Commercially pure titanium (c.p. Ti) is one of the best metallic biomaterials for bone tissue replacement. However, one of its main drawbacks, which compromises the service reliability of the implants, is the stress-shielding phenomenon (Young's modulus mismatch with respect to that one of the bone). Several previous works attempted to solve this problem. One alternative to solve that problem has been the development of biocomposites implants and, more recently, the fabrication of titanium porous implants. In this work, porous samples of c.p. Ti grade 4 were obtained using conventional powder metallurgy technique. The influence of the processing parameters (compacting pressure and sintering temperature) on the microstructure features (size, type, morphology, and percentage of porosity), as well as on the mechanical properties (compressive yield strength, and conventional and dynamic Young's modulus) were investigated. The results indicated that there is an increment in density, roundness of pores, and mean free path between them as compacting pressure and/or sintering temperature is increased. The Young's modulus (conventional and dynamic) and yield strength showed the same behavior. Better stiffness results, in the central part of cylindrical samples, were obtained for a uniaxial compression of 38.5 MPa using a sintering temperature of 1273 K and 1373 K (1000°C and 1100°C). An evaluation of porosity and Young's modulus along a cylindrical sample divided in three parts showed that is possible to obtain a titanium sample with graded porosity that could be used to design implants. This approach opens a new alternative to solve the bone resorption problems associated with the stress-shielding phenomenon.

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Porous ceramic materials have been thoroughly developed due to the wide number of applications in different areas, such as filters for environmental clean-up and reuse, bioreactors, gas or chemical sensors and support materials for catalysts or absorbents. One of the forming methods that can be selected for these applications is the freeze drying of suspensions. This method has received increased attention for manufacturing near net shaped parts with directional porosity. This work deals with the manufacture of porous alumina bodies by a freeze casting route. The different parameters of the process, such as the solids content of the suspension, the addition of cryoprotector (glycerol) and the freezing conditions (temperature and device) have been studied to determine their influence on the microstructure, density and porosity of the green and sintered pieces. Materials with different degrees of porosity and distribution of pores (aligned in the freezing direction or homogeneously distributed) have been obtained.

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Aqueous gelcasting of alumina is optimised by preparing concentrated agarose solutions under overpressure conditions. The better dissolution reduces the viscosity and improves the microstructural control leading to green densities higher than 60 % of TD. The enhancement of the green strength is not accompanied by a significant increase of the plastic behaviour during fracture for agarose contents < 1 wt.%. Sintered densities > 99 % of theoretical are obtained.