials : a publication of the American Chemical Society},
  volume    = {31},
  journal   = {Chemistry of materials : a publication of the American Chemical Society},
  number    = {15},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0897-4756},
  doi       = {10.1021/acs.chemmater.9b00363},
  pages     = {5402 -- 5407},
  year      = {2019},
  abstract  = {Chemoresponsive polymers are of technological significance for smart sensors or systems capable of molecular recognition. An important key requirement for these applications is the material's structural integrity after stimulation. We explored whether covalently cross-linked metal ion-phosphine coordination polymers (MPN) can be shaped into any temporary shape and are capable of recovering from this upon chemoresponsive exposure to triphenylphosphine (Ph3P) ligands, whereas the MPN provide structural integrity. Depending on the metal-ion concentration used during synthesis of the MPN, the degree of swelling of the coordination polymer networks could be adjusted. Once the MPN was immersed into Ph3P solution, the reversible ligand-exchange reaction between the metal ions and the free Ph3P in solution causes a decrease of the coordination cross-link density in MPN again. The Ph3P-treated MPN was able to maintain its original shape, indicating a certain stability of shape even after stimulation. In this way, chemoresponsive control of the elastic properties (increase in volume and decrease of mechanical strength) of the MPN was demonstrated. This remarkable behavior motivated us to explore whether the MPN are capable of a chemoresponsive shape-memory effect. In initial experiments, shape fixity of around 60\% and shape recovery of almost 90\% were achieved when the MPN was exposed to Ph3P in case of rhodium. Potential applications for chemoresponsive shape-memory systems could be shapable semiconductors, e.g., for lighting or catalysts, which provide catalytic activity on demand.},
  language  = {en}
}
@article{LiangBehlLuetzowetal.2021,
  author    = {Liang, Xiao and Behl, Marc and L{\"u}tzow, Karola and Lendlein, Andreas},
  title     = {Cooligomers from morpholine-2,5-dione and para-dioxanone and catalyst complex SnOct(2)/2-hydroxyethyl sulfide},
  series = {MRS advances : a journal of the Materials Research Society (MRS)},
  volume    = {6},
  journal   = {MRS advances : a journal of the Materials Research Society (MRS)},
  number    = {32},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {2059-8521},
  doi       = {10.1557/s43580-021-00082-5},
  pages     = {764 -- 768},
  year      = {2021},
  abstract  = {Complexes from catalysts and initiator can be used to insert a specific number of additional chemical functional groups in (co)polymers prepared by ring-opening polymerization (ROP) of lactones. We report on the synthesis of cooligomers from sec-butyl-morpholine-2,5-dione (SBMD) and para-dioxanone (PDX) by ROP with varied feed ratios in the bulk using the catalyst complex SnOct(2)/2-hydroxyethyl sulfide. M-n of the cooligomers (determined by GPC) decreased with decreasing SBMD feed ratio from 4200 +/- 420 to 800 +/- 80 g mol(-1). When the feed ratio was reduced from 80 to 50 mol\% the molar ratio of SBMD of the cooligomers (determined by H-1-NMR) remained nearly unchanged between 81 and 86 mol\% and was attributed to a higher reactivity of SBMD. This assumption was confirmed by fractionation of GPC, in which an increase of SBMD with increasing molecular weight was observed. The catalyst/initiator system provides a high potential to create orthogonal building blocks by cleavage of the sulfide bond.},
  language  = {en}
}
@article{SaatchiBehlNoecheletal.2015,
  author    = {Saatchi, Mersa and Behl, Marc and N{\"o}chel, Ulrich and Lendlein, Andreas},
  title     = {Copolymer Networks From Oligo(epsilon-caprolactone) and n-Butyl Acrylate Enable a Reversible Bidirectional Shape-Memory Effect at Human Body Temperature},
  series = {Macromolecular rapid communications},
  volume    = {36},
  journal   = {Macromolecular rapid communications},
  number    = {10},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1022-1336},
  doi       = {10.1002/marc.201400729},
  pages     = {880 -- 884},
  year      = {2015},
