RESUMEN

Triply periodic minimal surface (TPMS) is widely used because it can be used to control the shape of porous scaffolds precisely by formula. In this paper, an I-wrapped package (I-WP) type porous scaffolds were constructed. The finite element method was used to study the relationship between the wall thickness and period, the morphology and mechanical properties of the scaffolds, as well as to study the compression and fluid properties. It was found that the porosity of I-WP type scaffolds with different wall thicknesses (0.1 ~ 0.2 mm) and periods (I-WP 1 ~ I-WP 5) ranged from 68.01% ~ 96.48%, and the equivalent elastic modulus ranged from 0.655 ~ 18.602 GPa; the stress distribution of the scaffolds tended to be uniform with the increase of periods and wall thicknesses; the equivalent elastic modulus of the I-WP type scaffolds was basically unchanged after the topology optimization, and the permeability was improved by 52.3%. In conclusion, for the I-WP type scaffolds, the period parameter can be adjusted first, then the wall thickness parameter can be controlled. Topology optimization can be combined to meet the design requirements. The I-WP scaffolds constructed in this paper have good mechanical properties and meet the requirements of repairing human bone tissue, which may provide a new choice for the design of artificial bone trabecular scaffolds.

Asunto(s)

RESUMEN

Batteries with high energy densities become essential with the increased uptake of electric vehicles. Battery housing, a protective casing encapsulating the battery, must fulfil competing engineering requirements of high stiffness and effective thermal management whilst being lightweight. In this study, a graded lattice design framework is developed based on topology optimisation to effectively tackle the multidisciplinary objectives associated with battery housing. It leverages the triply periodic minimal surfaces lattices, aiming for high mechanical stiffness and efficient heat dissipation considering heat conduction and convection. The effectiveness of the proposed framework was demonstrated through the battery housing design, showcasing its ability to address multidisciplinary objectives as evidenced by the analysis of the Pareto front. This study identifies the potential of lattices in lightweight applications incorporating multiphysics and offers an efficient lattice design framework readily extended to other engineering challenges.

RESUMEN

The goal of this paper is to improve the mechanical strength-to-weight ratios of metal cubic lattice structures using unit cells with fillet shapes inspired by triply periodic minimal surfaces (TPMS). The lattice structures here presented were fabricated from AA6082 aluminum alloy using lost-PLA processing. Static and dynamic flat and wedge compression tests were conducted on samples with varying fillet shapes and fill factors. Finite element method simulations followed the static tests to compare numerical predictions with experimental outcomes, revealing a good agreement. The TPSM-type fillet shape induces a triaxial stress state that significantly improves the mechanical strength-to-weight ratio compared to fillet radius-free lattices, which was also confirmed by analytical considerations. Dynamic tests exhibited high resistance to flat impacts, while wedge impacts, involving a high concentrated-load, brought out an increased sensitivity to strain rates with a short plastic deformation followed by abrupt fragmentation, indicating a shift towards brittle behavior.

RESUMEN

Porous polymeric scaffolds are used in tissue engineering to maintain or replace damaged biological tissues. Once embedded in body, they are involved into different physical and biological processes, among which their degradation and dissolution of their material can be singled out as one of the most important ones. Degradation parameters depend mostly on the properties of both the material and surrounding native tissues, which can substantially alter the original mechanical parameters of the scaffolds. The aim of this study is to examine the change in the effective mechanical properties of functionally graded additively manufactured polylactide scaffolds with a linear porosity gradient and morphology based on triply periodic minimal surfaces during simultaneous degradation and compressive loading. Two main types of scaffold-degradation processes, bulk and surface erosions are simulated with two suggested modelling methods. The fundamental differences in the proposed approaches are identified and the influence of different types of scaffold morphology on the change in effective elastic properties is evaluated. The results of this study can be useful for design of optimal scaffolds taking into account the effect of the degradation process on their structural integrity.

