Page 169 - IJB-9-3

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

Figure 1. Definition: (a) line structure; (b) surface structure; and (c) volume structure.
structure, and the structure obtained by closing surfaces
was called volume structure, as shown in Figure 1.
In 3D-design software (Rhinoceros, McNeel, America
and SolidWorks, Dassault Systemes, French), unit cells
(5 × 5 × 5 mm) which were common in these three kinds
of structure were designed and established by the above
methods, as shown in Figure 2. The shape parameters of
porous structures like volume, porosity, surface area, and
specific surface area of each unit cell were closely related to
their biological performance of structures. The volume and
surface area could be automatically analyzed in Rhinoceros
software, and the porosity and specific surface area could
be calculated as
V − V
p = 0 ×100% (I)
V 0
V
s = (II)
S
Where p is the porosity; s is the specific surface area; V and
0
V are the volumes of the solid initial structure and porous
structure; and S is the surface area of porous structure.
Porosity is the most important parameter of porous
implants, and it is necessary to control other parameters
quantitatively to obtain the porosity required. Fewer
parameters are more conducive to regulate; therefore,
Octet truss (OT), Gyroid (G), and Schwarz P (P) were Figure 2. (a) Octet truss; (b) Diamond; (c) Rhombic; (d) Gyroid;
(e) Double diamond; (f) Schwarz P (surface); (g) Schwarz P (volume);
selected as research objects, where the porosity of OT and (h) Tetrakaidecahedron; and (i) I-WP.
G could be controlled by changing the thickening degree
directly; the original surface of P was defined by implicit realize the change of porosity. In other words, the constant
function (Equation III), and changing the constant C, parameter Φ is the only variable controlling the porosity
3
which represented the isosurface of the function, to of the P structure, and its function was completely same
determine the shape of the surface before closing could as Φ and Φ . Accordingly, by changing the strut size Φ of
1
2
1
control its porosity, as shown in Figure 3. For structures OT, the wall thickness Φ of G, and the constant parameter
2
modeled by implicit function methods, the implicit Φ of P, the unit cells with different porosities could be
3
function equation which controlled the surface structure established.
was composed of function part and constant part. The cos( )cos() cos( )x + y + z + C = 0 (III)
function part determined the shape category of the surface,
and the constant part determined the contour surface of the 2.2. Control design of porous scaffolds
surface. This meant that changing the constant parameter Appropriate shape parameters were selected to establish
without changing the function could realize the purpose of unit cells (5 × 5 × 5 mm) with porosity of 40%, 50%, 60%,
morphological change of the same surface, and the body and 70%. The unit cells were periodically repeated along
structure obtained after the surface was closed could also the X, Y, and Z axes to construct three kinds of porous

Volume 9 Issue 3 (2023) 161 https://doi.org/10.18063/ijb.700