Page 191 - IJB-9-6

International Journal of Bioprinting 3D-printed assembly anatomical patella fracture bone plate

Table 5. Results of variation in the fractured gap distances at the medial/lateral sides before and after dynamic tests and corresponding
maximum forces
Fixation Sample Medial side (mm) Lateral side (mm) Maximum force (N)
TBW #1 2.05 2.26 320
#2 3.4 2.81 427.25
#3 2.16 2.24 292.5
#4 2.13 2.06 330
#5 2.17 2.11 318.15
Mean ± Std 2.38 ± 0.57 2.30 ± 0.30 337.58 ± 52.00
AATBP #1 0.03 0.1 262.25
#2 0.02 0.02 271.25
#3 0.03 0.08 238.13
#4 0.03 0.04 242.13
#5 0.04 0.05 260.52
Mean ± Std 0.03 ± 0.01 0.06 ± 0.03 254.86 ± 14.12

The titanium alloy bone plate with ductile material properties The most important issue in AATBP 3D printing is that
can be bent during the surgical process when the plate is the assembly tightness error of the two thin bone plates
manufactured using a traditional cutting method. However, at the proximal and distal ends must be minimized. The
the bone plate is no longer bendable and exhibits brittleness ratchet manufacturing must be sufficiently accurate to allow
when the manufactured process is changed to 3D printing. assembly surface flatness control within the unsuitable skin
The design accuracy for the curved surface becomes more touch feeling range. The maximum value for the average
important. The AATBP anatomical anterior surface was tightness error for two thin bone plate assemblies was
obtained by capturing the Sawbone patella surface, and it only 0.34 mm when produced by our metal 3D printing
was confirmed that this bone plate surface shape design is machine, with values of 30 μm for both the manufacturing
feasible since the largest gap distance between the AATBP accuracy and the layer thickness. This value cannot be
and the normal patella surface is only 0.91 mm. perceived through the touch with hand and is also less than
the total thickness of 1.6 mm for the AATBP. This implies
Since there is no comparable fixation bone plate
mechanical strength for patella fractures, the proof load that a similar assembly bone plate design can be fabricated
when the manufacturing accuracy requirement for the
and bending strength of the commercial dorsal fixation metal 3D printing machine is less than 30 μm.
bone plate for distal radius fracture obtained using the same
testing method according to ASTM F382 were selected as Commercial locking and compressive bone screws
the comparable index to identify the mechanical capability were selected to match our AATBP because bone screws
of our AATBP. The proof load and bending strength were did not need to be manufactured by 3D printing. This is
47.36 ± 5.36 N and 1183 ± 134 N·mm obtained from the beneficial for reducing manufacturing cost, time, and
[21]
literature . Since the center span (a) and the loading span accuracy requirements. In the traditional manufacturing
distance (h) of these two bone plate tests were different, process, the required accuracy for bone screws can be
bending strength was only compared, and we found that 0.02 mm, with relatively good ductility and suitability for a
there was no significant difference between the radius large allowable rotation angle for bone insertion. However,
dorsal fixation plate and the AATBP. This implied that the 3D printing manufacturing process usually confers
the mechanical strength of the AATBP developed in this a tendency for the material to be brittle and not suitable
study met the clinical needs. For the surface roughness for bone screw manufacturing when no special post-
compression, the average surface roughness of an oblique processing is performed. We therefore only tapped threads
lumbar interbody fusion cage used in this study was 9.143 µm, or drilled holes into our AATBP using five-axis machining
which is from literature . This value was about 1.92 for the corresponding bone screw insertion.
[22]
times (9.143 µm/4.74 µm) the AATBP average roughness
measured [(4.42 + 5.59 + 5.39 + 3.56)/4 = 4.74 µm] in Fifteen-kilogram downward weights were applied on
this study. This phenomenon also showed that the surface the dynamic cyclic loads because a volatility in force was
roughness of the components manufactured by 3D printing found at the critical value in the force–displacement curve
fell within a reasonable range. during the static test for TBW fixation. This implied that

Volume 9 Issue 6 (2023) 183 https://doi.org/10.36922/ijb.0117