Asunto(s)

RESUMEN

Lattice structures are a type of lightweight structure that is more commonly being applied to engineering systems as a way to reduce mass and enhance mechanical properties. The cantilever beam case is one of the primary modes of loading in many engineering applications, where light-weighting is also crucial. However, lightweight lattice structured cantilever beams have not been investigated considerably due to design and manufacturing limitations. Therefore, the aim of this study was to investigate the response of four different lattice structured cantilever beams comprising of unit cells made from Schwarz-P, Schwarz-D, Gyroid, and Octet-truss structures fabricated using Multi Jet Fusion additive manufacturing technology. An investigation into the cross-sections of these structures leads to a conclusion that the beams made from such structures are non-prismatic in nature as a result of variation in cross-sections. This led to the development of equations for the moment of inertia of these structures, which helped in calculating symmetric and un-symmetric bending. These beams were subjected to cantilever loading until failure, which provided insights into flexural properties such as flexural stress, stiffness, and strain energy. Experimental results indicate that the surface-based structures, due to better surface-area-to-volume ratio, have better ability in transferring loads and hence perform better than the beam-based Octet-truss beam. The Schwarz-D beam had performed the best among all the beams, which is further supported in literature due to its stretch-dominated topology that results in higher values of modulus. The finite element analysis (FEA) findings also validate these findings in which the distribution of stresses can be seen to be better transmitted than the other structures. The FEA validation shows that the distribution of Von-Mises stress and their position in experimental tests and failure of these structures is also very close, which provides validation to the experimental setup and the testing of beams.

RESUMEN

This study investigates the effect of porosity and pore shape on the biological and mechanical behavior of additively manufactured scaffolds for bone tissue engineering (BTE). Polylactic acid scaffolds with varying porosity levels (15-78%) and pore shapes, including regular (rectangular pores), gyroid, and diamond (triply periodic minimal surfaces) structures, are fabricated by fused filament fabrication. Murine-derived macrophages and human bone marrow-derived mesenchymal stromal cells (hBMSCs) are seeded onto the scaffolds. The compressive behavior and surface morphology of the scaffolds are characterized. The results show that scaffolds with 15%, 30%, and 45% porosity display the highest rate of macrophage and hBMSC growth. Gyroid and diamond scaffolds exhibit a higher rate of macrophage proliferation, while diamond scaffolds exhibit a higher rate of hBMSC proliferation. Additionally, gyroid and diamond scaffolds exhibit better compressive behavior compared to regular scaffolds. Of particular note, diamond scaffolds have the highest compressive modulus and strength. Surface morphology characterization indicates that the surface roughness of diamond and gyroid scaffolds is greater than that of regular scaffolds at the same porosity level, which is beneficial for cell attachment and proliferation. This study provides valuable insights into porosity and pore shape selection for additively manufactured scaffolds in BTE.

Asunto(s)

RESUMEN

Introduction: Triply periodic minimal surface (TPMS) is widely used in the design of bone scaffolds due to its structural advantages. However, the current approach to designing bone scaffolds using TPMS structures is limited to a forward process from microstructure to mechanical properties. Developing an inverse bone scaffold design method based on the mechanical properties of bone structures is crucial. Methods: Using the machine learning and genetic algorithm, a new inverse design model was proposed in this research. The anisotropy of bone was matched by changing the number of cells in different directions. The finite element (FE) method was used to calculate the TPMS configuration and generate a back propagation neural network (BPNN) data set. Neural networks were used to establish the relationship between microstructural parameters and the elastic matrix of bone. This relationship was then used with regenerative genetic algorithm (RGA) in inverse design. Results: The accuracy of the BPNN-RGA model was confirmed by comparing the elasticity matrix of the inverse-designed structure with that of the actual bone. The results indicated that the average error was below 3.00% for three mechanical performance parameters as design targets, and approximately 5.00% for six design targets. Discussion: The present study demonstrated the potential of combining machine learning with traditional optimization method to inversely design anisotropic TPMS bone scaffolds with target mechanical properties. The BPNN-RGA model achieves higher design efficiency, compared to traditional optimization methods. The entire design process is easily controlled.

