Lightweight and strong structural materials attract much attention due to their strategic applications in sports, transportation, aerospace, and biomedical industries. Nacre exhibits high strength and toughness from the brick-and-mortar–like structure. Here, we present a route to build nacre-inspired hierarchical structures with complex three-dimensional (3D) shapes by electrically assisted 3D printing. Graphene nanoplatelets (GNs) are aligned by the electric field (433 V/cm) during 3D printing and act as bricks with the polymer matrix in between as mortar. The 3D-printed nacre with aligned GNs (2 weight %) shows lightweight property (1.06 g/cm 3 ) while exhibiting comparable specific toughness and strength to the natural nacre. In addition, the 3D-printed lightweight smart armor with aligned GNs can sense its damage with a hesitated resistance change. This study highlights interesting possibilities for bioinspired structures, with integrated mechanical reinforcement and electrical self-sensing capabilities for biomedical applications, aerospace engineering, as well as military and sports armors.
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3D Printing of Nacre-Inspired Structures with Exceptional Mechanical and Flame-Retardant Properties
Flame-retardant and thermal management structures have attracted great attention due to the requirement of high-temperature exposure in industrial, aerospace, and thermal power fields, but the development of protective fire-retardant structures with complex shapes to fit arbitrary surfaces is still challenging. Herein, we reported a rotation-blade casting-assisted 3D printing process to fabricate nacre-inspired structures with exceptional mechanical and flame-retardant properties, and the related fundamental mechanisms are studied. 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) modified boron nitride nanoplatelets (BNs) were aligned by rotation-blade casting during the 3D printing process to build the “brick and mortar” architecture. The 3D printed structures are more lightweight, while having higher fracture toughness than the natural nacre, which is attributed to the crack deflection, aligned BN (a-BNs) bridging, and pull-outs reinforced structures by the covalent bonding between TMSPMA grafted a-BNs and polymer matrix. Thermal conductivity is enhanced by 25.5 times compared with pure polymer and 5.8 times of anisotropy due to the interconnection of a-BNs. 3D printed heat-exchange structures with vertically aligned BNs in complex shapes were demonstrated for efficient thermal control of high-power light-emitting diodes. 3D printed helmet and armor with a-BNs show exceptional mechanical and fire-retardant properties, demonstrating integrated mechanical and thermal protection.
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- Award ID(s):
- 1943598
- NSF-PAR ID:
- 10326685
- Date Published:
- Journal Name:
- Research
- Volume:
- 2022
- ISSN:
- 2639-5274
- Page Range / eLocation ID:
- 1 to 12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Microneedle arrays show many advantages in drug delivery applications due to their convenience and reduced risk of infection. Compared to other microscale manufacturing methods, 3D printing easily overcomes challenges in the fabrication of microneedles with complex geometric shapes and multifunctional performance. However, due to material characteristics and limitations on printing capability, there are still bottlenecks to overcome for 3D printed microneedles to achieve the mechanical performance needed for various clinical applications. The hierarchical structures in limpet teeth, which are extraordinarily strong, result from aligned fibers of mineralized tissue and protein‐based polymer reinforced frameworks. These structures provide design inspiration for mechanically reinforced biomedical microneedles. Here, a bioinspired microneedle array is fabricated using magnetic field‐assisted 3D printing (MF‐3DP). Micro‐bundles of aligned iron oxide nanoparticles (aIOs) are encapsulated by polymer matrix during the printing process. A bioinspired 3D‐printed painless microneedle array is fabricated, and suitability of this microneedle patch for drug delivery during long‐term wear is demonstrated. The results reported here provide insights into how the geometrical morphology of microneedles can be optimized for the painless drug delivery in clinical trials.
