de Wild, Michael

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Michael
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de Wild, Michael

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2002 - 200982010 - 201611
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Enddatum: 2019 × Thema: 600 - Technik, Medizin, angewandte Wissenschaften ×

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Gerade angezeigt 1 - 10 von 19
  • Vorschaubild nicht verfügbar
    Publikation
    Track E. Bioprinting and additive manufacturing
    (De Gruyter, 2016) Wohlfender, Fabian; Rüegg, Jasmine; Vogt, Nicola; Marek, Romy; de Wild, Michael [in: Biomedical Engineering]
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    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, Gernot [in: Journal of Biomedical Materials Research Part B: Applied Biomaterials]
    Biomaterials 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 Zeitschrift
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    Publikation
    Cell viability on titanium implant surfaces modified with antibacterial copper
    (2015) Jung, Christiane; Mathes, Stephanie; Bono, Epifania; Walker, Cyril; Kessler, Anja; Straumann, Lukas; de Wild, Michael; de Haller, Emmanuel B. [in: European Cells and Materials]
    01A - Beitrag in wissenschaftlicher Zeitschrift
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    Publikation
    All-inside meniscal repair devices compared with their matched inside-out Vertical mattress suture repair. Introducing 10,000 and 100,000 loading cycles
    (SAGE, 01.09.2014) Rosso, Claudio; Müller, Sebastian; Buckland, Daniel M.; Schwenk, Tanja; Zimmermann, Simon; de Wild, Michael; Valderrabano, Victor [in: The American Journal of Sports Medicine]
    All-inside arthroscopic meniscal repairs are favored by most clinicians because of their lower complication rate and decreased morbidity compared with inside-out techniques. Until now, only 1000 cycles have been used for biomechanical testing. Hypothesis: All-inside meniscal repairs will show inferior biomechanical response to cyclic loading (up to 100,000 cycles) and load-to-failure testing compared with inside-out suture controls. Study Design: Controlled laboratory study. Methods: Bucket-handle tears in 72 porcine menisci were repaired using the Omnispan and Fast-Fix 360 (all-inside devices) and Orthocord 2-0 and Ultrabraid 2-0 sutures (matched controls). Initial displacement, displacement after cyclic loading (100, 500, 1000, 2000, 5000, 10,000, and 100,000 cycles) between 5 and 20 N, ultimate load to failure, and mode of failure were recorded, as well as stiffness. Results: Initial displacement and displacement after cyclic loading were not different between the groups. The Omnispan repair demonstrated the highest load-to-failure force (mean 6 SD, 151.3 6 21.5 N) and was significantly stronger than all the other constructs (Orthocord 2-0, 105.5 6 20.4 N; Ultrabraid 2-0, 93.4 6 22.5 N; Fast-Fix 360, 76.6 6 14.2 N) (P \ .0001 for all). The Orthocord vertical inside-out mattress repair was significantly stronger than the Fast-Fix 360 repair (P = .003). The Omnispan (30.8 6 3.5 N/mm) showed significantly higher stiffness compared with the Ultrabraid 2-0 (22.9 6 6.9 N/mm, P \ .0001) and Fast-Fix 360 (23.7 6 3.9 N/mm, P = .001). The predominant mode of failure was suture failure. Conclusion: All-inside meniscal devices show comparable biomechanical properties compared with inside-out suture repair in cyclic loading, even after 100,000 cycles. Clinical Relevance: Eight to 10 weeks of rehabilitation might not pose a problem for all repairs in this worst-case scenario.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    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, Bert [in: International Journal of Materials Research]
    Selective 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 Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Combining micro computed tomography and three-dimensional registration to evaluate local strains in shape memory scaffolds
    (Elsevier, 02/2014) Bormann, Therese; Schulz, Georg; Deyhle, Hans; Beckmann, Felix; de Wild, Michael; Küffer, Jürg; Münch, Christoph; Hoffmann, Waldemar; Müller, Bert [in: Acta Biomaterialia]
    Appropriate mechanical stimulation of bony tissue enhances osseointegration of load-bearing implants. Uniaxial compression of porous implants locally results in tensile and compressive strains. Their experimental determination is the objective of this study. Selective laser melting is applied to produce open-porous NiTi scaffolds of cubic units. To measure displacement and strain fields within the compressed scaffold, the authors took advantage of synchrotron radiation-based micro computed tomography during temperature increase and non-rigid three-dimensional data registration. Uniaxial scaffold compression of 6% led to local compressive and tensile strains of up to 15%. The experiments validate modeling by means of the finite element method. Increasing the temperature during the tomography experiment from 15 to 37 °C at a rate of 4 K h−1, one can locally identify the phase transition from martensite to austenite. It starts at ∼24 °C on the scaffolds bottom, proceeds up towards the top and terminates at ∼34 °C on the periphery of the scaffold. The results allow not only design optimization of the scaffold architecture, but also estimation of maximal displacements before cracks are initiated and of optimized mechanical stimuli around porous metallic load-bearing implants within the physiological temperature range.
