Dysphagia (DP) is a growing health concern in today's ageing population, leading to high demand for DP-oriented food. 3D printing is a promising novel technology for developing new attractive and appetising products. Therefore, we aimed to develop a 3D-printed shaped meal, to serve as a nutritious DP-oriented food. The texture was modified with the addition of different thickeners: 2.0% (w/w) k-carrageenan gum (KC) and 1.0 or 1.5% (w/w) guar gum (GG), xanthan gum (XG), locust bean gum (LBG), and gum arabic (GA). Upon characterising and mapping the rheological behaviour involved in extrusion-based 3D printing, the higher concentrations of GG, XG, LBG and GA were found to significantly increase the yield stress and apparent viscosities of the ink formulations. In addition, the colour attributes were examined, while a low population of total viable bacteria (TVC) was observed. The DP-oriented formulations had high fibre content, regulating bowel function and glucose metabolism in the elderly. According to the International dysphagia diet standardisation initiative (IDDSI), KC/XG1 and KC/LBG1 were classified as level 5 indicative of minced and moist dysphagia diet, while KC/GA1, KC/GA1.5, KC/XG1.5, and KC/GG1.5 were classified as level 4, that can be bitten or chewed if the tongue control is reduced. All ink formulations demonstrated high printing precision with excellent self-supporting capability and smooth surface texture that were easy to extrude and print complex samples. This study provides valuable insights into addressing dysphagia by developing a nutritious meal using 3D printing.

Cu/Ni heterogeneous materials integrate excellent thermal conductivity and high-temperature mechanical properties, enabling them to be widely used in the aerospace domain. Differences in the thermal and physical properties of the Cu and Ni materials, however, make them difficult to be processed using the laser powder bed fusion (LPBF) additive manufacturing process. This study systematically examines the effects of various LPBF process parameters on microstructure, element diffusion, bonding strength and microhardness at the Cu/Ni interface, as well as investigating the mechanisms of defect formation within Cu/Ni heterogeneous materials. The results indicate that a reasonable control of laser energy input (<100 J/mm3) facilitates the Cu/Ni components through strong interfacial metallurgical bonding without pore defect formation. Compared to single-material Cu alloy, the ultimate tensile strength (UTS) of the horizontally bonded Cu/Ni specimen increased by 55.25 %, without significant reductions in elongation. The vertically bonded Cu/Ni tensile specimen fractured in the middle of the Cu region rather than the interfacial region, indicating superb interfacial bonding strength. Another advantage lies in the enhancement of thermophysical properties, with a 109.5 % increase in thermal conductivity achieved in the LPBF-fabricated Cu/Ni heterogeneous materials compared to the single-material Ni alloy. Quasi-static compression experiments indicated that the Cu/Ni lattice structure could absorb more energy when compressed parallel to the build direction (BD), compared to being perpendicular to the BD. This study provides guidance for the design and manufacture of high-performance Cu/Ni heterogeneous components via LPBF.

Selective laser melting (SLM) is a metal additive manufacturing process that shows significant advantages in manufacturing lattice structures. In this paper, a novel surface-based square origami structure made of a nickel-based superalloy was fabricated using SLM. Three different wall thicknesses (50, 75 and 100 μm) were used to examine the manufacturability and corresponding compressive behaviour of the manufactured lattice components. Finite element analysis (FEA) was conducted to determine the uniaxial compression and then verified by quasi-static compression testing. The results showed that the components with thinner walls more easily folded and buckled than those with thicker walls, indicating that higher densification strains and energy absorption values may be achieved with thinner walls, although the thicker walls were stronger and could withstand larger loads. This research offers insights into the design and manufacture of advanced lattice structures by providing an improved understanding of the compressive behaviour of surface-based square origami structures.

