@article{TarazonaMachatschekLendlein2019,
  author    = {Tarazona, Natalia A. and Machatschek, Rainhard Gabriel and Lendlein, Andreas},
  title     = {Unraveling the interplay between abiotic hydrolytic degradation and crystallization of bacterial polyesters comprising short and medium side-chain-length Polyhydroxyalkanoates},
  series = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences},
  volume    = {21},
  journal   = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences},
  number    = {2},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1525-7797},
  doi       = {10.1021/acs.biomac.9b01458},
  pages     = {761 -- 771},
  year      = {2019},
  abstract  = {Polyhydroxyalkanoates (PHAs) have attracted attention as degradable (co)polyesters which can be produced by microorganisms with variations in the side chain. This structural variation influences not only the thermomechanical properties of the material but also its degradation behavior. Here, we used Langmuir monolayers at the air-water (A-W) interface as suitable models for evaluating the abiotic degradation of two PHAs with different side-chain lengths and crystallinity. By controlling the polymer state (semi crystalline, amorphous), the packing density, the pH, and the degradation mechanism, we could draw several significant conclusions. (i) The maximum degree of crystallinity for a PHA film to be efficiently degraded up to pH = 12.3 is 40\%. (ii) PHA made of repeating units with shorter side-chain length are more easily hydrolyzed under alkaline conditions. The efficiency of alkaline hydrolysis decreased by about 65\% when the polymer was 40\% crystalline. (iii) In PHA films with a relatively high initial crystallinity, abiotic degradation initiated a chemicrystallization phenomenon, detected as an increase in the storage modulus (E'). This could translate into an increase in brittleness and reduction in the material degradability. Finally, we demonstrate the stability of the measurement system for long-term experiments, which allows degradation conditions for polymers that could closely simulate real-time degradation.},
  language  = {en}
}
@article{HoffmannMachatschekLendlein2020,
  author    = {Hoffmann, Falk and Machatschek, Rainhard Gabriel and Lendlein, Andreas},
  title     = {Understanding the impact of crystal lamellae organization on small molecule diffusion using a Monte Carlo approach},
  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    = {52-53},
  publisher = {Cambridge University Press},
  address   = {Cambridge},
  issn      = {2059-8521},
  doi       = {10.1557/adv.2020.386},
  pages     = {2737 -- 2749},
  year      = {2020},
  abstract  = {Many physicochemical processes depend on the diffusion of small molecules through solid materials. While crystallinity in polymers is advantageous with respect to structure performance, diffusion in such materials is difficult to predict. Here, we investigate the impact of crystal morphology and organization on the diffusion of small molecules using a lattice Monte Carlo approach. Interestingly, diffusion determined with this model does not depend on the internal morphology of the semi-crystalline regions. The obtained insight is highly valuable for developing predictive models for all processes in semi-crystalline polymers involving mass transport, like polymer degradation or drug release, and provide design criteria for the time-dependent functional behavior of multifunctional polymer systems.},
  language  = {en}
}
@article{ZhangLiuMachatscheketal.2022,
  author    = {Zhang, Shanshan and Liu, Yue and Machatschek, Rainhard Gabriel and Lendlein, Andreas},
  title     = {Ultrathin collagen type I films formed at the air-water interface},
  series = {MRS advances : a journal of the Materials Research Society (MRS)},
  volume    = {7},
  journal   = {MRS advances : a journal of the Materials Research Society (MRS)},
  number    = {4},
  publisher = {Springer Nature Switzerland AG},
  address   = {Cham},
  issn      = {2059-8521},
  doi       = {10.1557/s43580-021-00160-8},
  pages     = {56 -- 62},
  year      = {2022},
  abstract  = {Collagen-based biomaterials with oriented fibrils have shown great application potential in medicine. However, it is still challenging to control the type I collagen fibrillogenesis in ultrathin films. Here, we report an approach to produce cohesive and well-organized type I collagen ultrathin films of about 10 nm thickness using the Langmuir-Blodgett technique. Ellipsometry, rheology, and Brewster angle microscopy are applied to investigate in situ how the molecules behave at the air-water interface, both at room temperature and 37 degrees C. The interfacial storage modulus observed at room temperature vanishes upon heating, indicating the existence and disappearance of the network structure in the protein nanosheet. The films were spanning over holes as large as 1 mm diameter when transferred at room temperature, proving the strong cohesive interactions. A highly aligned and fibrillar structure was observed by atomic force microscopy (AFM) and optical microscopy.},
