TY - JOUR A1 - Gu, Sasa A1 - Risse, Sebastian A1 - Lu, Yan A1 - Ballauff, Matthias T1 - Mechanism of the oxidation of 3,3′,5,5′-tetramethylbenzidine catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes BT - a kinetic study JF - ChemPhysChem N2 - Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3 ',5,5 '-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H2O2) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Pt). Due to the high stability of SPB-Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H2O2 and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir-Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles. KW - kinetics KW - nanoparticles KW - reaction mechanisms KW - spherical polyelectrolyte KW - brushes KW - UV KW - vis spectroscopy Y1 - 2019 U6 - https://doi.org/10.1002/cphc.201901087 SN - 1439-4235 SN - 1439-7641 VL - 21 IS - 5 SP - 450 EP - 458 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Lendlein, Andreas T1 - Fundamental insights in PLGA degradation from thin film studies JF - Journal of controlled release : official journal of the Controlled Release Society and of the Japanese Society of Drug Delivery Systems N2 - Poly(lactide-co-glycolide)s are commercially available degradable implant materials, which are typically selected based on specifications given by the manufacturer, one of which is their molecular weight. Here, we address the question whether variations in the chain length and their distribution affect the degradation behavior of Poly[(rac-lactide)-co-glycolide]s (PDLLGA). The hydrolysis was studied in ultrathin films at the air-water interface in order to rule out any morphological effects. We found that both for purely hydrolytic degradation as well as under enzymatic catalysis, the molecular weight has very little effect on the overall degradation kinetics of PDLLGAs. The quantitative analysis suggested a random scission mechanism. The monolayer experiments showed that an acidic micro-pH does not accelerate the degradation of PDLLGAs, in contrast to alkaline conditions. The degradation experiments were combined with interfacial rheology measurements, which showed a drastic decrease of the viscosity at little mass loss. The extrapolated molecular weight behaved similar to the viscosity, dropping to a value near to the solubility limit of PDLLGA oligomers before mass loss set in. This observation suggests a solubility controlled degradation of PDLLGA. Conclusively, the molecular weight affects the degradation of PDLLGA devices mostly in indirect ways, e.g. by determining their morphology and porosity during fabrication. Our study demonstrates the relevance of the presented Langmuir degradation method for the design of controlled release systems. KW - PDLLGA KW - Degradation KW - Langmuir monolayer Y1 - 2019 U6 - https://doi.org/10.1016/j.jconrel.2019.12.044 SN - 0168-3659 SN - 1873-4995 VL - 319 SP - 276 EP - 284 PB - Elsevier CY - New York ER - TY - JOUR A1 - Mink, Albert A1 - McHardy, Christopher A1 - Bressel, Lena A1 - Rauh, Cornelia A1 - Krause, Mathias J. T1 - Radiative transfer lattice Boltzmann methods BT - 3D models and their performance in different regimes of radiative transfer JF - Journal of quantitative spectroscopy & radiative transfer N2 - The numerical prediction of radiative transport is a challenging task due to the complexity of the radiative transport equation. We apply the lattice Boltzmann method (LBM), originally developed for fluid flow problems, to solve the radiative transport in volume. One model (meso RTLBM) is derived directly from a discretization of the radiative transport equation, yielding in a precise but numerical costly scheme. The second model (macro RTLBM) solves the Helmholtz equation, which is a proper approximation for highly scattering volumes. Both numerical algorithms are validated against Monte-Carlo data for a set of 35 optical parameters, which correspond to radiative transport ranging from ballistic to diffuse regimes. Together with a set of four benchmark simulations, the comprehensive validation concludes the overall quality and detects asymptotic trends for radiative transport LBM. Furthermore, an accuracy map is presented, which summarizes the error for all parameters. This graph allows to determine the validity range for both radiative transport LBM at a glance. Finally, comprehensive guidelines are formulated to facilitate the choice of the radiative transport LBM model. KW - Radiative transport KW - Lattice Boltzmann methods KW - Monte-Carlo KW - Analysis scattering kernel KW - Optical parameter set Y1 - 2019 U6 - https://doi.org/10.1016/j.jqsrt.2019.106810 SN - 0022-4073 SN - 1879-1352 VL - 243 PB - Pergamon Press CY - Oxford ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre BT - simple means to characterize the electron distribution of carbenes JF - Magnetic resonance in chemistry N2 - Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures). KW - C-13 chemical shift KW - carbenes KW - zwitterions KW - carbene electron deficiency KW - nucleus-independent chemical shifts (NICS) KW - through space NMR shieldings