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High-performance biocompatible flame-retardant polymer composites are considered one of the most promising candidates for next-generation biomedical engineering material. However, the practical applications are thought to appropriately contain flame retardancy and structural mechanical properties. In this study, the carbon nanotube (CNT), ZIF-67, and PVP have synergistically boosted polyvinyl alcohol (PVA)/sodium alginate (SA) composite with both excellent fire safety and mechanical properties, which first prepared with aqueous-phase mixed and freeze-drying method. As the addition of nano-fillers significantly improved the fire protection capability of PS nanocomposites, char residues were produced by aerogels at high temperatures. And the inorganic phase serves as a thermal barrier to prevent heat from spreading. The incorporation of CNTm/ZIF-67/PVP reduced the peak smoke release rate and peak heat release rate by 50% and 20.36%, respectively. In addition, the incorporation of nano-fillers also improved the compressive strength of the PS composites significantly, from 1.34 MPa to 2.45 MPa (Increased 82.8%). ZIFs heterogeneous nanoparticles synthesized with a high concentration of reactive groups provide a workable perspective on the future development of designing nano-filling flame-retardant polymer composites. [Display omitted] • Successfully prepared CNT-loaded PVP-modified ZIF-67 synergistically reinforced PVA/SA aerogel. • PS-Cm/Z/P composites have excellent flame retardancy, heat resistance and compression resistance. • Revealed the flame-retardant mechanism of CNT-loaded PVP-modified ZIF-67 nanoparticles enhanced PVA/SA aerogel. [ABSTRACT FROM AUTHOR]

Triply Periodic Minimal Surface (TPMS) porous structures are recognized as the most promising bionic artificial structures for tissue engineering. The fatigue properties of additive manufactured porous structures are essential for long-term use in a dynamical bio-skeletal environment. The aim of this study is to study the compression–compression fatigue behaviour and the underlying fatigue mechanism of Gyroid cellular structures (GCS), a typical TPMS porous structure. The high-cycle fatigue results show that both cyclic ratcheting and fatigue damage phenomena contribute to the failure of GCS during fatigue testing. For most fatigue loading stress, the failure samples have nearly 45° fracture bands along the diagonal surface. The fatigue ratio of GCS reaches 0.35 for as-built samples and can be raised to 0.45 after sandblasting treatment. The fatigue ratio values are higher than most of the other bending-dominated lattice structures, suggesting superior fatigue resistance properties of GCSs due to the smooth surface connection between struts. Besides, a systematic investigation of the crack initiation and propagation was conducted by both deformation analysis and finite element method to support experimental phenomena. The results also indicate that the fatigue resistance properties of GCSs are significantly enhanced by sandblasting post-treatment, through removing the adhered powder particles, inducing compressive residual stress on the surface and generating a nanocrystalline zone. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A liquid bridge induced assembly (LBIA) strategy has been introduced for assembling nanomaterials in one direction. • Location, as well as the structure, of LBIA yielded 1D assembles can be precisely controlled. • Three criteria have been proposed for the selection of assembled materials in the LBIA process. • 1D assembly of functional nanomaterials can find diverse device applications in electrical, optical and magnetic fields. One-dimensional (1D) assemblies/structures of functional nanomaterials are able to directionally transport electrons, excitons, photons or phonons, and gather scientists' attentions due to their potential applications in diverse fields. However, overlapped, crosslinking or other randomly dispersed 1D assemblies/structures appear after the solution process, which greatly restricts their practical device applications. In this Review, recent progresses in precisely positioning 1D patterning, from small molecules to macromolecules and nanomaterials, through a liquid bridge induced assembly (LBIA) strategy have been summarized. The keys to tailor the location, as well as the structure of as-prepared 1D assembles are discussed. Then, a rule for the selection of materials in the LBIA strategy has been proposed. Finally, some representative device applications of 1D assembles are demonstrated. It is believed that ordered 1D assemblies/structures of functional nanomaterials through the LBIA process will offer new opportunities that might favor different application fields. [ABSTRACT FROM AUTHOR]

