TY - JOUR A1 - Rottke, Falko O. A1 - Schulz, Burkhard A1 - Richau, Klaus A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - An ellipsometric approach towards the description of inhomogeneous polymer-based Langmuir layers JF - Beilstein journal of nanotechnology N2 - The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(omega-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, R-q. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified. KW - ellipsometric mapping KW - Langmuir monolayer KW - polyester KW - root mean square roughness KW - spectroscopic ellipsometry Y1 - 2016 U6 - https://doi.org/10.3762/bjnano.7.107 SN - 2190-4286 VL - 7 SP - 1156 EP - 1165 PB - Beilstein-Institut zur Förderung der Chemischen Wissenschaften CY - Frankfurt, Main ER - TY - JOUR A1 - Rossberg, Joana A1 - Rottke, Falko O. A1 - Schulz, Burkhard A1 - Lendlein, Andreas T1 - Enzymatic Degradation of Oligo(epsilon-caprolactone)s End-Capped with Phenylboronic Acid Derivatives at the Air-Water Interface JF - Macromolecular rapid communications N2 - The influence of terminal functionalization of oligo(epsilon-caprolactone)s (OCL) with phenylboronic acid pinacol ester or phenylboronic acid on the enzymatic degradation behavior at the air-water interface is investigated by the Langmuir monolayer degradation technique. While the unsubstituted OCL immediately degrades after injection of the enzyme lipase from Pseudomonas cepacia, enzyme molecules are incorporated into the films based on end-capped OCL before degradation. This incorporation of enzymes does not inhibit or suppress the film degradation, but retards it significantly. A specific binding of lipase to the polymer monolayer allows studying the enzymatic activity of bound proteins and the influence on the degradation process. The functionalization of a macromolecule with phenyl boronic acid groups is an approach to investigate their interactions with diol-containing biomolecules like sugars and to monitor their specified impact on the enzymatic degradation behavior at the air-water interface. Y1 - 2016 U6 - https://doi.org/10.1002/marc.201600471 SN - 1022-1336 SN - 1521-3927 VL - 37 SP - 1966 EP - 1971 PB - Wiley-VCH CY - Weinheim 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 - Bhuvanesh, Thanga A1 - Saretia, Shivam A1 - Roch, Toralf A1 - Schöne, Anne-Christin A1 - Rottke, Falko O. A1 - Kratz, Karl A1 - Wang, Weiwei A1 - Ma, Nan A1 - Schulz, Burkhard A1 - Lendlein, Andreas T1 - Langmuir-Schaefer films of fibronectin as designed biointerfaces for culturing stem cells JF - Polymers for advanced technologies N2 - Glycoproteins adsorbing on an implant upon contact with body fluids can affect the biological response in vitro and in vivo, depending on the type and conformation of the adsorbed biomacromolecules. However, this process is poorly characterized and so far not controllable. Here, protein monolayers of high molecular cohesion with defined density are transferred onto polymeric substrates by the Langmuir-Schaefer (LS) technique and were compared with solution deposition (SO) method. It is hypothesized that on polydimethylsiloxane (PDMS), a substrate with poor cell adhesion capacity, the fibronectin (FN) layers generated by the LS and SO methods will differ in their organization, subsequently facilitating differential stem cell adhesion behavior. Indeed, atomic force microscopy visualization and immunofluorescence images indicated that organization of the FN layer immobilized on PDMS was uniform and homogeneous. In contrast, FN deposited by SO method was rather heterogeneous with appearance of structures resembling protein aggregates. Human mesenchymal stem cells showed reduced absolute numbers of adherent cells, and the vinculin expression seemed to be higher and more homogenously distributed after seeding on PDMS equipped with FN by LS in comparison with PDMS equipped with FN by SO. These divergent responses could be attributed to differences in the availability of adhesion molecule ligands such as the Arg-Gly-Asp (RGD) peptide sequence presented at the interface. The LS method allows to control the protein layer characteristics, including the thickness and the protein orientation or conformation, which can be harnessed to direct stem cell responses to defined outcomes, including migration and differentiation. Copyright (c) 2016 John Wiley & Sons, Ltd. KW - Langmuir-Schaefer method KW - protein adsorption KW - stem cell adhesion KW - cell culture KW - fibronectin Y1 - 2017 U6 - https://doi.org/10.1002/pat.3910 SN - 1042-7147 SN - 1099-1581 VL - 28 SP - 1305 EP - 1311 PB - Wiley CY - Hoboken 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 - Machatschek, Rainhard Gabriel A1 - Schulz, Burkhard A1 - Lendlein, Andreas T1 - The influence of pH on the molecular degradation