3D Printing of Periodic Porous Metamaterials for Tunable Electromagnetic Shielding Across Broad Frequencies.

The new-generation electronic components require a balance between electromagnetic interference shielding efficiency and open structure factors such as ventilation and heat dissipation. In addition, realizing the tunable shielding of porous shields over a wide range of wavelengths is even more challenging. In this study, the well-prepared thermoplastic polyurethane/carbon nanotubes composites were used to fabricate the novel periodic porous flexible metamaterials using fused deposition modeling 3D printing. Particularly, the investigation focuses on optimization of pore geometry, size, dislocation configuration and material thickness, thus establishing a clear correlation between structural parameters and shielding property. Both experimental and simulation results have validated the superior shielding performance of hexagon derived honeycomb structure over other designs, and proposed the failure shielding size (Df ≈λ/8 - λ/5) and critical inclined angle (θf ≈43° - 48°), which could be used as new benchmarks for tunable electromagnetic shielding. In addition, the proper regulation of the material thickness could remarkably enhance the maximum shielding capability (85 - 95 dB) and absorption coefficient A (over 0.83). The final innovative design of the porous shielding box also exhibits good shielding effectiveness across a broad frequency range (over 2.4 GHz), opening up novel pathways for individualized and diversified shielding solutions.

SLS 3D Printing To Fabricate Poly(vinyl alcohol)/Hydroxyapatite Bioactive Composite Porous Scaffolds and Their Bone Defect Repair Property.

Poly(vinyl alcohol) (PVA) exhibits a wide range of potential applications in the biomedical field due to its favorable mechanical properties and biocompatibility. However, few studies have been carried out on selective laser sintering (SLS) of PVA due to its poor thermal processability. In this study, in order to impart PVA powder the excellent thermal processability, the molecular complexation technology was performed to destroy the strong hydrogen bonds in PVA and thus significantly reduced the PVA melting point and crystallinity to 190.9 °C and 27.9%, respectively. The modified PVA (MPVA) was then compounded with hydroxyapatite (HA) to prepare PVA/HA composite powders suitable for SLS 3D printing. The final SLS 3D-printed MPVA/HA composite porous scaffolds show high precision and interconnected pores with a porosity as high as 68.3%. The in vitro cell culture experiments revealed that the sintered composite scaffolds could significantly promote the adhesion and proliferation of osteoblasts and facilitate bone regeneration, and the quantitative real-time polymerase chain reaction results further demonstrate that the printed MPVA/20HA scaffold could significantly enhance the expression levels of both early osteogenic-specific marker of alkaline phosphatase stain and runt-related transcription factor 2. Meanwhile, in in vivo experiments, it is encouragingly found that the resultant MPVA/20HA SLS 3D-printed part has an obvious effect on promoting the growth of new bone tissue as well as a better bone regeneration capability. This work could provide a promising strategy for fabrication of PVA scaffolds through SLS 3D printing, exhibiting a great potential for clinical applications in bone tissue engineering.

Combining Solid-State Shear Milling and FFF 3D-Printing Strategy to Fabricate High-Performance Biomimetic Wearable Fish-Scale PVDF-Based Piezoelectric Energy Harvesters.

High-performance flexible piezoelectric polymer-ceramic composites are in high demand for increasing wearable energy-harvesting applications. In this work, a strategy combining solid-state shear milling (S3M) and fused filament fabrication (FFF) 3D-printing technology is proposed for the fabrication of high-performance biomimetic wearable piezoelectric poly(vinylidene fluoride) (PVDF)/tetraphenylphosphonium chloride (TPPC)/barium titanate (BaTiO3) nanocomposite energy harvesters with a biomimetic fish-scale-like metamaterial. The S3M technology could greatly improve the dispersion of BaTiO3 sub-micrometer particles and the interfacial compatibility, resulting in better processability and piezoelectric performance of the nanocomposites. Typically, the FFF 3D printed energy harvester incorporating 30 wt % BaTiO3 showed the highest piezoelectric outputs with an open-circuit voltage of 11.5 V and a short-circuit current of 220 nA. It could hence drive nine green LEDs to work normally. In addition, a 3D-printed biomimetic wearable energy harvester inspired by an environmentally adaptive fish-scale-like metamaterial was further fabricated. The fish-scale-like energy harvester could harvest energy through different deformation motions and successfully recharge a 4.7 µF capacitor by being mounted on a bicycle tire and the tire's rolling. This work not only provides a 3D printing strategy for designing diversified and complex geometric structures but also paves the way for further applications in flexible, wearable, self-powered electromechanical energy harvesters.

A Facile Fabrication of PA12/CNTs Nanocomposites with Enhanced Three-Dimensional Segregated Conductive Networks and Electromagnetic Interference Shielding Property through Selective Laser Sintering.

The material design could be very critical in the preparation of conductive polymer composites for electromagnetic interference (EMI) shielding applications. In this work, two methods were proposed to prepare PA12 composite powders coated with CNTs, including ball-milling (BM) and ultrasonic dispersion-liquid phase deposition strategies. Then, by applying selective laser sintering printing (SLS) 3D printing, the segregated network structures were successfully constructed. Various characterization techniques were employed to validate the presence of the formed segregated network structure in the SLS 3D printed parts. The BM SLS 3D printed part at a loading of 5.66 wt % CNTs exhibited an optimum electrical conductivity of 3.0 S/m and an electromagnetic interference shielding (EMI SE) of 23.9 dB (2.0 mm thickness), while its electrical percolation threshold was found to be at 0.347 wt %. However, the EMI SE values of homogenous PA12/CNTs composites prepared by the melt compounding-cryogenic pulverization (MP) method and melt compounding-compression molding were only 9.8 and 15.6 dB, respectively. In addition, the incorporation of CNTs decreased the mechanical performance of the PA12/CNTs printed part due to their negative effect on the sintering. However, such a decrease could be inhibited by increasing the laser energy density. The related investigation could offer a solution to the preparation of the conductive polymer composite and the EMI shielded material through SLS 3D printing processing.