Cardiac tissue growth and remodelling (G & R) occur in response to the changing physiological demands of the heart after birth. The early shift to pulmonary circulation produces an immediate increase in ventricular workload, causing microstructural and biomechanical changes that serve to maintain overall physiological homoeostasis. Such cardiac G & R continues throughout life. Quantifying the tissue's mechanical and microstructural changes because of G & R is of increasing interest, dovetailing with the emerging fields of personalised and precision solutions. This study aimed to determine equibiaxial, and non-equibiaxial extension, stress-relaxation, and the underlying microstructure of the passive porcine ventricles tissue at four time points spanning from neonatal to adulthood. The three-dimensional microstructure was investigated via two-photon excited fluorescence and second-harmonic generation microscopy on optically cleared tissues, describing the 3D orientation, rotation and dispersion of the cardiomyocytes and collagen fibrils. The results revealed that during biomechanical testing, myocardial ventricular tissue possessed non-linear, anisotropic, and viscoelastic behaviour. An increase in stiffness and viscoelasticity was noted for the left and right ventricular free walls from neonatal to adulthood. Microstructural analyses revealed concomitant increases in cardiomyocyte rotation and dispersion. This study provides baseline data, describing the biomechanical and microstructural changes in the left and right ventricular myocardial tissue during G & R, which should prove valuable to researchers in developing age-specific, constitutive models for more accurate computational simulations. STATEMENT OF SIGNIFICANCE: There is a dearth of experimental data describing the growth and remodelling of left and right ventricular tissue. The published literature is fragmented, with data reported via different experimental techniques using tissues harvested from a variety of animals, with different gender and ages. This prevents developing a continuum of data spanning birth to death, so limiting the potential that can be leveraged to aid computational modelling and simulations. In this study, equibiaxial, non-equibiaxial, and stress-relaxation data are presented, describing directional-dependent material responses. The biomechanical data is consolidated with equivalent microstructural data, an important element for the development of future material models. Combined, these data describe microstructural and biomechanical changes in the ventricles, spanning G &R from neonatal to adulthood.

Advances in computational modelling now offer an efficient route to developing novel helmet liners that could exceed contemporary materials' performance. Furthermore, the rise of accessible additive manufacturing presents a viable route to achieving otherwise unobtainable material structures. This study leverages an established finite element-based approach to the optimisation of cellular structures for the loading conditions of a typical helmet impact. A novel elastomeric pre-buckled honeycomb structure is adopted and optimised, the performance of which is baselined relative to vinyl nitrile foam under direct and oblique loading conditions. Results demonstrate that a simplified optimisation strategy is scalable to represent the behaviour of a full helmet. Under oblique impact conditions, the optimised pre-buckled honeycomb liner exceeds the contemporary material performance when considering computed kinematic metrics head and rotational injury criterion, by up to 49.9% and 56.6%. Furthermore, when considering tissue-based severity metrics via finite element simulations of a human brain model, maximum principal strain and cumulative strain density measures are reduced by 14.9% and 66.7% when comparing the new material, to baseline.

Finite element simulation was used to analyse the response of an elastomeric pre-buckled honeycomb structure under impact loading, to establish its suitability for use in helmet liners. A finite element-based optimisation was performed using a search algorithm based on a radial basis function. This approach identified optimisation configurations of a pre-buckled honeycomb structure, based on structural bounds subject to impact loading conditions. Furthermore, the influence of objective function, peak acceleration and head injury criterion was analysed with respect to the resultant mechanical behaviour of the structure. Numerical results demonstrate that this class of structure can exceed the performance threshold of a common helmet design standard and minimise the resultant injury index. Experimental testing, facilitated through laser sintering of thermoplastic polyurethane powder, validated the output of the numerical optimisation. When subject to initial impact loading, the fabricated samples satisfied their objective functions. Successive impact loading was performed to assess the performance and degradation. Samples optimised for peak acceleration demonstrated superior performance after stabilisation, relative to their initial response. The culmination of this study establishes a numerical design pathway for future optimisation of candidate structures for head impact protection. Furthermore, the optimised pre-buckled honeycomb structure represents a new class of energy absorbing structure, which can exceed the thresholds prescribed by the design standard.

Selective laser sintering has been used to manufacture different structural variations of a pre-buckled circular honeycomb. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic impact loading. Pre-buckled circular honeycombs with aspect ratios e = 0.8 and e = 0.6 were compared to a traditional, straight-walled honeycomb. It has been found that the mechanical behaviour of the honeycomb can be tailored to yield different mechanical responses. Principally, decreasing the aspect ratio reduced the stress at yield, as well as the total energy absorbed until densification, however, this alleviated the characteristic stress-softening response of traditional honeycombs under static and dynamic conditions. When subjected to multiple cycles of loading, a stabilised response was observed. The numerical response closely agreed with the experimental results. A simplified, periodic boundary condition model also closely agreed with the experimental results whilst alleviating computational run time by nominally 75%. The numerical full factorial parameter design sweep identified a broad range of mechanical behaviour. This represents a valuable tool to identify optimal design configurations for future impact mitigating applications.