RESUMEN

Mechanical environment plays a crucial role in regulating bone regeneration in bone defects. Assessing the mechanobiological behavior of patient-specific orthopedic scaffolds in-silico could help guide optimal scaffold designs, as well as intra- and post-operative strategies to enhance bone regeneration and improve implant longevity. Additively manufactured porous scaffolds, and specifically triply periodic minimal surfaces (TPMS), have shown promising structural properties to act as bone substitutes, yet their ability to induce mechanobiologially-driven bone regeneration has not been elucidated. The aim of this study is to i) explore the bone regeneration potential of TPMS scaffolds made of different stiffness biocompatible materials, to ii) analyze the influence of pre-seeding the scaffolds and increasing the post-operative resting period, and to iii) assess the influence of patient-specific parameters, such as age and mechanosensitivity, on outcomes. To perform this study, an in silico model of a goat tibia is used. The bone ingrowth within the scaffold pores was simulated with a mechano-driven model of bone regeneration. Results showed that the scaffold's architectural properties affect cellular diffusion and strain distribution, resulting in variations in the regenerated bone volume and distribution. The softer material improved the bone ingrowth. An initial resting period improved the bone ingrowth but not enough to reach the scaffold's core. However, this was achieved with the implantation of a pre-seeded scaffold. Physiological parameters like age and health of the patient also influence the bone regeneration outcome, though to a lesser extent than the scaffold design. This analysis demonstrates the importance of the scaffold's geometry and its material, and highlights the potential of using mechanobiological patient-specific models in the design process for bone substitutes.

Asunto(s)

RESUMEN

Invar36 alloy is a low expansion alloy, and the triply periodic minimal surfaces (TPMS) structures have excellent lightweight, high energy absorption capacity and superior thermal and acoustic insulation properties. It is, however, difficult to manufacture by traditional processing methods. Laser powder bed fusion (LPBF) as a metal additive manufacturing technology, is extremely advantageous for forming complex lattice structures. In this study, five different TPMS cell structures, Gyroid (G), Diamond (D), Schwarz-P (P), Lidinoid (L), and Neovius (N) with Invar36 alloy as the material, were prepared using the LPBF process. The deformation behavior, mechanical properties, and energy absorption efficiency of these structures under different load directions were studied, and the effects and mechanisms of structure design, wall thickness, and load direction were further investigated. The results show that except for the P cell structure, which collapsed layer by layer, the other four TPMS cell structures all exhibited uniform plastic collapse. The G and D cell structures had excellent mechanical properties, and the energy absorption efficiency could reach more than 80%. In addition, it was found that the wall thickness could adjust the apparent density, relative platform stress, relative stiffness, energy absorption, energy absorption efficiency, and deformation behavior of the structure. Printed TPMS cell structures have better mechanical properties in the horizontal direction due to intrinsic printing process and structural design.

RESUMEN

The pore morphology design of bioceramic scaffolds plays a substantial role in the induction of bone regeneration. Specifically, the effects of different scaffold pore geometry designs on angiogenesis and new bone regeneration remain unclear. Therefore, we fabricated Mg/Sr co-doped wollastonite bioceramic (MS-CSi) scaffolds with three different pore geometries (gyroid, cylindrical, and cubic) and compared their effects on osteogenesis and angiogenesis in vitro and in vivo. The MS-CSi scaffolds were fabricated by digital light processing (DLP) printing technology. The pore structure, mechanical properties, and degradation rate of the scaffolds were investigated. Cell proliferation on the scaffolds was evaluated using CCK-8 assays while angiogenesis was assessed using Transwell migration assays, tube formation assays, and immunofluorescence staining. The underlying mechanism was explored by western blotting. Osteogenic ability of scaffolds was evaluated by alkaline phosphatase (ALP) staining, western blotting, and qRT-PCR. Subsequently, a rabbit femoral defect model was prepared to compare differences in the scaffolds in osteogenesis and angiogenesis in vivo. Cell culture experiments showed that the gyroid pore scaffold downregulated YAP/TAZ phosphorylation and enhanced YAP/TAZ nuclear translocation, thereby promoting proliferation, migration, tube formation, and high expression of CD31 in human umbilical vein endothelial cells (HUVECs) while strut-based (cubic and cylindrical pore) scaffolds promoted osteogenic differentiation in bone marrow mesenchymal stem cells and upregulation of osteogenesis-related genes. The gyroid pore scaffolds were observed to facilitate early angiogenesis in the femoral-defect model rabbits while the strut-based scaffolds promoted the formation of new bone tissue. Our study indicated that the pore geometries and pore curvature characteristics of bioceramic scaffolds can be precisely tuned for enhancing both osteogenesis and angiogenesis. These results may provide new ideas for the design of bioceramic scaffolds for bone regeneration.

