Wolfgang Pompe

Publications of Wolfgang Pompe

• Formation of tubes during self-assembly of bacterial surface layers.

  Authors: Manfred Bobeth, Andreas Blecha, Anja Blüher, Michael Mertig, Nuriye Korkmaz, Kai Ostermann, Gerhard Rödel, Wolfgang Pompe

  Langmuir : the ACS journal of surfaces and colloids. 12/2011; 27(24):15102-11.

  Based on experimental studies on tube formation during self-assembly of bacterial surface (S)-layers, a mechanistic model for describing the underlying basic mechanisms is proposed and the effect ofBased on experimental studies on tube formation during self-assembly of bacterial surface (S)-layers, a mechanistic model for describing the underlying basic mechanisms is proposed and the effect of process parameters on growth velocity and tube radius is investigated. The S-layer is modeled as a curved sheet with discrete binding sites for the association of monomers distributed along the S-layer edges. Reported changes of the tube radius owing to genetic protein modifications are explained within the framework of continuum mechanics. S-layer growth velocity and shape development are analyzed by Monte Carlo simulation in their dependence on the attachment and detachment frequencies of monomers at the S-layer. For curved S-layer patches, a criterion for the formation of S-layer tubes is derived. Accordingly, tubes can form only within a certain range of the initial monomer concentration. Furthermore, the effect of calcium ion concentration on tube formation is discussed, including recent experimental findings on the calcium effect.

• Friction-controlled traction force in cell adhesion.

  Authors: Tilo Pompe, Martin Kaufmann, Maria Kasimir, Stephanie Johne, Stefan Glorius, Lars Renner, Manfred Bobeth, Wolfgang Pompe, Carsten Werner

  Biophysical journal. 10/2011; 101(8):1863-70.

  The force balance between the extracellular microenvironment and the intracellular cytoskeleton controls the cell fate. We report a new (to our knowledge) mechanism of receptor force control in cellThe force balance between the extracellular microenvironment and the intracellular cytoskeleton controls the cell fate. We report a new (to our knowledge) mechanism of receptor force control in cell adhesion originating from friction between cell adhesion ligands and the supporting substrate. Adherent human endothelial cells have been studied experimentally on polymer substrates noncovalently coated with fluorescent-labeled fibronectin (FN). The cellular traction force correlated with the mobility of FN during cell-driven FN fibrillogenesis. The experimental findings have been explained within a mechanistic two-dimensional model of the load transfer at focal adhesion sites. Myosin motor activity in conjunction with sliding of FN ligands noncovalently coupled to the surface of the polymer substrates is shown to result in a controlled traction force of adherent cells. We conclude that the friction of adhesion ligands on the supporting substrate is important for mechanotransduction and cell development of adherent cells in vitro and in vivo.

• pH- and salt-dependent molecular combing of DNA: experiments and phenomenological model.

  Authors: Annegret Benke, Michael Mertig, Wolfgang Pompe

  Nanotechnology. 01/2011; 22(3):035304.

  λ-DNA as well as plasmids can be successfully deposited by molecular combing on hydrophobic surfaces, for pH values ranging from 4 to 10. On polydimethylsiloxane (PDMS) substrates, the deposited DNAλ-DNA as well as plasmids can be successfully deposited by molecular combing on hydrophobic surfaces, for pH values ranging from 4 to 10. On polydimethylsiloxane (PDMS) substrates, the deposited DNA molecules are overstretched by about 60-100%. There is a significant influence of sodium ions (NaCl) on the surface density of the deposited DNA, with a maximum near to 100 mM NaCl for a DNA solution (28 ng µl(-1)) at pH 8. The combing process can be described by a micromechanical model including: (i) the adsorption of free moving coiled DNA at the substrate; (ii) the stretching of the coiled DNA by the preceding meniscus; (iii) the relaxation of the deposited DNA to the final length. The sticky ends of λ-DNA cause an adhesion force in the range of about 400 pN which allows a stable overstretching of the DNA by the preceding meniscus. The exposing of hidden hydrophobic bonds of the overstretched DNA leads to a stable deposition on the hydrophobic substrate. The pH-dependent density of deposited DNA as well as the observed influence of sodium ions can be explained by their screening of the negatively charged DNA backbone and sticky ends, respectively. The final DNA length can be derived from a balance of the stored elastic energy of the overstretched molecules and the energy of adhesion.

