Analytical model for the prediction of permeability of triply periodic minimal surfaces

Triply periodic minimal surfaces (TPMS) are mathematically defined cellular structures whose geometry can be quickly adapted to target desired mechanical response (structural and fluid). This has made them desirable for a wide range of bioengineering applications; especially as bioinspired materials for bone replacement. The main objective of this study was to develop a novel analytical framework which would enable calculating permeability of TPMS structures based on the desired architecture, pore size and porosity. To achieve this, computer-aided designs of three TPMS structures (Fisher-Koch S, Gyroid and Schwarz P) were generated with varying cell size and porosity levels. Computational Fluid Dynamics (CFD) was used to calculate permeability for all models under laminar flow conditions. Permeability values were then used to fit an analytical model dependent on geometry parameters only. Results showed that permeability of the three architectures increased with porosity at different rates, highlighting the importance of pore distribution and architecture. The computed values of permeability fitted well with the suggested analytical model (R2>0.99, p<0.001). In conclusion, the novel analytical framework presented in the current study enables predicting permeability values of TPMS structures based on geometrical parameters within a difference <5%. This model, which could be combined with existing structural analytical models, could open new possibilities for the smart optimisation of TPMS structures for biomedical applications where structural and fluid flow properties need to be optimised

Laser powder bed fusion of porous graded structures: a comparison between computational and experimental analysis

Functionally graded porous structures (FGPSs) are gaining interest in the biomedical sector, specifically for orthopaedic implants. In this study, the compressive behaviour of seven different FGPSs comprised of Face Centred Cubic (FCC) and the Octet truss unit cells (OCT) were analysed. The porosity of the structures were graded in different directions (radially, longitudinally, laterally and longitudinally & radially) by varying the strut diameters or by combining the two types of unit cells. The structures were manufactured by laser power bed fusion and compression tests were performed. Radially and laterally porous graded structures were found to outperform uniform porous structures with an increase in stiffness of 13.7% and 21.1% respectively. The experimental and finite element analysis (FEA) results were in good agreement with differences in elastic modulus of 9.4% and yield strength of 15.8%. A new FEA beam model is proposed in this study to analyse this type of structures with accurate results and the consequent reduction of computational time. The accuracy of the Kelvin-Voight model and the rule of mixtures for predicting the mechanical behaviour of different FGPSs was also investigated. The results demonstrate the adequacy of the analytical models specifically for hybrid structures and for structures with smooth diameter transitions

Understanding elastic anisotropy in diamond based lattice structures produced by laser powder bed fusion: Effect of manufacturing deviations

Laser powder bed fusion (L-PBF) allows the production of metal lattice cellular structures with tailored mechanical properties. In order to generate the specific structural behavior it is of utmost importance to understand the response of the unit cells when different load conditions are considered. In this article the mechanical response of diamond based cellular structures has been investigated focusing on the impact of geometrical inaccuracy generated by the manufacturing process on the elastic anisotropy of the mentioned unit cell. The μ-CT analysis of the structures shows that the manufacturing deviations occur in certain orientations that depend highly on the building direction and proximity to nodes. The measured imperfection types were implemented in a finite element model in order to predict their single and combined effects in the elastic directional response. The results indicate that the L-PBF process can induce a significant change of elastic anisotropy in the diamond unit cells, including a substantial variation of the optimal orientation for minimal compliance. Methods are presented to calculate this anisotropy such that it can be taken into account when designing and using such lattice structures in real-life applications with multi-axial load condition

Additively manufactured lattice structures with controlled transverse isotropy for orthopedic porous implants

Additively manufactured lattice structures enable the design of tissue scaffolds with tailored mechanical properties, which can be implemented in porous biomaterials. The adaptation of bone to physiological loads results in anisotropic bone tissue properties which are optimized for site-specific loads; therefore, some bone sites are stiffer and stronger along the principal load direction compared to other orientations. In this work, a semi-analytical model was developed for the design of transversely isotropic lattice structures that can mimic the anisotropy characteristics of different types of bone tissue. Several design possibilities were explored, and a particular unit cell, which was best suited for additive manufacturing was further analyzed. The design of the unit cell was parameterized and in-silico analysis was performed via Finite Element Analysis. The structures were manufactured additively in metal and tested under compressive loads in different orientations. Finite element analysis showed good correlation with the semi-analytical model, especially for elastic constants with low relative densities. The anisotropy measured experimentally showed a variable accuracy, highlighting the deviations from designs to additively manufactured parts. Overall, the proposed model enables to exploit the anisotropy of lattice structures to design lighter scaffolds with higher porosity and increased permeability by aligning the scaffold with the principal direction of the load