This paper reports on a comprehensive investigation of gyroid lattice structures subject to impact loading. AlSi10Mg samples were manufactured using selective laser melting (SLM) and mechanically characterized using Digital Image Correlation (DIC). Universal testing machines, drop weight rig, and a split pressure Hopkinson bar were used to mechanically characterize the aluminium alloy at strain rates ranging from, epsilon = 10-3 s(-1) up to 5500 s(-1). Gyroid samples were tested in a drop-weight rig at different impact conditions, where tests results were validated by a FE analysis. These tests, measurements, and analysis enabled the development of a modified gyroid isosurface equation, providing an opportunity to investigate their impact response, where the gyroid wall thickness, unit cell size, and modified isosurface curvature were studied at low-velocity impact conditions. The results indicate that changes in gyroid isosurface topology substantially affect its impact performance.

Antimicrobial 3D printed surfaces made of PLA and TPU polymers loaded with copper (Cu), and silver (Ag) nanoparticles (NPs) were developed via fused deposition modeling (FDM). The potential antimicrobial effect of the 3D printed surfaces against Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus was evaluated. Furthermore, the mechanical characteristics, including surface topology and morphology, tensile test of specimens manufactured in three different orientations (XY, XZ, and ZX), water absorption capacity, and surface wettability were also assessed. The results showed that both Cu and Ag-loaded 3D printed surfaces displayed a higher inhibitory effect against S. aureus and L. monocytogenes biofilms compared to S. Typhimurium and E. coli biofilms. The results of SEM analysis revealed a low void fraction for the TPU and no voids for the PLA samples achieved through optimization and the small height (0.1 mm) of the printed layers. The best performing specimen in terms of its tensile was XY, followed by ZX and XZ orientation, while it indicated that Cu and Ag-loaded material had a slightly stiffer response than plain PLA. Additionally, Cu and Agloaded 3D printed surfaces revealed the highest hydrophobicity compared to the plain polymers making them excellent candidates for biomedical and food production settings to prevent initial bacterial colonization. The approach taken in the current study offers new insights for developing antimicrobial 3D printed surfaces and equipment to enable their application towards the inhibition of the most common nosocomial and foodborne pathogens and reduce the risk of cross-contamination and disease outbreaks.

Cu15Ni8Sn is widely used in the aerospace and electronics domains because of its good conductivity and toughness. Due to the material's high laser reflectivity and thermal conductivity, however, employing the laser powder bed fusion (LPBF) additive manufacturing process on Cu15Ni8Sn alloy has been a challenge. This issue was addressed in the present study by modifying the Cu15Ni8Sn powder by adding 1 wt% submicrometre TiB2 ceramic particles. The results indicate that the LPBF's processability was improved by the increased laser absorption rate caused by the addition of 1 wt% TiB2, which eliminated pores and unmelted area defects. The addition of 1 wt% TiB2 also improved the components' surface quality by reducing the surface roughness value of 39.3% compared to the original Cu15Ni8Sn. The findings also indicate that the added TiB2 particles reduced Sn-segregation behaviour, implying that the content and size of the segregated phase could be tailored by the suitable selection of ceramic materials and LPBF process parameters. Another advantage lies in the enhancement of mechanical performance, where a 11% increase in yield strength and 14% increase in ultimate tensile strength were achieved in the LPBF-fabricated modified Cu15Ni8Sn material. In this study, the primary strengthening mechanisms for LPBF-fabricated original Cu15Ni8Sn were found to include dislocation strengthening and grain boundary strengthening. Orowan precipitation strengthening also played a significant role in the Cu15Ni8Sn-1wt.% TiB2 material, as did dislocation strengthening and grain boundary strengthening. These findings provide a promising strategy to improve the LPBF processability of the advanced copper-based materials used in several key fields.

