Hierarchically structured titanium foams for tissue scaffold applications

Department of Materials, Imperial College London, London SW7 2AZ, UK.
Acta biomaterialia (Impact Factor: 6.03). 12/2010; 6(12):4596-604. DOI: 10.1016/j.actbio.2010.06.027
Source: PubMed


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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    • "Adopting a hierarchical structure is an alternative way to enhance the mechanical properties of light-weight materials and structures [12]. Several studies on hierarchical cores are mainly focused on the development of multiscale theoretical models of hierarchical materials [13] [14], the design of hierarchical composite structures [15] [16], and the mechanical properties of sandwich structures with hierarchical cores [17] [18] [19] [20]. Functionally graded foams are typical materials that feature a hierarchical structure [21]. "
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    • "The present paper concerns the scope for producing useful material by controlled oxidation of a particular type of (relatively coarse, high porosity) open cell metallic foam. There have been various studies [5] [6] [7] on the production of highly porous metallic materials incorporating surface oxides. However, none of these production techniques were based on plasma electrolytic oxidation (PEO), a process being increasingly used to create relatively thick oxide layers on the surfaces of aluminium, magnesium and titanium alloys [8] [9] [10] [11] [12]. "
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