Cellular Materials Research Articles

Nickel-based superalloy architectures with surface mechanical attrition treatment: Compressive properties and collapse behaviour

Surface modifications can introduce natural gradients or structural hierarchy into human-made microlattices, making them simultaneously strong and tough. Herein, we describe our investigations of the mechanical properties and the underlying mechanisms of additively manufactured nickel–chromium superalloy (IN625) microlattices after surface mechanical attrition treatment (SMAT). Our results demonstrated that SMAT increased the yielding strength of these microlattices by more than 64.71% and also triggered a transition in their mechanical behaviour. Two primary failure modes were distinguished: weak global deformation, and layer-by-layer collapse, with the latter enhanced by SMAT. The significantly improved mechanical performance was attributable to the ultrafine and hard graded-nanograin layer induced by SMAT, which effectively leveraged the material and structural effects. These results were further validated by finite element analysis. This work provides insight into collapse behaviour and should facilitate the design of ultralight yet buckling-resistant cellular materials.

Microfluidic Chip Fabrication for Tumor Cell 3D Culture Based on Microwell Arrays.

Compared with traditional 2D cell culture, 3D cell culture more closely resembles the original state of cells in vivo and enables the establishment of in vivo-like microenvironments and cell-cell interactions, thereby providing valuable cellular materials for numerous studies. The direct establishment of in vitro patient tumor models can enhance drug testing, cancer research, and individualized precision therapy. In this study, we propose a microfluidic chip based on microwell arrays for 3D tumor cell culture. This chip combines nanoscale channels and microwell arrays to precisely control cell distribution and nutrient diffusion, thus closely mimicking the tumor microenvironment. The incorporation of microwell arrays allows for simple and rapid high-throughput preparation of tumor spheroids, while promoting the formation of cell-cell and cell-matrix interactions, ultimately enhancing cell viability and function. Preliminary experiments using tumor cell lines validate the ability of the chip to support 3D tumor growth with enhanced physiological relevance. The microfluidic chip serves as a reliable and scalable platform for studying tumor biology and evaluating therapeutic efficacy and is anticipated to expedite cancer research and drug discovery.

Architected metallic cellular materials with random pore features: computer design, LPBF fabrication and mechanical properties

Porous materials with heterogeneous pore features are used in many branches of technology, from lightweight structures to biomedical implants and electrodes. These materials derive their properties from their internal architecture, which is often poorly controlled via conventional manufacturing routes (e.g. foaming, templating). Here, we combine laser powder bed fusion (LPBF) additive manufacturing technology with computer design to fabricate metallic cellular architectures with heterogeneous, yet precisely controlled, pore features. The materials of this study contain through thickness pores - with arbitrary micrometric size and shape - randomly dispersed into a dense metallic matrix. Their porous architecture is generated numerically using a random sequential absorption algorithm, and is 3D-printed out of two metallic powders. Using image analysis, we statistically quantify the Influence of the LPBF process parameters on the 3D-printed pore geometry (i.e. morphology and size), and develop image-based finite-element models to measure numerically the resulting homogenized elastic mechanical properties. Collectively, our results help elucidate the role of geometric (i.e. topological) defects induced by the LPBF process on the structural performance of metallic cellular materials with random pore features.

Eklemeli İmalat Yöntemiyle Üretilen PLA Öksetik Tasarımların Mekanik Özelliklerinin İncelenmesi