This study evaluates a fluid-filled, closed-cell lattice as a novel route to reducing peak acceleration in impact environments. A conical structure was designed and built using fused filament fabrication. One structure was manufactured hollow (100% air), another 70% filled with water (50% by height) and a third 100% water-filled. Peak acceleration was evaluated by performing 4.1 kg impacts at 1, 2, 3 m/s. Impacts were then simulated in shell and solid finite element analysis models, employing the smooth particle hydrodynamic method for the water and a surface-based fluid-filled cavity method for air. The air-filled, conventional closed-cell structures achieved the lowest peak accelerations at lower impact energies, however, water infill improved impact performance at higher energies. For low to medium impact energies, shell and solid modelling accurately simulated experimental trends, although the latter is more computationally expensive. Solid modelling is the only viable solution for scenarios achieving structural densification, due to the inaccuracies in shell-based models caused by the inter-surface penetrations. This work has demonstrated that fluid-filled structures provide a promising approach to reduce acceleration and so achieving enhanced protection, whilst also presenting a computational pathway that will enable efficient design of new and novel structures.

American football has a comparatively high rate of sports-related concussions, despite mitigating strategies including the use of protective helmets. The traditional energy absorbing component, elastomeric foam pads, have limited scope for leveraging any further protection. Alternative structures and materials that exhibit novel deformation mechanics have been proposed as a route to increased energy absorption capacity. This study investigated a metamaterial based on the Miura Ori folding pattern. Eighty-one potential structural variations were conceptualised and evaluated via the Taguchi method. Twenty-seven geometries were then additively manufactured using commercially available thermoplastic polyurethane, before being impacted at multiple velocities. Experimental data were then extrapolated to predict the impact behaviour across all 81 variants. An optimised geometry was then proposed, which reduced linear accelerations across the test conditions and performed favourably when compared to current, elastomeric foam solutions. This work provides a promising foundation for future investigation.

In the original version of the book, the author name has been updated from “Khaled Gaisin” to “Khaled Giasin” in the Chapter “Using FFF and topology optimisation to increase crushing strength in equestrian helmets”. The chapter and book have been updated with the changes.

Additive Manufacturing of cellular lattice structures offers opportunities to fine-tune the mechanical response by altering geometric variables. It is known that heat treatment cycles provide an effective way of altering mechanical properties while relieving residual stress. By exploiting the combined influence of these two variables, this study demonstrates the possibility of optimising energy absorption in AlSi10Mg honeycomb lattice structures, manufactured using selective laser melting. This finding indicates that heat treatment and powder quality have a significant influence on the mechanical response of the honeycomb. Additionally, this highlights the opportunity to establish an energy absorption diagram, via mapping the relative performance of variable lattice geometries and heat treatment cycles. At the same time, the consistency of powder quality can be tightly controlled.

International standards ensure that equestrian helmets achieve high performance. Recently, one such standard (PAS 015) was revised to include a lateral deformation requirement, ensuring helmets can withstand the potential crushing forces associated with equestrian. This increased performance needs to be achieved against a minimal mass penalty, which is an important consumer consideration. This paper explores how shell design optimisation can improve crush resistance, validated using additive manufacturing and mechanical testing. This approach achieved a 73% increase in crush force, for only an 11% mass increase.

Nickel-based superalloys such as Hastelloy X (HX) are widely used in gas turbine engine applications and the aerospace industry. HX is susceptible to hot cracking, however, when processed using additive manufacturing technologies such as laser powder bed fusion (LPBF). This paper studies the effects of minor alloying elements on microcrack formation and the influences of hot cracking on the mechanical performance of LPBF-fabricated HX components, with an emphasis on the failure mechanism of the lattice structures. The experimental results demonstrate that a reduction in the amount of minor alloying elements used in the alloy results in the elimination of hot cracking in the LPBF-fabricated HX; however, this modification degrades the tensile strength by around 140 MPa. The microcracks were found to have formed uniformly at the high-angle grain boundaries, indicating that the cracks were intergranular, which is associated with Mo-rich carbide segregation. The study also shows that the plastic-collapse strength tends to increase with increasing strut sizes (i.e. relative density) in both the 'with cracking' and 'cracking-free' HX lattice structures, but the cracking-free HX exhibit a higher strength value. Under compression, the cracking-free HX lattice structures' failure mechanism is controlled by plastic yielding, while the failure of the with-cracking HX is dominated by plastic buckling due to the microcracks formed within the LPBF process. The novelty of this work is its systematic examination of hot cracking on the compressive performance of LPBF-fabricated lattice structures. The findings will have significant implications for the design of new cracking-free superalloys, particularly for high-temperature applications.

