Institut für Medizintechnik und Medizininformatik
Dauerhafte URI für die Sammlunghttps://irf.fhnw.ch/handle/11654/23
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Ergebnisse nach Hochschule und Institut
Publikation Molecular assembly and self‐assembly: molecular nanoscience for future technologies(2003) de Wild, Michael; Berner, Simon; Suzuki, Hitoshi; Ramoino, Luca; Baratoff, Alexis; Jung, Thomas A.In this review the emerging science of single molecules is discussed in the perspective of nanoscale molecular functions and devices. New methods for the controlled assembly of well-defined molecular nanostructures are pre- sented: self assembly and single molecular positioning. The observation and selective modification of conformation, electronics, and molecular mechanics of individual molecules and molecular assemblies by scanning probes is dem- onstrated. To complement this scientific review, some of the possible conse- quences and visions for future developments are discussed, as far as they derive from the presented systems. The prospects of nanoscale science to stim- ulate technological evolution are exemplified.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Microstructure of selective laser melted nickel–titanium(Elsevier, 2014) Bormann, Therese; Müller, Bert; Schinhammer, Michael; Kessler, Anja; Thalmann, Peter; de Wild, MichaelIn selective laser melting, the layer-wise local melting of metallic powder by means of a scanning focused laser beam leads to anisotropic microstructures, which reflect the pathway of the laser beam. We studied the impact of laser power, scanning speed, and laser path onto the microstructure of NiTi cylinders. Here, we varied the laser power from 56 to 100 W and the scanning speed from about 100 to 300 mm/s. In increasing the laser power, the grain width and length increased from (33 ± 7) to (90 ± 15) μm and from (60 ± 20) to (600 ± 200) μm, respectively. Also, the grain size distribution changed from uni- to bimodal. Ostwald-ripening of the crystallites explains the distinct bimodal size distributions. Decreasing the scanning speed did not alter the microstructure but led to increased phase transformation temperatures of up to 40 K. This was experimentally determined using differential scanning calorimetry and explained as a result of preferential nickel evaporation during the fabrication process. During selective laser melting of the NiTi shape memory alloy, the control of scanning speed allows restricted changes of the transformation temperatures, whereas controlling the laser power and scanning path enables us to tailor the microstructure, i.e. the crystallite shapes and arrangement, the extent of the preferred crystallographic orientation and the grain size distribution.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Modulation of human osteoblasts by metal surface chemistry(Wiley, 2013) Hofstetter, Wilhelm; Sehr, Harald; de Wild, Michael; Portenier, Jeannette; Gobrecht, Jens; Hunziker, Ernst B.The use of metal implants in dental and orthopedic surgery is continuously expanding and highly successful. While today longevity and load-bearing capacity of the implants fulfill the expectations of the patients, acceleration of osseo integration would be of particular benefit to shorten the period of convalescence. To further clarify the options to a ccelerate the kinetics of osseo integration, within this study,the osteogenic properties of structurally identical surfaces with different metal coatings were investigated. To assess the development and function of primary human osteoblastson metal surfaces, cell viability, differentiation, and gene expression were determined. Titanium surfaces were used as positive, and surfaces coated with gold were used as negative controls. Little differences in the cellular parameters tested for were found when the cells were grown ontitanium discs sputter coated with titanium, zirconium, niobium, tantalum, gold, and chromium. Cell number, activity of cell layer-associated alkaline phosphatase (ALP), and levels of transcripts encoding COL1A1 and BGLAP did not vary significantly in dependence of the surface chemistry.Treatment of the cell cultures with 1,25(OH)2D3/Dex,however, significantly increased ALP activity and BGLAP messenger RNA levels. The data demonstrate that the metallayer coated onto the titanium discs exerted little modulatory effects on cell behavior. It is suggested that the micro-environment regulated by the periimplant tissues is more effective in regulating the tissue response than is the mate-rial of the implant itself.