Page 168 - IJB-9-3

International Journal of Bioprinting Flow performance of porous implants with different geometry

realize precise control of characteristic parameters, and is another method commonly used in porous implants
achieve personalized customization of complex structures design . Starting from the predefined block geometry
[23]
in practical applications . Controllable pore size, structure, this method gradually removes the volume and
[3]
distribution, and shape can bring stable mechanical and increases the porosity while ensuring the required physical
biological properties to porous implants, which is of great properties, and find the most efficient mass distribution
significance for their clinical application [4,5] . mode . However, the physical and biological properties
[24]
In addition to providing appropriate mechanical of the strut structure, TPMS structure, and block structure
strength and avoiding stress shielding in terms of used in the three design methods above have not been
mechanical properties , ideal porous implants should compared yet. In clinical practice, how to select the
[6]
also have the ability to promote cell adhesion, migration, appropriate type of structure for a specific environment,
proliferation, and differentiation and to induce tissue rather than being limited to a specific single shape of
regeneration in terms of biological properties , which structure, is still not clear.
[7]
are closely related to the physical parameters of porous Generally, in methods for evaluating the biological
structures . As the most important parameter of porous properties of bone implants, in vitro cell cultures, in vivo
[8]
structure, the change of porosity will affect all the shape animal experiments, and in vivo clinical trials are more
parameters of the structure, which is directly reflected in accurate in assessing biological performance to some
the change of physical properties like permeability and extent, but longer time and more investments are required
wall shear stress, and indirectly change the biological to carry out sufficient number of repeated experiments in
properties of the implant ultimately . For example, pore these methods. In addition, the evaluation results will be
[9]
size, influenced by porosity, has an effect on the process affected by a variety of factors, which are difficult to be
of tissue formation. The minimum pore size required for adjusted by the methods listed above. Comparatively, the
bone regeneration is more than 100–400 μm . Under numerical analysis based on computational fluid dynamics
[10]
the condition of hypoxia, an aperture of about 100 μm is (CFD) is a fast and low-cost method, which provides
conducive to cartilage formation, and an aperture greater precise control for varying factors . The CFD method
[25]
than 300 μm is conducive to osteogenesis . Mechanical not only researches the situation of fluid flow through
[11]
stimuli, such as fluid shear stress, can bring about different the scaffold and the interaction between the fluid and the
mechanical signals contributing to cell differentiation [12-14] . scaffold , but also in turn provides the data to optimize
[26]
Shear stress at 0.05–25 mPa had a positive effect on in vitro the structure. Many studies have confirmed that CFD is
cell culture . In addition, in the in vitro perfusion culture, a reliable method for evaluating flow fluid and biological
[15]
permeability reflects the ability of scaffold in nutrition, property [27,28] .
waste transport, and cell migration, which translate into In summary, based on the three design methods and
favorable conditions for cell growth [16,17] . Although there corresponding to the strut structure, TPMS structure and
is no consistent quantitative relationship between different block structure, this study designed and established three
physical properties and biological properties of implants, it types of unit cells with line structure, surface structure, and
is undeniable that the change of physical properties caused volume structure, and selected one unit of each structure
by the change of porosity is an important factor that cannot to establish implant scaffolds with different porosity (40%,
be ignored in the design of ideal porous implants.
50%, 60%, and 70%). The CFD method was used to simulate
Computer-aided design (CAD) method is the most the physical properties of different scaffolds in Dulbecco’s
popular method for designing porous implants because of modified Eagle’s medium (DMEM) under different
its intuitiveness, high modifiability, and controllability . porosity conditions, such as flow velocity, permeability,
[18]
The strut structure obtained by CAD can easily control and wall shear stress, and the results were compared and
the characteristic parameters of porous implant (pore evaluated to predict the biological properties of different
size, porosity, volume, surface area, etc.) to get the ideal scaffolds.
structure . Recently, surface modeling method, controlled
[19]
by the implicit function, is also used in the design of porous 2. Methods
implants . Triply periodic minimal surface (TPMS)
[20]
structure generated by this method is determined by the 2.1. Definition
implicit function expression so that the change of function Due to the complexity of bone tissue structure, it was
parameters can be easily adjusted with the pore size and necessary to define the line structure, surface structure,
porosity, and the characteristic of its high connectivity and volume structure first. The structure obtained by
and surface smooth can provide a suitable environment thickening lines was called line structure, the structure
for cell growth [21,22] . Topology optimization design method obtained by thickening surfaces was called surface

Volume 9 Issue 3 (2023) 160 https://doi.org/10.18063/ijb.700