U Gross

Technische Universität Berlin, Berlín, Berlin, Germany

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Publications (65)171.53 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 3D imaging at a subcellular resolution is a powerful tool in the life sciences to investigate cells and their interactions with native tissues or artificial objects. While a tomographic experimental setup achieving a sufficient structural resolution can be established with either X-rays or electrons, the use of electrons is usually limited to very thin samples in transmission electron microscopy due to the poor penetration depths of electrons. The combination of a serial sectioning approach and scanning electron microscopy in state of the art dual beam experimental setups therefore offers a means to image highly resolved spatial details using a focused ion beam for slicing and an electron beam for imaging. The advantage of this technique over X-ray μCT or X-ray microscopy attributes to the fact that absorption is not a limiting factor in imaging and therefore even strong absorbing structures can be spatially reconstructed with a much higher possible resolution. This approach was used in this study to elucidate the effect of an electric potential on the morphology of cells from a hippocampal cell line (HT22) deposited on gold microelectrodes. While cells cultivated on two different controls (gold and polymer substrates) did show the expected stretched morphology, cells on both the anode and the cathode differed significantly. Cells deposited on the anode part of the electrode exhibited the most extreme deviation, being almost spherical and showed signs of chromatin condensation possibly indicating cell death. Furthermore, EDX was used as supplemental methodology for combined chemical and structural analyses.
    Ultramicroscopy 03/2011; 111(4):259-66. DOI:10.1016/j.ultramic.2010.12.017 · 2.44 Impact Factor

