T. Kollmann

Max Planck Institute for Chemical Physics of Solids, Dresden, Saxony, Germany

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Publications (3)1.29 Total impact

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    ABSTRACT: Although bone minerals have been widely studied by various techniques in previous studies, crystal structures, morphology of bone minerals and its building pathway remained still controversy. In this work, the ultrastructure of the mineralization front of rabbit femur has been studied by conventional and high-resolution (HR) transmission electron microscopy (TEM). In order to induce a healing and demineralization process the animals were subjected to a standardized osteotomy stabilized with titan screws and sonic pins. After 84 days follow-up time the newly build bone was investigated. The mineralization front of rabbit femur osteotomy contains partly mineralized collagen fibrils with a pronounced striped pattern together with a large number of agglomerated apatite platelets. The striation is caused by mineralization in the hole zones of the collagen fibrils, corresponding to the early stage of mineralization. In the TEM micrographs, the mineralization zone appears denser and compact when compared with fully mineralized bone, although most of the collagen fibrils are completely mineralized in the latter (higher concentration of interfibrillar apatite platelets within the mineralization zone). In bone some partly mineralized collagen fibrils are also observed, revealing the same arrangement, regular shape, and size of apatite platelets as collagen fibrils in the mineralization zone. Apatite platelets with irregular shapes are observed at the vortex-shaped outer boundary of the mineralization zone, i.e. at the interfaces with nonmineralized collagen or osteoblasts. HR TEM micrographs reveal that the platelets are assumably semicrystalline and that within the platelet nanocrystalline domains of apatite are embedded in an amorphous calciumphosphate matrix. SCANNING 00: 1-14, 2012. © 2012 Wiley Periodicals, Inc.
    Scanning 08/2012; · 1.29 Impact Factor
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    ABSTRACT: The local environment in biomimetic hydroxy-apatite (HAp) nanocomposites containing 0 and 33 wt % gelatin was characterized by 31P solid-state NMR spectroscopy. The presence of crystalline HAp and amorphous calcium phosphate phases was found in both materials. The latter can appear at the grain surfaces or at the boundaries of the crystalline phases. In the 31P cross-polarization MAS NMR spectra of HAp containing 33 wt % of built-in gelatin, an additional signal at 0.9 ppm was observed, which demonstrates the spatial correlation to hydrogen atoms of nonmineral origin, as indicated by 31P−1H heteronuclear correlation (HETCOR) NMR spectroscopy. This site is identified as a phosphate species present at the surfaces of the mineral component (HAp) interacting with the surrounding organic matrix.
    The Journal of Physical Chemistry C, v.115, 1513-1519 (2011). 01/2011;
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    ABSTRACT: Nanocomposites consisting of gelatin and hydroxyapatite as well as of gelatin and mixtures of hydroxyapatite and different amounts of octacalcium phosphate were prepared as bulk-materials. The composites were precipitated from aqueous solutions of CaCl2·2H2O and (NH4)2(HPO4), respectively, with varying amounts of gelatin at 25 °C and pH 7. The influence of prestructuring effects of calcium and phosphate ions, respectively, on gelatin and by this on the precipitated materials was investigated in detail. X-ray-diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), and high-resolution transmission electron microscopy (HR-TEM) revealed that the prestructuring components as well as the total amount of gelatin involved in the reactions have a substantial influence on the composition and shape of the nanocomposites formed. In the case of CaCl2·2H2O used as the prestructuring agent for gelatin, hydroxyapatite is the inorganic phase obtained, independent of the initial amount of gelatin. By the prestructuring of gelatin with (NH4)2(HPO4), a strong dependency of the reaction products on the amount of gelatin was observed. Low gelatin quantities favor the formation of hydroxyapatite, whereas high gelatin concentrations lead to the formation of octacalcium phosphate. Moreover, the morphology of the composites changes gradually. Samples prepared by means of the Ca-prestructuring (CPS) reaction consist of small plate-like particles (50 nm × 33 nm). When the PO4-prestructuring (PPS) reaction is used, the particle size is highly influenced by the amount of gelatin. Lower gelatin concentrations lead to small, plate-like particles (60 nm × 35 nm), while higher gelatin concentrations cause the development of large foils (730 nm × 410 nm). The thickness of the composite particles varies from 2 to 13 nm as determined by means of electron holography. The calcium phosphate−gelatin nanocomposites obtained by the precipitation reactions were investigated for use as dentine repair materials with a special focus on the closing of open tubuli of sensitive tooth necks.
    Chemistry of Materials, v.22, 5137-5153 (2010). 01/2010;