Page 377 - IJB-10-2

International Journal of Bioprinting AM evaluation of medical device companies

For a complete quality assessment of a pelvic implant microscope was used to observe the polished surface of
production, further analyses should be included, such as each sample with several magnifications. These images
porous structures, biocompatibility, adequate cleaning, were obtained in similar light conditions and were
and mechanical testing. In the current study, as a first step, binarized with the same threshold.
we focused on geometrical accuracy and microstructural
integrity of the parts to identify the best 3D printing 2.4.4. Communication
practices in the industry. A fluent communication between the implant designer
and the manufacturer is crucial to develop defect-free AM
2.4.1. Visual inspection parts. This communication was encouraged during all
The main aspects evaluated were: (i) macro geometrical the stages of the study. The feedback from manufacturers
deviations: the prototypes were assembled to a polylactic assessing the feasibility of fabricating the proposed pelvic
anatomical model of the pelvic bone manufactured design with their manufacturing capacities was expected.
by fused deposition modeling, assessing their fit; this When companies proposed modifications to optimize the
included an evaluation of the integrity of the lattice design, to adapt it to their AM machines and processes,
structures. Furthermore, a “pass” or “not pass” check their feedback was considered if such amendments would
was performed for the screw holes in the prototypes with not compromise implant function.
real cortical screws of various sizes; (ii) the prototypes
were produced following the specifications agreed before 3. Results
manufacturing; and (iii) the presence of residues from
support material or powder that could reveal improper 3.1. Prototypes manufactured
postprocessing and cleaning. The eight prototypes manufactured by the seven companies
are displayed in Figure 2. C2 manufactured two prototypes,
2.4.2. Geometrical precision analysis P2 with mirror finish and P6 with matte finish.
The prototypes manufactured were CT scanned with a
Nikon XT H 225 scanner (Nikon, Tokyo, Japan) to obtain The correspondence between the companies (C) that
their digital geometry. The following parameters were used: manufacture each of the prototypes (P) is presented in
150 kVp, 350 µA, 2.5 mm Cu filtration, and 40 µm voxel Table 2.
size. An automatic registration was performed between 3.2. Prototypes analysis and quality assessment
the scanned digital geometries and the CAD design files
for each implant for comparison. Geometrical deviations 3.2.1. Visual inspection
were mapped and quantified with our own metrical The visual inspection showed important irregularities in
module developed with 3D Slicer software, identifying five out of the eight prototypes received. The main defects
nonconformities over the 0.2 mm permitted tolerance. The identified are described in Table 3 and displayed in Figure 3.
potential consequences these variations could have caused
in surgery were explored. 3.2.2. Geometrical precision analysis
All the prototypes showed values of geometrical deviations
2.4.3. Microstructural analysis over the 0.2 mm of tolerance permitted. However, some
Eight samples were extracted from the longest extracortical deviations were critical, and others could be ignored. The
plate (flange) of the eight implant prototypes so that the maximum deviation for P4, P5, and P6 was presented in
surfaces for analysis were parallel to the building platform very small and localized areas of lattice structures, and
for each sample. The specimens were cut with an abrasive therefore, such deviations could be neglected with no
wheel, mechanically ground, polished with colloidal clinical consequences. The mean deviations for these
suspension, and etched with Kroll’s reagent. Microstructures prototypes P4, P5, and P6 were 0.14 mm, 0.15 mm,
were analyzed using a Zeiss Axio Scope A1 multi-faceted and 0.14 mm, respectively, therefore within the 0.2 mm
polarized light microscope (Zeiss Industrial Metrology, allowed. On the other hand, the rest of prototypes P1,
Oberkochen, Germany) at different stages: after polishing, P2, P3, P7, and P8 presented large maximum deviations
to study the presence of defects at the periphery as well of 3.00, 2.53, 4.94, 4.88, and 3.60 mm, respectively,
as in the central area of the samples; and after etching, to that could have potentially compromised implant
identify the material phases of this alpha-beta alloy and the performance. 15,22,23 The most recurrent issue was the
microstructural grain morphology. inadequate fabrication of large areas of L2. Furthermore,
Voids were analyzed by micrographic observation. for P2, P3, and P7, the mean deviation was also over 0.2
For each sample, one of the side surfaces was ground mm, and these prototypes also presented some deviations
and polished, but not etched. Then, the metallographic in the extracortical plates. The qualitative and quantitative

Volume 10 Issue 2 (2024) 369 doi: 10.36922/ijb.0140