FDM (fused deposition modeling) is one of the most commonly used technologies in additive manufacturing. This technology is used to additively manufacture components from various polymer materials, mostly PLA (polylactic acid), etc. PLA filament is a widely used polymer for 3D printing due to its biodegradability, biocompatibility, and processability. In the study, PLA raw material and cellular auxetic structures were used in the design. Auxetic designs are called metamaterials, they are structures with advanced properties and can be obtained with various geometries. The auxetic designs used in the study are missing rib, re-entrant honeycomb and chiral. One of the biggest advantages of auxetic cellular materials is that it is not bulk material. Having a skeletal structure provides high strength at low density. Today, based on this mechanism, designs that can be used in engineering applications are being studied. It has an important place especially in the medical field, as well as in the areas where high precision and specific products are designed and produced. Considering its relationship with 3D printing technology, 3D printing enables the fabrication of auxetic structures for complex and personal designs. The novelty of auxetic structures comes from their topological features, which display counterintuitive response to the applied load. For the purpose of compare the properties of mechanical tensile, compression, surface roughness tests were applied. It is concluded that the presence of chiral structures improves mechanical performance. The chiral auxetic sample exhibited a maximum stress of 6.68 MPa, the missing-rib auxetic sample displayed a maximum stress of 2.26 MPa, and the re-entrant auxetic sample demonstrated a maximum stress of 3.68 MPa. These results obtained from the tests align well with the range reported in the literature, which falls between 1-12 MPa. The surface roughness of the all-auxtetic structure, perpendicular to the printing direction was higher than the measurements taken parallel to the printing direction.

Using Live-Cell Imaging to Measure the Effects of Pathological Proteins on Axonal Transport in Primary Hippocampal Neurons.

Bidirectional transport of cargos along the axon is critical for maintaining functional synapses, neural connectivity, and healthy neurons. Axonal transport is disrupted in multiple neurodegenerative diseases, and projection neurons are particularly vulnerable because of the need to transport cellular materials over long distances and sustain substantial axonal mass. Pathological modifications of several disease-related proteins negatively affect transport, including tau, amyloid-β, α-synuclein, superoxide dismutase, and huntingtin, providing a potential common mechanism by which pathological proteins exert toxicity in disease. Methods to study these toxic mechanisms are necessary to understand neurodegenerative disorders and identify potential therapeutic interventions. Here, cultured primary rodent hippocampal neurons are co-transfected with multiple plasmids to study the effects of pathological proteins on fast axonal transport using live-cell confocal imaging of fluorescently-tagged cargo proteins. We begin with the harvest, dissociation, and culturing of primary hippocampal neurons from rodents. Then, we co-transfect the neurons with plasmid DNA constructs to express fluorescent-tagged cargo protein and wild-type or mutant tau (used as an exemplar of pathological proteins). Axons are identified in live cells using an antibody that binds an extracellulardomain of neurofascin, an axon initial segment protein, and an axonal region of interest is imaged to measure fluorescent cargo transport. Using KymoAnalyzer, a freely available ImageJ macro, we extensively characterize the velocity, pause frequency, and directional cargo density of axonal transport, all of which may be affected by the presence of pathological proteins. Through this method, we identify a phenotype of increased cargo pause frequency associated with the expression of pathological tau protein. Additionally, gene-silencing shRNA constructs can be added to the transfection mix to test the role of other proteins in mediating transport disruption. This protocol is easily adaptable for use with other neurodegenerative disease-related proteins and is a reproducible method to study the mechanisms of how those proteins disrupt axonal transport.

Smart Lattice Structures with Self-Sensing Functionalities via Hybrid Additive Manufacturing Technology.

Lattice structures are a group of cellular materials composed of regular repeating unit cells. Due to their extraordinary mechanical properties, such as specific mechanical strength, ultra-low density, negative Poisson's ratio, etc., lattice structures have been widely applied in the fields of aviation and aerospace, medical devices, architecture, and automobiles. Hybrid additive manufacturing (HAM), an integrated manufacturing technology of 3D printing processes and other complementary processes, is becoming a competent candidate for conveniently delivering lattice structures with multifunctionalities, not just mechanical aspects. This work proposes a HAM technology that combines vat photopolymerization (VPP) and electroless plating process to fabricate smart metal-coated lattice structures. VPP 3D printing process is applied to create a highly precise polymer lattice structure, and thereafter electroless plating is conducted to deposit a thin layer of metal, which could be used as a resistive sensor for monitoring the mechanical loading on the structure. Ni-P layer and copper layer were successfully obtained with the resistivity of 8.2×10-7Ω⋅m and 2.0 ×10-8 Ω⋅m, respectively. Smart lattice structures with force-loading self-sensing functionality are fabricated to prove the feasibility of this HAM technology for fabricating multifunctional polymer-metal lattice composites.