Abstract Materials used for hard tissue replacement should match the elastic properties of human bone tissue. Therefore, cellular structures are more favourable for the use of implants than solid materials for their custom-designed mechanical properties. The superimposed load from various directions in vivo makes uniaxial compression testing insufficient for describing the mechanical responses. In this paper, the rotational symmetry of Gyroid cellular structure (GCS) was discussed. An approach using structural simplification and analytical solution was presented to investigate the relationship between Young's modulus and volume fraction, as well as the orientation dependence of the mechanical responses for GCS loaded in various orientations. It is concluded that the analytical solution is reasonable for a low volume fraction, through the comparison between analytical results, finite element (FE) and experimental data. Gained polar diagrams illustrate the anisotropic property of GCS and also confirm the superiority for their stable mechanical responses of diverse loading directions. Graphical abstract fx1 Highlights • The Gyroid TPMS cellular was simplified to strut-based cellular. • The analytical solution was used to calculate the elastic response. • The predicted results match well with FEA results and experimental data. • Polar diagrams were gained to investigate the orientation dependence. • Polar diagrams show Gyroid's superiority of stable mechanical response. [ABSTRACT FROM AUTHOR]

Highlights • A material model based on the SLM-built porous materials was proposed. • The detailed stress and strain distribution were predicted from the FE results. • The fracture can be predicted and was verified by the experimental testing. • The predicted mechanical responses match well with the experimental results. • The Gibson–Ashby formulations were obtained from the FE analysis. Abstract Cellular structures with controllable mechanical properties and porous architecture are the most promising candidates for many applications such as bone implants. Selective laser melting (SLM), one of the additive manufacturing (AM) technologies, enables manufacturing of space filling lattice structures with exceptional load bearing efficiency, customizable stiffness, controllable cell topology, cell size, and porosity. In this work, Schoen Gyroid (SG) unit cell, a triply periodic minimal surface (TPMS) structure, was used to design the cellular structures. As opposed to many other types of unit cells, SG has superior characteristics of self-supporting and high manufacturability for AM technologies. The titanium alloy (Ti–6Al–4V) SG cellular structures were manufactured by SLM. Finite element (FE) method was employed to predict the elastic modulus, compressive yield strength and stress/strain distributions of the SG cellular structures, and the failure occurrence mechanisms were analyzed. The FE results were compared with the experimental data. The results show that through FE method, the mechanical responses of the SG cellular structures can be accurately described and it is possible to customize the mechanical properties of SLM-produced titanium alloy TPMS lattices. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

A significant requirement for a bone implant is to replicate the functional gradient across the bone to mimic the localization change in stiffness. In this work, continuous functionally graded porous scaffolds (FGPSs) based on the Schwartz diamond unit cell with a wide range of graded volume fraction were manufactured by selective laser melting (SLM). The micro-topology, strut dimension characterization and effect of graded volume fraction on the mechanical properties of SLM-processed FGPSs were systematically investigated. The micro-topology observations indicate that diamond FGPSs with a wide range of graded volume fraction from 7.97% to 19.99% were fabricated without any defects, showing a good geometric reproduction of the original designs. The dimensional characterization demonstrates the capability of SLM in manufacturing titanium diamond FGPSs with the strut size of 483–905 µm. The elastic modulus and yield strength of the titanium diamond FGPSs can be tailored in the range of 0.28–0.59 GPa and 3.79–17.75 MPa respectively by adjusting the graded volume fraction, which are comparable to those of the cancellous bone. The mathematical relationship between the graded porosity and compression properties of a FGPS was revealed. Furthermore, two equations based on the Gibson and Ashby model have been established to predict the modulus and yield strength of SLM-processed diamond FGPSs. Compared to homogeneous diamond porous scaffolds, FGPSs provide a wide range of mutative pore size and porosity, which are potential to be tailored to optimize the pore space for bone tissue growth. The findings provide a basis of new methodologies to design and manufacture superior graded scaffolds for bone implant applications. [ABSTRACT FROM AUTHOR]