• Dissociative adsorption of methane on surface oxide structures of Pd-Pt alloys

  Authors: Arezoo Dianat, Nicola Seriani, Lucio Colombi Ciacchi, Wolfgang Pompe, Gianaurelio Cuniberti, Manfred Bobeth

  03/2010;

  The dissociative adsorption of methane on variously oxidized Pd, Pt and Pd-Pt surfaces is investigated using density-functional theory, as a step towards understanding the combustion of methane onThe dissociative adsorption of methane on variously oxidized Pd, Pt and Pd-Pt surfaces is investigated using density-functional theory, as a step towards understanding the combustion of methane on these materials. For Pd-Pt alloys, models of surface oxide structures are built on the basis of known oxides on Pd and Pt. The methane adsorption energy presents large variations depending on the oxide structure and composition. Adsorption is endothermic on the bare Pd(111) metal surface as well as on stable thin layer oxide structures such as the ($\sqrt{5}\times\sqrt{5}$) surface oxide on Pd(100) and the PtO$_2$-like oxide on Pt(111). Instead, large adsorption energies are obtained for the (100) surface of bulk PdO, for metastable mixed Pd$_{1-x}$Pt$_x$O$_{4/3}$ oxide layers on Pt(100), and for Pd-Pt(111) surfaces covered with one oxygen monolayer. In the latter case, we find a net thermodynamic preference for a direct conversion of methane to methanol, which remains adsorbed on the oxidized metal substrates via weak hydrogen-bond interactions.

• Dielectrophoretic Growth of Metallic Nanowires and Microwires: Theory and Experiments.

  Authors: Nitesh Ranjan, Michael Mertig, Gianarelio Cuniberti, Wolfgang Pompe

  Langmuir : the ACS journal of surfaces and colloids. 11/2009;

  Dielectrophoresis-assisted growth of metallic nanowires from an aqueous salt solution has been previously reported, but so far there has been no clear understanding of the process leading to such aDielectrophoresis-assisted growth of metallic nanowires from an aqueous salt solution has been previously reported, but so far there has been no clear understanding of the process leading to such a bottom-up assembly. The present work, based on a series of experiments to grow metallic nano- and microwires by dielectrophoresis, provides a general theoretical description of the growth of such wires from an aqueous salt solution. Palladium nanowires and silver microwires have been grown between gold electrodes from their aqueous salt solution via dielectrophoresis. Silver microwire growth has been observed in situ using light microscopy. From these experiments, a basic model of dielectrophoresis-driven wire growth is developed. This model explains the dependence of the growth on the frequency and the local field enhancement at the electrode asperities. Such a process proves instrumental in the growth of metallic nanowires with controlled morphology and site specificity between the electrodes.

• Selective targeting of green fluorescent nanodiamond conjugates to mitochondria in HeLa cells.

  Authors: Msaukiranji Mkandawire, Andrea Pohl, Tatiana Gubarevich, Victoria Lapina, Dietmar Appelhans, Gerhard Rödel, Wolfgang Pompe, Jürgen Schreiber, Jörg Opitz

  Journal of biophotonics. 06/2009;

  Fluorescent cellular biomarkers play a prominent role in biosciences. Most of the available biomarkers have some drawbacks due to either physical and optical or cytotoxic properties. In view of this,Fluorescent cellular biomarkers play a prominent role in biosciences. Most of the available biomarkers have some drawbacks due to either physical and optical or cytotoxic properties. In view of this, we investigated the potential of green fluorescent nanodiamonds as biomarkers in living cells. Nanodiamonds were functionalized by attaching antibodies that target intracellular structures such as actin filaments and mitochondria. Then, the nanodiamond conjugates were transfected into HeLa cells. Transfections were mediated by 4(th)-generation dendrimers, cationic liposomes and protamine sulfate. Using fluorescence microscopy, we confirmed successful transfections of the nanodiamonds into HeLa cells. Nanodiamond fluorescence could be easily differentiated from cellular autofluorescence. Furthermore, nanodiamonds could be targeted selectively to intracellular structures. Therefore, nanodiamonds are a promising tool for intracellular assays. ((c) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

• Toxicity of tungsten carbide and cobalt-doped tungsten carbide nanoparticles in mammalian cells in vitro.