Quality assurance thermophysical aspects of highly porous implants with cellular structure obtained by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process that involves the layer-by-layer construction of a three-dimensional object by local melting of a powder layer based on a prepared CAD model. This technology makes it possible to manufacture products of complex configuration, including internal channels of complex geometry. Such products include personalized highly porous implants, which are subject to very strict requirements in the field of elastic and strength properties, ensuring their compliance with the properties of the biological objects being replaced. The quality of highly porous cellular products formed by the selective laser melting method based on metal powder compositions is determined by a significant number of factors, the combined influence of which is difficult to control. At the same time, the structure and mechanical properties of highly porous cellular materials (HPCM) obtained by laser synthesis are largely determined by the melt bath shape stability, which depends on the ability of local heat dissipation, which in turn is determined by the fused product geometry. Under these conditions, simulation of thermal processes, including the prediction of the part fusion temperature modes, is of paramount importance. This study focuses on the numerical analysis of the powder layer thermophysical parameters during the laser melting process, which is difficult to analyze by direct measurements, and a computational model based on COMSOL Multiphysics has been created to predict the melt bath temperature field. The numerical model made it possible to quantify the influence of the selective laser melting process parameters (laser power and scanning speed) in combination with the choice of material and topology of the part on the temperature fields formation to determine the process technological parameter and the features of creating geometry for additive manufacturing, which make it possible to obtain products of proper quality. Cellular implants based on Ti6Al4V powder have been grown by selective laser melting.

Application of human platelet lysate in chondrocyte expansion promotes chondrogenic phenotype and slows senescence progression via BMP–TAK1–p38 pathway

Osteoarthritis (OA) is one of the most common musculoskeletal degenerative. OA treatments are aiming to slow down disease progression; however, lack of cartilage regeneration efficacy. Autologous chondrocyte implantation (ACI) is a promising cartilage-regeneration strategy that uses human articular chondrocytes (HACs) as cellular materials. However, the unreadiness of HACs from prolonged expansion, cellular senescence, and chondrogenic dedifferentiation occurred during conventional expansion, thus, minimizing the clinical efficacy of ACI. We aimed to examine the effects of a human platelet lysate (HPL) as an alternative human-derived HAC medium supplement to overcome the limitations of conventional expansion, and to explain the mechanism underlying the effects of HPL. During passages 2–4 (P2-P4), HPL significantly increased HAC proliferation capacities and upregulated chondrogenic markers. Simultaneously, HPL significantly reduced HAC senescence compared with conventional condition. HACs treated with LDN193189 exhibited a reduction in proliferation capacity and chondrogenic marker expression, whereas the HAC senescence increased slightly. These findings indicated involvement of BMP-2 signaling transduction in the growth-assistive, anti-senescent, and chondrogenic-inductive properties of HPL, which demonstrated its beneficial effects for application as HAC medium supplement to overcome current expansion limitations. Finally, our findings support the roles of platelets in platelet-rich plasma as a promising treatment for patients with OA.

Numerical Prediction of the Yield Surface of a Chiral Auxetic Structure

For today's requirements, the material itself is often not sufficient anymore. This leads to structural cellular materials and metamaterials, which allow for more degrees of freedom by a strong structure–property relationship. Auxetic structures investigated in this contribution belong to metamaterials. Auxetic metamaterials show huge advantages in their properties, e.g., an enhanced specific energy absorption capacity (SEAC) as well as a negative Poisson's ratio, combined with a very high stiffness‐to‐weight ratio. Experimental probing of these structures is very challenging, hence, up to now, auxetic materials have only been investigated in uniaxial, bending, or shear loading. But for an industrial application, the knowledge of the multiaxial yield behavior is inevitable. For the first time, the present study deals with the numerical probing of the yield surface for a chiral auxetic structure applying multiaxial loading. The changes in Poisson's ratio, SEAC, and the resulting nonconvex yield surface are studied numerically. It shows that the highest specific energy absorption capacities are reached under compression load cases while higher stiffnesses and yield stresses are achieved under tensile loading. There is a strong structure–property relationship and load case dependency for Poisson's ratio as well as for the SEAC.