  • Advances in Medicine and Biology, Edited by Leon V. Berhardt, 01/2011: pages 285-306; Nova Biomedical Press., ISBN: 978-1-61122-791-8
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    ABSTRACT: Restoring peripheral nerve trauma is an important research field in regenerative medicine. One therapeutical approach is to use tissue engineered nerve conduits consisting of biodegradable polymers. These materials can be designed to include active agents to further stimulate or influence proliferation, maturation, differentiation or migration of specific neuronal cell in these nerve guides. We have developed a method to electrically deposit and immobilize neuronal cells and extracellular matrix proteins on self structured micro electrodes. These electrodes also present a feasible methodology to investigate electrical stimulation of nerve cells. In our approach, poly-D, L-lactide-co-glycolides ( PLGA) were investigated as possible substrate for these electrodes, while further allowing for the integration of model substances in a drug release concept. In a first approach, caffeine was used due to its well known effect of both stimulating and inhibiting effects on certain neuronal cells, while also allowing easy incorporation into PLGA via chemical means. A Plackett-Burman experimental design was used to find the optimum composition among different parameters such as drug concentration, polymer concentration, type of solvent and film-drying condition. The optimized drug loaded polymer films were tested for their release and degradation profile, and their behavior in cell culture. Finally, we are currently establishing an integrated experimental setup, combining caffeine modified PLGA film substrates with the manufacturing of the electrode structures to investigate cell deposition via electrical means and stimulation/ inhibition via chemical release.
    Advanced Materials Research 01/2010; 89-91:497-502. DOI:10.4028/www.scientific.net/AMR.89-91.497
  • R Zehbe · J Goebbels · Y Ibold · U Gross · H Schubert ·
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    ABSTRACT: Synchrotron radiation-based microcomputed tomography (SR-microCT) has become a valuable tool in the structural characterization of different types of materials, achieving volumetric details with micrometre resolution. Biomedical research dealing with porous polymeric biomaterials is one of the research fields which can benefit greatly from the use of SR-microCT. This study demonstrates that current experimental set-ups at synchrotron beamlines achieve a sufficiently high resolution in order to visualize the positions of individual cartilage cells cultivated on porous gelatine scaffolds made by a freeze-structuring technique. Depending on the processing parameters, the pore morphology of the scaffolds investigated was changed from large-pore sized but non-ordered structures to highly directional and fine pored. The cell-seeded scaffolds were stained with a combined Au/Ag stain to enhance the absorption contrast in SR-microCT. While only some cells showed enhanced absorption contrast, most cells did not show any difference in contrast to the surrounding scaffold and were consequently not detectable using conventional greyscale threshold methods. Therefore, using an image-based three-dimensional segmentation tool on the tomographic data revealed a multitude of non-stained cells. In addition, the SR-microCT data were compared with data obtained from scanning electron microscopy, energy dispersive X-ray spectroscopy and histology, while further linking the initial cell density measured via a MTT assay to the pore size as determined by SR-microCT.
    Acta biomaterialia 11/2009; 6(6):2097-107. DOI:10.1016/j.actbio.2009.11.020 · 6.03 Impact Factor
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    ABSTRACT: Macrophages play a pivotal role in tissue reaction and immune response. They recognize, phagocytose particles and generate cytokines to influence local cellular reactions. Friction and wear of implant components usually generates microparticles (MP) in a size range of 1-10 mum and nanoparticles (NP) in the range of 10-1000 nm. To investigate the possible impact of MP or NP on cellular reactions, we exposed murine macrophages (RAW264.7) to corundum MP and NP. The same mass was used in both NP and MP cell culture solutions, i.e. there were more NP than MP per identical volumes of culture solution. After 4, 24, 48, 72, and 96 h aliquots of cell culture supernatants were tested for different cytokines, growth factors and nitric oxide. Macrophages were stained with MGG (May-Grünwald Giemsa), counted and morphologically characterized by scanning electron microscopy and transmission electron microscopy. Particles were attached to cell surfaces and phagocytosed within cells. Cells stimulated with particles or lipopolysaccharides for positive controls showed surface modifications indicating enhanced function. Although only marginal differences between negative controls and particle-stimulated cells were observed in respect to cytokine production, exposure to corundum particles led to a decrease in the number of vital macrophages and to an increase in the number of giant cells. Corundum NP formed micron-sized aggregates in the cell culture medium and led to the production of more giant cells than MP. Sodiumdodecylsulfate polyacrylamide gel electrophoresis of the cell culture medium with particles proved the adsorption of proteins to particles.
    Journal of Biomedical Materials Research Part A 05/2009; 89(2):390-401. DOI:10.1002/jbm.a.32121 · 3.37 Impact Factor
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    ABSTRACT: The aim of this work was to select and characterize model particles, which correspond to real wear products from artificial hip joints, and to investigate the dispersing behavior of these powders. Commercially available nano and microparticles of corundum, graphite, and chromium oxide were selected or alternatively self-produced by milling. These powders were characterized regarding density, specific surface area, crystalline phases, particle size distributions and shape. Volume-based particle size distributions Q(3)(d) were measured after dispersing in water, water with dispersant, Ringers solution, and cell culture solution (Dulbecco's Modified Eagle's Medium (DMEM)) by laser diffraction and ultrasonic spectroscopy. Nanopowders formed agglomerates in the micrometer range in cell culture solutions. The micropowders showed only a marginal agglomeration. The median diameters of the dispersed nanopowders were even bigger than those of micropowders. Calculations of the number-based size distribution Q(0)(d) showed that in spite of the agglomeration the predominant number of the nano and microparticles is in the sub micrometer range, with only one exception, the micrographite powder.
    Journal of Biomedical Materials Research Part A 05/2009; 89(2):379-89. DOI:10.1002/jbm.a.31952 · 3.37 Impact Factor
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    ABSTRACT: Current light microscopic methods such as serial sectioning, confocal microscopy or multiphoton microscopy are severely limited in their ability to analyse rather opaque biological structures in three dimensions, while electron optical methods offer either a good three-dimensional topographic visualization (scanning electron microscopy) or high-resolution imaging of very thin samples (transmission electron microscopy). However, sample preparation commonly results in a significant alteration and the destruction of the three-dimensional integrity of the specimen. Depending on the selected photon energy, the interaction between X-rays and biological matter provides semi-transparency of the specimen, allowing penetration of even large specimens. Based on the projection-slice theorem, angular projections can be used for tomographic imaging. This method is well developed in medical and materials science for structure sizes down to several micrometres and is considered as being non-destructive. Achieving a spatial and structural resolution that is sufficient for the imaging of cells inside biological tissues is difficult due to several experimental conditions. A major problem that cannot be resolved with conventional X-ray sources are the low differences in density and absorption contrast of cells and the surrounding tissue. Therefore, X-ray monochromatization coupled with a sufficiently high photon flux and coherent beam properties are key requirements and currently only possible with synchrotron-produced X-rays. In this study, we report on the three-dimensional morphological characterization of articular cartilage using synchrotron-generated X-rays demonstrating the spatial distribution of single cells inside the tissue and their quantification, while comparing our findings to conventional histological techniques.
    Journal of The Royal Society Interface 04/2009; 7(42):49-59. DOI:10.1098/rsif.2008.0539 · 3.92 Impact Factor

