@article{TetaliJankowskiLuetzowetal.2016, author = {Tetali, Sarada D. and Jankowski, Vera and Luetzow, Karola and Kratz, Karl and Lendlein, Andreas and Jankowski, Joachim}, title = {Adsorption capacity of poly(ether imide) microparticles to uremic toxins}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {61}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-152026}, pages = {657 -- 665}, year = {2016}, abstract = {Uremia is a phenomenon caused by retention of uremic toxins in the plasma due to functional impairment of kidneys in the elimination of urinary waste products. Uremia is presently treated by dialysis techniques like hemofiltration, dialysis or hemodiafiltration. However, these techniques in use are more favorable towards removing hydrophilic than hydrophobic uremic toxins. Hydrophobic uremic toxins, such as hydroxy hipuric acid (OH-HPA), phenylacetic acid (PAA), indoxyl sulfate (IDS) and p-cresylsulfate (pCRS), contribute substantially to the progression of chronic kidney disease (CKD) and cardiovascular disease. Therefore, objective of the present study is to test adsorption capacity of highly porous microparticles prepared from poly(ether imide) (PEI) as an alternative technique for the removal of uremic toxins. Two types of nanoporous, spherically shaped microparticles were prepared from PEI by a spraying/coagulation process. PEI particles were packed into a preparative HPLC column to which a mixture of the four types of uremic toxins was injected and eluted with ethanol. Eluted toxins were quantified by analytical HPLC. PEI particles were able to adsorb all four toxins, with the highest affinity for PAA and pCR. IDS and OH-HPA showed a partially non-reversible binding. In summary, PEI particles are interesting candidates to be explored for future application in CKD.}, language = {en} } @article{RottkeSchulzRichauetal.2016, author = {Rottke, Falko O. and Schulz, Burkhard and Richau, Klaus and Kratz, Karl and Lendlein, Andreas}, title = {An ellipsometric approach towards the description of inhomogeneous polymer-based Langmuir layers}, series = {Beilstein journal of nanotechnology}, volume = {7}, journal = {Beilstein journal of nanotechnology}, publisher = {Beilstein-Institut zur F{\~A}\Prderung der Chemischen Wissenschaften}, address = {Frankfurt, Main}, issn = {2190-4286}, doi = {10.3762/bjnano.7.107}, pages = {1156 -- 1165}, year = {2016}, abstract = {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.}, language = {en} } @article{GhobadiHeuchelKratzetal.2014, author = {Ghobadi, Ehsan and Heuchel, Matthias and Kratz, Karl and Lendlein, Andreas}, title = {Atomistic simulation of the shape-memory effect in dry and water swollen Poly[(rac-lactide)-co-glycolide] and copolyester urethanes thereof}, series = {Macromolecular chemistry and physics}, volume = {215}, journal = {Macromolecular chemistry and physics}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201300507}, pages = {65 -- 75}, year = {2014}, abstract = {An atomistic molecular dynamics simulation approach is applied to model the influence of urethane linker units as well as the addition of water molecules on the simulated shape-memory properties of poly[(rac-lactide)-co-glycolide] (PLGA) and PLGA-based copolyester urethanes comprising different urethane linkers. The shape-memory performance of these amorphous packing models is explored in a simulated heating-deformation-cooling-heating procedure. Depending on the type of incorporated urethane linker, the mechanical properties of the dry copolyester urethanes are found to be significantly improved compared with PLGA, which can be attributed to the number of intermolecular hydrogen bonds between the urethane units. Good shape-memory properties are observed for all the modeled systems. In the dry state, the shape fixation is found to be improved by implementation of urethane units. After swelling of the copolymer models with water, which results in a reduction of their glass transition temperatures, the relaxation kinetics during unloading and shape recovery are found to be substantially accelerated.}, language = {en} } @article{WangBaudisKratzetal.2015, author = {Wang, Li and Baudis, Stefan and Kratz, Karl and Lendlein, Andreas}, title = {Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization}, series = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry}, volume = {87}, journal = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry}, number = {11-12}, publisher = {De Gruyter}, address = {Berlin}, issn = {0033-4545}, doi = {10.1515/pac-2015-0607}, pages = {1085 -- 1097}, year = {2015}, abstract = {A versatile strategy to integrate multiple functions in a polymer based material is the formation of polymer networks with defined nanostructures. Here, we present synthesis and comprehensive characterization of covalently surface functionalized magnetic nanoparticles (MNPs) comprising a bi-layer oligomeric shell, using Sn(Oct)(2) as catalyst for a two-step functionalization. These hydroxy-terminated precursors for degradable magneto-and thermo-sensitive polymer networks were prepared via two subsequent surfaceinitiated ring-opening polymerizations (ROPs) with omega-pentadecalactone and e-caprolactone. A two-step mass loss obtained in thermogravimetric analysis and two distinct melting transitions around 50 and 85 degrees C observed in differential scanning calorimetry experiments, which are attributed to the melting of OPDL and OCL crystallites, confirmed a successful preparation of the modified MNPs. The oligomeric coating of the nanoparticles could be visualized by transmission electron microscopy. The investigation of degrafted oligomeric coatings by gel permeation chromatography and H-1-NMR spectroscopy showed an increase in number average molecular weight as well as the presence of signals related to both of oligo(omega-pentadecalactone) (OPDL) and oligo(e-caprolactone) (OCL) after the second ROP. A more detailed analysis of the NMR results revealed that only a few.