mechanism of PLGA JF - MRS Advances N2 - Poly[(rac-lactide)-co-glycolide] (PLGA) is used in medicine to provide mechanical support for healing tissue or as matrix for controlled drug release. The properties of this copolymer depend on the evolution of the molecular weight of the material during degradation. which is determined by the kinetics of the cleavage of hydrolysable bonds. The generally accepted description of the degradation of PLGA is a random fragmentation that is autocatalyzed by the accumulation of acidic fragments inside the bulk material. Since mechanistic studies with lactide oligomers have concluded a chain-end scission mechanism and monolayer degradation experiments with polylactide found no accelerated degradation at lower pH, we hypothesize that the impact of acidic fragments on the molecular degradation kinetics of PLGA is overestimated By means of the Langmuir monolayer degradation technique. the molecular degradation kinetics of PLGA at different pH could be determined. Protons did not catalyze the degradation of PLGA. The molecular mechanism at neutral pH and low pH is a combination of random and chainend-cut events, while the degradation under strongly alkaline conditions is determined by rapid chainend cuts. We suggest that the degradation of bulk PLGA is not catalyzed by the acidic degradation products. Instead. increased concentration of small fragments leads to accelerated mass loss via fast chain-end cut events. In the future, we aim to substantiate the proposed molecular degradation mechanism of PLGA with interfacial rheology. Y1 - 2018 U6 - https://doi.org/10.1557/adv.2018.602 SN - 2059-8521 VL - 3 IS - 63 SP - 3883 EP - 3889 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Bhuvanesh, Thanga A1 - Machatschek, Rainhard Gabriel A1 - Lysyakova, Liudmila A1 - Kratz, Karl A1 - Schulz, Burkhard A1 - Ma, Nan A1 - Lendlein, Andreas T1 - Collagen type-IV Langmuir and Langmuir-Schafer layers as model biointerfaces to direct stem cell adhesion JF - Biomedical materials : materials for tissue engineering and regenerative medicine N2 - In biomaterial development, the design of material surfaces that mimic the extra-cellular matrix (ECM) in order to achieve favorable cellular instruction is rather challenging. Collagen-type IV (Col-IV), the major scaffolding component of Basement Membranes (BM), a specialized ECM with multiple biological functions, has the propensity to form networks by self-assembly and supports adhesion of cells such as endothelial cells or stem cells. The preparation of biomimetic Col-IV network-like layers to direct cell responses is difficult. We hypothesize that the morphology of the layer, and especially the density of the available adhesion sites, regulates the cellular adhesion to the layer. The Langmuir monolayer technique allows for preparation of thin layers with precisely controlled packing density at the air-water (A-W) interface. Transferring these layers onto cell culture substrates using the Langmuir-Schafer (LS) technique should therefore provide a pathway for preparation of BM mimicking layers with controlled cell adherence properties. In situ characterization using ellipsometry and polarization modulation-infrared reflection absorption spectroscopy of Col-IV layer during compression at the A-W interface reveal that there is linear increase of surface molecule concentration with negligible orientational changes up to a surface pressure of 25 mN m(-1). Smooth and homogeneous Col-IV network-like layers are successfully transferred by LS method at 15 mN m(-1) onto poly(ethylene terephthalate) (PET), which is a common substrate for cell culture. In contrast, the organization of Col-IV on PET prepared by the traditionally employed solution deposition method results in rather inhomogeneous layers with the appearance of aggregates and multilayers. Progressive increase in the number of early adherent mesenchymal stem cells (MSCs) after 24 h by controlling the areal Col-IV density by LS transfer at 10, 15 and 20 mN m(-1) on PET is shown. The LS method offers the possibility to control protein characteristics on biomaterial surfaces such as molecular density and thereby, modulate cell responses. KW - collagen-IV KW - basement membrane KW - Langmuir-Schafer films KW - stem cell adhesion KW - protein KW - ellipsometry Y1 - 2019 U6 - https://doi.org/10.1088/1748-605X/aaf464 SN - 1748-6041 SN - 1748-605X VL - 14 IS - 2 PB - Inst. of Physics Publ. CY - Bristol ER - TY - JOUR A1 - Tarazona, Natalia A. A1 - Machatschek, Rainhard Gabriel A1 - Schulz, Burkhard A1 - Auxiliadora Prieto Jiménez, M. A1 - Lendlein, Andreas T1 - Molecular Insights into the Physical Adsorption of Amphiphilic Protein PhaF onto Copolyester Surfaces JF - Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences N2 - Phasins are amphiphilic proteins located at the polymer-cytoplasm interface of bacterial polyhydroxyalkanoates (PHA). The immobilization of phasins on biomaterial surfaces is a promising way to enhance the hydrophilicity and supply cell- directing elements in bioinstructing processes. Optimizing the physical adsorption of phasins requires deep insights into molecular processes during polymer-protein interactions to preserve their structural conformation while optimizing surface coverage. Here, the assembly, organization, and stability of phasin PhaF from Pseudomonas putida at interfaces is disclosed. The Langmuir technique, combined with in situ microscopy and spectroscopic methods, revealed that PhaF forms stable and robust monolayers at different temperatures, with an almost flat orientation of its alpha-helix at the air-water interface. PhaF adsorption onto preformed monolayers of poly[(3-R-hydroxyoctanoate)-co-(3-R-hydroxyhexanoate)] (PHOHHx), yields stable mixed layers below pi = similar to 15.7 mN/m. Further insertion induces a molecular reorganization. PHOHHx with strong surface hydrophobicity is a more adequate substrate for PhaF adsorption than the less hydrophobic poly[(rac-lactide)-co-glycolide] (PLGA). The observed orientation of the main axis of the protein in relation to copolyester interfaces ensures the best exposure of the hydrophobic residues, providing a suitable coating strategy for polymer functionalization. Y1 - 2019 U6 - https://doi.org/10.1021/acs.biomac.9b00069 SN - 1525-7797 SN - 1526-4602 VL - 20 IS - 9 SP - 3242 EP - 3252 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Lavrenko, Peter N. A1 - Strelina, Irina A. A1 - Okatova, Olga V. A1 - Schulz, Burkhard T1 - Orientation of naphthylene ring in the new poly(naphthylen-1,3,4-oxadiazole)s molecules Y1 - 1996 ER - TY - JOUR A1 - Bruma, Maria A1 - Hamciuc, Corneliu A1 - Hamciuc, Elena A1 - Mercer, Frank W. A1 - Belomoina, Nataliya A1 - Schulz, Burkhard T1 - Heterocyclic polyamides containing hexafluoroisopropylidene groups Y1 - 1996 ER - TY - JOUR A1 - Bruma, Maria A1 - Hamciuc, Corneliu A1 - Sava, Ion A1 - Hamciuc, Elena A1 - Mercer, Frank W. A1 - Fritzsche, P. A1 - Schulz, Burkhard T1 - High temperature polyamides containing pendant imide groups Y1 - 1996 ER - TY - JOUR A1 - Zhu, Shigen A1 - Schulz, Burkhard A1 - Bruma, Maria A1 - Brehmer, Ludwig T1 - Comparative study of the thermal properties of related aromatic polyhydrazides and poly(1,3,4-oxadiazole)s Y1 - 1996 UR - http://www3.interscience.wiley.com/journal/5401/home?CRETRY=1&SRETRY=0 U6 - https://doi.org/10.1002/(SICI)1099-1581(199612)7:12<879::AID-PAT600>3.0.CO;2-X SN - 1042-7147 ER - TY - JOUR A1 - Freydank, Anke-Christine A1 - Janietz, Silvia A1 - Schulz, Burkhard T1 - Synthesis and electrochemical behaviour of Amphiphilic 1,3,4-Oxadiazole derivatives Y1 - 1998 ER - TY - JOUR A1 - Hamciuc, Elena A1 - Hamciuc, Corneliu A1 - Bruma, Maria A1 - Stoleriu, Andre A1 - Schulz, Burkhard T1 - Poly(hydrazide-ester)s and poly(1,3,4-oxadiazole-ester)s containing pendent phenoxy groups N2 - A series of new arornatic poly(hydrazide-ester)s has been synthesized by solution polycondensation of two diacid dichlorides containing preformed ester groups with phenoxyterephthaloyl dihydrazide or with a mixture of phenoxyterephthaloyl dihydrazide with terephthaloyl- or isophthaloyl dihydrazide in N-methyl-2-pyrrolidinone. The thermal cyclization of the poly(hydrazide-ester)s gave the corresponding poly(1,3,4-oxadiazole-ester)s containing pendent phenoxy groups. The polymers were characterized by viscometry, solubility measurements, IR spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Y1 - 1997 ER - TY - JOUR A1 - Orgzall, Ingo A1 - Lorenz, Bernd A1 - Mikat, Jürgen E. R. A1 - Dietel, Reinhard A1 - Knochenhauer, Gerald A1 - Schulz, Burkhard T1 - Raman and IR spectroscopic investigation of aromatic 1,3,4-oxadiazole polymers and oligomers N2 - The molecular structure of poly(p-phenylene-1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the a- and b-POD forms that are most obvious in the spectral region between 1500 and 1650 cm-1. The spectra for dimer and tetramer compounds already show the same features as found for longer chains. Based on molecular modelling calculations these differences are assigned to cis and trans conformations of the main chain segments. High pressure measurements show a linear shift of the Raman lines and support the result of the thermodynamic stability of the trans conformation. Y1 - 1997 ER - TY - JOUR A1 - Schulz, Burkhard A1 - Stiller, Burkhard A1 - Zetzsche, Thomas A1 - Knochenhauer, Gerald A1 - Brehmer, Ludwig T1 - Characterization of crystals based on 1,3,4-oxadiazoles by atomic force microscopy N2 - The surface structures of crystals based on aromatic oxadiazoles