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    ABSTRACT: Tribological screening tests (simple, reciprocating ball-on-flat tests) were performed with the objective to identify an appropriate coating for the articulating surfaces of artificial hip joints whose acetabular cups and femoral stems are made from Ti–6Al–4V alloy, which is appreciated for its light weight, good biocompatibility and elastic properties similar to those of natural bone. Standard coatings like TiN or CrN performed better than more complicated multi-layer systems, though not as good as different types of amorphous carbon coatings, generally referred to as diamond-like carbon or DLC coatings. Among the latter, hydrogenated amorphous carbon (a-C:H) displayed the best properties, especially if the hydrogen content was increased by reducing the bias voltage during PA-CVD-deposition.
    Wear 03/2008; 264(7):505-517. DOI:10.1016/j.wear.2007.04.001 · 1.91 Impact Factor
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    ABSTRACT: Tissue engineering of articular cartilage remains an ongoing challenge. Since tissue regeneration recapitulates ontogenetic processes the growth plate can be regarded as an innovative model to target suitable signalling molecules and growth factors for the tissue engineering of cartilage. In the present study we analysed the expression of cyclooxygenases (COX) in a short-term chondrocyte culture in gelatin-based scaffolds and in articular cartilage of rats and compared it with that in the growth plate. Our results demonstrate the strong cellular expression of COX-1 but only a focal weak expression of COX-2 in the seeded scaffolds. Articular cartilage of rats expresses homogeneously COX-1 and COX-2 with the exception of the apical cell layer. Our findings indicate a functional role of COX in the metabolism of articular chondrocytes. The expression of COX in articular cartilage and in the seeded scaffolds opens interesting perspectives to improve the proliferation and differentiation of chondrocytes in scaffold materials by addition of specific receptor ligands of the COX system.
    Bio-medical materials and engineering 02/2008; 18(1):15-23. · 1.09 Impact Factor