Triply periodic minimal surface (TPMS) structures have already been shown to be a versatile source of biomorphic scaffold designs. Therefore, in this work, Ti–6Al–4V Gyroid and Diamond TPMS lattices having an interconnected high porosity of 80–95% and pore sizes in the range of 560–1600 μm and 480–1450 μm respectively were manufactured by selective laser melting (SLM) for bone implants. The manufacturability, microstructure and mechanical properties of the Ti–6Al–4V TPMS lattices were evaluated. Comparison between 3D micro-CT reconstructed models and original CAD models of the Ti–6Al–4V TPMS lattices shows excellent reproduction of the designs. The as-built Ti–6Al–4V struts exhibit the microstructure of columnar grains filled with very fine and orthogonally oriented α′ martensitic laths with the width of 100–300 nm and have the microhardness of 4.01±0.34 GPa. After heat treatment at 680 °C for 4 h, the α′ martensite was converted to a mixture of α and β, in which the α phase being the dominant fraction is present as fine laths with the width of 500–800 nm and separated by a small amount of narrow, interphase regions of dark β phase. Also, the microhardness is decreased to 3.71±0.35 GPa due to the coarsening of the microstructure. The 80–95% porosity TPMS lattices exhibit a comparable porosity with trabecular bone, and the modulus is in the range of 0.12–1.25 GPa and thus can be adjusted to the modulus of trabecular bone. At the same range of porosity of 5–10%, the moduli of cortical bone and of the Ti–6Al–4V TPMS lattices are in a similar range. Therefore, the modulus and porosity of Ti–6Al–4V TPMS lattices can be tailored to the levels of human bones and thus reduce or avoid “stress shielding” and increase longevity of implants. Due to the biomorphic designs, and high interconnected porosity and stiffness comparable to human bones, SLM-made Ti–6Al–4V TPMS lattices can be a promising material for load bearing bone implants. [ABSTRACT FROM AUTHOR]

This work evaluated the processibility of a low-isotacticity polypropylene (PP) powder by selective laser sintering (SLS), and systematically analyzed and compared the melting and crystallization characteristics, crystalline structure, tensile properties and thermo-mechanical properties of the PP specimens fabricated by SLS and injection molding (IM). The results show that the PP powder has a nearly spherical shape, smooth surfaces, appropriate particle sizes, a wide sintering window and a low degree of crystallinity, consequently indicating good SLS processibility. In SLS, the molten PP continues to maintain at a high part bed temperature until the whole manufacturing process finished, thus demonstrating a low cooling rate. This gives rise to a high degree of crystallinity, formation of γ phase and coarse microstructure. On the contrary, in IM, the fully molten PP is rapidly cooled down to room temperature after injection, and thus show a higher cooling rate and rapid crystallization, leading to a lower degree of crystallinity, absence of γ phase and finer microstructure. Owing to these differences in crystallization characteristics and crystalline structure mentioned above, the SLS PP parts exhibit higher tensile strengths, tensile moduli and storage moduli, but lower elongation at break, toughness and glass transition temperatures, compared with the IM counterparts. [ABSTRACT FROM AUTHOR]

The capability to monitor the mechanical forces on the intervertebral disc (IVD) after discectomy could develop personalized rehabilitation strategies to benefit the patients´ healthy recovery. However, traditional nucleus pulposus (NP) substitutes are mainly hydrogels which can only physically fill the defect after discectomy without sense the mechanical stress. Here we demonstrate an additive manufactured NP substitute (AMNPS) that can sense the mechanical stress in the IVD with a self-powered capacity. When the AMNPS suffers the stress from the spine bending, the mechanical energy can be converted into electrical signal by the AMNPS and the whole mechanical sensing process is self-powered. To illustrate the capabilities of the AMNPS, we use it to monitor the spine bending of a goat in vivo , illustrating the potential application of the device to monitor the tissue rehabilitation after discectomy. [Display omitted] • A nucleus pulposus substitute that can self-powered sense bending of the spine is proposed. • The nucleus pulposus substitute can monitor the stress in the intervertebral disc in vivo. • The multi-layered 3D printing technique has been used to generate the nucleus pulposus substitute. [ABSTRACT FROM AUTHOR]

