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Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Smart Materials".

Deadline for manuscript submissions: closed (10 May 2023) | Viewed by 12486

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Special Issue Editors

Dr. Ahmad Baroutaji

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Guest Editor

Aston Professional Engineering Centre, School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham B4 7ET, UK
Interests: metamaterials; design optimisation; numerical modelling; crashworthiness; additive manufacturing
Special Issues, Collections and Topics in MDPI journals

Dr. Arun Arjunan

E-Mail Website
Guest Editor

1. Additive Manufacturing of Functional Materials Research Group, Centre for Engineering Innovation and Research, University of Wolverhampton, Telford Innovation Campus, Telford TF2 9NT, UK
2. School of Engineering, University of Wolverhampton, Telford Innovation Campus, Telford TF2 9NT, UK
Interests: additive manufacturing; metamaterials; tissue engineering; vibroacoustics; structural mechanics

Special Issue Information

Dear Colleagues,

Mechanical metamaterials with their unique and tailorable characteristics are receiving increased attention for a wide range of applications, such as energy absorption, functional load-bearing, indentation resistance, tissue engineering biomaterials, and enhanced vibro-acoustics. The recent advancements in metamaterials are largely driven by developments in modern manufacturing technologies, such as additive manufacturing (3D printing). As a result, novel metamaterials are emerging from a variety of materials, including metals, thermoplastic, and ceramics.

In addition to modern manufacturing technologies, the application of computational modelling techniques is critical in enabling a comprehensive understanding of the behaviour of metamaterials. As such, there is an opportunity for the development, control, and optimisation of metamaterials under a variety of mechanical load and use cases.

The aim of this Special Issue is to highlight recent advances in the field of mechanical metamaterials and their associated applications and fabrication techniques. The Special Issue covers all aspects related to the development of mechanical metamaterials, including novel designs, application, manufacturing methods, new materials, numerical modelling, experimental testing, and performance characterisation.

Dr. Ahmad Baroutaji
Dr. Arun Arjunan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

metamaterials
microlattice
auxetic
mechanical responses
additive manufacturing
SLM
FDM
SLS
numerical modelling
optimization

Published Papers (5 papers)

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Research

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14 pages, 5935 KiB

Open AccessArticle

Suitability of Gelatin Methacrylate and Hydroxyapatite Hydrogels for 3D-Bioprinted Bone Tissue

by Paul Stolarov, Jonathan de Vries, Sean Stapleton, Lauren Morris, Kari Martyniak and Thomas J. Kean

Materials 2024, 17(5), 1218; https://0-doi-org.brum.beds.ac.uk/10.3390/ma17051218 - 06 Mar 2024

Viewed by 1064

Abstract

Background: Complex bone defects are challenging to treat. Autografting is the gold standard for regenerating bone defects; however, its limitations include donor-site morbidity and increased surgical complexity. Advancements in 3D bioprinting (3DBP) offer a promising alternative for viable bone grafts. In this experiment, gels composed of varying levels of gelatin methacrylate (GelMA) and hydroxyapatite (HA) and gelatin concentrations are explored. The objective was to increase the hydroxyapatite content and find the upper limit before the printability was compromised and determine its effect on the mechanical properties and cell viability. Methods: Design of Experiments (DoE) was used to design 13 hydrogel bioinks of various GelMA/HA concentrations. These bioinks were assessed in terms of their pipettability and equilibrium modulus. An optimal bioink was designed using the DoE data to produce the greatest stiffness while still being pipettable. Three bioinks, one with the DoE-designed maximal stiffness, one with the experimentally defined maximal stiffness, and a literature-based control, were then printed using a 3D bioprinter and assessed for print fidelity. The resulting hydrogels were combined with human bone-marrow-derived mesenchymal stromal cells (hMSCs) and evaluated for cell viability. Results: The DoE ANOVA analysis indicated that the augmented three-level factorial design model used was a good fit (p < 0.0001). Using the model, DoE correctly predicted that a composite hydrogel consisting of 12.3% GelMA, 15.7% HA, and 2% gelatin would produce the maximum equilibrium modulus while still being pipettable. The hydrogel with the most optimal print fidelity was 10% GelMA, 2% HA, and 5% gelatin. There were no significant differences in the cell viability within the hydrogels from day 2 to day 7 (p > 0.05). There was, however, a significantly lower cell viability in the gel composed of 12.3% GelMA, 15.7% HA, and 2% gelatin compared to the other gels with a lower HA concentration (p < 0.05), showing that a higher HA content or print pressure may be cytotoxic within hydrogels. Conclusions: Extrusion-based 3DBP offers significant advantages for bone–tissue implants due to its high customizability. This study demonstrates that it is possible to create printable bone-like grafts from GelMA and HA with an increased HA content, favorable mechanical properties (145 kPa), and a greater than 80% cell viability. Full article

(This article belongs to the Special Issue Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques)

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14 pages, 7136 KiB

Open AccessArticle

Miniaturization of Non-Assembly Metallic Pin-Joints by LPBF-Based Additive Manufacturing as Perfect Pivots for Pantographic Metamaterials

by Florian Gutmann, Maximilian Stilz, Sankalp Patil, Frank Fischer, Klaus Hoschke, Georg Ganzenmüller and Stefan Hiermaier