KW - (TSNMRS) Y1 - 2019 U6 - https://doi.org/10.1002/mrc.4979 SN - 0749-1581 SN - 1097-458X VL - 58 IS - 3 SP - 280 EP - 292 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Nie, Yan A1 - Wang, Weiwei A1 - Xu, Xun A1 - Zou, Jie A1 - Bhuvanesh, Thanga A1 - Schulz, Burkhard A1 - Ma, Nan A1 - Lendlein, Andreas T1 - Enhancement of human induced pluripotent stem cells adhesion through multilayer laminin coating JF - Clinical hemorheology and microcirculation : blood flow and vessels N2 - Bioengineered cell substrates are a highly promising tool to govern the differentiation of stem cells in vitro and to modulate the cellular behavior in vivo. While this technology works fine for adult stem cells, the cultivation of human induced pluripotent stem cells (hiPSCs) is challenging as these cells typically show poor attachment on the bioengineered substrates, which among other effects causes substantial cell death. Thus, very limited types of surfaces have been demonstrated suitable for hiPSC cultures. The multilayer coating approach that renders the surface with diverse chemical compositions, architectures, and functions can be used to improve the adhesion of hiPSCs on the bioengineered substrates. We hypothesized that a multilayer formation based on the attraction of molecules with opposite charges could functionalize the polystyrene (PS) substrates to improve the adhesion of hiPSCs. Polymeric substrates were stepwise coated, first with dopamine to form a polydopamine (PDA) layer, second with polylysine and last with Laminin-521. The multilayer formation resulted in the variation of hydrophilicity and chemical functionality of the surfaces. Hydrophilicity was detected using captive bubble method and the amount of primary and secondary amines on the surface was quantified by fluorescent staining. The PDA layer effectively immobilized the upper layers and thereby improved the attachment of hiPSCs. Cell adhesion was enhanced on the surfaces coated with multilayers, as compared to those without PDA and/or polylysine. Moreover, hiPSCs spread well over this multilayer laminin substrate. These cells maintained their proliferation capacity and differentiation potential. The multilayer coating strategy is a promising attempt for engineering polymer-based substrates for the cultivation of hiPSCs and of interest for expanding the application scope of hiPSCs. KW - Polymeric substrate KW - surface coating KW - induced pluripotent stem cells KW - cell adhesion Y1 - 2019 U6 - https://doi.org/10.3233/CH-189318 SN - 1386-0291 SN - 1875-8622 VL - 70 IS - 4 SP - 531 EP - 542 PB - IOS Press CY - Amsterdam ER - TY - JOUR A1 - Breternitz, Joachim A1 - Lehmann, Frederike A1 - Barnett, Sarah A. A1 - Nowell, Harriott A1 - Schorr, Susan T1 - Role of the Iodide-methylammonium interaction in the ferroelectricity of CH3NH3PbI3 JF - Angewandte Chemie - international edition N2 - Excellent conversion efficiencies of over 20% and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long-range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions. Y1 - 2019 VL - 59 IS - 1 PB - John Wiley & Sons, Inc. CY - New Jersey ER - TY - JOUR A1 - Unuabonah, Emmanuel Iyayi A1 - Nöske, Robert A1 - Weber, Jens A1 - Günter, Christina A1 - Taubert, Andreas T1 - New micro/mesoporous nanocomposite material from low-cost sources for the efficient removal of aromatic and pathogenic pollutants from water JF - Beilstein journal of nanotechnology N2 - A new micro/mesoporous hybrid clay nanocomposite prepared from kaolinite clay, Carica papaya seeds, and ZnCl2 via calcination in an inert atmosphere is presented. Regardless of the synthesis temperature, the specific surface area of the nanocomposite material is between approximate to 150 and 300 m(2)/g. The material contains both micro- and mesopores in roughly equal amounts. X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy suggest the formation of several new bonds in the materials upon reaction of the precursors, thus confirming the formation of a new hybrid material. Thermogravimetric analysis/differential thermal analysis and elemental analysis confirm the presence of carbonaceous matter. The new composite is stable up to 900 degrees C and is an efficient adsorbent for the removal of a water micropollutant, 4-nitrophenol, and a pathogen, E. coli, from an aqueous medium, suggesting applications in water remediation are feasible. KW - 4-nitrophenol KW - Carica papaya seeds KW - clay KW - E. coli KW - micro/mesoporous KW - nanocomposite KW - water remediation Y1 - 2019 U6 - https://doi.org/10.3762/bjnano.10.11 SN - 2190-4286 VL - 10 SP - 119 EP - 131 PB - Beilstein-Institut zur Förderung der Chemischen Wissenschaften CY - Frankfurt, Main ER - TY - JOUR A1 - Saretia, Shivam A1 - Machatschek, Rainhard Gabriel A1 - Schulz, Burkhard A1 - Lendlein, Andreas T1 - Reversible 2D networks of oligo(epsilon-caprolactone) at the air-water interface JF - Biomedical Materials N2 - Hydroxyl terminated oligo(epsilon-caprolactone) (OCL) monolayers were reversibly cross-linked forming two dimensional networks (2D) at the air-water interface. The