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Langmuir-Blodgett (LB) films of Cd arachidate and Ca arachidate with thicknesses of 1, 3, 9, and 25 layers were investigated using near edge x-ray absorption fine structure (NEXAFS spectroscopy), small angle x-ray scattering (SAXS), and reflected high energy electron diffraction (RHEED). The results from the x-ray diffraction experiments on layer thickness and interface roughness complement the structural information from NEXAFS on the average tilt angle of the alkyl chains in real space. The RHEED measurements confirm these findings and give additional information on the lateral order in these organic films. We find that the monolayer film shows a substantial degree of disorder, while for three and more LB layers, the molecular orientation is virtually identical to that of the corresponding fatty acid salts, i.e., the hydrocarbon chains are oriented perpendicular to the substrate surface in an all-trans conformation. Furthermore, a simplified and more robust analysis scheme for NEXAFS data obtained for hydrocarbon chains is presented. 7722

Background: The bone substitute NanoBone® consists of nanocrystalline hydroxyapatite embedded in a highly porous matrix of silica gel. It promotes the healing of bone defects and is degraded by osteoclasts during bone remodeling. The present study investigates the interactions of NanoBone® with bone tissue. Methods: Granules of NanoBone® were implanted in defects of critical size in the mandible of minipigs. Samples were taken after 5 and 10 weeks and demineralized. The composition of the implanted granules was analyzed by means of transmission and scanning electron microscopy and EDX. Enzymeand immunohistochemistry was used to investigate organic components of NanoBone® granules that arised after implantation in the host. Results: EDX demonstrated that 5 weeks after implantation the silica gel was degraded and replaced by an organic matrix. Ultrastructurally, the matrix appeared amorphous with only single collagen fibrillae. PAS-staining indicated the presence of carbohydrates. Immunohistochemically, the bone proteins osteopontin, osteocalcin and BMP-2 were found as constituents of the new matrix. Alkalic phosphatase activity was located in osteoblasts and newly formed bone on NanoBone® and focally in particles. Osteoclasts with ruffled borders, sealing zones, and acid phosphatase activity were situated in resorption lacunae at granule surfaces not covered by new bone. Conclusions:In vivo, the silica gel of NanoBone® is replaced by bone matrix glycoproteins with known functions in attraction, adhesion, and differentation of bone cells as osteoblasts and osteoclasts. We assume that the deposition of these molecules supports the early phase of NanoBone® degradation by osteoclasts and promotes the production of new bone tissue.

We have investigated the magnetic properties of mass-selected iron clusters using the MagnetoOptical Kerr effect (MOKE) in longitudinal geometry. For the production of these clusters, a newly developed continuous arc cluster ion source (ACIS) was applied. The source is based on cathodic arc erosion in inert gas environment and subsequent expansion into high vacuum. Its intensity and stability allows mass selection within a wide size range. The source efficiency is demonstrated in deposition experiments and transmission electron microscopy. For mass-selected iron particles deposited into a silver matrix we could observe a change in the magnetic behaviour from ferromagnetism to superparamagnetism around a size of 10 nm at room temperature.

Silicified regions in the stem and leaf of the horsetail Equisetum arvensewere studied by scanning and transmission electron microscopy. The silica was present as a thin layer on the outer surface with variation in the size of this layer depending on the part investigated. There was a dense arrangement of silica spheres with some density fluctuations. A loose arrangement of silica particles with variation in their size was found beneath this dense arrangement suggesting the agglomeration of silica. An electron diffraction pattern showed the presence of amorphous silica, with the short range order being comparable to that of silica from other chemical sources. The medium range order shows the presence of silica with a high inner surface. SAXS measurements correlate with the particle size observed in TEM, and provide values for surface fractals. A new method of plasma ashing to remove the organics is also described.

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A nanocrystalline bone substitute embedded in a highly porous silica gel matrix (NanoBone) has previously been shown to bridge bone defects by an organic matrix. As the initial host response on the bone graft substitute might be a determinant for subsequent bone formation, our present purpose was to characterize the early tissue reaction on this biomaterial. After implantation of 80 mg of NanoBone into the adipose neck tissue of a total of 35 rats, grafts were harvested for subsequent analysis at days 3, 6, 9, 12, and 21. The biomaterial was found encapsulated by granulation tissue which partly penetrated the implant at day 3 and completely pervaded the graft at day 12 on implantation. Histology revealed tartrate-resistant acid phosphatase (TRAP)-positive giant cells covering the biomaterial. ED1 (CD68) immunopositivity of these cells further indicated their osteoclast-like phenotype. Scanning electron microscopy revealed organic tissue components within the periphery of the graft already at day 9, whereas the central hematoma region still presented the silica-surface of the biomaterial. Energy dispersive X-ray spectroscopy further demonstrated that the silica gel was degraded faster in the peripheral granulation tissue than in the central hematoma and was replaced by organic host components by day 12. In conclusion, the silica gel matrix is rapidly replaced by carbohydrate macromolecules. This might represent a key step in the process of graft degradation on its way toward induction of bone formation. The unique composition and structure of this nanoscaled biomaterial seem to support its degradation by host osteoclast-like giant cells.

a b s t r a c tThe growth of diamond from fullerene C60 was studied by spark plasma sintering (SPS). The phases and microstructures were analyzed by Raman spectroscopy, Synchrotron X-ray, scanning electron microscopy and transmission electron microscopy. Experimental results show that C60 becomes unstable and can be directly transformed into diamond by SPS under a pressure of 50 MPa at temperatures above 1150 1C, without any catalyst being involved. Polycrystalline diamond crystals with sizes up to 250 mm and transition rate about 30 vol% are obtained at SPS temperature of 1300 1C. The mechanism indicates that the high fraction of sp 3 hybrids in the fullerene C60 and the generated plasmas in the SPS lead to its transformation into diamond at such low temperatures and pressures. The transformation from C60 to diamond is a direct transition process with a structural reconstruction of carbon atoms without intermediate phases being involved.