  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}
}
@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{FarhanRudolphKratzetal.2018,
  author    = {Farhan, Muhammad and Rudolph, Tobias and Kratz, Karl and Lendlein, Andreas},
  title     = {Torsional Fiber Actuators from Shape-memory Polymer},
  series = {MRS Advances},
  volume    = {3},
  journal   = {MRS Advances},
  number    = {63},
  publisher = {Cambridge Univ. Press},
  address   = {New York},
  issn      = {2059-8521},
  doi       = {10.1557/adv.2018.621},
  pages     = {3861 -- 3868},
  year      = {2018},
  abstract  = {Humanoid robots, prosthetic limbs and exoskeletons require soft actuators to perform their primary function, which is controlled movement. In this wont we explored whether crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) fibers, with different vinyl acetate (VA) content can serve as torsional fiber actuators. exhibiting temperature controlled reversible rotational changes. Broad melting transitions ranging from 50 to 90 degrees C for cPEVA18-165 or from 40 to 80 degrees C for cPEVA28-165 fibers in combination with complete crystallization at temperatures around 10 degrees C make them suitable actuating materials with adjustable actuation temperature ranges between 10 and 70 degrees C during repetitive cooling and heating. The obtained fibers exhibited a circular cross section with diameters around 0.4 +/- 0.1 mm, while a length of 4 cm was employed for the investigation of reversible rotational actuation after programming by twist insertion using 30 complete rotations at a temperature above melting transition. Repetitive heating and cooling between 10 to 60 degrees C or 70 degrees C of one-end-tethered programmed fibers revealed reversible rotations and torsional force. During cooling 3 +/- 1 complete rotations (Delta theta(r) = + 1080 +/- 360 degrees) in twisting direction were observed, while 4 +/- 1 turns in the opposite direction (Delta theta(r) = - 1440 +/- 1360 degrees) were found during heating. Such torsional fiber actuators, which are capable of approximately one rotation per cm fiber length, can serve as miniaturized rotary motors to provide rotational actuation in futuristic humanoid robots.},
  language  = {en}
}
@article{FolikumahBehlLendlein2021,
  author    = {Folikumah, Makafui Yao and Behl, Marc and Lendlein, Andreas},
  title     = {Thiol-Thioester exchange reactions in precursors enable pH-triggered hydrogel formation},
  series = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences},
  volume    = {22},
  journal   = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences},
  number    = {5},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1525-7797},
  doi       = {10.1021/acs.biomac.0c01690},
  pages     = {1875 -- 1884},
  year      = {2021},
  abstract  = {Bio-interactive hydrogel formation in situ requires sensory capabilities toward physiologically relevant stimuli. Here, we report on pH-controlled in situ hydrogel formation relying on latent cross-linkers, which transform from pH sensors to reactive molecules. In particular, thiopeptolide/thio-depsipeptides were capable of pH-sensitive thiol-thioester exchange reactions to yield a,co-dithiols, which react with maleimide-functionalized multi-arm polyethylene glycol to polymer networks. Their water solubility and diffusibility qualify thiol/thioester-containing peptide mimetics as sensory precursors to drive in situ localized hydrogel formation with potential applications in tissue regeneration such as treatment of inflamed tissues of the urinary tract.},
  language  = {en}
}
@article{FolikumahNeffeBehletal.2019,
  author    = {Folikumah, Makafui Yao and Neffe, Axel T. and Behl, Marc and Lendlein, Andreas},
  title     = {Thiol Michael-Type reactions of optically active mercapto-acids in aqueous medium},
  series = {MRS advances : a journal of the Materials Research Society},
  volume    = {4},
  journal   = {MRS advances : a journal of the Materials Research Society},
  number    = {46-47},
  publisher = {Springer Nature Switzerland AG},
  address   = {Cham},
  issn      = {2059-8521},
  doi       = {10.1557/adv.2019.308},
  pages     = {2515 -- 2525},
  year      = {2019},