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Carbon fiber reinforced polymer (CFRP) composites have been increasingly used in many vehicles such as airplanes, automobiles, and ships due to the advantages of high-strength, high-modulus, lightweight, and corrosion resistance. CFRP structures enhance the vehicle's performance, energy-efficiency, comfort, and safety. However, a common safety concern is how the CFRP materials perform when the vehicle is in fire and if there are enough time to safely evacuate the passengers. The elevated temperature can soften and decompose the polymer matrix, delaminate the CFRP laminate, and burn the CFRP through the contact with oxygen. As a result, the thermal and flammability response of CFRP is important for considering CFRP for vehicle applications; and some specialty high-temperature or flame/smoke/toxicity-proven resins have been investigated for CFRP parts manufacturing due to the needs. In this paper, a novel flame resistant hypothesis of utilizing the unique nano/micro- interlocked fiber reinforcing structure of the long-range carbon nanofiber z-threaded CFRP (ZT-CFRP) composite laminates for improving the flammability performance will be investigated. The carbon nanofibers (CNT) and carbon nanotubes (CNT), which have excellent thermal and mechanical properties, will be dispersed in an epoxy resin and will zig-zag thread through a carbon fiber fabric using an electrical/flow assisted impregnation process to create the unidirectional ZT-CFRP prepregs, respectively, which will be further processed into ZT-CFRP composite laminates. The UL-94 flammability test will be employed to characterize the ZT-CFRP laminates' flammability performance against the control baseline data of the regular CFRP, all without using any flame retardant chemicals. An impressive self-extinguishing flammability characteristic of the CNF based ZT-CFRP samples has been distinctly identified from all the samples. The UL-94 testing results and the effectiveness of using the long-range nanofiber z-threading strategy for enabling the novel nano/microstructure-induced flame resistant and self-extinguishing characteristics will be discussed.more » « less
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Abstract Composites play progressively significant roles across a spectrum of applications involving high‐performance materials and products within industries such as aerospace, naval, automotive, construction, missiles, and defense technology. Notably, oriented fiber composites have garnered substantial attention due to their advantageous attributes like a high strength‐to‐weight ratio and controlled anisotropy. Nonetheless, challenges persist in uneven fiber alignment, fiber clustering within the matrix material, and constraints on fiber volume, impeding the mass production of oriented fiber‐reinforced composites. In this study, we present a novel approach to 3D printing of uniformly aligned short fiber reinforcement in a composite of heavily loaded carbon and nylon. Capitalizing on the additive manufacturing potential of rapidity and precision, the extrusion process induces carbon fiber (CF) alignments in filaments via shear forces. The 3D‐printed structures that were created displayed impressive potential for customization. They consistently demonstrated improved mechanical and thermal properties when compared to the original nylon structures. Our methodology for producing uniformly dispersed and aligned short fiber reinforcement in polymer composites promises to propel the advancement of design and manufacturing for high‐performance composite materials and components.
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Abstract Thermoset elastomers are widely used high‐performance materials due to their thermal stability, chemical resistance, and mechanical properties. However, established casting and molding techniques limit the overall 3D complexity of parts that can be fabricated. Advanced manufacturing methods such as 3D printing have improved design flexibility and reduced development time but have proved challenging using thermally‐cured thermosets due to their viscosity, slow gelation kinetics, and high surface tension. To address this, freeform reversible embedding (FRE) 3D printing extrudes thermosets such as polydimethylsiloxane (PDMS) elastomer within a carbomer support bath, but due to the liquid‐like state of the prepolymer during extrusion has been limited to hollow structures. Here, FRE printing is significantly improved through rheological modification of PDMS with a thixotropic additive (1.0–10.0 wt.%) that imparts a yield stress (30–120 Pa) to help control filament morphology. Further, print process controls consisting of region‐specific slicing, filament retraction, and nonprint travel moves outside of the print to minimize the interaction of the nozzle with previously printed PDMS are implemented. The combined result is the FRE printing of PDMS in complex 3D parts with high fidelity, establishing a 3D printing methodology that can be used broadly with thermally‐cured thermoset elastomers and related polymers.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.34133/2022/9840574
