Design and evaluation of mechanical strength of multi-material polymeric implants for mandibular reconstruction.

Reconstruction of mandible implants to address segmental abnormalities is still a challenging task, both in vitro and in vivo. The mechanical strength of the materials used is a critical factor that determines how well bone is regenerated. The reconstruction technique of mandibular abnormalities widely uses polymeric implants. It is critical to evaluate the mechanical resilience under different load cases, including axial, combined, and flexural loading conditions. This study developed implants for mandibular defects using a combination of four materials: polylactic acid (PLA), polyethylene terephthalate glycol (PETG), thermoplastic polyurethane (TPU), and polycaprolactone (PCL), with the aim of mimicking the inherent characteristics of cortical and cancellous bone structures and evaluating their mechanical properties to support bone Osseo integration. The eleven of these combinations of structures result below the micro strain threshold level of <3000 µÎµ, and the five combinations of the structures result in micro strain above the threshold value. The intact bone study results show that the stress under axial, combined, and flexural loading conditions is 27.6, 38.9, and 64.9 MPa, respectively. This study's stress results are lower than those from the intact bone study. The study found that the combinations of PLA and TPU material were most preferred for the cortical and cancellous bone regions of polymeric implants. These materials are also compatible with 3D printing. The results of this study can be used to find multi-material combinations that are strong and flexible.

Numerical Simulation of the Evaporation Behavior of Fe-Mn Heterogeneous Powder in Selective Laser Melting Process.

Multi-material additive manufacturing using heterogeneous powders as raw materials is one of the important development directions of metal additive manufacturing technology. The evaporation behavior of heterogeneous powders in the selective laser melting (SLM) process has a significant influence on the accuracy of chemical composition control and the quality of the final product. In this paper, the fusion process of Fe20Mn (80 wt.% Fe and 20 wt.% Mn) heterogeneous powder, Fe and Mn elemental powders, and Fe20Mn pre-alloyed powder is numerically simulated using FLOW-3D® software and partially validated through SLM experimental results. The morphology and the characteristics of the flow field and temperature field in the melt pool for four kinds of powder materials are analyzed. The influence of the elemental evaporation behavior of different powders on the mass loss of the Mn element is discussed. The results show that the excessive accumulation of heat increases the maximum temperature of the melt pool, thus increasing mass loss. The Fe20Mn heterogeneous powder has a wider heat-affected zone and a higher peak value of temperature, nearly 400 K higher than that of the Fe20Mn pre-alloyed powders, which exhibits an intensive evaporation behavior. The mass loss of the Mn element obtained from the SLM experiment for Fe20Mn heterogeneous powders forming parts is more than the Fe20Mn pre-alloyed powders' forming parts for different laser powers, up to 17 wt.% at P = 120 W. This tendency is consistent with the numerical analysis of the effect of evaporation behavior of Fe-Mn heterogeneous powder during the SLM process. This study provides the necessary theoretical reference and process guidance for realizing the precise control of the SLM composition of a heterogeneous powder in multi-material additive manufacturing caused by evaporation behavior.

Design of dissimilar material joint for defect-free multi-material additive manufacturing via laser-directed energy deposition.

Additive manufacturing technology has advanced beyond creating optimized features, from strengthening materials to make them lightweight to fabricating multi-material combinations that offer functionalities beyond the capabilities of individual materials. In this study, a lamination method for laser-directed energy deposition (LDED) is developed to achieve dense multi-material features, and a design that combines different and dissimilar materials is developed. To evaluate these novel developments, two materials-AISI 316L stainless steel and Inconel 625-are introduced. Tensile specimens, fabricated via multi-material additive manufacturing using LDED, are subjected to tensile tests that are recorded on video for digital image correlation. After the tests, fracture surface analyses of the fractured specimens are performed via scanning electron microscopy, and optical monitoring analyses are performed on the specimens that are not subjected to the tensile tests. The results indicate that the specimens demonstrate varied mechanical properties due to the influence of lamination direction and order, which affect the formation of critical cracks and pores.

The Application of a Multi-Material Flexible Chain Mail for the Design of an Artificial Spinal Disc to Reproduce Natural Nonlinear and Anisotropic Rotational Behavior.

