Browsing by Author "Torres, Yadir"

One of the most important concerns in long-term prostheses is bone resorption as a result of the stress shielding due to stiffness mismatch between bone and implant. The aim of this study was to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both loose-sintering processing and space-holder technique with NaCl between 40 and 70% in volume fraction. Both mechanical properties and porosity morphology were assessed. Young's modulus was measured using uniaxial compression testing, as well as ultrasound methodology. Complete characterization and mechanical testing results allowed us to determine some important findings: (i) optimal parameters for both processing routes; (ii) better mechanical response was obtained by using space-holder technique; (iii) pore geometry of loose sintering samples becomes more regular with increasing sintering temperature; in the case of the space-holder technique that trend was observed for decreasing volume fraction; (iv) most reliable Young's modulus measurements were achieved by ultrasound technique.

A great variety of powder metallurgy techniques can produce biomimetic porous titanium structures with similar mechanical properties to host bone tissue. In this work, loose sintering and space holder techniques, two frequently used metallurgical techniques, are compared to evaluate the influences of porosity (content, size, morphology and wall roughness), mechanical properties (stiffness and yield strength) and in-vitro cellular responses (adhesion and proliferation of myoblasts and osteoblasts). These comparisons are made to achieve the best balance between biomechanical and bifunctional behavior of a partial porous implant for cortical bone replacement. Cell adhesion (filopodia presence) and spreading were promoted on both porous surfaces and fully dense substrates (non-porous control surfaces). Porous scaffold samples designed using 50 vol.% NaCl space holder technique had an improved bioactive response over those obtained with the loose sintering technique due to higher roughness and scaffold pore diameter. However, the presence of large and heterogeneous pores compromises the mechanical reliability of the implant. Considering both scenarios, the substrates obtained with 40 vol.% NH4HCO3 and pore size ranges between 100 and 200 μm provide a balanced optimization of size and strength to promote in-vitro osseointegration.

Bone resorption and possible fracture of host tissue are some consequences resulting from the mismatch between the Young's Modulus of the constituent materials of implants and bone that compromises the reliability of implants for replacing damaged bone tissue. The use of functional graded porous materials presents an interesting approach that could help decrease the Young's modulus while simultaneously mimicking highly hierarchical porosity of the bone structure. However, these structures are more difficult to fabricate than those with homogenous porosity. The design and distribution of this porosity in the implant must ensure the biomechanical and biofunctional balance of the bone tissue it is intended to replace. In this study, Ti radially graded structures were successfully fabricated using Spark Plasma Sintering combined with Space Holder Technique. The effects of temperature on porosity and mechanical properties were thoroughly examined. The results indicated that this processing route allows to achieve good control of porosity, close to the amount of added spacer. Yield stress of 181 MPa and an elastic modulus of 56 GPa were obtained for samples sintered at 800 °C for 5 min under a pressure of 6.3 MPa. These mechanical properties make the structure a viable candidate for replacing human long bones.

Titanium and its alloys are reference materials in biomedical applications because of their desirable properties. However, one of the most important concerns in long-term prostheses is bone resorption as a result of the stress-shielding phenomena. Development of porous titanium for implants with a low Young’s modulus has accomplished increasing scientific and technological attention. The aim of this study is to evaluate the viability, industrial implementation and potential technology transfer of different powder-metallurgy techniques to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both conventional powder metallurgy (PM) and space-holder technique. The conventional PM frontier (Loose-Sintering) was evaluated. Additionally, the technical feasibility of two different space holders (NH4HCO3 and NaCl) was investigated. The microstructural and mechanical properties were assessed. Furthermore, the mechanical properties of titanium porous structures with porosities of 40% were studied by Finite Element Method (FEM) and compared with the experimental results. Some important findings are: (i) the optimal parameters for processing routes used to obtain low Young’s modulus values, retaining suitable mechanical strength; (ii) better mechanical response was obtained by using NH4HCO3 as space holder; and (iii) Ti matrix hardening when the interconnected porosity was 36–45% of total porosity. Finally, the advantages and limitations of the PM techniques employed, towards an industrial

The utilization of porous biomedical implants featuring a bimodal microstructure has garnered substantial interest within the scientific community. This study delves into the intricate interplay between processing parameters, microstructural attributes, and the tribo-mechanical performance of titanium grade 4, showcasing its potential to serve as implants to address compromised cortical bone tissue. The investigation meticulously examines the impact of milling duration (10 and 20 h), proportion of milled powder (50 and 75 wt%), and the volume fraction of space-holding agents (40–60 vol% NaCl) on the resulting characteristics of the bimodal microstructure, which plays a crucial role in achieving optimal biomechanical equilibrium. The Vickers microhardness, conventional and instrumented (P-h curves), and the wear behavior (ball-on disk) are discussed in terms of bimodal microstructure distribution, particle size and porosity level inherent to the fabrication conditions (mechanical milling + space-holder + hot-pressing). In general terms, milling time and milled powder fraction were the most influent parameters on the final properties of the materials. With the processing route used, the achieved microhardness values and wear behavior are comparable with those obtained by means of surface modifications or alloys. The Young's moduli obtained were in the range of 30–50 GPa, which could help to reduce the shielding phenomenon, while presenting a good mechanical resistance and wear behavior. In light of these findings, the fabricated specimen, composed of 75 wt% milled powder subjected to a 10-h milling duration, supplemented by a 60 vol% fraction of NaCl, emerges as a prime candidate manifesting superior biomechanical equilibrium. This judicious configuration exhibits a promising trajectory for its application in bone replacement endeavors.