Meeting high precision requirements of additively manufactured components through hybrid manufacturing

A hybrid approach combining the laser powder bed fusion (LPBF) process and post-processing operations through 5-axis milling was employed to manufacture a Ti6Al4V aerospace component. From the design step, the requirements and needs in all the stages of the Hybrid Additive Manufacturing process were taken into account. A numerical simulation of distortions promoted by residual stresses during the additive process was employed to consider material allowance. The status of the as-built and post-processed component was analysed through scanning and CMM inspection and roughness measurements. The 3D scanned model of the as-built LPBF-ed component was used to understand the distortion behaviour of the component and compared to the numerical simulation. Finally, 5-axis milling operations were conducted in some critical surfaces in order to improve surface quality and dimensional accuracy of the as-built com-ponent. The inspection of the as-built and post-processed component showed the improvement achieved through the proposed hybrid approach. The work aims to provide the baselines needed to enable the metal Hybrid Additive Manufacturing of components with complex geometries where mandatory precision is required by integrating high accuracy machining operations as post-processing technique.(c) 2022 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/)

Influence of the Local Curvature on the Abdominal Aortic Aneurysm Wall Stress and New Methodologies for Manufacturing Realistic Phantoms.

El aneurisma de aorta abdominal (AAA) es una dilatación focalizada de la aorta abdominal de al menos 1.5 veces su diámetro habitual. La rotura de AAA causa alrededor de 1.3% de muertes en países desarrollados en hombres con una edad comprendida entre 65 y 85 años. En la práctica todavía existe incertidumbre con respecto al momento correcto de llevar a cabo la operación, sin embargo, el criterio de diámetro máximo es aceptado habitualmente como el factor de predicción de rotura; generalmente a aquellos pacientes cuyo diámetro del AAA supera los 5 cm se les recomienda reparar el AAA siempre y cuando estén en condiciones para ello. No obstante, el porcentaje de fallo de este criterio es considerable y falla en torno al 10% y 25% de los casos: 13% de los aneurismas con diámetros inferiores a 50 mm rompieron, mientras que el 60% de aneurismas con diámetros superiores a 50 mm permanecieron intactos. Varios estudios numéricos han intentado encontrar nuevos parámetros que puedan ayudar a los médicos a la hora de estimar el riesgo de rotura del AAA. Por el contrario, se han realizado pocos estudios experimentales debido al alto coste y tiempo que lleva la fabricación de réplicas de AAAs de pacientes. Esta tesis abarca tanto el estudio numérico como el experimental. Por un lado se ha estudiado la influencia de nuevos parámetros geométricos en la distribución de esfuerzos en la pared del AAA. Por otro lado se han investigado nuevas metodologías para la fabricación de réplicas de AAA. Con lo referido a los estudios numéricos, después de analizar 30 geometrías de AAAs de pacientes, se ha descubierto que la curvatura local afecta de forma considerable a la distribución de esfuerzos en la pared, y consecuentemente al riesgo de rotura del AAA. Los resultados sugieren que considerar este parámetro en un futuro para estimar la rotura de AAA puede ayudar a las decisiones clínicas. Con respecto al apartado experimental, se ha definido una nueva metodología para fabricar réplicas de AAA más realistas mediante la técnica de inyección al vacío. Esta metodología nueva tiene en cuenta el espesor variable de la pared y el comportamiento anisótropo del AAA. Asimismo, la tecnología de fabricación aditiva multi-material se ha utilizado para fabricar réplicas de AAA ideales con propiedades anisótropas. Los resultados de los ensayos uniaxiales y biaxiales certifican la idoneidad de las dos metodologías para la fabricación de réplicas de AAA con propiedades similares a las del tejido del AAA. Por último, se ha realizado un estudio experimental con las réplicas de AAA fabricadas y se ha verificado la distribución de esfuerzos en la pared del AAA. Este último estudio se llevó a cabo en la Universidad de Texas en San Antonio (UTSA) gracias a la colaboración con el Dr. Ender Finol.An abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta that is at least 1.5 times its normal diameter. AAA rupture causes around 1.3% of deaths in developed countries among men aged 65-85. In clinical practice, uncertainty still remains about the correct time to operate, but the criterion of maximum diameter is commonly accepted as a rupture prediction factor. The general consensus is that patients with AAA diameters bigger than 5 cm warrant elective repair if they are reasonable operative candidates. However, the failure rate of this criterion is high, ranging from 10% to 25% of cases: 13% of aneurysms with a maximum diameter under 50 mm ruptured, while 60% of aneurysms with diameters over 50 mm remained intact. Several numerical studies have attempted to find new parameters that can help physicians estimate AAA rupture risk. In contrast, few experimental studies have been carried out due to the cost and time-consuming nature of manufacturing patient-specific AAA replicas. This thesis comprises both numerical and experimental studies. The numerical approach investigates new geometric parameters that influence AAA wall stress distribution, while the experimental approach studies new methodologies for manufacturing AAA replicas. In the numerical studies, 30 patient-specific AAA geometries were analyzed, and it was found that the local curvature significantly affects the wall stress distribution, which in turn affects the risk of AAA rupture. The results suggest that considering this parameter in future AAA rupture estimations can assist in clinical decision-making. In terms of the experimental studies, a new methodology for manufacturing more realistic AAA phantoms was developed via vacuum casting technique. This new methodology considers the regionally varying wall thickness and the anisotropic behavior of the AAA. Additionally, the multi-material additive manufacturing technology has been used to fabricate idealized AAA phantoms with anisotropic properties. The results of uniaxial and biaxial tests verify the suitability of both methodologies in manufacturing AAA replicas with properties similar to AAA tissue. Finally, an experimental study was run on the fabricated AAA phantoms and the AAA wall stress distribution was verified. This study was carried out at the University of Texas at San Antonio (UTSA) in collaboration with Dr. Ender Finol