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Novel microcalorimetric assay for antibacterial activity of implant coatings. The cases of silver‐doped hydroxyapatite and calcium hydroxide(Wiley, 08/2015) Braissant, Olivier; Chavanne, Philippe; de Wild, Michael; Pieles, Uwe; Stevanovic, Sabrina; Schumacher, Ralf; Straumann, Lukas; Wirz, Dieter; Gruner, Philipp; Bachmann, Alexander; Bonkat, GernotBiomaterials with antimicrobial properties are now commonly used in different clinical specialties including orthopedics, endodontic, and traumatology. As a result, assessing the antimicrobial effect of coatings applied on implants is of critical importance. In this study, we demonstrate that isothermal microcalorimetry (IMC) can be used for monitoring bacterial growth and biofilm formation at the surface of such coatings and for determining their antimicrobial effects. The antibacterial effects of silver doped hydroxyapatite (HA) and calcium hydroxide coatings on Staphylococcus epidermidis were determined with a minimal workload. Using the Gompertz growth model we determined biofilm growth rates close to those values reported in the literature. Furthermore, we were able to estimate the reduction in the bacterial inocula originally applied at the surface of the coatings. Therefore, in addition to monitoring the antimicrobial effect of silver doped HA and calcium hydroxide coatings, we also demonstrate that IMC might be a valuable tool for assessing such antimicrobial properties of implant coatings at a minimal workload.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Tailoring selective laser melting process parameters for NiTi implants(Springer, 12/2012) Bormann, Therese; Schumacher, Ralf; Müller, Bert; Mertmann, Matthias; de Wild, MichaelComplex-shaped NiTi constructions become more and more essential for biomedical applications especially for dental or cranio-maxillofacial implants. The additive manufacturing method of selective laser melting allows realizing complex-shaped elements with predefined porosity and three-dimensional micro-architecture directly out of the design data. We demonstrate that the intentional modification of the applied energy during the SLM-process allows tailoring the transformation temperatures of NiTi entities within the entire construction. Differential scanning calorimetry, x-ray diffraction, and metallographic analysis were employed for the thermal and structural characterizations. In particular, the phase transformation temperatures, the related crystallographic phases, and the formed microstructures of SLM constructions were determined for a series of SLM-processing parameters. The SLM-NiTi exhibits pseudoelastic behavior. In this manner, the properties of NiTi implants can be tailored to build smart implants with pre-defined microarchitecture and advanced performance.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Fabrication of TiO2‐coated epoxy replicas with identical dual‐type surface topographies used in cell culture assays(Wiley, 01/2009) Schuler, Martin; Kunzler, Tobias P.; de Wild, Michael; Sprecher, Christoph M.; Trentin, Diana; Brunette, Donald M.; Textor, Marcus; Tosatti, Samuele G. P.The goal of this study was to reproducibly generate samples with complex surface topographies and chemistries identical to a "master surface" and to test their response in cell culture using rat calvarial cells. Negative replicas of dual-type topography were fabricated using dental impression material with half of the surface exhibiting smooth and rough topography, respectively. Positive epoxy resin replicas were cast from the same negative replica eight times consecutively and coated with a 60-nm thin film of titanium dioxide using a vapor deposition technique. Atomic force microscopy, scanning electron microscopy, confocal white light microscopy, and X-ray photoelectron spectroscopy indicated that TiO2-coated epoxy replicas had surface topographical features and surface compositions nearly indistinguishable from the original titanium master surfaces. The described technique showed high reproducibility over at least eight generations of replication using the same negative replica. Rat calvarial osteoblasts proliferated just as well on dual topography surfaces as on single topography surfaces. The advantage of the dual-type substrates is that they facilitate comparison within a single culture dish, thus eliminating dish-to-dish variation as well as saving material, time and costs compared to the usual method of evaluating surfaces in separate dishes.