    01A - Beitrag in wissenschaftlicher Zeitschrift
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    Publikation
    Rapid prototyped porous nickel–titanium scaffolds as bone substitutes
    (SAGE, 17.01.2014) Hoffmann, Waldemar; Bormann, Therese; Rossi, Antonella; Müller, Bert; Schumacher, Ralf; Martin, Ivan; de Wild, Michael; Wendt, David [in: Journal of Tissue Engineering]
    While calcium phosphate–based ceramics are currently the most widely used materials in bone repair, they generally lack tensile strength for initial load bearing. Bulk titanium is the gold standard of metallic implant materials, but does not match the mechanical properties of the surrounding bone, potentially leading to problems of fixation and bone resorption. As an alternative, nickel–titanium alloys possess a unique combination of mechanical properties including a relatively low elastic modulus, pseudoelasticity, and high damping capacity, matching the properties of bone better than any other metallic material. With the ultimate goal of fabricating porous implants for spinal, orthopedic and dental applications, nickel–titanium substrates were fabricated by means of selective laser melting. The response of human mesenchymal stromal cells to the nickel–titanium substrates was compared to mesenchymal stromal cells cultured on clinically used titanium. Selective laser melted titanium as well as surface-treated nickel–titanium and titanium served as controls. Mesenchymal stromal cells had similar proliferation rates when cultured on selective laser melted nickel–titanium, clinically used titanium, or controls. Osteogenic differentiation was similar for mesenchymal stromal cells cultured on the selected materials, as indicated by similar gene expression levels of bone sialoprotein and osteocalcin. Mesenchymal stromal cells seeded and cultured on porous three-dimensional selective laser melted nickel–titanium scaffolds homogeneously colonized the scaffold, and following osteogenic induction, filled the scaffold’s pore volume with extracellular matrix. The combination of bone-related mechanical properties of selective laser melted nickel–titanium with its cytocompatibility and support of osteogenic differentiation of mesenchymal stromal cells highlights its potential as a superior bone substitute as compared to clinically used titanium.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Microstructure of selective laser melted nickel–titanium
    (Elsevier, 2014) Bormann, Therese; Müller, Bert; Schinhammer, Michael; Kessler, Anja; Thalmann, Peter; de Wild, Michael [in: Materials Characterization]
    In 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 Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Assessing the morphology of selective laser melted NiTi-scaffolds for a three-dimensional quantification of the one-way shape memory effect
    (03/2013) Bormann, Therese; de Wild, Michael; Beckmann, Felix; Müller, Bert; Goulbourne, Nakhiah C.; Naguib, Hani E. [in: Behavior and Mechanics of Multifunctional Materials and Composites 2013]
    NiTi is promising for the use as bone scaffold, because the pseudoelasticity or the one- and two-way shape memory effect in the physiological window can mechanically stimulate the adherent cells. Such stimuli can enhance osseo integration and might reduce stress shielding associated with load bearing implants. The present study is based on the additive manufacturing technique of selective laser melting (SLM) to fabricate three-dimensional NiTi scaffolds. We demonstrate that the morphology of the scaffolds can be quantified using synchrotron radiation-based micro computed tomography (SRµCT) and sophisticated registration software. Comparing the CAD file with the SLM scaffolds, quality factors are derived. With respect to the CAD file, the overlap corresponds to (92.5 ± 0.6) %. (7.4 ± 0.42) % of material was missing and (48.9 ± 2.3) % of excess material found. This means that the actual scaffold is less porous than expected, a fact that has to be considered for the scaffold design. In order to quantify the shape memory effect during the shape recovery process, we acquired radiographs rotating an initially deformed scaffold in angular steps of 0.2 degree during controlled heating. The continuously acquired radiographs were combined to tomography data, showing that the quality factors evolved with temperature as the scaffold height, measured by conventional thermo-mechanical analysis. Furthermore, the data comprise the presence of compressive and tensile local strains in the three-dimensional scaffolds to be compared with the physiological situation.
    04B - Beitrag Konferenzschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Modulation of human osteoblasts by metal surface chemistry
    (Wiley, 2013) Hofstetter, Wilhelm; Sehr, Harald; de Wild, Michael; Portenier, Jeannette; Gobrecht, Jens; Hunziker, Ernst B. [in: Journal of Biomedical Materials Research Part A]
    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 Zeitschrift