Page 426 - IJB-9-3

International Journal of Bioprinting 3DP PILF cage for osteoporotic

A geometric size. Conversely, our CS-type cage is likely to
be standardized and defined as the worst cage (usually the
smallest cage) to perform the mechanical tests required by
the FDA.
In general, STO can only calculate the structural
optimization under a single load. However, WTO needed
to be applied in this study to solve multi-directional spine
load conditions in daily life. The WTO is represented by
values between 0 and 1 for each condition, corresponding
with proportions of different load conditions. In the
present study, 21.5% for flexion and extension, 33% for
bending, and 24% for axial rotation correspond to values
of 0.215, 0.33, and 0.24 of weight coefficient for each
element, respectively [20,21] . Therefore, our designed cage
B structure (gray mesh found in Figure 2) was calculated by
multiplying the respective weight coefficients of different
loads to the corresponding STO result (Figure 2). This
kind of protocol using WTO considering different load
percentages can also be a new mode for designing other
cages, such as anterior lumbar interbody fusion (ALIF)
and transforaminal lumbar interbody fusion (TLIF).
The combination of internal cavity lattice design
in the cage structure has been proven to increase
the ingrowth capability of bone cells with strong
stabilization. However, there are many lattice design
parameters, such as porosity, pore size, and unit size,
that still cannot be confirmed to integrate with implant
design [9-13] . At present, we only considered the spiral
Figure 8. The CS-type cage fracture pattern after in vitro test: (A) ISO lattice provided by the CAD software. Other lattice
view and (B) back view.
design parameters can be further considered in the
future. However, the complex contour surface combined
the posterior side under extension, and at the lateral side with the internal cage cavity lattice design cannot be
under bending and torsion. manufactured by traditional mechanical cutting. Three-

This study screened elderly osteoporosis patients to dimensional printing techniques are well established for
obtain the endplate curved surface characteristics, which building complex 3D constructions from CAD models.
are more in line with the fit of the general population 3D printing techniques have great potential to solve the
of osteoporosis patients for the cage and the endplate. problems of creating a porous (lattice) surface coating
Although the curved surface design of our CS-type cage on dense titanium and porous titanium body [9-13] .
may not be able to achieve 100% endplate-conformation for Therefore, this study utilized metal 3D printing to
each patient, that is, patient-specific endplate morphology fabricate our designed CS-type cage to perform the
can match compatibility. However, a CS-type cage with following functional tests. Our 3D printer laboratory
enhanced load-bearing surfaces can be applied in clinical was approved by ISO13485 quality management system
practice for design and manufacture purposes. The cage (Certificate Number: 1760.190828) to ensure that
complex surface can be manufactured using traditional implants manufactured by 3D printing can provide a
machining or 3D printing fabrication if the internal lattice practical foundation to meet the regulations as well as
design is not considered. According to the Food and Drug demonstrate a commitment to safety and quality.
Administration (FDA) regulations, a spine cage must pass Although the current in vitro mechanical experiment
5 million fatigue functional tests, such as compression, in this study only considers the static state, the results
compression-shear, and torsion, before it can be marketed. found that the yielding load and stiffness under all load
A patient-specific design is unlikely to perform relevant conditions were much higher than the recommended ISO
mechanical tests alone due to excessive variation in the 23089 values . This document specifies requirements
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Volume 9 Issue 3 (2023) 418 https://doi.org/10.18063/ijb.697