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Biomechanical evaluation of the interfacial strength of a chemically modified sandblasted and acid-etched titanium surface(Wiley, 06/2006) Ferguson, Stephen J.; Broggini, Nina; Wieland, Marco; de Wild, Michael; Rupp, Frank; Geis-Gerstorfer, Jürgen; Cochran, David L.; Buser, DanielThe functional capacity of osseointegrated dental implants to bear load is largely dependent on the quality of the interface between the bone and implant. Sandblasted and acid-etched (SLA) surfaces have been previously shown to enhance bone apposition. In this study, the SLA has been compared with a chemically modified SLA (modSLA) surface. The increased wettability of the modSLA surface in a protein solution was verified by dynamic contact angle analysis. Using a well-established animal model with a splitmouth experimental design, implant removal torque testing was performed to determine the biomechanical properties of the bone-implant interface. All implants had an identical cylindrical shape with a standard thread configuration. Removal torque testing was performed after 2, 4, and 8 weeks of bone healing (n = 9 animals per healing period, three implants per surface type per animal) to evaluate the interfacial shear strength of each surface type. Results showed that the modSLA surface was more effective in enhancing the interfacial shear strength of implants in comparison with the conventional SLA surface during early stages of bone healing. Removal torque values of the modSLA-surfaced implants were 8-21% higher than those of the SLA implants (p = 0.003). The mean removal torque values for the modSLA implants were 1.485 N m at 2 weeks, 1.709 N m at 4 weeks, and 1.345 N m at 8 weeks; and correspondingly, 1.231 N m, 1.585 N m, and 1.143 N m for the SLA implants. The bone-implant interfacial stiffness calculated from the torque-rotation curve was on average 9-14% higher for the modSLA implants when compared with the SLA implants (p = 0.038). It can be concluded that the modSLA surface achieves a better bone anchorage during early stages of bone healing than the SLA surface; chemical modification of the standard SLA surface likely enhances bone apposition and this has a beneficial effect on the interfacial shear strength.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Assessing the grain structure of highly X-ray absorbing metallic alloys(De Gruyter, 07/2014) Bormann, Therese; Beckmann, Felix; Schinhammer, Michael; Deyhle, Hans; de Wild, Michael; Müller, BertSelective laser melting allows the fabrication of NiTi implants with pre-defined, complex shapes. The control of the process parameters regulates the arrangement of the granular microstructure of the NiTi alloy. We prepared specimens with elongated grains, which build a sound basis for diffraction contrast tomography experiments using synchrotron radiation and for electron backscatter diffraction measurements. Both approaches reveal the orientation and size of the individual grains within the specimen. Still, electron backscatter diffraction is confined to two-dimensional cross-sections while diffraction contrast tomography reveals these microstructural features in three dimensions. We demonstrate that the grains in the selective laser melted specimen, which are oriented along the building direction, do not exhibit a well-defined planar grain orientation but are twisted. These twisted grains give rise to diffraction spots observable for several degrees of specimen rotation simultaneously to the acquisition of tomography data.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Track E. Bioprinting and additive manufacturing(De Gruyter, 2016) Wohlfender, Fabian; Rüegg, Jasmine; Vogt, Nicola; Marek, Romy; de Wild, Michael01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Supramolecular patterned surfaces driven by cooperative assembly of C60 and porphyrins on metal substrates(Wiley, 04.09.2004) Bonifazi, Davide; Spillmann, Hannes; Kiebele, Andreas; de Wild, Michael; Seiler, Paul; Cheng, Fuyong; Güntherodt, Hans‐Joachim; Jung, Thomas; Diederich, FrançoisPlenty of room on top: Unprecedented one- and two-dimensional fullerene patterns were obtained upon evaporation of pristine C60 onto pre-organized porphyrin monolayers on silver surfaces following a bottom-up approach. The arrangement of the fullerene molecules on the patterned layer can be controlled by the porphyrin structure (see scanning tunneling microscopy images).01A - Beitrag in wissenschaftlicher Zeitschrift