RESUMEN

The design of biomimetic porous scaffolds has been gaining attention in the biomedical sector lately. Shells, marine sponges, shark teeth, cancellous bone, sea urchin spine, and the armadillo armor structure are examples of biological systems that have already been studied to drive the design of innovative, porous, and multifunctional structures. Among these, triply periodic minimal surfaces (TPMSs) have attracted the attention of scientists for the fabrication of biomimetic porous scaffolds. The interest stems from their outstanding properties, which include mathematical controllable geometry features, highly interconnected porous architectures, high surface area to volume ratio, less stress concentration, tunable mechanical properties, and increased permeability. All these distinguishing features enable better cell adhesion, optimal integration to the surrounding tissue avoiding stress shieldings, a good permeability of fluid media and oxygen, and the possibility of vascularization. However, the sophisticated geometry of these TPMS-based structures has proven challenging to fabricate by conventional methods. The emergence of additive manufacturing (AM) and the enhanced manufacturing freedoms and flexibility it guarantees could solve some of the bottlenecks, thus leading to a surge of interest in designing and fabricating such structures in this field. Also, the feasibility of using AM technologies allows for obtaining size programmable TPMS printable in various materials, from polymers to metal alloys. Here, a comprehensive overview of 3D-printed TPMS porous structures is provided from a design for additive manufacturing (DfAM) and application perspective. First, design strategies, geometry design algorithms, and related topological optimization are introduced according to diverse requirements. Based on that, the performance control of TPMS and the pros and cons of the different AM processes for fabricating TPMS scaffolds are summarized. Lastly, practical applications of 3D-printed biomimetic TPMS porous structures for the biomedical field are presented to clarify the advantages and potential of such structures.

Asunto(s)

RESUMEN

Multiscale techniques, namely homogenization, result in significant computational time savings in the analysis of complex structures such as lattice structures, as in many cases it is inefficient to model a periodic structure in full detail in its entire domain. The elastic and plastic properties of two TPMS-based cellular structures, the gyroid, and the primitive surface are studied in this work through numerical homogenization. The study enabled the development of material laws for the homogenized Young's modulus and homogenized yield stress, which correlated well with experimental data from the literature. It is possible to use the developed material laws to run optimization analyses and develop optimized functionally graded structures for structural applications or reduced stress shielding in bio-applications. Thus, this work presents a study case of a functionally graded optimized femoral stem where it was shown that the porous femoral stem built with Ti-6Al-4V can minimize stress shielding while maintaining the necessary load-bearing capacity. It was shown that the stiffness of cementless femoral stem implant with a graded gyroid foam presents stiffness that is comparable to that of trabecular bone. Moreover, the maximum stress in the implant is lower than the maximum stress in trabecular bone.

RESUMEN

Here, we compare the performance of various three-dimensional-printed Monolith Adsorption (PMA) columns designed from a triply periodic minimal surface geometry, the Schoen gyroid. The structures examined had designed hydraulic diameters between 203 and 458 µm and voidages of 40%-60%. We compare column efficiency, porosity, static binding capacity and dynamic binding capacity for various load volumes and flow rates. The results show that all structures allowed efficient passage of yeast cells (>97%) over a wide range of interstitial velocities (191 to 1911 cm/h) while maintaining a low pressure drop (<0.1 MPa). The structure with a voidage of 40% and a hydraulic diameter of 203 µm showed the best performance in all aspects evaluated. Bovine serum albumin (BSA) recoveries for all structures (27%-91% when the loaded volume was 180 mL) were significantly affected by hydraulic diameter, mean channel wall thickness, velocity and voidage. Moreover, biomass addition resulted in a decrease in BSA recovery, which became more obvious at high velocities. However, this did not lead to a dramatic reduction in saturated binding capacity, significant changes in axial dispersion, or blockage of channels and could be compensated for by recirculation of the feed, even at high velocity. PMA thus potentially provides an appealing alternative to Expanded Bed Adsorption, retaining the latter's advantages, while eliminating fluidization issues and minimizing both processing time and buffer consumption.