  abstract  = {Exploiting the tremendous potential of the recently discovered reversible bidirectional shape-memory effect (rbSME) for biomedical applications requires switching temperatures in the physiological range. The recent strategy is based on the reduction of the melting temperature range (T-m) of the actuating oligo(epsilon-caprolactone) (OCL) domains in copolymer networks from OCL and n-butyl acrylate (BA), where the reversible effect can be adjusted to the human body temperature. In addition, it is investigated whether an rbSME in the temperature range close or even above T-m,T-offset (end of the melting transition) can be obtained. Two series of networks having mixtures of OCLs reveal broad T(m)s from 2 degrees C to 50 degrees C and from -10 degrees C to 37 degrees C, respectively. In cyclic, thermomechanical experiments the rbSME can be tailored to display pronounced actuation in a temperature interval between 20 degrees C and 37 degrees C. In this way, the application spectrum of the rbSME can be extended to biomedical applications.},
  language  = {en}
}
@article{LiangBehlLendlein2021,
  author    = {Liang, Xiao and Behl, Marc and Lendlein, Andreas},
  title     = {Dihydroxy terminated teroligomers from morpholine-2,5-diones},
  series = {European polymer journal : EPJ},
  volume    = {143},
  journal   = {European polymer journal : EPJ},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0014-3057},
  doi       = {10.1016/j.eurpolymj.2020.110189},
  pages     = {9},
  year      = {2021},
  abstract  = {Oligodepsipeptides (ODPs) attract increasing attention as degradable materials in controlled drug delivery or as building blocks for nano-carriers. Their strong intermolecular interactions provide high stability. Tailoring the side groups of the amino acid repeating units to achieve a strong affinity to particular drugs allows a high drug-loading capacity. Here we describe synthesis and characterization of dihydroxy terminated teroligodepsipeptides (ter-ODPs) by ring-opening copolymerization (ROP) of three different morpholine-2,5-diones (MDs) in bulk in order to provide a set of teroligomers with structural variation for drug release or transfection. Ter-ODPs with equivalent co-monomer feed ratios were prepared as well as ter-ODPs, in which the co-monomer feed ratio was varied between 9 mol\% and 78 mol\%. Ter-ODPs were synthesized by ROP using 1,1,10,10-tetra-n-butyl-1,10-distanna-2,9,11,18-tetraoxa-5,6,14,15-tetrasulfur-cyclodecane (tin(IV) alkoxide) that was obtained by the reaction of dibutyl tin(II) oxide with 2-hydroxyethyl disulfide. The number average molecular weight (M-n) of ter-ODPs, determined by H-1 NMR and gel permeation chromatography (GPC), ranged between 4000 g center dot mol(-1) and 8600 g center dot mol(-1). Co-monomer compositions in ter-ODPs could be controlled by changing the feed ratio of co-monomers as observed by H-1 NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The amount of remaining monomers as determined by H-1 NMR could be kept below 1 wt\%. Macrocycles as main sources of byproducts as determined from MALDI-TOF-MS measurements were significantly lower as compared to polymerization by Sn(Oct)(2). Glass-transition temperature (T-g) of ter-ODPs ranged between 59 degrees C and 70 degrees C.},
  language  = {en}
}
@article{FarhanChaudharyNoecheletal.2020,
  author    = {Farhan, Muhammad and Chaudhary, Deeptangshu and N{\"o}chel, Ulrich and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Electrical actuation of coated and composite fibers based on poly[ethylene-co-(vinyl acetate)]},
  series = {Macromolecular materials and engineering},
  volume    = {306},
  journal   = {Macromolecular materials and engineering},
  number    = {2},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1438-7492},
  doi       = {10.1002/mame.202000579},
  pages     = {8},
  year      = {2020},
