Page 49 - IJB-9-6

International Journal of Bioprinting Sub-regional design of the bionic bone scaffolds

1. Introduction Topology optimization is the most classic method of
mechanical optimization. According to the mechanical
With the acceleration of population aging and the frequent conditions and the optimization objectives, researchers
occurrence of traffic accidents, bone defect has become can obtain the optimal configuration of the internal
a hot issue in the field of bone tissue engineering. Since structure of the model through iterative calculation of
the self-healing cycle of natural bone takes a long time finite element analysis, and they can achieve the optimal
and its reconstruction ability is limited, appropriate distribution of materials with respect to the targeted
[1]
artificial implants have become the primary choice . performance [21,22] . Many studies believe that FGPMs and
Porous scaffold is the most common form of artificial topology optimization methods are highly unified in
implants. The introduction of porous features can reduce nature [23,24] , and that the latter can be used as the basis
the apparent elastic modulus of artificial implants to a for FGPMs design [25,26] . For example, Alzahrani et al.
level close to that of a natural bone, yielding to reduces the proposed a relative density mapping (RDM) method,
phenomenon of stress shielding [2,3] . With the development which introduced the topology optimization method into
of additive manufacturing technology, it is quite mature the lattice structure design . In addition, Zhao et al. used
[27]
to realize the direct manufacturing of ultra-high precision the local relative density mapping method to generate the
porous scaffolds [4,5] . In order to unify the mechanical and corresponding two-dimensional cellular porous structure
biological properties of implants, Ti-6Al-4V scaffolds, according to the optimized solid isotropic material with
fabricated by the laser powder bed fusion (LPBF) process, penalization (SIMP) continuum topology optimization
are one of the common artificial prostheses [6-9] .
results with variable density . Wang et al. carried out
[28]
Human bone has a natural graded-pore distribution, concurrent design of hierarchical structures for regular
allowing it to realize special functions at different gradient porous structures according to the results of continuum
positions [10,11] . In the clinical environment, the porous topology optimization . Radman et al. optimized the
[29]
scaffolds from previous studies cannot simulate the graded topology of the porous structure with regular basic
distribution of natural bone, leading to a mismatch in elastic structure units, which showed the characteristic of graded
modulus with the surrounding bone after implantation [12,13] ; distribution of density . It was found that the FGPMs
[26]
therefore, it will be losing the mechanical stability and the design, using topology optimization information, targets
positive stress stimulation to primary bone tissue . These mainly the two-dimensional regular porous structures
[14]
losses will lead to osteoporosis and even atrophy, ending or the three-dimensional (3D) structures with repeated
up with a failure to implant because of the looseness at the simple basic structural units. Introducing the topology
interface . In order to simulate the graded distribution of optimization into the bionic bone scaffolds design field
[15]
a natural bone, an increasing number of researchers turn has broad prospects. In engineering applications, the bi-
their attention to functionally graded porous materials directional evolutionary structural optimization (BESO) is
(FGPMs) [16,17] . In bone tissue engineering, FGPMs mimic widely used as a common topology optimization method.
the gradient of the bone by controlling the nucleating The simultaneous deletion and growth of materials reflects
points distribution of the porous scaffolds, or by setting the bidirectional nature of the BESO method, which
the graded porosity . Therefore, FGPMs have a more greatly ensures the geometric and mechanical continuity of
[18]
complex internal structure, which also puts forward higher the topology optimization continuum. BESO reduces the
requirements for researchers. In previous studies, Wang maximum stress inside the structure to the greatest extent,
et al. designed a Voronoi porous scaffold with graded providing a highly accurate solution for optimizing the
distribution in the z-axis direction, which lacked clear stress distribution inside the structure [30-32] . In addition, the
graded distribution standard . Deering et al. generated results of BESO can show the main load-bearing area and
[12]
an anisotropic Voronoi porous implant by dividing the the force transfer path inside the macroscopic model [33,34] .
plane unevenly along the z-axis direction, which was too It is a pioneering and a reasonable attempt to take the
subjective to reflect the graded distribution of natural BESO information as the design basis of the bionic bone
bone . In addition, Liu et al. established an elasticity- scaffolds, and to show how to establish the relationship
[19]
to-density mapping model, and generated FGPMs based between the topology optimization design and the porous
on the Voronoi tessellation, which relied on the intensive structure design. This will present the main challenge in
division of a finite element mesh, resulting in a huge this work.
amount of data . From the above studies, it is clear that
[20]
there are still many limitations in the current research and In our previous studies, a parametric design method of
the designs of FGPMs. In addition, there are few studies on the porous scaffolds based on the Voronoi tessellation was
controllable and graded design of the bionic bone scaffolds, proposed, and the mechanical and biological properties
and many pivotal problems still remain unsolved. were fully discussed [12,13,35,36] . Regrettably, however, our

Volume 9 Issue 6 (2023) 41 https://doi.org/10.36922/ijb.0222