-pentadecalactone repeating units are present in the degrafted oligomeric bi-layers, whereby a considerable degree of transesterification could be observed when OPDL was polymerized in the 2nd ROP step. These findings are supported by a low degree of crystallinity for OPDL in the degrafted oligomeric bi-layers obtained in wide angle X-ray scattering experiments. Based on these findings it can be concluded that Sn(Oct)(2) was suitable as catalyst for the preparation of nanosized bi-layered coated MNP precursors by a two-step ROP.}, language = {en} } @article{SchoeneSchulzRichauetal.2014, author = {Sch{\"o}ne, Anne-Christin and Schulz, Burkhard and Richau, Klaus and Kratz, Karl and Lendlein, Andreas}, title = {Characterization of Langmuir films prepared from copolyesterurethanes based on oligo(omega-pentadecalactone) and oligo(epsilon-caprolactone)segments}, series = {Macromolecular chemistry and physics}, volume = {215}, journal = {Macromolecular chemistry and physics}, number = {24}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201400377}, pages = {2437 -- 2445}, year = {2014}, abstract = {A series of multiblock copolymers (PDLCL) synthesized from oligo(omega-pentadecalactone) diol (OPDL) and oligo(epsilon-caprolactone) diol (OCL), which are linked by 2,2(4), 4-trimethyl-hexamethylene diisocyanate (TMDI), is investigated by the Langmuir monolayer technique at the air-water interface. Brewster angle microscopy (BAM) and spectroscopic ellipsometry are employed to characterize the polymer film morphologies in situ. PDLCL containing >= 40 wt\% OCL segments form homogeneous Langmuir monofilms after spreading. The film elasticity modulus decreases with increasing amounts of OPDL segments in the copolymer. In contrast, the OCL-free polyesterurethane OPDL-TMDI cannot be spread to monomolecular films on the water surface properly, and movable slabs are observed by BAM even at low surface pressures. The results of the in situ morphological characterization clearly show that essential information concerning the reliability of Langmuir monolayer degradation (LMD) experiments cannot be obtained from the evaluation of the pi-A isotherms only. Consequently, in situ morphological characterization turns out to be indispensable for characterization of Langmuir layers before LMD experiments.}, language = {en} } @article{BhuvaneshMachatschekLysyakovaetal.2019, author = {Bhuvanesh, Thanga and Machatschek, Rainhard Gabriel and Lysyakova, Liudmila and Kratz, Karl and Schulz, Burkhard and Ma, Nan and Lendlein, Andreas}, title = {Collagen type-IV Langmuir and Langmuir-Schafer layers as model biointerfaces to direct stem cell adhesion}, series = {Biomedical materials : materials for tissue engineering and regenerative medicine}, volume = {14}, journal = {Biomedical materials : materials for tissue engineering and regenerative medicine}, number = {2}, publisher = {Inst. of Physics Publ.}, address = {Bristol}, issn = {1748-6041}, doi = {10.1088/1748-605X/aaf464}, pages = {17}, year = {2019}, abstract = {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.}, language = {en} } @article{KruegerGengeSchulzKratzetal.2018, author = {Kr{\"u}ger-Genge, Anne and Schulz, Christian and Kratz, Karl and Lendlein, Andreas and Jung, Friedrich}, title = {Comparison of two substrate materials used as negative control in endothelialization studies}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {69}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, number = {3}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-189904}, pages = {437 -- 445}, year = {2018}, abstract = {The endothelialization of synthetic surfaces applied as cardiovascular implant materials is an important issue to ensure the anti-thrombotic quality of a biomaterial. However, the rapid and constant development of a functionallycon-fluent endothelial cell monolayer is challenging. In order to investigate the compatibility of potential implant materials with endothelial cells several in vitro studies are performed. Here, glass and tissue culture plates (TCP) are often used as reference materials for in vitro pre-testing. However, a direct comparison of both substrates is lacking. Therefore, a comparison of study results is difficult, since results are often related to various reference materials. In this study, the endothelialization of glass and TCP was investigated in terms of adherence, morphology, integrity, viability and function using human umbilical vein endothelial cells (HUVEC). On both substrates an almost functionally confluent HUVEC monolayer was developed after nine days