Design, modeling and characterization of lattice structures for orthopedic implant applications.

Interest in lattice structures has soared in recent years thanks to the advances in the field of additive manufacturing, which has led to increasingly complex designs and the production of parts which was impossible up to not long ago. These advances enabled to create lattice structures that mimic the cellular solids of nature, which attracted broad attention due to its applicability in the aerospace and biomedical industries. These structures can be designed to have predefined stiffness and strength values, which enables the production of parts with engineered mechanical properties. One problem of traditional implants made of monolithic parts of Ti6Al4V, CoCr, pure Ti, etc., is the mismatch between the stiffness of the host bone and the metallic implant, which creates the so-called stress shielding. Stress shielding occurs when the bone adjacent to the implant does not have to withstand the main physiological loads because the much stiffer implant bears them in its place. Bone is a living tissue, which is created or resorbed (diluted in blood) depending on the loads to optimize its functionality. Thus, the stiffness mismatch between bone and the implant leads to the bone resorption due to the lack of mechanical stimuli on the host bone. The bone surrounding the implant loses density and weakens, which causes pain to the patient, affects implant stability, and may lead to the loosening of the implant. Lattice structures offer the possibility to create porous implants with tailored mechanical properties to match the stiffness of the surrounding bone, thus avoiding stress shielding and subsequent bone loss. Furthermore, lattice structures form porous parts with high surface to volume ratios, and this porosity enables the bone ingrowth within the implant, improving its fixation and long-term stability. This work is devoted to the development of tools to design lattice structures with controlled mechanical properties, as well as to deepen into the factors that affect such properties. Thus, the main purpose of this dissertation is to create lattice structures that mimic bone stiffness and could be implemented in orthopedic implants to avoid the stress shielding. In addition, orthopedic implants must withstand millions of load cycles throughout the lifetime of the patients, thus the fatigue behavior of the structures was also studied in this thesis. Finally, the small feature sizes required to implement such structures in orthopedic implants requires to reach the manufacturing limits of current additive manufacturing technologies, which induces important deviations from the actually designed geometry and in turn the mechanical properties. Another goal of this work is to understand the impact of such manufacturing deviations on the stiffness of the structures. The obtained results show that there are different possibilities to design structures with stiffness levels comparable to bone. The developed analytical or semi-analytical models predict and enable to design the mechanical properties of the structures for different topologies. These models can be used with personalized bone data to mimic the bone stiffness of each patient. Furthermore, the anisotropy of the structures can also be controlled to adapt it to the complex loads that arise in various anatomical sites. Regarding dynamic loads, fatigue life prediction tools in literature were compared and adapted to improve their applicability, and a fatigue failure surface was developed to easily predict the fatigue life of the structures. Moreover, it was concluded that hot isostatic pressing enhanced the fatigue strength of the structures. Finally, the manufacturing deviations were studied, developing a methodology to consider the proximity to the nodes in the analysis of the imperfection level, and to include such imperfections in a numerical model that predicts the change of