Hierarchically structured titanium foams for tissue scaffold applications.
ABSTRACT We present a novel route for producing a new class of titanium foams for use in biomedical implant applications. These foams are hierarchically porous, with both the traditional large (>300μm) highly interconnected pores and, uniquely, wall struts also containing micron scale (0.5-5μm) interconnected porosities. The fabrication method consists of first producing a porous oxide precursor via a gel casting method, followed by electrochemical reduction to produce a metallic foam. This method offers the unique ability to tailor the porosity at several scales independently, unlike traditional space-holder techniques. Reducing the pressure during foam setting increased the macro-pore size. The intra-strut pore size (and percentage) can be controlled independently of macro-pore size by altering the ceramic loading and sintering temperature during precursor production. Typical properties for an 80% porous Ti foam were a modulus of ∼1GPa, a yield strength of 8MPa and a permeability of 350 Darcies, all of which are in the range required for biomedical implant applications. We also demonstrate that the micron scale intra-strut porosities can be exploited to allow infiltration of bioactive materials using a novel bioactive silica-polymer composite, resulting in a metal-bioactive silica-polymer composite.
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ABSTRACT: Biological soil crusts are important cover in arid desert landscapes, yet their importance as habitats to secondary producers such as ants is relatively unknown. This study was conducted to determine if the presence and development of biological soil crusts on dune surfaces stabilized by revegetation facilitates ant establishment and survival. We measured topsoil properties and crustal features during different successional stages, which were characterized by cyanobacteria and algae, lichens, and mosses, respectively. The species richness and abundance (nest density) of ants were closely associated with silt content, soil organic matter, nitrogen and soil moisture, as well as topsoil temperature. However, ant nest distribution was largely dependent on the biomass and thickness of crusts and topsoil. These findings provide evidence that the recovery or development of biological soil crusts on dune surfaces in the Tengger Desert could favor and maintain higher ant species diversity. Therefore, the disturbance of crusts would result in a reduction of ant species richness and abundance in desert systems.Applied Soil Ecology 01/2011; 47(1):59-66. · 2.21 Impact Factor
Article: Quantitative X-ray tomographyInternational Materials Reviews 01/2014; 59(1):1-43. · 6.55 Impact Factor
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ABSTRACT: Porous titanium implants are a common choice for bone augmentation. Implants for spinal fusion and repair of non-union fractures must encourage blood flow after implantation so that there is sufficient cell migration, nutrient and growth factor transport to stimulate bone ingrowth. Additive manufacturing techniques allow a large number of pore network designs. This study investigates how the design factors offered by selective laser melting technique can be used to alter the implant architecture on multiple length scales to control and even tailor the flow. Permeability is a convenient parameter that characterises flow, correlating to structure openness (interconnectivity and pore window size), tortuosity and hence flow shear rates. Using experimentally validated computational simulations, we demonstrate how additive manufacturing can be used to tailor implant properties by controlling surface roughness at a microstructual level (microns), and by altering the strut ordering and density at a mesoscopic level (millimetre).Materials science & engineering. C, Materials for biological applications. 10/2013; 33(7):4055-62.