  Authors: Susanne Bastian, Wibke Busch, Dana Kühnel, Armin Springer, Tobias Meissner, Roland Holke, Stefan Scholz, Maria Iwe, Wolfgang Pompe, Michael Gelinsky, Annegret Potthoff, Volkmar Richter, Chrysanthy Ikonomidou, Kristin Schirmer

  Environmental health perspectives. 05/2009; 117(4):530-6.

  BACKGROUND: Tungsten carbide nanoparticles are being explored for their use in the manufacture of hard metals. To develop nanoparticles for broad applications, potential risks to human health and theBACKGROUND: Tungsten carbide nanoparticles are being explored for their use in the manufacture of hard metals. To develop nanoparticles for broad applications, potential risks to human health and the environment should be evaluated and taken into consideration. OBJECTIVE: We aimed to assess the toxicity of well-characterized tungsten carbide (WC) and cobalt-doped tungsten carbide (WC-Co) nanoparticle suspensions in an array of mammalian cells. METHODS: We examined acute toxicity of WC and of WC-Co (10% weight content Co) nanoparticles in different human cell lines (lung, skin, and colon) as well as in rat neuronal and glial cells (i.e., primary neuronal and astroglial cultures and the oligodendrocyte precursor cell line OLN-93). Furthermore, using electron microscopy, we assessed whether nanoparticles can be taken up by living cells. We chose these in vitro systems in order to evaluate for potential toxicity of the nanoparticles in different mammalian organs (i.e., lung, skin, intestine, and brain). RESULTS: Chemical-physical characterization confirmed that WC as well as WC-Co nanoparticles with a mean particle size of 145 nm form stable suspensions in serum-containing cell culture media. WC nanoparticles were not acutely toxic to the studied cell lines. However, cytotoxicity became apparent when particles were doped with Co. The most sensitive were astrocytes and colon epithelial cells. Cytotoxicity of WC-Co nanoparticles was higher than expected based on the ionic Co content of the particles. Analysis by electron microscopy demonstrated presence of WC nanoparticles within mammalian cells. CONCLUSIONS: Our findings demonstrate that doping of WC nanoparticles with Co markedly increases their cytotoxic effect and that the presence of WC-Co in particulate form is essential to elicit this combinatorial effect.

• Histologic study of incorporation and resorption of a bone cement-collagen composite: an in vivo study in the minipig.

  Authors: Ronald Mai, Antje Reinstorf, Eckart Pilling, Matthias Hlawitschka, Roland Jung, Michael Gelinsky, Matthias Schneider, Richard Loukota, Wolfgang Pompe, Uwe Eckelt, Bernd Stadlinger

  Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. 04/2008; 105(3):e9-14.

  OBJECTIVE: Calcium phosphates are clinically established as bone defect fillers. They have the capability of osseoconduction and are characterized by a slow resorption process. The present studyOBJECTIVE: Calcium phosphates are clinically established as bone defect fillers. They have the capability of osseoconduction and are characterized by a slow resorption process. The present study evaluated the suitability of a newly developed calcium phosphate cement modified with collagen type I. STUDY DESIGN: The modified cement paste was inserted in differently designed defects of 10 minipigs. Further, an alveolar ridge augmentation was performed, applying the cement paste. The cement hardened in situ during the operation, forming a hydroxyapatite collagen composite. Animals were sacrificed after 1, 3, 6, 12, and 18 months. The tissue integration and resorption process was then evaluated using nondecalcified microsections. All animals were evaluated for histology. RESULTS: The implanted material showed osseoconductive characteristics. Resorption started from the edge of the defect zone, and bone substitution followed rapidly. Twelve months after placement of the cement, complete remodeling was observed. CONCLUSION: It can be concluded that the applied hydroxyapatite-collagen cement composite shows good resorption and bone integration.