of cell seeding with clearly visible cell rims, decreased stress fiber formation and a pronounced marginal filament band. The viability of HUVEC was comparable for both substrates nine days after cell seeding with only a few dead cells. According to that, the cell membrane integrity as well as the metabolic activity showed no differences between TCP and glass. However, a significant difference was observed for the secretion of IL-6 and IL-8. The concentration of both cytokines, which are associated with migratory activity, was increased in the supernatant of HUVEC seeded on TCP. This result matches well with the slightly increased number of adherent HUVEC on TCP. In conclusion, these findings indicate that both reference materials are almost comparable and can be used equivalently as control materials in in vitro endothelialization studies.}, language = {en} } @misc{ReicheKratzHofmannetal.2011, author = {Reiche, J{\"u}rgen and Kratz, Karl and Hofmann, Dieter and Lendlein, Andreas}, title = {Current status of Langmuir monolayer degradation of polymeric biomaterials}, series = {The international journal of artificial organs}, volume = {34}, journal = {The international journal of artificial organs}, number = {2}, publisher = {Wichtig}, address = {Milano}, issn = {0391-3988}, doi = {10.5301/IJAO.2011.6401}, pages = {123 -- 128}, year = {2011}, abstract = {Langmuir monolayer degradation (LMD) experiments with polymers possessing outstanding biomedical application potential yield information regarding the kinetics of their hydrolytic or enzymatic chain scission under well-defined and adjustable degradation conditions. A brief review is given of LMD investigations, including the author's own work on 2-dimensional (2D) polymer systems, providing chain scission data, which are not disturbed by simultaneously occurring transport phenomena, such as water penetration into the sample or transport of scission fragments out of the sample. A knowledge-based approach for the description and simulation of polymer hydrolytic and enzymatic degradation based on a combination of fast LMD experiments and computer simulation of the water penetration is briefly introduced. Finally, the advantages and disadvantages of this approach are discussed.}, language = {en} } @article{SauterKratzFarhanetal.2022, author = {Sauter, Tilman and Kratz, Karl and Farhan, Muhammad and Heuchel, Matthias and Lendlein, Andreas}, title = {Design and fabrication of fiber mesh actuators}, series = {Applied materials today}, volume = {29}, journal = {Applied materials today}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-9407}, doi = {10.1016/j.apmt.2022.101562}, pages = {13}, year = {2022}, abstract = {Soft actuator performance can be tuned by chemistry or mechanical manipulation, but this adjustability is limited especially in view of their growing technological relevance. Inspired from textile engineering, we designed and fabricated fiber mesh actuators and introduced new features like anisotropic behavior and soft-tissue like elastic deformability. Design criteria for the meshes are the formation of fiber bundles, the angle between fiber bundles in different stacked layers and covalent crosslinks forming within and between fibers at their interfacial contact areas. Through crosslinking the interfiber bond strength increased from a bond transmitting neither axial nor rotational loads (pin joint) to a bond strength capable of both (welded joint). For non-linear elastic stiffening, stacked fiber bundles with four embracing fibers were created forming microstructural rhombus shapes. Loading the rhombus diagonally allowed generation of "soft tissue"-like mechanics. By adjustment of stacking angles, the point of strong increase in stress is tuned. While the highest stresses are observed in aligned and crosslinked fiber mats along the direction of the fiber, the strongest shape-memory actuation behavior is found in randomly oriented fiber mats. Fiber mesh actuators controlled by temperature are of high significance as soft robot skins and as for active patches supporting tissue regeneration.}, language = {en} } @article{KumarBasuLemkeetal.2016, author = {Kumar, Reddi K. and Basu, Sayantani and Lemke, Horst-Dieter and Jankowski, Joachim and Kratz, Karl and Lendlein, Andreas and Tetali, Sarada D.}, title = {Effect of extracts of poly(ether imide) microparticles on cytotoxicity, ROS generation and proinflammatory effects on human monocytic (THP-1) cells}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {61}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-152027}, pages = {667 -- 680}, year = {2016}, abstract = {A high cell viability of around 99 +/- 18\% and 99 +/- 5\% was observed when THP-1 cells were cultured in the presence of aqueous extracts of the PEI microparticles in medium A and medium B respectively. The obtained microscopic data suggested that PEI particle extracts have no significant effect on cell death, oxidative stress or differentiation to macrophages. It was further found that the investigated proinflammatory markers in THP-1 cells were not up-regulated. These results are promising with regard to the biocompatibility of PEI microparticles and in a next step the hemocompatibility of the microparticles will be examined.}, language = {en} }