Highlights: [•] A unique cell type called gyroid is designed to construct lattice structures. [•] Curved cell surface as a self-supported feature avoids support structures. [•] Lattice structures with a wide volume fraction range were made. [•] Lattice structures were made at different orientations. [•] Strength and modulus increase with the increase in the volume fraction. [ABSTRACT FROM AUTHOR]

Abstract: Metallic additive manufacturing techniques, in particular the selective laser melting (SLM) process, are capable of fabricating strong, lightweight and complex metallic lattice structures. However, they still face certain process limitations such as geometrical constraints and in some cases the need for support structures. This study evaluates the manufacturability and performance of SLM produced periodic cellular lattice structures, which are designed by repeating a unit cell type called gyroid consisting of circular struts and a spherical core. The effect of unit cell size on the manufacturability, density and compression properties of the manufactured cellular lattice structures were investigated. Micro-computer tomography (CT) scan results reveal that the gyroid cellular lattice structures with various unit cell sizes ranging from 2 to 8mm can be manufactured free of defects by the SLM process without the need of additional support structures. The Scanning Electron Microscope (SEM) micrographs show that the lattice structures made by SLM have a good geometric agreement with the original computer-aided design (CAD) models, but many partially melted metal particles are bonded to strut surfaces. The struts within the gyroid cellular lattice structures with smaller unit cell sizes have higher densities due to their shorter scan vector lengths in the SLM process. The yield strength and Young''s modulus of the Gyroid cellular lattice structures increase with the decrease in the unit cell size due to the denser struts of the lattice structures with smaller unit cell sizes. [Copyright &y& Elsevier]

Abstract: Aiming at developing carbon fibre/polyamide-12 (CF/PA) composite powders for manufacturing high-performance components by selective laser sintering (SLS), the preparation, characteristics and sintering process of the composite powders and mechanical properties of sintered components were studied. Surfaces of the carbon fibres were treated by the oxidation modification and coated with polyamide-12 through the dissolution–precipitation process to provide good interfacial adhesion and homogenous dispersion within the polyamide-12 matrix. The particle size and micro-morphology analyses show that the CF/PA composite powders with 30wt%, 40wt% and 50wt% carbon fibres present the suitable powder sizes and format for SLS. The incorporation of carbon fibres into the polyamide-12 matrix decreases the initial melting temperature and consequently lowers the SLS part bed temperatures, implying lower energy requirement and less thermal degradation in the sintering process. The CF/PA composites also represent higher thermal stability than the pure polyamide-12. The CF/PA sintered components with 30wt%, 40wt% and 50wt% carbon fibres exhibit the greatly enhanced flexural strengths by 44.5%, 83.3%, 114%, and the flexural modulus by 93.4%, 129.4%, 243.4%, respectively, as compared with the pure polyamide-12 sintered parts. Fractured surface analysis shows that the carbon fibres are encapsulated and bonded well with the polyamide matrix. The complex SLS parts with the thinnest wall of 0.6mm, the density of 1.09±0.02g/cm3 and the relatively density of 94.13±1.72% were manufactured using the CF/PA composite powder with 30wt% carbon fibres. This study demonstrates that the CF/PA composite powders prepared by the surface treatment and dissolution–precipitation method represent suitable interfacial adhesion, filler dispersion, particle sizes and sintering behaviours for SLS and enable the manufacture of complex components with high performance. [Copyright &y& Elsevier]