  abstract  = {Defined chemical reactions in a physiological environment are a prerequisite for the in situ synthesis of implant materials potentially serving as matrix for drug delivery systems, tissue fillers or surgical glues. 'Click' reactions like thiol Michael-type reactions have been successfully employed as bioorthogonal reaction. However, due to the individual stereo-electronic and physical properties of specific substrates, an exact understanding their chemical reactivity is required if they are to be used for in-situ biomaterial synthesis. The chiral (S)-2-mercapto-carboxylic acid analogues of L-phenylalanine (SH-Phe) and L-leucine (SH-Leu) which are subunits of certain collagenase sensitive synthetic peptides, were explored for their potential for in-situ biomaterial formation via the thiol Michael-type reaction. In model reactions were investigated the kinetics, the specificity and influence of stereochemistry of this reaction. We could show that only reactions involving SH-Leu yielded the expected thiol-Michael product. The inability of SH-Phe to react was attributed to the steric hindrance of the bulky phenyl group. In aqueous media, successful reaction using SH-Leu is thought to proceed via the sodium salt formed in-situ by the addition of NaOH solution, which was intented to aid the solubility of the mercapto-acid in water. Fast reaction rates and complete acrylate/maleimide conversion were only realized at pH 7.2 or higher suggesting the possible use of SH-Leu under physiological conditions for thiol Michael-type reactions. This method of in-situ formed alkali salts could be used as a fast approach to screen mercapto-acids for thio Michael-type reactions without the synthesis of their corresponding esters.},
  language  = {en}
}
@article{MachatschekHeuchelLendlein2021,
  author    = {Machatschek, Rainhard Gabriel and Heuchel, Matthias and Lendlein, Andreas},
  title     = {Thin-layer studies on surface functionalization of polyetherimide},
  series = {Journal of materials research : JMR / Materials Research Society},
  volume    = {37},
  journal   = {Journal of materials research : JMR / Materials Research Society},
  number    = {1},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {0884-2914},
  doi       = {10.1557/s43578-021-00339-7},
  pages     = {67 -- 76},
  year      = {2021},
  abstract  = {Among the high-performance and engineering polymers, polyimides and the closely related polyetherimide (PEI) stand out by their capability to react with nucleophiles under relatively mild conditions. By targeting the phthalimide groups in the chain backbone, post-functionalization offers a pathway to adjust surface properties such as hydrophilicity, solvent resistance, and porosity. Here, we use ultrathin PEI films on a Langmuir trough as a model system to investigate the surface functionalization with ethylene diamine and tetrakis(4-aminophenyl)porphyrin as multivalent nucleophiles. By means of AFM, Raman spectroscopy, and interfacial rheology, we show that hydrolysis enhances the chemical and mechanical stability of ultrathin films and allows for the formation of EDC/NHS-activated esters. Direct amidation of PEI was achieved in the presence of a Lewis acid catalyst, resulting in free amine groups rather than cross-linking. When comparing amidation with hydrolysis, we find a greater influence of the latter on material properties.},
  language  = {en}
}
@article{NeffeLoewenbergJulichGruneretal.2021,
  author    = {Neffe, Axel T. and L{\"o}wenberg, Candy and Julich-Gruner, Konstanze K. and Behl, Marc and Lendlein, Andreas},
  title     = {Thermally-induced shape-memory behavior of degradable gelatin-based networks},
  series = {International journal of molecular sciences},
  volume    = {22},
  journal   = {International journal of molecular sciences},
  number    = {11},
  publisher = {Molecular Diversity Preservation International},
  address   = {Basel},
  issn      = {1422-0067},
  doi       = {10.3390/ijms22115892},
  pages     = {15},
  year      = {2021},
  abstract  = {Shape-memory hydrogels (SMH) are multifunctional, actively-moving polymers of interest in biomedicine. In loosely crosslinked polymer networks, gelatin chains may form triple helices, which can act as temporary net points in SMH, depending on the presence of salts. Here, we show programming and initiation of the shape-memory effect of such networks based on a thermomechanical process compatible with the physiological environment. The SMH were synthesized by reaction of glycidylmethacrylated gelatin with oligo(ethylene glycol) (OEG) alpha,omega-dithiols of varying crosslinker length and amount. Triple helicalization of gelatin chains is shown directly by wide-angle X-ray scattering and indirectly via the mechanical behavior at different temperatures. The ability to form triple helices increased with the molar mass of the crosslinker. Hydrogels had storage moduli of 0.27-23 kPa and Young's moduli of 215-360 kPa at 4 degrees C. The hydrogels were hydrolytically degradable, with full degradation to water-soluble products within one week at 37 degrees C and pH = 7.4. A thermally-induced shape-memory effect is demonstrated in bending as well as in compression tests, in which shape recovery with excellent shape-recovery rates R-r close to 100\% were observed. In the future, the material presented here could be applied, e.g., as self-anchoring devices mechanically resembling the extracellular matrix.},
  language  = {en}
}