Inspired by the potential of architected materials for achieving biomimicking functionalities and the advancement of multi-material additive manufacturing to fabricate parts with complex structures and heterogeneous material distributions, this study investigates the feasibility of using a multi-material, flexible chain mail sheet for the design of an additively manufactured artificial spinal disc for reproducing patient-specific anisotropic and nonlinear rotational behaviors. The application of a chain mail-based structure is motivated by its similarities in behaviors compared with a natural disc's fiber network that likewise has negligible bending stiffness and shape-changing ability. The proposed approach for the chain mail sheet design includes an initial characterization of the uniaxial tensile responses of the chain mail unit cell defined as the basic building block of the chain mail sheet, modeling and response calculation, and material optimization. Results show that the additively manufactured chain mail sheet is not only able to exhibit a natural strain-stiffening rotational response but also is able to reproduce natural anisotropy of three natural disc specimens in the six most common rotational scenarios in daily life. This study shows the potential of additively manufactured mechanical-metamaterials-inspired structures for implant design to restore natural mechanics.

Additive manufacturing of multi-material parts - Design guidelines for manufacturing of 316L/CuCrZr in laser powder bed fusion.

Additive manufacturing (AM) can be used to produce multi-material parts in which the material can be varied voxel-wise in all three spatial directions. This means that the paradigm of the homogeneous material can be abandoned and local effects such as heat conduction or damping can be selectively adjusted in the part. Recently, continuous development of machine technology has allowed the production of multi-metal materials in laser powder bed fusion (PBF-LB/MM). Compared to other additive manufacturing processes for multi-material production, this allows greater design freedom and detail accuracy to be realized. However, due to the novel character of multi-material manufacturing in PBF-LB, the process knowledge for successful and reproducible fabrication is currently lacking. This paper focuses on establishing design guidelines for manufacturing the material pairing of stainless steel 316L (1.4404) and copper alloy CuCrZr (CW106C). The article is accompanied by the development of a specific process chain. As a result of this work, design guidelines for multi-material parts are available for the first time, in regard to arrangement, size, overhangs, economy, powder quality and laser scanning.

Ultrasonic bandgaps in viscoelastic 1D-periodic media: Mechanical modeling and experimental validation.

Multi-material additive manufacturing is receiving increasing attention in the field of acoustics, in particular towards the design of micro-architectured periodic media used to achieve programmable ultrasonic responses. To unravel the effect of the material properties and spatial arrangement of the printed constituents, there is an unmet need in developing wave propagation models for prediction and optimization purposes. In this study, we propose to investigate the transmission of longitudinal ultrasound waves through 1D-periodic biphasic media, whose constituent materials are viscoelastic. To this end, Bloch-Floquet analysis is applied in the frame of viscoelasticity, with the aim of disentangling the relative contributions of viscoelasticity and periodicity on ultrasound signatures, such as dispersion, attenuation, and bandgaps localization. The impact of the finite size nature of these structures is then assessed by using a modeling approach based on the transfer matrix formalism. Finally, the modeling outcomes, i.e., frequency-dependent phase velocity and attenuation, are confronted with experiments conducted on 3D-printed samples, which exhibit a 1D periodicity at length-scales of a few hundreds of micrometers. Altogether, the obtained results shed light on the modeling characteristics to be considered when predicting the complex acoustic behavior of periodic media in the ultrasonic regime.

Supportless Lattice Structure for Additive Manufacturing of Functional Products and the Evaluation of Its Mechanical Property at Variable Strain Rates.

This study proposes an innovative design solution based on the design for additive manufacturing (DfAM) and post-process for manufacturing industrial-grade products by reducing additive manufacturing (AM) time and improving production agility. The design of the supportless open cell Sea Urchin lattice structure is analyzed using DfAM for material extrusion (MEX) process to print support free in any direction. The open cell is converted into a global closed cell to entrap secondary foam material. The lattice structure is 3D printed with Polyethylene terephthalate glycol (PETG) material and is filled with foam using the Hybrid MEX process. Foam-filling improves the lattice structure's energy absorption and crash force efficiency when tested at different strain rates. An industrial case study demonstrates the importance and application of this lightweight and tough design to meet the challenging current and future mass customization market. A consumer-based industrial scenario is chosen wherein an innovative 3D-printed universal puck accommodates different shapes of products across the supply line. The pucks are prone to collisions on the supply line, generating shock loads and hazardous noise. The results show that support-free global closed-cell lattice structures filled with foam improve energy absorption at a high strain rate and enhance the functional requirement of noise reduction during the collision.

Equine hoof wall: Structure, properties, and bioinspired designs.