Abstract: A dissolution–precipitation process was successfully developed to prepare nylon-12 coated carbon steel powders. The SEM and laser diffraction particle size analysis results show that the metal particles are well coated by nylon-12 resin; therefore, an effective method for preparing nylon-12 coated metal powders is provided. Green parts were formed from the coated powders by selective laser sintering (SLS) process, and when the nylon-12 content in the coated powder was 1.0wt% and the applied laser energy density was 0.06J/mm2, the SLS green parts had sufficient strengths for features as small as 0.1mm to be built and post-processed, and relatively high dimensional accuracy. The SLS green parts were post-processed by binder decomposition and epoxy resin infiltration, and the obtained epoxy-infiltrated parts have the dimensional errors in the X, Y and Z directions of −0.30, −0.32 and −0.25% respectively, and the bend strength, bend modulus, tensile strength and impact strength of 93.4MPa, 14.7GPa, 70.3MPa and 12.4MPa respectively. [Copyright &y& Elsevier]

SiC graded ceramic lattice structure (GCLS) offers superior mechanical strength and its impact on fatigue warrants investigation. In this work, SiC triply periodic minimal surface (TPMS) GCLSs were prepared via laser powder bed fusion technology and liquid silicon infiltration process, alongside SiC TPMS uniform ceramic lattice structure (UCLS) as a reference. Fatigue properties, fatigue failure, and strengthening mechanisms were systematically investigated through compression fatigue tests, finite element (FE) simulations, and theoretical analysis. Fatigue failures of SiC UCLSs and GCLSs are influenced by cyclic ratcheting and fatigue damage, with cyclic ratcheting dominance. The fatigue strength ratios of UCLS and GCLS are 0.7 and 0.74, indicating that GCLSs exhibit stronger deformation resistance and superior fatigue performance. FE results show that surface tensile stress level in GCLS is lower than in UCLS, resulting in slower fatigue crack initiation. Stress redistribution and higher crack thresholds contribute to enhanced fatigue resistance in SiC TPMS GCLSs. [Display omitted] • SiC graded lattice structures were made with good manufacturing repeatability. • Fatigue failure in SiC lattice is affected by cyclic ratcheting and fatigue damage. • Gradient design improves deformation resistance and fatigue properties. • Graded SiC lattice has lower tensile stress and slower crack propagation. • Stress redistribution and higher crack thresholds make for fatigue improvement. [ABSTRACT FROM AUTHOR]

Silicon Carbide (SiC) ceramic lattice structures were pivotal in advancing space technology and other sectors by merging structural lightness with high strength. This study explored non-uniform lattice designs tailored for specific load-bearing applications to maximize lightness, although machining such SiC structures proved challenging due to their high hardness and wear resistance. Selective Laser Sintering (SLS) was employed to fabricate non-uniform lattice structures featuring graded volume fractions. Micro computed tomography (Miro-CT) characterized the geometric characteristics of the macroscopic non-uniform lattice structure. Extensive investigations were conducted on the impact of these gradient structures on the quasi-static compressive behavior and mechanical properties of SiC ceramics, revealing that the R-A structure achieved a maximum compressive strength of 14.989 MPa and a specific strength of 13.268 × 10³ N·m/kg, approximately double that of a uniform structure. Furthermore, a finite element model (FEM) was established to verify and predict the mechanical and fracture responses of SiC-based structures, showing effective dispersion of stress concentration along the outer rim of the R-A structure, markedly alleviating the usual stress concentration found in traditional lattices and averting catastrophic failure. The alignment between experimental and simulation outcomes substantiated these findings. [Display omitted] [ABSTRACT FROM AUTHOR]