anisotropy in the structure.El interés en las estructuras lattice ha incrementado en los últimos años gracias a los avances en la fabricación aditiva. Esto a devenido en diseños cada vez más complejos y la fabricación de piezas que hasta hace poco eran imposibles de producir. Estos avances han posibilitado la creación de estructuras lattice que imitan los sólidos celulares de la naturaleza, lo que ha atraído la atención debido a sus posibles aplicaciones en la industria aeronáutica y biomédica. Estas estructuras se pueden diseñar para que tengan una rigidez y resistencia personalizadas Uno de los problemas de los implantes tradicionales, hechos de piezas monolíticas de Ti6Al4V, CoCr, Ti puro, etc., es la diferencia de rigidez entre el hueso y el implante metálico, lo que crea el denominado “stress shielding”. El “stress shielding” se da cuando el hueso alrededor del implante deja de soportar las principales cargas fisiológicas porque el implante, al ser más rígido, las soporta en su lugar. El hueso es un tejido vivo que se crea o reabsorbe dependiendo de las cargas para optimizar su funcionamiento. Por ello, la diferencia de rigidez entre el hueso y el implante provoca la resorción ósea debida a la falta de estímulo mecánico en el hueso. Así, el hueso alrededor del implante pierde densidad y se debilita. Esto causa dolor al paciente y afecta la estabilidad del implante, que puede llegar a soltarse. Las estructuras lattices ofrecen la posibilidad de crear implantes porosos con propiedades mecánicas personalizadas para que coincidan con la rigidez del hueso que los aloja, evitando así el “stress shielding” y la posterior resorción ósea. Además, las estructuras lattice forman piezas porosas con una gran relación superficie/volumen, lo que posibilita la creación de hueso dentro del implante, ayudando a su fijación y estabilidad a largo plazo. Este trabajo está dedicado al desarrollo de herramientas para diseñar estructuras lattice con propiedades mecánicas prefijadas, además de profundizar en los factores que afectan a dichas propiedades. Así, el principal objetivo de esta tesis es crear estructuras lattice que imiten la rigidez del hueso y que se puedan aplicar en implantes ortopédicos para evitar el “stress shielding”. Además, los implantes ortopédicos deben soportar millones de ciclos de carga durante la vida de los pacientes, por lo que el estudio de la fatiga en las estructuras también se ha estudiado en esta tesis. Por último, la gran resolución requerida para utilizar las estructuras en implantes ortopédicos lleva a las máquinas de fabricación aditiva a los límites de su capacidad. Esto causa importantes desviaciones respecto a las geometrías diseñadas, y por tanto de sus propiedades mecánicas. Otro objetivo de este trabajo es entender el impacto de las desviaciones en la fabricación en la rigidez de las estructuras. Los resultados obtenidos muestran que hay diferentes posibilidades a la hora de diseñar estructuras con rigideces comparables al hueso. Los modelos analíticos y semi analíticos desarrollados predicen y permiten diseñar las propiedades mecánicas de las estructuras para diferentes topologías. Estos modelos se pueden usar junto con datos personalizados del hueso para imitar su rigidez. Asimismo, la anisotropía de la estructura se puede controlar para que se adapte mejor a las condiciones de carga que se dan en diferentes zonas. En cuanto a las cargas dinámicas, se han comparado las herramientas de predicción de la vida a fatiga en la literatura, y se ha desarrollado una superficie de fallo a fatiga para predecir de manera simple la vida a fatiga de las estructuras. También se ha concluido que el prensado isostático en caliente mejora la resistencia a fatiga de las estructuras. Por último, se han estudiado las desviaciones de fabricación desarrollando un procedimiento para analizar el nivel de imperfección, e incluyendo esas imperfecciones en modelos numéricos que predicen la anisotropía de las estructuras