• Mineralised collagen--an artificial, extracellular bone matrix--improves osteogenic differentiation of bone marrow stromal cells.

  Authors: Anne Bernhardt, Anja Lode, Sabine Boxberger, Wolfgang Pompe, Michael Gelinsky

  Journal of materials science. Materials in medicine. 02/2008; 19(1):269-75.

  In the field of bone tissue engineering there is a high demand on bone graft materials which promote bone formation. By combination of collagen type I with nanocrystalline hydroxyapatite (HA) weIn the field of bone tissue engineering there is a high demand on bone graft materials which promote bone formation. By combination of collagen type I with nanocrystalline hydroxyapatite (HA) we generated a resorbable material which structure and composition is close to those of the extracellular bone matrix. This nanocomposite material was produced in a biomimetic process in which collagen fibril assembly and mineralisation with hydroxyapatite occur simultaneously. In this study the proliferation and osteogenic differentiation of human bone marrow-derived stromal cells (hBMSC) on membranes of biomimetically mineralised collagen type I was investigated. To this end, we optimised biochemical assays for determination of cell number and alkaline phosphatase activity corresponding to the special properties of this biomaterial. For cell experiments hBMSC were seeded on the mineralised collagen membranes and cultivated over 35 days, both in static and perfusion culture, in the presence and absence of dexamethasone, beta-glycerophosphate and ascorbate. Compared to cells grown on tissue culture polystyrene we found attenuated proliferation rates, but markedly increased activity of alkaline phosphatase on the mineralised collagen indicating its promoting effect on the osteogenic differentiation of hBMSC. Therefore this bone-like material may act as a suitable artificial extracellular matrix for bone tissue engineering. Perfusion of the 2D cell matrix constructs with cell culture medium did not improve proliferation and osteogenic differentiation of the hBMSC.

• Effect of modification of hydroxyapatite/collagen composites with sodium citrate, phosphoserine, phosphoserine/RGD-peptide and calcium carbonate on bone remodelling.

  Authors: Wolfgang Schneiders, Antje Reinstorf, Wolfgang Pompe, Rene Grass, Achim Biewener, Michael Holch, Hans Zwipp, Stefan Rammelt

  Bone. 05/2007; 40(4):1048-59.

  This study describes the early interface reaction of cancellous bone to a nanocrystalline hydroxyapatite cement containing type I collagen (HA/Coll) and its modifications with sodium citrate (CI),This study describes the early interface reaction of cancellous bone to a nanocrystalline hydroxyapatite cement containing type I collagen (HA/Coll) and its modifications with sodium citrate (CI), calcium carbonate (CA), phosphoserine (P) and phosphoserine plus RGD-peptide (RGD). Cylindrical implants of HA/Coll and its modifications were inserted into the tibia of Wistar rats. We analysed 6 specimens per group at days 2, 4, 7, 14 and 28. CI, P and RGD modifications showed improved material properties (finer microstructure and higher compressive strength) compared to CA and HA/Coll implants. The powder X-ray diffraction (XRD) showed that the addition of P and CI led to an increase of alpha-TCP peaks while the diffraction patterns of the non-modified cement (HA/Coll) were quite similar with that of natural bone. All of the implants healed without adverse reactions. A significantly higher number of TRAP-positive osteoclasts were observed around CI, RGD and P on day 7 compared to CA and HA/Coll. Around CI, P and RGD a significantly delayed increase of ED1-positive mononuclear cells was detected. The amount of direct bone contact after 28 days was significantly higher around CI, P and RGD compared to CA and HA/Coll implants. The addition of CI, P and RGD appears to enhance bone remodelling at the early stages of bone healing, leading to increased bone formation around HA/Coll composite cements.

• Electrostatic interactions modulate the conformation of collagen I.

