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The gradation of porosity in a biomaterial can be very useful for a variety of medical engineering applications such as filtration, bone replacement and implant development. However, the preparation of such structures is not a technologically trivial task and replication methods do not offer an easy solution. In this work, we elucidate the preparation of structures having a graded porosity by electrohydrodynamic spraying, using zirconia (ZrO 2 ), which is widely used in biomedical and other applications. The processes are generic and can be achieved using other bioactive ceramics with similar particle characteristics. The pores on the sprayed surface, the innermost surface and lengthwise cross sections have been analysed in addition to the change in depth of penetration as a function of spraying time. Control of porosity, pore size and depth of penetration has been obtained by varying parameters such as the spraying time, sintering temperature and the sacrificial template. It has been possible to obtain structures with interconnected pore networks of pore size greater than 100 mm as well as scattered pores smaller than 10 mm in size.

Porous scaffolds are considered a key strategy in the concept of bone tissue engineering. Hydroxyapatite, which is a bioceramic has been used as a popular scaffold material due to its bioactive and osteoconductive properties. A combination of slurry-dipping and electrospraying has been used as a new foam fabrication method to produce porous and interconnected foam structures. The combined method has shown to overcome the shortcomings of the individual methods and it has produced open pores in the desired range of 100-350 microm. The porosity which was determined by calculation and microtomography was between 84% and 88%. Reduced cracks and thicker struts were observed in the microstructure, pointing to improved mechanical properties.

A novel fabrication technique, a combination of slurry dipping and electrospraying, was used to produce hydroxyapatite foams as potential matrices for bone tissue engineering applications. In this study, scaffolds that were slurry dipped and electrosprayed for different time intervals were compared with foams prepared by the individual methods of dipping and electrospraying. Significant differences in the distribution of cracks on the struts, the strut thickness and porosity were observed on the sintered foams prepared under the varied conditions. All the sintered structures had average porosities in the range 84-94% and desirable pore interconnections, while the combined method produced foams of uniform pore distribution, thicker struts and improved mechanical properties. Further improvement of the mechanical properties has also been achieved by altering the sintering conditions.

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