On the influence of space holder in the development of porous titanium implants: Mechanical, computational and biological evaluation

• We obtained porous samples of titanium by the space holder technique, with different level of porosity.
• We characterized the porous morphology and the mechanical behavior of porous compacts.
• We characterized the biological behavior of porous compacts.
• We proposed a numerical model to simulate the mechanical behavior of porous material.

Commercially pure titanium (cpTi) is frequently used for bone replacement in both dentistry and orthopedics applications, primarily due to its bioinert behavior, but also for providing optimum biomechanical behavior. It is recognized that the high elastic modulus of cpTi is associated with the stress-shielding phenomena, which promotes bone resorption. Development of implants with low elastic modulus, providing suitable mechanical strength and optimum osseointegration, is the focus of emergent research in advanced Ti-based alloy biomaterials. Porous metals and, in particular, porous titanium can provide the optimal combination of biocompatibility, high strength and minimal stiffness that best mimic bone. Synthesis of porous Ti, controlling porosity and interfacial properties, which optimizes in-vivo integration, remains the subject of recent research. In this work, porous samples of cpTi grade IV obtained by space-holder technique with ammonium bicarbonate (NH4HCO3) have been studied. For a fixed value of compaction pressure, evaluation of porosity and mechanical properties were performed to determine the influence of space-holder content (from 30 to 70 vol.%) in the global performance of the cpTi porous samples. Porous materials with enhanced mechanical behavior has been achieved, exhibiting an appropriate Young's modulus, which reduces stress shielding, as well as reasonable good mechanical strength. Additionally, in order to go in-depth on the study of these porous cpTi samples, a finite element model has been proposed and the macroscopic mechanical response of porous compacts analyzed, showing a good agreement with experimental results. In addition, stress distribution around pores of the compacts has been analyzed, and the influence of the compact microstructure on the obtained stress distribution has been studied. Finally, biological tests in the obtained porous compacts have been carried out. Adhesion of bone cells inside the pores has been analyzed, which is a good indicator of their potential improvement of osseointegration. Cells behavior inside the pores appears to be clearly sensitive to roughness and geometry of pores (diameter and curvature).