Porous Titanium Cylinders Obtained by the Freeze-Casting Technique: Influence of Process Parameters on Porosity and Mechanical Behavior

Abstract

The discrepancy between the stiffness of commercially pure titanium and cortical bone tissue compromises its success as a biomaterial. The use of porous titanium has been widely studied, however, it is still challenging to obtain materials able to replicate the porous structure of the bones (content, size, morphology and distribution). In this work, the freeze-casting technique is used to manufacture cylinders with elongated porosity, using a home-made and economical device. The relationship between the processing parameters (diameter and material of the mold, temperature gradient), microstructural features and mechanical properties is established and discussed, in terms of ensuring biomechanical and biofunctional balance. The cylinders have a gradient porosity suitable for use in dentistry, presenting higher Young’s modulus at the bottom, near the cold spot and, therefore better mechanical resistance (it would be in contact with a prosthetic crown), while the opposite side, the hot spot, has bigger, elongated pores and walls.

Characterization and Monitoring of Titanium Bone Implants with Impedance Spectroscopy

“…In our work we used two of the most established techniques used to characterize the porosity at different levels (superficial and volumetric porosities): The Archimedes´method (ASTM C373-88), and image analysis (IA) on the samples surface, as described in the Materials and Methods section. As we can see in Table 1, and in accordance with other previous works [20][21][22][23], there are many cases where neither of the two methods is effective to discriminate the volumetric porosity or the pore size range, lacking statistical significance. Our results, and this more detailed comparison with the existing techniques, showed the efficiency and advantages of the proposed method in the characterization of porous titanium samples, in a precise, simple, and affordable way.…”

Use of Impedance Spectroscopy for the Characterization of In-Vitro Osteoblast Cell Response in Porous Titanium Bone Implants

“…The need to characterize porosity is a fact. Different techniques have been used in the literature: Archimedes, helium pycnometry, micro-tomography, image analysis [42][43][44][45] and electrical impedance spectroscopy [35,[46][47][48]. Some preliminary studies were developed using the latter technique to correlate porosity of titanium, pore size and electrical conductivity, although the influence of the electric frequency in the measured impedance was not described [35].…”

Biofunctionalization of Porous Ti Substrates Coated with Ag Nanoparticles for Potential Antibacterial Behavior

“…The microstructural characterization (porosity parameters) of the uncoated titanium substrates using the Archimedes' method and image analysis, as well as the mechanical properties estimated from the these experimentally values [60,69], are summarized in Table 1. The pore sizes and contents obtained corroborate the effectiveness of the use of the space-holder technique.…”

“…Furthermore, the total area occupied by the micropores (less than 50 µm), macropores (associated with the spacer particles used), and the flat area of remaining Ti were evaluated using the image analysis software and with at least five pictures of 5× for each type of substrate. Finally, the mechanical behavior of the porous substrates (dynamic Young's modulus, E d , yield strength, and σ y ), was estimated from the experimental porosity results (at least three measurements for each processing condition) and using fit equations reported in the literature [60].…”