  abstract  = {Robots are typically controlled by electrical signals. Resistive heating is an option to electrically trigger actuation in thermosensitive polymer systems. In this study electrically triggerable poly[ethylene-co-(vinyl acetate)] (PEVA)-based fiber actuators are realized as composite fibers as well as polymer fibers with conductive coatings. In the coated fibers, the core consists of crosslinked PEVA (cPEVA), while the conductive coating shell is achieved via a dip coating procedure with a coating thickness between 10 and 140 mu m. The conductivity of coated fibers sigma = 300-550 S m(-1) is much higher than that of the composite fibers sigma = 5.5 S m(-1). A voltage (U) of 110 V is required to heat 30 cm of coated fiber to a targeted temperature of approximate to 65 degrees C for switching in less than a minute. Cyclic electrical actuation investigations reveal epsilon '(rev) = 5 +/- 1\% reversible change in length for coated fibers. The fabrication of such electro-conductive polymeric actuators is suitable for upscaling so that their application potential as artificial muscles can be explored in future studies.},
  language  = {en}
}
@misc{FarhanChaudharyNoecheletal.2020,
  author    = {Farhan, Muhammad and Chaudhary, Deeptangshu and N{\"o}chel, Ulrich and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Electrical actuation of coated and composite fibers based on poly[ethylene-co-(vinyl acetate)]},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {2},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-57167},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-571679},
  pages     = {10},
  year      = {2020},
  abstract  = {Robots are typically controlled by electrical signals. Resistive heating is an option to electrically trigger actuation in thermosensitive polymer systems. In this study electrically triggerable poly[ethylene-co-(vinyl acetate)] (PEVA)-based fiber actuators are realized as composite fibers as well as polymer fibers with conductive coatings. In the coated fibers, the core consists of crosslinked PEVA (cPEVA), while the conductive coating shell is achieved via a dip coating procedure with a coating thickness between 10 and 140 mu m. The conductivity of coated fibers sigma = 300-550 S m(-1) is much higher than that of the composite fibers sigma = 5.5 S m(-1). A voltage (U) of 110 V is required to heat 30 cm of coated fiber to a targeted temperature of approximate to 65 degrees C for switching in less than a minute. Cyclic electrical actuation investigations reveal epsilon '(rev) = 5 +/- 1\% reversible change in length for coated fibers. The fabrication of such electro-conductive polymeric actuators is suitable for upscaling so that their application potential as artificial muscles can be explored in future studies.},
  language  = {en}
}
@article{BalkBehlNoecheletal.2021,
  author    = {Balk, Maria and Behl, Marc and N{\"o}chel, Ulrich and Lendlein, Andreas},
  title     = {Enzymatically triggered Jack-in-the-box-like hydrogels},
  series = {ACS applied materials \& interfaces / American Chemical Society},
  volume    = {13},
  journal   = {ACS applied materials \& interfaces / American Chemical Society},
  number    = {7},
  publisher = {American Chemical Society},
  address   = {Washington, DC},
  issn      = {1944-8244},
  doi       = {10.1021/acsami.1c00466},
  pages     = {8095 -- 8101},
  year      = {2021},
  abstract  = {Enzymes can support the synthesis or degradation of biomacromolecules in natural processes. Here, we demonstrate that enzymes can induce a macroscopic-directed movement of microstructured hydrogels following a mechanism that we call a "Jack-in-the-box" effect. The material's design is based on the formation of internal stresses induced by a deformation load on an architectured microscale, which are kinetically frozen by the generation of polyester locking domains, similar to a Jack-in-thebox toy (i.e., a compressed spring stabilized by a closed box lid). To induce the controlled macroscopic movement, the locking domains are equipped with enzyme-specific cleavable bonds (i.e., a box with a lock and key system). As a result of enzymatic reaction, a transformed shape is achieved by the release of internal stresses. There is an increase in entropy in combination with a swelling-supported stretching of polymer chains within the microarchitectured hydrogel (i.e., the encased clown pops-up with a pre-stressed movement when the box is unlocked). This utilization of an enzyme as a physiological stimulus may offer new approaches to create interactive and enzyme-specific materials for different applications such as an optical indicator of the enzyme's presence or actuators and sensors in biotechnology and in fermentation processes.},
  language  = {en}
}