  Authors: Uwe Freudenberg, Sven H Behrens, Petra B Welzel, Martin Müller, Milauscha Grimmer, Katrin Salchert, Tilman Taeger, Kati Schmidt, Wolfgang Pompe, Carsten Werner

  Biophysical journal. 04/2007; 92(6):2108-19.

  The pH- and electrolyte-dependent charging of collagen I fibrils was analyzed by streaming potential/streaming current experiments using the Microslit Electrokinetic Setup. Differential scanningThe pH- and electrolyte-dependent charging of collagen I fibrils was analyzed by streaming potential/streaming current experiments using the Microslit Electrokinetic Setup. Differential scanning calorimetry and circular dichroism spectroscopy were applied in similar electrolyte solutions to characterize the influence of electrostatic interactions on the conformational stability of the protein. The acid base behavior of collagen I was found to be strongly influenced by the ionic strength in KCl as well as in CaCl(2) solutions. An increase of the ionic strength with KCl from 10(-4) M to 10(-2) M shifts the isoelectric point (IEP) of the protein from pH 7.5 to 5.3. However, a similar increase of the ionic strength in CaCl(2) solutions shifts the IEP from 7.5 to above pH 9. Enhanced thermal stability with increasing ionic strength was observed by differential scanning calorimetry in both electrolyte systems. In line with this, circular dichroism spectroscopy results show an increase of the helicity with increasing ionic strength. Better screening of charged residues and the formation of salt bridges are assumed to cause the stabilization of collagen I with increasing ionic strength in both electrolyte systems. Preferential adsorption of hydroxide ions onto intrinsically uncharged sites in KCl solutions and calcium binding to negatively charged carboxylic acid moieties in CaCl(2) solutions are concluded to shift the IEP and influence the conformational stability of the protein.

• Parallel manipulation of bifunctional DNA molecules on structured surfaces using kinesin-driven microtubules.

  Authors: Cerasela Zoica Dinu, Jörg Opitz, Wolfgang Pompe, Jonathon Howard, Michael Mertig, Stefan Diez

  Small (Weinheim an der Bergstrasse, Germany). 09/2006; 2(8-9):1090-8.

  We have developed a technique to manipulate bifunctional DNA molecules: One end is thiolated to bind to a patterned gold surface and the other end is biotinylated to bind to a microtubule glidingWe have developed a technique to manipulate bifunctional DNA molecules: One end is thiolated to bind to a patterned gold surface and the other end is biotinylated to bind to a microtubule gliding over a kinesin-coated surface. We found that DNA molecules can be stretched and overstretched between the gold pads and the motile microtubules, and that they can form dynamic networks. This serves as a proof-of-principle that biological machineries can be used in vitro to accomplish the parallel formation of structured DNA templates that will have applications in biophysics and nanoelectronics.

• Catalytic oxidation activity of Pt3O4 surfaces and thin films.

  Authors: Nicola Seriani, Wolfgang Pompe, Lucio Colombi Ciacchi

  The journal of physical chemistry. B. 09/2006; 110(30):14860-9.

  The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-richThe catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. Here we study the thermodynamic stability of platinum oxide surfaces and thin films and their reactivities toward oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive toward either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favored at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than that on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.

• Modeling of pattern development during fibronectin nanofibril formation.

  Authors: Tilo Pompe, Jörn Starruss, Manfred Bobeth, Wolfgang Pompe

  Biointerphases. 09/2006; 1(3):93-7.

  Formation of fibrillar fibronectin networks is a major process during embryogenesis and tissue formation, but the molecular details of fibril assembly remain poorly understood. Based on current ideasFormation of fibrillar fibronectin networks is a major process during embryogenesis and tissue formation, but the molecular details of fibril assembly remain poorly understood. Based on current ideas of fibronectin fibrillogenesis, a stochastic model was developed to enlighten the mechanism of the formation of paired fibronectin nanofibrils by adherent endothelial cells, which has been observed recently. The development of fibronectin clusters and fibrils was investigated by means of Monte Carlo simulations, including diffusion-controlled aggregation and myosin-driven transport of fibronectin-integrin complexes in the vicinity of a focal adhesion. Different evolving growth patterns were summarized in a morphological diagram as a function of the fibronectin substrate and fibronectin-fibronectin interaction energies. The formation of paired nanofibrils was found to occur in a certain region of interaction parameters. Beyond this region branched fibronectin clusters as well as tear-off of fibronectin fibrils were observed.

