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: A commercially-available low density aluminium network material (Duocel™) has been processed by plasma electrolytic oxidation to produce a ceramic hybrid material comprising an assembly of ceramic struts with metallic cores. The architecture and microstructure of this material were studied using X-ray tomography, scanning electron microscopy and densitometry. Conversion fractions were determined from mass gains and by image analysis of cross-sections, and the ceramic density was evaluated by hydrostatic weighing. Tensile and compressive testing of the hybrid material was used to study the toughness, as a function of the conversion fraction. Such material retains some of the beneficial mechanical properties of a metal (ductility and toughness), while also exhibiting a low overall density and a high specific surface area of ceramic. It can thus be considered as a highly permeable ceramic scaffold, with a relatively high toughness.Composites Science and Technology 04/2011; 71(6):908-915. DOI:10.1016/j.compscitech.2011.02.007 · 3.63 Impact Factor
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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. DOI:10.1016/j.apsoil.2010.10.010 · 2.21 Impact Factor
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ABSTRACT: Demand to develop a simple and adaptable method for preparation the hierarchical porous scaffolds for bone tissue regeneration is ever increasing. This study presents a novel and reproducible method for preparing the scaffolds with pores structure spanning from nano, micro to macro scale. A macroporous Sr-Hardystonite (Sr–Ca2ZnSi2O7, Sr–HT) scaffold with the average pore size of ~1200μm and porosity of ~95% was prepared using polymer sponge method. The struts of the scaffold were coated with a viscous paste consisted of salt (NaCl) particles and polycaprolactone (PCL) to provide a layer with thickness of ~300–800μm. A hierarchical porous scaffold was obtained with macro, micro and nanopores in the range of 400–900μm, 1–120μm and 40–290nm, after salt leaching process. These scales could be easily adjusted based on the starting foam physical characteristics, salt particle size, viscosity of the paste and salt/PCL weight ratio.Materials Letters 09/2011; 65(17-18-17-18):2578-2581. DOI:10.1016/j.matlet.2011.06.019 · 2.27 Impact Factor