Analytical model for the prediction of permeability of triply periodic minimal surfaces

Triply periodic minimal surfaces (TPMS) are mathematically defined cellular structures whose geometry can be quickly adapted to target desired mechanical response (structural and fluid). This has made them desirable for a wide range of bioengineering applications; especially as bioinspired materials for bone replacement. The main objective of this study was to develop a novel analytical framework which would enable calculating permeability of TPMS structures based on the desired architecture, pore size and porosity. To achieve this, computer-aided designs of three TPMS structures (Fisher-Koch S, Gyroid and Schwarz P) were generated with varying cell size and porosity levels. Computational Fluid Dynamics (CFD) was used to calculate permeability for all models under laminar flow conditions. Permeability values were then used to fit an analytical model dependent on geometry parameters only. Results showed that permeability of the three architectures increased with porosity at different rates, highlighting the importance of pore distribution and architecture. The computed values of permeability fitted well with the suggested analytical model (R2>0.99, p<0.001). In conclusion, the novel analytical framework presented in the current study enables predicting permeability values of TPMS structures based on geometrical parameters within a difference <5%. This model, which could be combined with existing structural analytical models, could open new possibilities for the smart optimisation of TPMS structures for biomedical applications where structural and fluid flow properties need to be optimised

Influence of the Local Curvature on the Abdominal Aortic Aneurysm Wall Stress and New Methodologies for Manufacturing Realistic Phantoms.

El aneurisma de aorta abdominal (AAA) es una dilatación focalizada de la aorta abdominal de al menos 1.5 veces su diámetro habitual. La rotura de AAA causa alrededor de 1.3% de muertes en países desarrollados en hombres con una edad comprendida entre 65 y 85 años. En la práctica todavía existe incertidumbre con respecto al momento correcto de llevar a cabo la operación, sin embargo, el criterio de diámetro máximo es aceptado habitualmente como el factor de predicción de rotura; generalmente a aquellos pacientes cuyo diámetro del AAA supera los 5 cm se les recomienda reparar el AAA siempre y cuando estén en condiciones para ello. No obstante, el porcentaje de fallo de este criterio es considerable y falla en torno al 10% y 25% de los casos: 13% de los aneurismas con diámetros inferiores a 50 mm rompieron, mientras que el 60% de aneurismas con diámetros superiores a 50 mm permanecieron intactos. Varios estudios numéricos han intentado encontrar nuevos parámetros que puedan ayudar a los médicos a la hora de estimar el riesgo de rotura del AAA. Por el contrario, se han realizado pocos estudios experimentales debido al alto coste y tiempo que lleva la fabricación de réplicas de AAAs de pacientes. Esta tesis abarca tanto el estudio numérico como el experimental. Por un lado se ha estudiado la influencia de nuevos parámetros geométricos en la distribución de esfuerzos en la pared del AAA. Por otro lado se han investigado nuevas metodologías para la fabricación de réplicas de AAA. Con lo referido a los estudios numéricos, después de analizar 30 geometrías de AAAs de pacientes, se ha descubierto que la curvatura local afecta de forma considerable a la distribución de esfuerzos en la pared, y consecuentemente al riesgo de rotura del AAA. Los resultados sugieren que considerar este parámetro en un futuro para estimar la rotura de AAA puede ayudar a las decisiones clínicas. Con respecto al apartado experimental, se ha definido una nueva metodología para fabricar réplicas de AAA más realistas mediante la técnica de inyección al vacío. Esta metodología nueva tiene en cuenta el espesor variable de la pared y el comportamiento anisótropo del AAA. Asimismo, la tecnología de fabricación aditiva multi-material se ha utilizado para fabricar réplicas de AAA ideales con propiedades anisótropas. Los resultados de los ensayos uniaxiales y biaxiales certifican la idoneidad de las dos metodologías para la fabricación de réplicas de AAA con propiedades similares a las del tejido del AAA. Por último, se ha realizado un estudio experimental con las réplicas de AAA fabricadas y se ha verificado la distribución de esfuerzos en la pared del AAA. Este último estudio se llevó a cabo en la Universidad de Texas en San Antonio (UTSA) gracias a la colaboración con el Dr. Ender Finol.An abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta that is at least 1.5 times its normal diameter. AAA rupture causes around 1.3% of deaths in developed countries among men aged 65-85. In clinical practice, uncertainty still remains about the correct time to operate, but the criterion of maximum diameter is commonly accepted as a rupture prediction factor. The general consensus is that patients with AAA diameters bigger than 5 cm warrant elective repair if they are reasonable operative candidates. However, the failure rate of this criterion is high, ranging from 10% to 25% of cases: 13% of aneurysms with a maximum diameter under 50 mm ruptured, while 60% of aneurysms with diameters over 50 mm remained intact. Several numerical studies have attempted to find new parameters that can help physicians estimate AAA rupture risk. In contrast, few experimental studies have been carried out due to the cost and time-consuming nature of manufacturing patient-specific AAA replicas. This thesis comprises both numerical and experimental studies. The numerical approach investigates new geometric parameters that influence AAA wall stress distribution, while the experimental approach studies new methodologies for manufacturing AAA replicas. In the numerical studies, 30 patient-specific AAA geometries were analyzed, and it was found that the local curvature significantly affects the wall stress distribution, which in turn affects the risk of AAA rupture. The results suggest that considering this parameter in future AAA rupture estimations can assist in clinical decision-making. In terms of the experimental studies, a new methodology for manufacturing more realistic AAA phantoms was developed via vacuum casting technique. This new methodology considers the regionally varying wall thickness and the anisotropic behavior of the AAA. Additionally, the multi-material additive manufacturing technology has been used to fabricate idealized AAA phantoms with anisotropic properties. The results of uniaxial and biaxial tests verify the suitability of both methodologies in manufacturing AAA replicas with properties similar to AAA tissue. Finally, an experimental study was run on the fabricated AAA phantoms and the AAA wall stress distribution was verified. This study was carried out at the University of Texas at San Antonio (UTSA) in collaboration with Dr. Ender Finol