Materials 2023, 16(5), 1797; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16051797 - 22 Feb 2023

Cited by 4 | Viewed by 1376

Abstract

This work introduced additively manufactured non-assembly, miniaturized pin-joints for pantographic metamaterials as perfect pivots. The titanium alloy Ti6Al4V was utilized with laser powder bed fusion technology. The pin-joints were produced using optimized process parameters required for manufacturing miniaturized joints, and they were printed at a particular angle to the build platform. Additionally, this process optimization will eliminate the requirement to geometrically compensate the computer-aided design model, allowing for even further miniaturization. In this work, pin-joint lattice structures known as pantographic metamaterials were taken into consideration. The mechanical behavior of the metamaterial was characterized by bias extension tests and cyclic fatigue experiments, showing superior levels of performance (no sign of fatigue for 100 cycles of an elongation of approximately 20%) in comparison to classic pantographic metamaterials made with rigid pivots. The individual pin-joints, with a pin diameter of 350 to 670 µm, were analyzed using computed tomography scans, indicating that the mechanism of the rotational joint functions well even though the clearance of 115 to 132 µm between the moving parts is comparable to the nominal spatial resolution of the printing process. Our findings emphasize new possibilities to develop novel mechanical metamaterials with actual moving joints on a small scale. The results will also support stiffness-optimized metamaterials with variable-resistance torque for non-assembly pin-joints in the future. Full article

(This article belongs to the Special Issue Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques)

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14 pages, 4451 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Atmospheric Oxygen Content on the Mechanical Properties of Selectively Laser Melted AlSi10Mg TPMS-Based Lattice

by Ahmad Baroutaji, Arun Arjunan, James Beal, John Robinson and Julio Coroado

Materials 2023, 16(1), 430; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16010430 - 02 Jan 2023

Cited by 7 | Viewed by 2527

Abstract

Selective Laser Melting (SLM) is an emerging Additive Manufacturing (AM) technique for the on-demand fabrication of metal parts. The mechanical properties of Selectively Laser Melted (SLMed) parts are sensitive to oxygen concentration within the SLM build chamber due to the formation of oxides, which may lead to various negative consequences. As such, this work explores the influence of SLM atmospheric Oxygen Content (OC) on the macroscopic mechanical properties of SLMed AlSi10Mg bulk material and Triply Periodic Minimal Surface (TPMS) lattices namely primitive, gyroid, and diamond. Standard quasi-static tensile and crushing tests were conducted to evaluate the bulk properties of AlSi10Mg and the compressive metrics of TPMS-lattices. Two oxygen concentrations of 100 ppm and 1000 were used during the SLM fabrication of the experimental specimens. The tensile test data revealed a small influence of the oxygen content on the bulk properties. The low oxygen concentration improved the elongation while slightly reduced the ultimate tensile strength and yield stress. Similarly, the influence of the oxygen content on the compressive responses of TPMS-lattices was generally limited and primarily depended on their geometrical configuration. This study elucidates the role of SLM atmospheric oxygen content on the macroscopic behaviour of SLMed AlSi10Mg parts. Full article

(This article belongs to the Special Issue Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques)

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19 pages, 5129 KiB

Open AccessArticle

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

by Mayur Jiyalal Prajapati, Chinmai Bhat, Ajeet Kumar, Saurav Verma, Shang-Chih Lin and Jeng-Ywan Jeng

Materials 2022, 15(22), 7954; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15227954 - 10 Nov 2022

Cited by 10 | Viewed by 2517

Abstract

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. Full article

(This article belongs to the Special Issue Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques)

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Review

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18 pages, 2235 KiB

Open AccessReview

Architected Materials for Additive Manufacturing: A Comprehensive Review

by Nikolaos Kladovasilakis, Konstantinos Tsongas, Dimitris Karalekas and Dimitrios Tzetzis

Materials 2022, 15(17), 5919; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15175919 - 26 Aug 2022

Cited by 20 | Viewed by 4030

Abstract

One of the main advantages of Additive Manufacturing (AM) is the ability to produce topologically optimized parts with high geometric complexity. In this context, a plethora of architected materials was investigated and utilized in order to optimize the 3D design of existing parts, reducing their mass, topology-controlling their mechanical response, and adding remarkable physical properties, such as high porosity and high surface area to volume ratio. Thus, the current re-view has been focused on providing the definition of architected materials and explaining their main physical properties. Furthermore, an up-to-date classification of cellular materials is presented containing all types of lattice structures. In addition, this research summarized the developed methods that enhance the mechanical performance of architected materials. Then, the effective mechanical behavior of the architected materials was investigated and compared through the existing literature. Moreover, commercial applications and potential uses of the architected materials are presented in various industries, such as the aeronautical, automotive, biomechanical, etc. The objectives of this comprehensive review are to provide a detailed map of the existing architected materials and their mechanical behavior, explore innovative techniques for improving them and highlight the comprehensive advantages of topology optimization in industrial applications utilizing additive manufacturing and novel architected materials. Full article

(This article belongs to the Special Issue Recent Advances in the Field of Mechanical Metamaterials and Their Associated Applications and Fabrication Techniques)

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