Nickel-based superalloys such as Hastelloy X (HX) are widely used in gas turbine engines for their exceptional oxidation resistance and high-temperature strength. The addition of ceramic reinforcement further enhances these superalloys’ mechanical performance and high-temperature properties. For this reason, this paper investigates the microstructure and mechanical property of laser powder bed fusion (LPBF) additively manufactured HX–1 wt% WC (tungsten carbide) composite specimens. The results demonstrate that the LPBF-fabricated composite was observed to have several pores and microcracks, whilst only pores were detected in the as-fabricated pure HX. Compared to the fabricated pure HX, the tensile yield strength of such HX composite parts was increased by 13% without undue sacrifices to ductility, suggesting that the very limited number of microcracks were not sufficient to degrade the mechanical performance. The significantly increased dislocations were considered to be the primary contributor for the mechanical performance enhancement in the LPBF-fabricated composite material. The findings offer a promising pathway to employ LPBF process to fabricate advanced microcrack-free composites with high-strength through a careful selection of ceramic reinforcement materials.

Additive manufacturing (AM) enables production of geometrically-complex elastomeric structures. The elastic recovery and strain-rate dependence of these materials means they are ideal for use in dynamic, repetitive mechanical loading. Their process-dependence, and the frequent emergence of new AM elastomers, commonly necessitates full material characterisation; however, accessing specialised equipment means this is often a time-consuming and expensive process. This work presents an innovative equi-biaxial rig that enables full characterisation via a conventional material testing machine (supplementing uni-axial tension and planar tension tests). Combined with stress relaxation data, this provides a novel route for hyperelastic material modelling with viscoelastic components. This approach was validated by recording the force-displacement and deformation histories from finite element modelling a honeycomb structure. These data compared favourably to experimental quasistatic and dynamic compression testing, validating this novel and convenient route for characterising complex elastomeric materials. Supported by data describing the potential for high build-quality production using an AM process with low barriers to entry, this study should serve to encourage greater exploitation of this emerging manufacturing process for fabricating elastomeric structures within industrial communities.

Constitutive laws that describe the mechanical responses of cardiac tissue under loading hold the key to accurately model the biomechanical behaviour of the heart. There have been ample choices of phenomenological constitutive laws derived from experiments, some of which are quite sophisticated and include effects of microscopic fibre structures of the myocardium. A typical example is the strain-invariant-based Holzapfel–Ogden 2009 model that is excellently fitted to simple shear tests. It has been widely used and regarded as the state-of-the-art constitutive law for myocardium. However, there has been no analysis to show if it has both adequate descriptive and predictive capabilities for other tissue tests of myocardium. Indeed, such an analysis is important for any constitutive laws for clinically useful computational simulations. In this work, we perform such an analysis using combinations of tissue tests, uniaxial tension, biaxial tension and simple shear from three different sets of myocardial tissue studies. Starting from the general 14-parameter myocardial constitutive law developed by Holzapfel and Ogden, denoted as the general HO model, we show that this model has good descriptive and predictive capabilities for all the experimental tests. However, to reliably determine all 14 parameters of the model from experiments remains a great challenge. Our aim is to reduce the constitutive law using Akaike information criterion, to maintain its mechanical integrity whilst achieving minimal computational cost. A competent constitutive law should have descriptive and predictive capabilities for different tissue tests. By competent, we mean the model has least terms but is still able to describe and predict experimental data. We also investigate the optimal combinations of tissue tests for a given constitutive model. For example, our results show that using one of the reduced HO models, one may need just one shear response (along normal-fibre direction) and one biaxial stretch (ratio of 1 mean fibre : 1 cross-fibre) to satisfactorily describe Sommer et al. human myocardial mechanical properties. Our study suggests that single-state tests (i.e. simple shear or stretching only) are insufficient to determine the myocardium responses. We also found it is important to consider transmural fibre rotations within each myocardial sample of tests during the fitting process. This is done by excluding un-stretched fibres using an “effective fibre ratio”, which depends on the sample size, shape, local myofibre architecture and loading conditions. We conclude that a competent myocardium material model can be obtained from the general HO model using AIC analysis and a suitable combination of tissue tests.