were investigated by AFM. The crystal structure for 2,5-di(p-tolyl)-1,3,4-oxadiazole (DTO) differs from that of 2,5-di (4-methoxycarbonyl-phenyl)-1,3,4- oxadiazole (DMPO). In DMPO all molecules show parallel orientation to the surface in such a way that the surface is formed as well as by the nitrogen atoms of the heterocyclic rings and the methyl groups of the ester substituents. By contrast, the oxadiazole molecules in DTO crystals are oriented perpendicular to the crystal surface. The experimental data are interpreted by molecular modelling. It is shown that there is a difference between molecular structure of the surface, as detected by AFM, and the bulk structure determined by X-ray diffraction. Y1 - 1997 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Zetzsche, Thomas A1 - Helms, Andreas A1 - Freydank, Anke-Christine A1 - Knochenhauer, Gerald A1 - Schulz, Burkhard A1 - Brehmer, Ludwig T1 - Organized molecular films of oxadiazole compounds formed by vacuum deposition Y1 - 1997 ER - TY - JOUR A1 - Schulz, Burkhard A1 - Bruma, Maria A1 - Brehmer, Ludwig T1 - Aromatic poly(1,3,4-oxadiazole)s as advanced materials N2 - Poly(1,3,4-oxadiazole)s have been the focus of considerable interest with regard to the- production of high- performance materials, particularly owing to their high thermal stability in oxidative atmosphere and specific properties determined by the structure of 1,3,4-oxadiazole ring, which, from the spectral and electronic points of view, is similar to a p-phenylene structure.[1] Besides their excellent resistance to high temperature, polyoxadiazoles have many desirable characteristics, such as good hydrolytic stability, high glass transition temperatures, low dielectric constants, and tough mechanical properties. Some polyoxadiazoles have semiconductive properties, other structures can be electrochemically doped and thus made conductive, and other have liquid-crystalline properties, which make them very attractive for a wide range of high-performance applications. They exhibit excellent fiber- and film-forming capabilities, thus being considered for use as heat-resistant reinforcing fibers for advanced composite materials, highly resistant fabrics for the filtration of hot gases, special membranes for gas separation or reverse osmosis, precursors for highly oriented graphite fibers, films, and blocks to be used in the construction of electronic instruments based on X-rays, neutron beams, or a-particles, or in the construction of nuclear reactor walls. Since they were first reported in 1961,[2] a wide variety of polymers containing 1,3,4-oxadiazole rings have been synthesized, and their preparation, characterization, and physico-mechanical properties have been periodically reviewed .[3-8] This article will present a general overview of this class of polymers and will refer to the work carried out by different researchers in the last ten years with the emphasis on the potential uses of such polymers as advanced materials. Y1 - 1997 ER - TY - JOUR A1 - Sava, Ion A1 - Szesztay, Marta A1 - Bruma, Maria A1 - Mercer, Frank W. A1 - Schulz, Burkhard T1 - Compared properties of aromatic polyamides containing silicon in the chain N2 - Two series of aromatic polyamides incorporating silicon together with phenylquinoxaline or with hexafluoroisopropylidene groups have been synthesized and their properties have been characterized and compared with those of related polymers. These polymers are easily soluble in polar amidic solvents such as N-rnethyl-2-pyrrolidinone and dimethylformamide, and in tetrahydrofuran, and can be cast into thin, transparent films from solution. The polyamides have weight- and number-average molecular weights in the range of 10000-40000 and 3000-6000, respectively, and polydispersities in the range of 3-10. They show glass transition temperatures in the range of 236 °C-275 °C and decomposition temperatures above 400 °C. The polymer films have low dielectric constants in the range of 3.26-3.68, and good mechanical properties (tensile strength 74-100 MPa, tensile modulus 180-386 MPa), thus being comparable with other high performance dielectrics. Y1 - 1997 ER - TY - JOUR A1 - Lavrenko, Peter N. A1 - Schulz, Burkhard A1 - Strelina, Irina A. A1 - Okatova, Olga V. T1 - Synthesis and molecular properties of new poly(naphthalene-1,3,4-oxadiazole)s N2 - Poly[(1,4-naphthalene)-2,5-diyl-1,3,4-oxadiazole] and poly[(2,6-naphthalene)-2,5-diyl-1,3,4-oxadiazole] have been synthesized and investigated in conc. H2S04, by the flow birefringence method in comparison with poly(1,4- phenylene)-2,5-diyl-1,3,4-oxadiazole]. Changes in conformation parameters and optical anisotropy of a chain unit induced by incorporation of the naphthalene groups into the macromolecule backbone have been evaluated. Y1 - 1997 ER -