• In vitro ossification and remodeling of mineralized collagen I scaffolds.

  Authors: Hagen Domaschke, Michael Gelinsky, Beatrice Burmeister, Richard Fleig, Thomas Hanke, Antje Reinstorf, Wolfgang Pompe, Angela Rösen-Wolff

  Tissue engineering. 05/2006; 12(4):949-58.

  A promising strategy of bone tissue engineering is to repair bone defects by implanting biodegradable scaffolds that can undergo remodeling and be replaced completely by autologous bone tissue. ForA promising strategy of bone tissue engineering is to repair bone defects by implanting biodegradable scaffolds that can undergo remodeling and be replaced completely by autologous bone tissue. For this purpose, it is necessary to create scaffolds that can be degraded by osteoclasts and enable osteoblasts to build new mineralized bone matrix. In order to achieve this goal a new porous material has been developed using biomimetically mineralized collagen I. These scaffolds were co-cultured with osteoclast-like cells and osteoblasts in order to characterize the capacity of these cells to remodel the material in vitro. It was possible to show the development of biologically active osteoclast- like cells that were able to invade and degrade the scaffold. They degraded the scaffold by internalizing it as intracellular vesicles, thereby making room for osteoblasts to invade and build new bone matrix. In addition, it could be shown that osteoblasts proliferated, differentiated, and produced new mineralized extracellular matrix. Hence, it could be shown that co-culture of osteoclastlike cells and osteoblasts on biomimetically mineralized collagen I is a promising approach for bone tissue engineering. In addition, it can be applied to study the process of bone remodeling in vitro.

• Biomimetic porous scaffolds with high elasticity made from mineralized collagen--an animal study.

  Authors: Atsuro Yokoyama, Michael Gelinsky, Takao Kawasaki, Takao Kohgo, Ulla König, Wolfgang Pompe, Fumio Watari

  Journal of biomedical materials research. Part B, Applied biomaterials. 12/2005; 75(2):464-72.

  Histological investigations of a new hydroxyapatite-collagen composite material were carried out to evaluate its possible suitability as a bone substitute. The three-dimensional scaffolds made fromHistological investigations of a new hydroxyapatite-collagen composite material were carried out to evaluate its possible suitability as a bone substitute. The three-dimensional scaffolds made from biomimetically mineralized collagen exhibit an interconnecting pore structure and elastic mechanical properties. They were implanted into the subcutaneous tissue and bone defects made in the femur of rats and harvested with the surrounding tissue at 1, 2, 4, 8, and 12 weeks after surgery. The materials implanted in the subcutaneous tissue were covered by fibrous connective tissue with a slight inflammatory response, and many foreign-body giant cells were observed on the surface of the scaffolds. Most of the material implanted in the subcutaneous tissue was resorbed at 8 weeks by phagocytosis. In the bone defects, new bone formation was observed on the surface of the material at 1 week. New bone increased with time, and osteoclasts were seen on the surface of the scaffolds at 2 weeks. Resorption and replacement by new bone of many parts of the materials implanted in the femur were observed by 12 weeks. These responses occurred faster than those of other hydroxyapatite-collagen composites. The results suggested that the new biomimetically mineralized collagen scaffolds were suitable as an implant material for bone-tissue reconstruction.

• Novel catalysts, room temperature, and the importance of oxygen for the synthesis of single-walled carbon nanotubes.

  Authors: Mark H Rümmeli, Ewa Borowiak-Palen, Thomas Gemming, Thomas Pichler, Martin Knupfer, Martin Kalbác, Lothar Dunsch, Oliver Jost, S Ravi P Silva, Wolfgang Pompe, Bernd Büchner

  Nano letters. 08/2005; 5(7):1209-15.

  In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesizedIn this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.

• Osteocalcin enhances bone remodeling around hydroxyapatite/collagen composites.