RESUMEN

A variety of intermetallic compounds possesses high enthalpies of formation. These compounds may be formed from reactive compacts or nanostructures comprised of unreacted precursor metals. These precursor structures support self-propagating high temperature synthesis (SHS) reactions which afford very high specific energy densities and rates, with excellent spatial control and a variety of useful applications. The present work compares the reactivity of notional bimetallic nanostructures based on well-known triply periodic minimal surfaces (TPMSes) with the popular reactive nanolaminate (RNL) modality for the Ni/Al system, using a molecular dynamics approach. TPMS-derived nanostructures were found to have lower ignition energies and faster reaction rates than RNLs of comparable periodicity, while the maximum achievable temperature of ignitions was found to be modulated by a complex interplay of factors including reaction rate and specific metal/metal interface density. Nanostructure reactivity and thermochemistry is also affected by effective diffusion dimensionality and recalescent precipitation of intermetallic crystallites. The TPMS-derived reactive nanostructures presented herein anticipate plausible advances in nanofabrication technology.

RESUMEN

A method to solve the crystallographic phase problem of materials with triply periodic minimal surface like structures, such as lyotropic liquid crystal bicontinuous cubic phases, is reported. In triply periodic minimal surface like structures, the difference between the maximum and minimum electron densities tends to be the smallest for the true phase combination among the possible combinations [Oka (2022). Acta Cryst. A78, 430-436]. Using this feature, a new iterative phase retrieval algorithm for structure determination was developed. The algorithm modifies electron densities outside the upper and lower thresholds in the iterative Fourier transformation process with fixed amplitudes for the structure factors, and efficiently searches for the structure with the smallest difference between the maximum and minimum electron densities. The proper structure was determined by this algorithm for all tested data for lyotropic liquid crystal bicontinuous cubic phases and mesoporous silicas. Although some cases required constraints such as the volume fraction for structure determination, more than half could be determined without any constraints, including space groups.

Asunto(s)

RESUMEN

The mechanical behaviors of three distinct lattice structures-Diamond, Gyroid, and Schwarz-synthesized through vat polymerization, were meticulously analyzed. This study aimed to elucidate the intricacies of these structures in terms of their stress-strain responses, energy absorption, and recovery characteristics. Utilizing the described experiments and analytical approaches, it was discerned, via the described experimental and analytical procedure, that the AM lattices showcased mechanical properties and stress-strain behaviors that notably surpassed theoretical predictions, pointing to substantial disparities between conventional models and experimental outcomes. The Diamond lattice displayed superior stiffness with higher average loading and unloading moduli and heightened energy absorption and dissipation rates, followed by the Gyroid and Schwarz lattices. The Schwarz lattice showed the most consistent mechanical response, while the Diamond and Gyroid showed capabilities of reaching larger strains and stresses. All uniaxial cyclic compressive tests were performed at room temperature with no dwell times. The efficacy of hyper-elastic-graded models significantly outperformed projections offered by traditional Ashby-Gibson models, emphasizing the need for more refined models to accurately delineate the behaviors of additively manufactured lattices in advanced engineering applications.

RESUMEN

3D printed custom chromatographic stationary phases have recently been demonstrated. Using the Lattice Boltzmann Method, we compared the model-predicted chromatographic performance of random packing of monodisperse spheres, open tubular columns (OTC) and stationary phases based on three triply periodic minimal surfaces (TPMS): Schwarz Diamond (SD), Schoen Gyroid (SG) and Schwarz Primitive (SP). Three performance metrics were employed in this comparison: i) reduced plate height, ii) Darcy number, iii) kinetic performance factor. Each simulated geometry was unconfined with an impermeable stationary phase to remove wall effects and pore diffusion. The performance was studied for macro-porosities in the range 0.2 to 0.8, depending on the geometry. OTCs were found to have superior permeability to both random sphere packing and TPMS structures across the entire porosity range. At porosity greater than 0.366, the Schwarz Diamond medium achieved the lowest levels of band broadening and greatest kinetic performance. The reduced plate height of all stationary phase geometries was shown to increase with bed porosity. The kinetic performance was found to increase with porosity for TPMS structures, decrease with porosity for random packing and be independent of porosity for OTCs. This work illustrates that chromatographic stationary phase geometries based on TPMS structures are theoretically competitive with random packing and open tubular columns and their feasibility for practical chromatography should continue to be explored.

