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International Journal of Bioprinting Versatile pomelo peel-inspired structures

structures of natural organisms [1,2] . After the long and a multi-material three-dimensional (3D) printer . The
[21]
harsh natural selection, the complex structures of research findings indicated that the gradient characteristic
organisms have been optimized for multiple purposes resulted in a decrease in damage compared to samples
and to adapt to the constraints imposed by the external with a uniform tubule distribution, highlighting the
environment . Mimicking the strategies used by natural significant potential of bionic gradient structures as
[3]
species is a promising way to obtain sophisticated bionic effective design elements. Moreover, the presence of
structures with the same exceptional performance [4,5] . a composition gradient zone at the multi-material
However, traditional manufacturing methods face several interface can contribute to a strong metallurgical bonding
limitations, including long manufacturing cycles, low between dissimilar materials , potentially modifying
[23]
forming accuracy, and difficulty in integrated processing, the mechanical properties. Another example is the quills
which hinder the development of bio-inspired structures . covering porcupine that can protect it from aggressors
[6]
In contrast, additive manufacturing (AM) technologies are and poke opponents due to their excellent hardness and
ideally applicable to fabricating these bionic structures rigidity. Drawing inspiration from the core-shell (C-S)
due to their layer-by-layer deposition manner [7-11] . Among structure of porcupine quills, a new lightweight and stiff
various AM technologies, laser powder bed fusion (LPBF) C-S architecture, which consists of a syntactic epoxy
has gained popularity for the processing of small- and foam core surrounded by a stiff carbon fiber-reinforced
medium-sized complex structures [12,13] . The key advantage epoxy composite shell, was fabricated using direct ink
of LPBF lies in fine resolution and good surface quality writing . The structural hierarchy of the bionic structure
[22]
of the fabricated products, rendering it particularly was consistent with that of porcupine quills, allowing for
well suited for printing these complex structures with the achievement of both lightweight and high specific
complicated details. Consequently, LPBF has become flexural stiffness. The potential of developing versatile
widely applied to the fabrication of complex metal and high-performance bionic structures was shown in
biomimetic structures [14-17] . the above research. However, there are shortcomings in

Multifunctional and high-performance bionic these regularly distributed structures, which do not fully
structures processed by AM technology have received express all the characteristics of stochastically distributed
much attention in recent years. Natural organisms with biological materials. Additionally, in contrast to structures
excellent performance and unique structures, such as with random distribution, it is challenging to achieve
[24]
the Norway spruce [18,19] , cuttlebone , horse hoof wall , smooth transitions between regular unit cells , which
[20]
[21]
and porcupine quills , have been a source of inspiration can reduce performance (e.g., heat dissipation and
[22]
for the construction of regular biomimetic structures. permeability) by impeding fluid flow. A random bone-
Inspired by Norway spruce, which can withstand strong inspired structure exhibited great mechanical properties,
winds in severe cold, Lin et al. and Hu et al. developed as well as properties related to cell penetration, nutrient
[18]
[19]
a series of integral multifunctional structures with four diffusion, and biodegradation, that are similar to all the
[25]
[26]
gradient hollow tubes. The results indicated that the characteristics of natural bone . Ge et al. found that
gradient structure, with the minimum tube size in the the compression strength and energy absorption capacity
center, exhibited the highest specific absorption energy of stochastic trabecular-inspired structures were superior
and the lowest effective thermal conductivity due to the to regular triply periodic minimal surface structures at
[27]
common influence of gradient characteristics and hollow the same porosity. Tee et al. further investigated the
tubes. Based on the cuttlebone, which enables the cuttle structure and performance of the porcupine quill and
to survive in the high-pressure environment of the deep constructed a randomly porous structure with excellent
sea, Yang et al. developed a cuttlebone-like lattice mechanical properties, revealing that the strut connectivity
[20]
(CLL). The mechanical properties of the graded/uniform and the uniformity of stress distribution are proportional
CLL structures were compared with those of the graded/ to the number of struts. Despite these advancements,
uniform body-centered-cubic (BCC) lattice. The study more research is needed to study stochastic biomimetic
revealed that the CLL demonstrated superior compressive structures, particularly those with gradient characteristics.
mechanical properties compared to the BCC, while the The pomelo peel structure has attracted much interest
graded CLL exhibited the highest energy absorption owing to its potential for both excellent thermal [28,29] and
capacity among the investigated structures. The horse hoof mechanical [30,31] applications. Zhang et al. developed a
[29]
wall possesses exceptional impact resistance and fracture biomaterial with exceptional heat exchange performance
control capabilities attributed to its gradient configurations, based on the high specific surface area of pomelo peel.
tubular structures, and lamellar structures. Inspired by Inspired by the distinguished mechanical properties
these structures, a bionic design was implemented using of pomelo peel, Zhang et al. designed a hierarchical
[32]

Volume 9 Issue 6 (2023) 414 https://doi.org/10.36922/ijb.1011