  • Tissue Engineering Research Trends, Edited by Giovanni N. Greco, 01/2008: chapter 9: pages 217-237; Novapublishers., ISBN: 978-1-60456-264-4
  • Rolf Zehbe · Ulrich Gross · Helmut Schubert ·
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    ABSTRACT: The micro structured deposition of vital cells is an important challenge in tissue engineering, biosensor technology, and in all research dealing with cell-cell and cell-substrate contacts. Hence, an inkjet printing technology has been developed to manufacture Au-based micro electrodes by sputter coating inversely printed polyester-foils. These electrodes feature minimal structure sizes of 35 microm and consist of an anode and a cathode part. They were used with fibrinogenic epithelial cell suspensions to deposit human keratinocytes (HaCaT), mouse fibroblasts (L-929) and the protein fibrin by applying DC voltage. Subsequently cells were electrophoretically attracted to the anode, following exactly its shape, while the insoluble fibrin was simultaneously precipitated due to the electrically mediated polymerization of the soluble fibrinogen molecule. Furthermore, it was demonstrated that this technique is suitable to co-deposit both cell types in a layered fashion. The lower voltage boundary for successful deposition was set at approximately 0.8 V needed for the conversion of fibrinogen into fibrin, while the upper voltage boundary was set at approximately 1.85 V, when commencing electrolysis inhibited the deposition of vital cells. Subsequent to the anodic cell-fibrin deposition, cells were cultivated for up to 4 days and then characterized by FDA+EB staining, methyl violet staining, MNF staining and SEM. The conversion from fibrinogen into fibrin was studied using ATR/FTIR.
    Biomolecular Engineering 12/2007; 24(5):537-42. DOI:10.1016/j.bioeng.2007.08.012 · 3.17 Impact Factor
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    ABSTRACT: Porous ceramics made of alumina and hydroxyapatite were created using a protein foaming method. Porosity and pore size distribution were successfully varied by means of chemical modification of the foaming protein Bovine serum albumin (BSA). The effectiveness of the BSA and of its chemical modifications as well as the influence of the dispersing agent were investigated using synchrotron tomography. Resulting porous ceramic materials were used as three-dimensional substrates for the cultivation of human peripheral stem cells. The cells proliferated and differentiated in culture. Five cell lines consistent with human blood cell lines were observed.
    Journal of Materials Science Materials in Medicine 08/2007; 18(7):1333-8. DOI:10.1007/s10856-006-0076-z · 2.59 Impact Factor
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    ABSTRACT: In this paper we report on the synthesis of three different gelatine based scaffold materials for the reconstruction of articular cartilage defects. The first scaffold design is based on an unmodified, oriented gelatine network, while the second design further comprises an attached inorganic hydroxyapatite layer and the third design includes poly(I-lactide) microspheres as a model material for future drug-release applications. All three scaffold designs were characterized and imaged using synchrotron mu-CT, obtaining a complete volumetric reconstruction of a previously defined sample region. Furthermore, two unmodified scaffolds were cultivated for one week with porcine chondrocytes. Afterwards the attached cells were labelled using a combination of Au-lysine and silver enhancer. In synchrotron mu-CT analysis we were thus able to map the cell distribution due to the difference in X-ray absorption of the labelled cells and the non labelled scaffolds in a volume of several millimetres.
    International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) 07/2007; 98(7):562-568. DOI:10.3139/146.101509 · 0.64 Impact Factor
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    ABSTRACT: Tissue engineering has become a fast growing interdisciplinary branch of research at the interface between life and engineering sciences with important clinical end-points. In this context the regeneration of articular cartilage represents an exciting challenge since hyaline cartilage has a limited capacity for self-repair. Today the use of different scaffold materials combined with in vitro expanded chondrocytes and signalling molecules poses great hopes for an optimal treatment of articular cartilage defects. However, until today the optimal construct of scaffolds, cells and signalling molecules has not yet been found. Since repair and regeneration recapitulate in part ontogenetic processes, the present paper summarizes the regulative mechanisms of endochondral ossification in the growth plate of the long bones to identify possible new signalling molecules for the improvement of tissue engineering-based solutions in the treatment of cartilage defects. The growth plate represents a highly organized structure of chondrocytes and extracellular matrix components in distinguishable proliferation and differentiation stages. It is regulated by various paracrine and hormonal factors. In a second part we present actual trends in scaffold design based on synthetic polymers and natural polymers, stressing their potential use in the regeneration of cartilage defects from the point of view of bioactivity and biocompatibility. In conclusion, both new signalling molecules from basic research and innovative scaffold materials with variable physico-chemical properties open up new and interesting perspectives for the research in optimized tissue engineeredbased therapeutic strategies to treat cartilage defects.
    Journal of applied biomaterials & biomechanics (JABB) 05/2007; 5(2):70-81. · 1.16 Impact Factor
  • R Zehbe · U Gross · C Knabe · R.J. Radlanski · H Schubert ·
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    ABSTRACT: The transformation of fibrinogen into fibrin is biologically activated in a complex multi-step process known as the coagulation cascade. This transformation can also be triggered by anodic surfaces. It has been suggested that this mechanism is a result of an electron transfer from the anode to the fibrinogen molecule resulting in the formation of fibrin. In this study we used this pathway to simultaneously deposit vital cells (fibroblasts and keratinocytes) and fibrin on micro structured gold electrodes. The electrodes were produced using a novel inverse inkjet-printing technology in combination with subsequent gold-sputtering, resulting in minimal structure-sizes of 35 microm (+/-6 microm). Cell deposition and fibrin-coagulation were found to occur on the anode only, following exactly the micro structured electrode surface. Successful deposition was limited by the minimal voltage (0.8 V) needed for the formation of fibrin and the maximum voltage (1.85 V) resulting in the deterioration of the Au-electrodes due to electrolysis and possible damaging of the deposited cells due to the formation of molecular chlorine. Furthermore, it was demonstrated that this technique is suitable to co-cultivate different cell types in a layered fashion. Subsequent to the electrically mediated anodic cell-protein deposition, cells were cultivated for up to 4 days and then characterized by vital fluorescence staining, methyl violet-staining and scanning electron microscopy. Cell-vitality was found to be dependent on the experimental setup; in this study non-vital cells were only observed, when sequentially depositing two different cell types. Finally, the coagulation mechanism was studied using HPLC, SDS-gel-chromatography and ATR/FTIR.
    Biosensors & Bioelectronics 03/2007; 22(7):1493-500. DOI:10.1016/j.bios.2006.07.002 · 6.41 Impact Factor
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    ABSTRACT: Die Veröffentlichung liegt als pdf und Hardcopy in der Abteilung vor