The horse hoof wall exhibits exceptional impact resistance and fracture control due to its unique hierarchical structure which contains tubular, lamellar, and gradient configurations. In this study, structural characterization of the hoof wall was performed revealing features previously unknown. Prominent among them are tubule bridges, which are imaged and quantified. The hydration-dependent viscoelasticity of the hoof wall is described by a simplified Maxwell-Weichert model with two characteristic relaxation times corresponding to nanoscale and mesoscale features. Creep and relaxation tests reveal that the specific hydration gradient in the hoof keratin likely leads to reduced internal stresses that arise from spatial stiffness variations. To better understand realistic impact modes for the hoof wall in-vivo, drop tower tests were executed on hoof wall samples. Fractography revealed that the hoof wall's reinforced tubular structure dominates at lower impact energies, while the intertubular lamellae are dominant at higher impact energies. Broken fibers were observed on the surface of the tubules after failure, suggesting that the physically intertwined nature of the tubule reinforcement and intertubular matrix improves the toughness of this natural fiber reinforced composite. The augmented understanding of the structure-mechanical property relationship in dynamic loading led to the design of additively manufactured bioinspired structures, which were evaluated in quasistatic and dynamic loadings. The inclusion of gradient structures and lamellae significantly reduced the damage sustained in drop tower tests, while tubules increased the energy absorption of samples tested in compact tension. The samples most similar to the hoof wall displayed remarkably consistent fracture control properties. STATEMENT OF SIGNIFICANCE: The horse hoof wall, capable of withstanding large, repeated, dynamic loads, has been touted as a candidate for impact-resistant bioinspiration. However, our understanding of this biological material and its translation into engineered designs is incomplete. In this work, new features of the horse hoof wall are quantified and the hierarchical failure mechanisms of this remarkable material under near-natural loading conditions are uncovered. A model of the hoof wall's viscoelastic response, based on studies of other keratinous materials, was developed. The role of hydration, strain rate, and impact energy on the material's response were elucidated. Finally, multi-material 3D printed designs based on the hoof's meso/microstructure were fabricated and exhibited advantageous energy absorption and fracture control relative to control samples.

Interlacing Infills for Multi-Material Fused Filament Fabrication Using Layered Depth Material Images.

One major concern regarding multi-material additive manufacturing (MMAM) is the strength at the interface between materials. Based on the observation of how nature puts materials together, this paper hypothesizes that overlapping and interlacing materials with each other enhance the interface bonding strength. To test this hypothesis, this research develops a new slicing framework that can efficiently identify the multi-material regions and develop interlaced infills. Based on a ray-tracing technology, we develop layered depth material images (LDMI) to process the material information of digital models for toolpath planning. Each sample point in the LDMI has an associated material and geometric properties that are used to recover the material distribution in each slice. With this material distribution, this work generates an interlocking joint and an interlacing infill in the regions with multiple materials. The experiments include comparisons between similar materials and different materials. Tensile tests have shown that our proposed infill outperforms the interlocking joint in all cases. Fractures occur even outside the interlacing area, meaning that the joint is at least as strong as the materials. The experimental results verify the enhancement of interface strength by overlapping and interlacing materials. In addition, existing computational tools have limitations in full use of material information. To the best of our knowledge, this is the first time a slicer can process overlapped material regions and create interlacing infills. The interlacing infills improve the bonding strength, making the interface no longer the weakest area. This enables MMAM to fabricate truly functional parts. In addition, the new LDMI framework has rich information on geometry and material, and it allows future research in multi-material modeling.

Dataset of angular and compressive responses of biomimetic artificial spinal discs fabricated using multi-material additive manufacturing.

To explore the influence of different biomimetic designs and multi-material additive manufacturing on the performance of a multi-material artificial spinal disc (ASD) in terms of restoring natural mechanics, four biomimetic ASD designs together with a control design are first fabricated using a Stratasys Connex3 Objet500 inkjet-based, multi-material 3D printer and their mechanical responses are measured using in-vitro mechanical testing. The mechanical tests include an angular test and a compression test to measure the ASD's behavior in the seven most frequent loading scenarios of a spine: flexion, extension, left/right lateral bending, left/right axial rotation, and compression. The angular test is performed using a custom six degrees of freedom, computer-controlled spine testing system together with an optoelectronic motion analysis system, while the compression test is performed using an Instron testing machine. The presented dataset includes 3D models of the five ASD designs, and raw data of the angular and compressive responses at different strain rates of the five ASD designs. This dataset is related to the article "Exploration of the influence of different biomimetic designs of 3D printed multi-material artificial spinal disc on the natural mechanics restoration" where the detailed designs and load responses of the five multi-material ASDs are presented (Yu et al., 2021). This dataset helps to gain insights into the influence of different biomimetic design concepts on the mechanics of a multi-material ASD and serves as a reference for the future design of multi-material ASDs.