Design, modeling and characterization of lattice structures for orthopedic implant applications.

Interest in lattice structures has soared in recent years thanks to the advances in the field of additive manufacturing, which has led to increasingly complex designs and the production of parts which was impossible up to not long ago. These advances enabled to create lattice structures that mimic the cellular solids of nature, which attracted broad attention due to its applicability in the aerospace and biomedical industries. These structures can be designed to have predefined stiffness and strength values, which enables the production of parts with engineered mechanical properties. One problem of traditional implants made of monolithic parts of Ti6Al4V, CoCr, pure Ti, etc., is the mismatch between the stiffness of the host bone and the metallic implant, which creates the so-called stress shielding. Stress shielding occurs when the bone adjacent to the implant does not have to withstand the main physiological loads because the much stiffer implant bears them in its place. Bone is a living tissue, which is created or resorbed (diluted in blood) depending on the loads to optimize its functionality. Thus, the stiffness mismatch between bone and the implant leads to the bone resorption due to the lack of mechanical stimuli on the host bone. The bone surrounding the implant loses density and weakens, which causes pain to the patient, affects implant stability, and may lead to the loosening of the implant. Lattice structures offer the possibility to create porous implants with tailored mechanical properties to match the stiffness of the surrounding bone, thus avoiding stress shielding and subsequent bone loss. Furthermore, lattice structures form porous parts with high surface to volume ratios, and this porosity enables the bone ingrowth within the implant, improving its fixation and long-term stability. This work is devoted to the development of tools to design lattice structures with controlled mechanical properties, as well as to deepen into the factors that affect such properties. Thus, the main purpose of this dissertation is to create lattice structures that mimic bone stiffness and could be implemented in orthopedic implants to avoid the stress shielding. In addition, orthopedic implants must withstand millions of load cycles throughout the lifetime of the patients, thus the fatigue behavior of the structures was also studied in this thesis. Finally, the small feature sizes required to implement such structures in orthopedic implants requires to reach the manufacturing limits of current additive manufacturing technologies, which induces important deviations from the actually designed geometry and in turn the mechanical properties. Another goal of this work is to understand the impact of such manufacturing deviations on the stiffness of the structures. The obtained results show that there are different possibilities to design structures with stiffness levels comparable to bone. The developed analytical or semi-analytical models predict and enable to design the mechanical properties of the structures for different topologies. These models can be used with personalized bone data to mimic the bone stiffness of each patient. Furthermore, the anisotropy of the structures can also be controlled to adapt it to the complex loads that arise in various anatomical sites. Regarding dynamic loads, fatigue life prediction tools in literature were compared and adapted to improve their applicability, and a fatigue failure surface was developed to easily predict the fatigue life of the structures. Moreover, it was concluded that hot isostatic pressing enhanced the fatigue strength of the structures. Finally, the manufacturing deviations were studied, developing a methodology to consider the proximity to the nodes in the analysis of the imperfection level, and to include such imperfections in a numerical model that predicts the change of