Multiscale modeling of shape memory polymers foams nanocomposites

Shape memory polymer foams (SMPFs) are defined as lightweight cellular materials with the ability to recover their undeformed shape by applying an external stimulus like light, temperature, magnetic field, etc. Reinforcement of the material with nano-clay filler leads to a significant improvement in its physical properties. As a result, a wide range of applications is occupied by SMPFs, especially in industry and biomedical applications. Because of the heterogeneous nature of the SMPFs at different scale levels, modeling the material with one scale numerical model which able to capture all the effects of the lower scale material structure is really a complex task. Within this work, a full multiscale modeling approach is employed to investigate the thermomechanical response of the SMPFs. Furthermore, a combination of the 3D Representative Volume Element (RVE) and finite element method is used to explore the effects of the nano-filler weight fractions and the material's cellular structure at different length scales on the material dynamics. The multiscale modeling process gives great and promising results with good agreement with the experimental results. Moreover, the model shows relatively high sensitivity parameters that are initiated from the lower scale level.

Crushing response of triply periodic minimal surface structures fabricated by investment casting and powder bed fusion method

Cellular materials, serving as alternatives to solid materials in applications demanding high mechanical efficiency and versatility, bring significant advantages to industries like automotive and aerospace. With attributes such as impressive strength-to-weight ratios, noise dampening, thermal shielding, and energy absorption, these materials are valuable assets. This study focuses on probing the energy absorption and deformation behavior of gyroid based triply periodic minimal surface (TPMS) structures under quasi-static compression. These gyroid structures, produced using AlSi10Mg through both investment casting and powder bed fusion (PBF) techniques, were designed at varying relative densities (7.5%, 11.2%, and 14.8%), adjusting cell wall thickness and cell numbers. Crushing response of these structures was also analyzed numerically using a commercial LS-DYNA finite element software. The study's findings indicate that gyroid structures printed through the PBF technique display around 150% greater specific energy absorption (SEA) capacity than those created using the investment casting method. However, the crush force efficiency of casted gyroid structures surpasses that of printed gyroid structures by 25%, owing to reduced peak stress values at the onset of crush dam

Numerical Simulation and Analysis of the Acoustic Properties of Bimodal and Modulated Macroporous Structures

In recent decades, cellular metallic materials have increasingly been used for control of reverberation and cutback. These materials offer a unique combination of expanded pores, high specific surfaces, improved structural performance, low weight, corrosion resistance at high temperatures, and a fixed/rigid pore network (i.e., at the boundaries, porosity does not change). This study examines the ability of sphere-packing models combined with numerical modelling and simulations to predict the acoustic properties of bimodal and modulated bottleneck-shaped macroporous structures that can realistically be achieved through liquid melts infiltration casting technique. The simulations show that porosity, openings, pore sizes and permeability of the material have significant effects on acoustics, and the predictions are consistent with experimental data substantiated in the literature. The modelling suggests that the creation of bimodal structures increases the capacity of the interstitial pores and pore contacts. The result is improved sound absorption properties and spectra, characterised by a pore volume fraction of 0.73 and a mean pore size to mean pore opening ratio of 4.8 for the 50% volume bimodal structure created at a 10 µm capillary radius. The importance of how pore structure-related parameters and existing fluid flow regimes can modulate the sound absorption performance of macroporous structures was revealed by numerical simulations of the sound absorption spectra for dual-porosity and dilated macroporous structures working from high-resolution tomography datasets. Sound absorption properties were optimised for structures having pore volume fractions between 0.68 and 0.76, maintaining the mean pore size to mean pore opening ratios between 4.0 and 6.0. Using this approach, enhanced and self-supporting macroporous structures may be designed and fabricated for efficient sound absorption in specific applications.