  Authors: Stefan Rammelt, Mirjam Neumann, Uwe Hanisch, Antje Reinstorf, Wolfgang Pompe, Hans Zwipp, Achim Biewener

  Journal of biomedical materials research. Part A. 07/2005; 73(3):284-94.

  The effect of osteocalcin (OC), an extracellular bone matrix protein, on bone healing around hydroxyapatite/collagen composites was investigated. Cylindrical nanocrystalline hydroxyapatite implantsThe effect of osteocalcin (OC), an extracellular bone matrix protein, on bone healing around hydroxyapatite/collagen composites was investigated. Cylindrical nanocrystalline hydroxyapatite implants of 2.5-mm diameter containing 2.5% biomimetically mineralized collagen type I were inserted press-fit into the tibial head of adult Wistar rats. To one implant group, 10 mug/g OC was added. Six specimens per group were analyzed at 2, 7, 14, 28, and 56 days. After 14 days, newly formed woven bone had reached the implant surface of the OC implants whereas a broad fibrous interface could still be observed around controls. Woven bone was formed directly around both implant groups after 28 days and had been replaced partially by lamellar bone around the OC implants only. No significant differences in total bone contact were seen between both groups after 56 days. The higher number of phagocytosing cells and osteoclasts characterized immunohistochemically with ED1, cathepsin D, and tartate-resistant alkaline phosphatase around the OC implants at the early stages of bone healing suggests an earlier onset of bone remodeling. The earlier and increased expression of bone-specific matrix proteins and multifunctional adhesion proteins (osteopontin, bone sialoprotein, CD44) at the interface around the OC implants indicates that OC may accelerate bone formation and regeneration. This study supports the observations from in vitro studies that OC activates both osteoclasts and osteoblasts during early bone formation.

• Electronic structure of regular bacterial surface layers.

  Authors: Denis V Vyalikh, Steffen Danzenbächer, Michael Mertig, Alexander Kirchner, Wolfgang Pompe, Yuriy S. Dedkov, Serguei L Molodtsov

  Physical review letters. 01/2005; 93(23):238103.

  We report photoemission and near-edge x-ray absorption fine structure measurements of the occupied and unoccupied valence electronic states of the regular surface layer of Bacillus sphaericus, whichWe report photoemission and near-edge x-ray absorption fine structure measurements of the occupied and unoccupied valence electronic states of the regular surface layer of Bacillus sphaericus, which is widely used as the protein template for the fabrication of metallic nanostructures. The two-dimensional protein crystal shows a semiconductorlike behavior with a gap value of approximately 3.0 eV and the Fermi energy close to the bottom of the lowest unoccupied molecular orbital. We anticipate that these results will open up new possibilities for the electric addressability of biotemplated low-dimensional hybrid structures.

• Single-walled carbon nanotube diameter.

  Authors: Oliver Jost, Andre Gorbunov, Xianjie Liu, Wolfgang Pompe, Jörg Fink

  Journal of nanoscience and nanotechnology. 05/2004; 4(4):433-40.

  Two different single-walled carbon nanotube (SWNT) growth modes (cap growth mode and circumference growth mode) are shown to exist. General SWNT diameter windows are derivable from catalyst particleTwo different single-walled carbon nanotube (SWNT) growth modes (cap growth mode and circumference growth mode) are shown to exist. General SWNT diameter windows are derivable from catalyst particle size considerations. In addition, an almost complete picture of nanotube diameter dependencies for the cap growth mode is drawn from experiment. The nanotube diameter always scales linear with temperature, but the degree of dependence varies with the catalyst element. The nanotube diameter scales logarithmically with the gas pressure and catalyst composition. Very few or exactly one atom of a catalyst additive is sufficient to induce SWNT diameter changes. The experimental data allow the conclusion that the observed nanotube diameter is based on materials properties of sp2-bonded carbon/graphene sheets, on individual properties of the catalyst elements, and on additional kinetic components from temperature and pressure changes. Indications are found for a specific and maybe decisive role of adsorbate atoms at the surface of a catalyst particle on the nanotube diameter and therefore on the process of nanotube nucleation and growth.