anisotropy in the structure.El interés en las estructuras lattice ha incrementado en los últimos años gracias a los avances en la fabricación aditiva. Esto a devenido en diseños cada vez más complejos y la fabricación de piezas que hasta hace poco eran imposibles de producir. Estos avances han posibilitado la creación de estructuras lattice que imitan los sólidos celulares de la naturaleza, lo que ha atraído la atención debido a sus posibles aplicaciones en la industria aeronáutica y biomédica. Estas estructuras se pueden diseñar para que tengan una rigidez y resistencia personalizadas Uno de los problemas de los implantes tradicionales, hechos de piezas monolíticas de Ti6Al4V, CoCr, Ti puro, etc., es la diferencia de rigidez entre el hueso y el implante metálico, lo que crea el denominado “stress shielding”. El “stress shielding” se da cuando el hueso alrededor del implante deja de soportar las principales cargas fisiológicas porque el implante, al ser más rígido, las soporta en su lugar. El hueso es un tejido vivo que se crea o reabsorbe dependiendo de las cargas para optimizar su funcionamiento. Por ello, la diferencia de rigidez entre el hueso y el implante provoca la resorción ósea debida a la falta de estímulo mecánico en el hueso. Así, el hueso alrededor del implante pierde densidad y se debilita. Esto causa dolor al paciente y afecta la estabilidad del implante, que puede llegar a soltarse. Las estructuras lattices ofrecen la posibilidad de crear implantes porosos con propiedades mecánicas personalizadas para que coincidan con la rigidez del hueso que los aloja, evitando así el “stress shielding” y la posterior resorción ósea. Además, las estructuras lattice forman piezas porosas con una gran relación superficie/volumen, lo que posibilita la creación de hueso dentro del implante, ayudando a su fijación y estabilidad a largo plazo. Este trabajo está dedicado al desarrollo de herramientas para diseñar estructuras lattice con propiedades mecánicas prefijadas, además de profundizar en los factores que afectan a dichas propiedades. Así, el principal objetivo de esta tesis es crear estructuras lattice que imiten la rigidez del hueso y que se puedan aplicar en implantes ortopédicos para evitar el “stress shielding”. Además, los implantes ortopédicos deben soportar millones de ciclos de carga durante la vida de los pacientes, por lo que el estudio de la fatiga en las estructuras también se ha estudiado en esta tesis. Por último, la gran resolución requerida para utilizar las estructuras en implantes ortopédicos lleva a las máquinas de fabricación aditiva a los límites de su capacidad. Esto causa importantes desviaciones respecto a las geometrías diseñadas, y por tanto de sus propiedades mecánicas. Otro objetivo de este trabajo es entender el impacto de las desviaciones en la fabricación en la rigidez de las estructuras. Los resultados obtenidos muestran que hay diferentes posibilidades a la hora de diseñar estructuras con rigideces comparables al hueso. Los modelos analíticos y semi analíticos desarrollados predicen y permiten diseñar las propiedades mecánicas de las estructuras para diferentes topologías. Estos modelos se pueden usar junto con datos personalizados del hueso para imitar su rigidez. Asimismo, la anisotropía de la estructura se puede controlar para que se adapte mejor a las condiciones de carga que se dan en diferentes zonas. En cuanto a las cargas dinámicas, se han comparado las herramientas de predicción de la vida a fatiga en la literatura, y se ha desarrollado una superficie de fallo a fatiga para predecir de manera simple la vida a fatiga de las estructuras. También se ha concluido que el prensado isostático en caliente mejora la resistencia a fatiga de las estructuras. Por último, se han estudiado las desviaciones de fabricación desarrollando un procedimiento para analizar el nivel de imperfección, e incluyendo esas imperfecciones en modelos numéricos que predicen la anisotropía de las estructuras