Dynamic instability characteristics of graphene‐reinforced cellular sandwich plates using a three‐variable isogeometric approach

AbstractThe primary objective of the current study is to introduce a potent computational model for analyzing the dynamic instability response of advanced sandwich plate models subjected to various time‐dependent in‐plane edge loadings. To achieve this, we employ the finite element formulations derived from high‐order shear deformation plate theory (HSDT) involving only three unknowns in conjunction with NURBS‐based isogeometric analysis. Additionally, advanced sandwich plate models are constituted by a middle layer with either a uniform or symmetric porosity distribution and two outer layers which are reinforced with graphene nanoplatelets (GNPs) to boost dynamic structural performance. The fundamental dynamic instability region of the sandwich plates can be then obtained by solving the Mathieu‐Hill equation using the Bolotin's method. Numerous numerical studies are performed to evaluate the impacts of numerous input parameters on the dynamic stability behavior of the cellular three‐layer plate structures. The crucial role of internal porosity distribution as well as GNPs reinforcement phase in enhancing the instability performance of the cellular structures is thoroughly evaluated. With the current results, this research provides important insights into the development and application of cellular materials as well as the GNPs for designing advanced engineering structures in the future.

Research of the numerical simulation and machine learning backpropagation networks analysis of the sound absorption properties of cellular soundproofing materials

Cellular soundproofing materials have been critical for lowering incidence pressure waves, which have led to their wide application in studios, auditoria, automotive and aerospace applications, among others. This work, therefore, premiers the utilisation of machine learning backpropagation algorithm of artificial neural networks (ANN) to develop and train a series of datasets of sound absorption properties (noise reduction coefficient, sound absorption average, and area under the sound absorption spectrum) obtained via numerical modelling and simulations. ANN models were established to analyze these sound absorption properties in relation to several non–acoustical parameters associated with cellular materials, including their thickness. Modelling and simulation revealed the relative importance of non–acoustic parameters on sound absorption spectra for these structures. ANN models predicted output signals that almost overlapped with their respective “real” signals with correlation coefficients over 95 %. Model confidence was proposed to analytically predict sound absorption phenomena accurately for cellular materials characterized by permeability ranging between 0.5–3.0 × 10−09 m2 or viscous characteristic lengths ranging between 80 and 300 μm. Analytical models based on optimised synaptic weights, biases, non–acoustic parameters, and material thickness could assist manufacturers design soundproofing materials for noise reduction and reverberation control.

A Biomimetic Structural Material with Adjustable Mechanical Property for Bone Tissue Engineering

AbstractThe development of cellular materials with adjustable mechanical properties, total porosity (Tp), and elastic modulus (E) similar to those of natural bone are eternal pursuits in the field of bone implants. Designing and manufacturing an implant that fulfills all these requirements is a challenging task. In this study, inspired by the trabecular structure of natural bone and developed a biomimetic structural material. Laser powder bed fusion (L‐PBF) is utilized to create the biomimetic structural material. Comprehensive valuations of both the natural trabecular bone and biomimetic structural material are conducted using micro‐CT scanning, nanoindentation testing, finite element (FE) analysis, and compression testing. The results demonstrate that the mechanical properties of the developed biomimetic structural material have excellent controllability. The rod‐plate‐like trabecular (RPT) biomimetic structural material exhibited significantly superior mechanical load‐bearing performance compared to the natural bone trabeculae while maintaining the natural bone's Tp (83.1%) and E (798.1 MPa). The biomimetic structural material effectively balances the combination of strength and E, providing a design template for the next generation of medical implants. It has great potential as a bone repair material for clinical applications, and its adjustable mechanical properties also make it highly promising in the field of tissue engineering.

Properties, Applications and Recent Developments of Cellular Solid Materials: A Review.

Cellular solids are materials made up of cells with solid edges or faces that are piled together to fit a certain space. These materials are already present in nature and have already been utilized in the past. Some examples are wood, cork, sponge and coral. New cellular solids replicating natural ones have been manufactured, such as honeycomb materials and foams, which have a variety of applications because of their special characteristics such as being lightweight, insulation, cushioning and energy absorption derived from the cellular structure. Cellular solids have interesting thermal, physical and mechanical properties in comparison with bulk solids: density, thermal conductivity, Young's modulus and compressive strength. This huge extension of properties allows for applications that cannot easily be extended to fully dense solids and offers enormous potential for engineering creativity. Their Low densities allow lightweight and rigid components to be designed, such as sandwich panels and large portable and floating structures of all types. Their low thermal conductivity enables cheap and reliable thermal insulation, which can only be improved by expensive vacuum-based methods. Their low stiffness makes the foams ideal for a wide range of applications, such as shock absorbers. Low strengths and large compressive strains make the foams attractive for energy-absorbing applications. In this work, their main properties, applications (real and potential) and recent developments are presented, summarized and discussed.