equilibrium reaction with glyoxal as the cross-linker is pH-sensitive. Pronounced contraction in the area of the prepared 2DOCL films in dependence of surface pressure and time revealed the process of the reaction. Cross-linking inhibited crystallization and retarded enzymatic degradation of the OCLfilm. Altering the subphase pH led to a cleavage of the covalent acetal cross-links. The reversibility of the covalent acetal cross-links was proved by observing an identical isotherm as non-cross-linked sample. Besides as model systems, these customizable reversible OCL2D networks are intended for use as pHresponsive drug delivery systems or functionalized cell culture substrates. KW - poly(epsilon-caprolactone) KW - langmuir monolayer KW - two dimensional network KW - crystallization KW - cross-linking Y1 - 2019 U6 - https://doi.org/10.1088/1748-605X/ab0cef SN - 1748-6041 SN - 1748-605X VL - 14 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Khodeir, Miriam A1 - Ernould, Bruno A1 - Brassinne, Jeremy A1 - Ghiassinejad, Sina A1 - Jia, He A1 - Antoun, Sayed A1 - Friebe, Christian A1 - Schubert, Ulrich S. A1 - Kochovski, Zdravko A1 - Lu, Yan A1 - Van Ruymbeke, Evelyne A1 - Gohy, Jean-Francois T1 - Synthesis and characterisation of redox hydrogels based on stable nitroxide radicals JF - Soft matter N2 - The principle of encapsulation/release of a guest molecule from stimuli responsive hydrogels (SRHs) is mainly realised with pH, temperature or light stimuli. However, only a limited number of redox responsive hydrogels have been investigated so far. We report here the development of a SRH that can release its guest molecule upon a redox stimulus. To obtain this redox hydrogel, we have introduced into the hydrogel the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) stable nitroxide radical, which can be reversibly oxidized into an oxoammonium cation (TEMPO+). Water solubility is provided by the presence of the (oligoethyleneglycol)methacrylate (OEGMA) comonomer. Electrochemical and mechanical characterization showed that those gels exhibit interesting physicochemical properties, making them very promising candidates for practical use in a wide range of applications. Y1 - 2019 U6 - https://doi.org/10.1039/c9sm00905a SN - 1744-683X SN - 1744-6848 VL - 15 IS - 31 SP - 6418 EP - 6426 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Hauser, Sandra A1 - Wodtke, Robert A1 - Tondera, Christoph A1 - Wodtke, Johanna A1 - Neffe, Axel T. A1 - Hampe, Jochen A1 - Lendlein, Andreas A1 - Löser, Reik A1 - Pietzsch, Jens T1 - Characterization of Tissue Transglutaminase as a Potential Biomarker for Tissue Response toward Biomaterials JF - ACS biomaterials science & engineering N2 - Tissue transglutaminase (TGase 2) is proposed to be important for biomaterial-tissue interactions due to its presence and versatile functions in the extracellular environment. TGase 2 catalyzes the cross-linking of proteins through its Ca2+-dependent acyltransferase activity. Moreover, it enhances the interactions between fibronectin and integrins, which in turn mediates the adhesion, migration, and motility of the cells. TGase 2 is also a key player in the pathogenesis of fibrosis. In this study, we investigated whether TGase 2 is present at the biomaterial tissue interface and might serve as an informative biomarker for the visualization of tissue response toward gelatin-based biomaterials. Two differently cross-linked hydrogels were used, which were obtained by the reaction of gelatin with lysine diisocyanate ethyl ester. The overall expression of TGase 2 by endothelial cells, macrophages, and granulocytes was partly influenced by contact to the hydrogels or their degradation products, although no clear correlation was evidenced. In contrast, the secretion of TGase 2 differed remarkably between the different cells, indicating that it might be involved in the cellular reaction toward gelatin-based hydrogels. The hydrogels were implanted subcutaneously in immunocompetent, hairless SKH1-Elite mice. Ex vivo immunohistochemical analysis of tissue sections over 112 days revealed enhanced expression of TGase 2 around the hydrogels, in particular at days 14 and 21 post-implantation. The incorporation of fluorescently labeled cadaverine derivatives for the detection of active TGase 2 was in accordance with the results of the expression analysis. The presence of an irreversible inhibitor of TGase 2 led to attenuated incorporation of the cadaverines, which verified the catalytic action of TGase 2. Our in vitro and ex vivo results verified TGase 2 as a potential biomarker for tissue response toward gelatin-based hydrogels. In vivo, no TGase 2 activity was detectable, which is mainly attributed to the unfavorable physicochemical properties of the cadaverine probe used. KW - extracellular matrix modifying enzymes KW - gelatin-based hydrogels KW - biomaterial-tissue interface KW - polyamines KW - optical imaging Y1 - 2019 U6 - https://doi.org/10.1021/acsbiomaterials.9b01299 SN - 2373-9878 VL - 5 IS - 11 SP - 5979 EP - 5989 PB - American Chemical Society CY - Washington ER -