Page 378 - IJB-10-1

International Journal of Bioprinting Design of dual-unit porous scaffold

availability of suitable bone grafts and poor performance cancellous bone involved buffer and nutrients transport.
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compatibility across different bone sites restrict its Thus, the scaffolds with gradient structure can be designed
application. Allogeneic bone transplantation presents by adjusting the porosity along the diameter. Wang et al.
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3,4
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an alternative option but carries inherent risks of immune designed gradient scaffolds using TPMS and found that the
rejection and infection that can lead to implantation gradient porous scaffolds had better mechanical properties
failure. Consequently, researchers have focused on and biocompatibility than the uniform ones. In a previous
5
exploring natural bone substitutes. In recent years, TC4 study, we designed variable gradient porous scaffolds,
(Ti6Al4V) alloy has gained widespread use as a biomedical which exhibited better mechanical properties than the
implant in the field of biomedicine owing to its exceptional uniform gradient ones.
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corrosion resistance, high specific strength, and favorable Previous studies have shown that the gradient structure
biocompatibility. However, the elevated elastic modulus
6–8
of titanium alloy can induce “stress shielding,” resulting can better meet the requirements of orthopedic implants,
in implant loosening or slippage and compromising the and the different units exhibit different mechanical
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effectiveness of bone implantation. Therefore, reducing properties and permeability. Wang et al. prepared the
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the elastic modulus in bone implants is a crucial part of the TC4 porous scaffold with TPMS structure by selective
ongoing research. laser melting (SLM) and found that the primitive (P)
structure exhibits better mechanical properties compared
The medical porous scaffold is viewed as an ideal with other TPMS units. Ma et al. and Yánez et al. found
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material for orthopedic applications, given its great that gyroid (G) unit has better permeability, which can
potential in the field of orthopedic implants. 10–12 On the promote cell growth. Therefore, it can be deduced that the
one hand, the existence of porous structure can decrease gradient porous scaffold designed by combining the two
the elastic modulus of the scaffold, thus reducing the “stress units can give full play to the performance advantages of
shielding” problem caused by obvious different elastic different units. However, due to the different structure of
modulus between bone and metal material. On the other various units, the scaffolds with a combination of different
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hand, the porous structure has a good permeability, which units can form an interface mutation, which can affect the
is conducive to the transport of nutrients. By adjusting performance of the scaffolds. If the interface is controlled
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the pore size and porosity, porous scaffolds with low elastic by the mathematical model to form a continuous transition
modulus, equivalent to that of human bone, and good interface, the advantages of the two-unit structures
permeability can be obtained. 15,16 can be maximized. Furthermore, the performance of
Numerous studies working on the design of medical the composite structure scaffold can be enhanced by
porous scaffolds have been conducted. 17–19 In the realm adjusting the porosity, element size, and internal structure
of structure units design, computer-aided design (CAD) radius through parametric control. This approach allows
method, micro-computed tomography (micro-CT) for the optimization of the scaffold’s characteristics to
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method, Voronoi method, 22,23 etc. have gradually been achieve superior performance in biomedical applications.
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developed. However, the porous scaffolds designed by the However, to the best of our knowledge, the study on multi-
above methods are often presented with limitations, such unit continuous transition connection of different units
as stress concentration, low strength, and uncontrollable has never been reported.
performance. 24,25 Given their smooth surfaces, highly Therefore, a novel gradient porous scaffold with dual-
interconnected porous structures, large specific surface unit continuous transition was designed and successfully
area, and mathematically controllable geometric fabricated using SLM technology, as illustrated in Figure
properties, 26–28 triply period minimal surfaces (TPMS) 1. The structures and mechanical properties of the
are known as an excellent solution for the preparation of porous scaffolds were comprehensively investigated using
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porous scaffolds in recent years. Zhao et al. employed scanning electron microscope (SEM), micro-CT scanning,
TPMS to fabricate a body-centered cubic (BCC) lattice compression testing, and ANSYS finite element simulation.
structure and conducted compression experiments on This work presents a new concept for the design of medical
both TPMS-based and CAD-based BCC lattice structures. porous scaffolds.
The experimental findings revealed that compared with
the CAD-based lattice structure, the TPMS-based lattice 2. Materials and methods
structure exhibited superior mechanical properties,
despite having the same porosity. It has been reported 2.1. Design of the porous scaffolds
that a new, real human bone-inspired porous scaffold The function expressions of the three TPMS units, i.e.,
with a gradient structure was developed, with the external primitive (P), diamond (D), and gyroid (G), are shown
dense bone primarily bearing the load and the internal in Table 1, where a is the constant coefficient related to
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Volume 10 Issue 1 (2024) 370 https://doi.org/10.36922/ijb.1263