  • Annals of the New York Academy of Sciences 12/2006; 523(1):262 - 267. DOI:10.1111/j.1749-6632.1988.tb38518.x · 4.38 Impact Factor
  • C Knabe · B Kraska · C Koch · U Gross · H Zreiqat · M Stiller ·
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    ABSTRACT: To evaluate the osteogenic potential of novel implant materials, it is important to examine their effect on osteoblastic differentiation. Characterizing the tissue response at the bone-biomaterial interface in vivo at a molecular level would contribute significantly to enhancing our understanding of tissue integration of endosseous implant materials. We describe here a new technique that overcomes difficulties commonly associated with performing immunohistochemistry on undecalcified sawed sections of bone. Sheep mandible specimens were fixed in an ethanol based fixative to maintain adequate antigenicity of the tissue. As a result, it was possible to omit antigen retrieval at high temperature for recovery of antigenicity, and detachment of sections from the slides was avoided. Following dehydration and infiltration, the specimens were embedded in a resin composed of polymethylmethacrylate and polybutylmethacrylate. Polymerization was achieved by adding benzoylperoxide and N,N-dimethyl-toluidine. This resin was selected because it maintained the antigenicity of the tissue, provided adequate properties for cutting 50 microm thick sections, and it facilitated deacrylizing the sawed sections. Acid-resistant acrylic slides were glued to the blocks using an epoxy resin based two-component adhesive to avoid detachment of the slides during the deacrylation procedure. Samples were stained for alkaline phosphatase, type I collagen, osteonectin, osteopontin, osteocalcin and bone sialoprotein. The EnVision + trade mark dextran polymer conjugate two-step visualization system was applied for immunohistochemical detection of these bone matrix proteins. This procedure yielded positive staining for the osteogenic markers in cells and matrix components. The protocol described here facilitates the use of immunohistochemistry on resin embedded sawed sections of bone and provides a convenient and reliable method that can be used routinely for immunohistochemical analysis of hard tissue specimens containing implant materials.
    Biotechnic and Histochemistry 01/2006; 81(1):31-9. DOI:10.1080/10520290600725474 · 1.44 Impact Factor

Publication Stats

1k Citations
171.53 Total Impact Points


  • 2009-2011
    • Technische Universität Berlin
      Berlín, Berlin, Germany
  • 2007-2009
    • Charité Universitätsmedizin Berlin
      Berlín, Berlin, Germany
  • 1988-2003
    • Freie Universität Berlin
      • Institute of Veterinary Pathology
      Berlín, Berlin, Germany