Page 423 - IJB-9-6

International Journal of Bioprinting Versatile pomelo peel-inspired structures

honeycomb structure imitating pomelo peel, whose W s displayed in Figure 1A, where the thickness of the pomelo
and equivalent plateau stress were notably higher than peel was about 20 mm. The micro-CT image of pomelo peel
the traditional honeycomb structure. Zhang et al. displays the stochastically porous structure characteristics
[33]
investigated the heat dissipation performance and (Figure 1B). The SEM image of pomelo peel from exocarp
mechanical properties of pomelo peel-inspired structures. to endocarp shows that the cavity size of the microstructure
However, the designed structural cell in the study was a from outside to inside gradually increased (Figure 1C),
regular Kelvin cell, which did not express the stochastically revealing the natural gradient structure characteristics
porous structure and gradient characteristics of pomelo of pomelo peel. The BPPS was designed based on the
peel. The heat dissipation performance was inevitably morphology and microstructure observed in the pomelo
affected by the unsmooth transition between cells. Besides, peel (Figure 2A). Precise control of the BPPS structure
for the low tortuosity of the flow paths in the traditional modeling was achieved by using Grasshopper software.
regular lattice structure, the interaction between the fluid The specific design tools (battery) in the Grasshopper
and the flow paths during heat dissipation is reduced. software mainly included “Populate 3D,” “Voronoi
This resulted in some fluid passing directly through 3D,” “Chromodoris,” etc. A 3D Voronoi wireframe was
the flow paths, leading to a significant decline in heat constructed with 70 randomly-distributed seed points,
transfer performance . Yang et al. conducted lattice exhibiting excellent similarity to the stochastically porous
[34]
[35]
structures composed of simple cubic cells with various structure of pomelo peel. The numerical parameters of
gradient characteristics, showing that the best mechanical gradient characteristics in the different VFs BPPSs were set
properties can be obtained if the structural gradient as the specified range (Figure 2F). The linear relationship
characteristics were consistent with those of pomelo peel. of the gradient parameters variation in a given numerical
The research further optimized the pomelo peel-inspired range was established by the distance between each
structure design and demonstrated the latent capability structural feature and the reference plane. The structure
of pomelo peel gradient characteristics in mechanical was precisely controlled at 12 × 12 × 12 mm³ by using the
properties, but there is still a gap between the designed Boolean operation tool. The obvious gradient structure
simple cubic lattice structure and the stochastically porous characteristics of BPPS-40% could be seen through the
structure of pomelo peel. Therefore, there is a possibility for comparison of the top surface (Figure 2B) and bottom
further improvement in the design of pomelo peel-inspired surface (Figure 2C) of BPPS. Figure 2D and E shows
structures. In order to satisfy multifunctional requirements, the longitudinal sections at a-a and b-b in Figure 2A,
a high-fidelity bio-inspired design and processing approach respectively, exhibiting the structural characteristics of the
were implemented based on the stochastically porous stochastic distribution. In order to investigate the influence
structure and gradient characteristics of pomelo peel. of structural parameters on mechanical properties and

In this study, the morphology and microstructure of heat dissipation performance, the VF was set as a structural
the pomelo peel structure were investigated by micro- variable (Figure 2F). BPPSs with four different VFs of 45%,
computed tomography (micro-CT) and scanning electron 40%, 35%, and 30% were designed based on the model of
microscopy (SEM). A high-fidelity biomimetic pomelo peel pomelo peel reconstructed by micro-CT scanning data.
structure (BPPS) was designed and processed using LPBF The different VFs in BPPSs were achieved through the
with Al-Mg-Sc-Zr alloy powder. The structural formability manipulation of rod diameters, leading to alterations in
and microstructure were analyzed, and the influence of the porosity and topological structure. The variation of
volume fraction (VF) on structural mechanical properties, BPPSs porosity along the gradient direction is presented
energy absorption performance, and deformation modes in Table 1.
was investigated by compression test and finite element
analysis (FEA). Additionally, the influence of the VF on 2.2. Materials and LPBF process
heat dissipation performance was investigated through The gas-atomized Al-4.2Mg-0.4Sc-0.2Zr alloy powder with
FEA, and the heat dissipation performance of the BPPSs an average particle size of 26.7 μm, which was primarily
and the traditional fin structure was compared. The regular spherical (Figure 3A), was applied in this study. In
lightweight multifunctional design and performance order to enhance the forming quality of the structure, the
control of the BPPS were achieved. powder was treated in a vacuum drying oven for 10 h and
maintained at a temperature of 120°C before LPBF process.
2. Materials and methods The LPBF equipment system developed by Nanjing
University of Aeronautics and Astronautics, mainly
2.1. Configuration of BPPS composed of a YLR-500 ytterbium fiber laser (Burbach,
Figure 1 shows the structure characteristic of the pomelo Germany), an automatic powder laying device, a gas
peel. A longitudinal section of the complete pomelo is circulation system, and a computer-aided control system,

Volume 9 Issue 6 (2023) 415 https://doi.org/10.36922/ijb.1011