Asunto(s)

RESUMEN

In this paper, thin layers of NiTi shape memory alloy (SMA) triply periodic minimal surface lattices (TPMS) are fabricated using laser powder bed fusion (LPBF), considering different laser scanning strategies and relative densities. The obtained architected samples are studied using experimental methods to characterize their microstructural features, including the formation of cracks and balling imperfections. It is observed that balling is not only affected by the parameters of the fabrication process but also by structural characteristics, including the effective densities of the fabricated samples. In particular, it is reported here that higher densities of the TPMS geometries considered are generally associated with increased dimensions of balling imperfections. Moreover, scanning strategies at 45° angle with respect to the principal axes of the samples resulted in increased balling.

RESUMEN

Cellular lattices with architectural intricacy or metamaterials have gained a substantial amount of attention in the past decade due to the recent advances in additive manufacturing methods. The lattice topology controls its physical and mechanical properties; therefore, the main challenge is selecting the appropriate lattice topology for a desired function and application. In this work, we comprehensively study the topology-property relationship of three classes of polymer metamaterials based on triply periodic minimal surfaces (TPMS) of sheet/shell and ligament types, and other types of well-known strut-based lattices. The study uses a holistic approach of designing, additive manufacturing, microstructural characterization, and compressive uniaxial mechanical testing of these polymer lattices that are 3D-printed using the laser powder bed fusion technique known as selective laser sintering (SLS). In total, 55 lattices with different topologies and relative densities were 3D-printed and tested. Printing quality was assessed using scanning electron microscopy and micro-computed tomography. The extracted mechanical properties of elastic modulus, yield strength, plateau strength, and energy absorption are thoroughly compared between the different lattice architectures. The results show that all the investigated ligament-based TPMS polymer lattices exhibit bending-dominated elastic and plastic behavior, indicating that they are suitable candidates for energy absorbing applications. The sheet-based TPMS polymer lattices, similarly to the well-known Octet-Truss lattice, exhibited an elastic stretching-dominated mode of deformation and proved to have exceptional stiffness as compared to all other topologies, especially at low relative densities. However, the sheet-based TPMS polymer lattices exhibited a bending-dominated plastic behavior which is mainly driven by manufacturing defects. Overall, however, sheet-based TPMS polymer lattices exhibited the best mechanical properties, followed by strut-based lattices and finally by ligament-based TPMS lattices. Finally, it is depicted that at high relative densities, the mechanical properties of lattices of various architectures tend to converge, which implies that the topological effect is more significant at low relative densities. Generally, this study provides important insights about the selection of polymer mechanical metamaterials for various applications, and shows the superiority of TPMS-based polymer metamaterials as compared to several other classes of polymer mechanical metamaterials.

RESUMEN

An indicator-based crystallographic phase retrieval method has been developed for diffraction data of bicontinuous cubic phases of lyotropic liquid crystals. Such liquid crystals have large structural disorder; the number of independent Bragg reflections that can be observed is limited. This paper proposes two indicators to identify plausible combination(s) of crystallographic phases, i.e. electron-density distribution. The indicators are based on the characteristics of the liquid crystals: amphiphilic molecules diffuse mainly in the direction parallel to polar-nonpolar interfaces and the electron density in the direction parallel to the interfaces is averaged. One indicator is the difference between the maximum and minimum electron density, and the other is calculated from the Hessian matrix of the electron density. Using test data, the electron densities were calculated for all possible phase combinations and indicators were obtained. The results indicated that the electron densities with the minimum indicators were close to the true electron density. Therefore, this method is effective for phase retrieval. The accuracy of the phase retrieval decreased when the volume fraction of the region including the triply periodic minimal surface increased.