Schwartz diamond graded porous structures (SDGPSs), constructed by a triply-periodic-minimal-surface diamond unit cell topology, were developed with various unit cell sizes and printed by laser powder bed fusion (LPBF) from a commercially pure titanium powder for bone implant applications. The effect of unit cell size on the printability, strut dimensions, stress and strain distributions, mechanical properties and energy absorption capability of SDGPSs was investigated. The results indicate the good printability of SDGPSs via LPBF with multiple unit cell sizes from 3.5 mm to 5.5 mm through the three-dimensional reconstruction from micro-computed tomography. The unit cell size plays a critical role in both strut diameters and specific surface areas of SDGPSs. An increase in the unit cell size leads to a reduction in the experimental Young's modulus from 673.08 MPa to 518.71 MPa and compressive yield strength from 11.43 MPa to 7.73 MPa. The mechanical properties of LPBF-printed SDGPSs are higher than those predicted by the finite element method, which is attributed to the higher volume fractions of the printed SDGPSs than the designed values. Furthermore, a rise in unit cell size leads to the decrease of energy absorption capability from 6.06 MJ/mm3 to 4.32 MJ/mm3 and exhibits little influence on the absorption efficiency. These findings provide a good understanding and guidance to the optimization on the unit cell size of functionally graded porous structures for desirable properties. [ABSTRACT FROM AUTHOR]

Coralline hydroxyapatite (CHA) has been used in clinical for over 20 years. However, coral is an endanger species and has been banned from mining. In addition, coral artificial bone has slow biodegradation of the defects, hindering the growth of new bone. In order to explore the natural coral artificial bone substitute materials, this work proposed using Selective Laser Sintering (SLS) to fabricate natural calcium carbonate/biopolymer composite imitation coral porous structures, and then the surface of the 3D printing product was transformed into a hydroxyapatite thin layer by hydrothermal conversion reaction. The mechanical properties and porosity were optimized by adjusting the SLS processing parameters including laser power, scanning speed and layer thickness. In the composites with the PLLA of 15 wt%, the SLS processing parameters with the laser power of 15 W, laser scanning speed of 1500 mm/s and single layer thickness of 0.08 mm result in the better mechanical properties. After hydrothermal conversion, the products were confirmed to be a mixture of hydroxyapatite (HA) and calcium carbonate by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDX). The TGA results revealed that increasing the reaction temperature or prolonging the reaction time can increase the degree of hydrothermal reaction and thus promote the transformation of calcium carbonate into hydroxyapatite. The results of cytotoxicity assay and Life/Dead staining showed that the scaffold is not toxic to L929 cells. This work has the materials system innovation and focuses on the study of the effects of the SLS and hydrothermal processes on the mechanical performance and the degree of hydroxylation. Then, the preparation process of imitation coral artificial bone preparation was optimized. it is concluded that the imitation coral artificial bone is a nontoxic biomaterial; however, further study on its osteogenic capacity should be warranted in the future. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) has emerged as an effective method for preparing complex structured silicon carbide (SiC) ceramics. However, the SiC components demonstrate low strength and high brittleness, which remain major challenges limiting its application. To overcome this limitation, short carbon fiber reinforced silicon carbide (C sf /SiC) composites are prepared by combining LPBF and phenolic resin binder impregnation (PRBI)-reactive melt infiltration (RMI), in which high char yield boron-and silicone-containing phenolic resin (BSiPF) impregnation is used to adjust the carbon density of green bodies and to reduce the pore size of green bodies. By optimizing the impregnation process, the carbon density can be brought close to the theoretical optimal value of 0.84 g/cm3, and the reduction of the pore size is conducive to the improvement of the reaction rate at the early stage of the reaction, which enhance the SiC phase content of C sf /SiC composites obtained by RMI. Meanwhile, the application of BSiPF results in a protective pyrolytic carbon (PyC) coating on the surface of C sf , which can reduce the erosion of C sf by molten Si during the RMI process, thus improving the fracture toughness of C sf /SiC composites. The final C sf /SiC composites exhibit the enhanced bulk density, bending strength and fracture toughness, reaching 2.90 ± 0.01 g/cm3, 257 ± 20 MPa, 3.52 ± 0.15 MPa m1/2, respectively. This study provides a new strategy for effective impregnation technique for the additive manufacturing (AM) of high strength and high toughness SiC composites. [Display omitted] [ABSTRACT FROM AUTHOR]