A Novel Equivalent Method for Computing Mechanical Properties of Random and Ordered Hyperelastic Cellular Materials.

Simulating the mechanical behavior of cellular materials stands as a pivotal step in their practical application. Nonetheless, the substantial multitude of unit cells within these materials necessitates a considerable finite element mesh, thereby leading to elevated computational expenses and requisites for formidable computer configurations. In order to surmount this predicament, a novel and straightforward equivalent calculation method is proposed for the computation of mechanical properties concerning both random and ordered hyper-elastic cellular materials. By amalgamating the classical finite element approach with the distribution attributes of cells, the proposed equivalent calculation method adeptly captures the deformation modes and force-displacement responses exhibited by cell materials under tensile and shear loads, as predicted through direct numerical simulation. This approach reflects the deformation characteristics induced by micro-unit cells, elucidates an equivalent principle bridging cellular materials and equivalent materials, and substantially curtails exhaustive computational burdens. Ultimately, this method furnishes an equivalent computational strategy tailored for the engineering applications of cellular materials.

Effective elastic and strength properties of triply periodic minimal surfaces lattice structures by numerical homogenization

This paper deals with the determination of the equivalent elastic and strength properties of triply periodic minimal surfaces (TMPS) lattice structures. Specifically, primitive and gyroid TPMS are analyzed, and their macroscopic properties, in terms of stiffness and strength, are derived as a function of the relative density. These properties are derived through numerical homogenization on the representative volume element (RVE) and via numerical analyses on specimens composed of an array of RVEs and compared to data available in the literature. These findings may potentially aid the creation of functionally graded cellular materials with variable density, optimizing structural stiffness and mass.

Density-graded Voronoi honeycombs – A local transversely isotropic description

Density-graded cellular materials, in which their relative density varies with location, are amenable to design for multi-functions, and have been used in mechanical buffers and protective structures. To estimate the force–deformation responses of density-graded cellular materials efficiently without resorting to modelling individual cells, a constitutive model based on local transverse isotropy is adopted. Metallic Voronoi honeycomb-like specimens with cell sizes that vary with position, are fabricated via 3D printing, to represent a density-graded cellular material with local transverse isotropy that varies with position. From quasi-static compression tests and cell-based finite element (FE) simulations, the influence of relative density on the continuum constitutive model is investigated and demonstrated to be significant. The model is then used to predict the global stress–strain response and deformation of cellular materials with positive and negative density-gradients, defined along the loading direction, subjected to uniaxial quasi-static compression, quasi-static indentation, and dynamic compression. The results show that for quasi-static compression, severe plastic deformation progresses from the low relative density region to the high relative density region; however, impact loading and indentation of negative density-gradient Voronoi honeycombs generates two zones of gross deformation – in the vicinity of the applied load and the opposite lower density end. Predictions based on the proposed constitutive model display good correlation with experimental and cell-based FE results.

From bio-sourced to bio-inspired cellular materials: A review on their mechanical behavior under dynamic loadings

Natural cellular materials can be used directly or as a constituent of bio-sourced composites for industrial applications involving dynamic loadings, usually for the purpose of absorbing mechanical energy. These biological materials can also be used as an inspiration to conceive more efficient heterogeneous structures for impact mitigation. In this review letter, we present two natural materials for which the properties have been studied dynamically: balsa wood and cork-based agglomerates. Both display an important strain-rate dependence but because of their different microstructure, this dependence is not the same. Consequently, a better understanding of the relationship between the hierarchical structure of natural cellular materials and their mechanical behavior, from quasi-static to dynamic, would be beneficial for the conception of new bio-inspired architected structures. We then focus on two types of bio-inspired architected structures: the functionally density graded cellular structures and the multi-layered architected structures. These two types of structures are gaining interest, but it appears that their dynamic behavior still lacks studying and understanding. More research linking the local strain mechanisms to their macroscopic mechanical behavior in quasi-static and dynamic would allow further architected structure optimization for mechanical energy absorption.