Page 158 - IJB-9-5

International Journal of Bioprinting Guide about the effects of sterilization on 3D-printed materials for medicine

involves the same steps as AU121 but with different ensure high accuracy in the measurement, the specimens
duration: were painted in white color and the reference point markers
(1) Preheating: (“little black dots”) were placed on the specimens to ensure
contrast and accurate references for scanning. In this way,
• Air removal: the air inside the autoclave is removed the digital gauges take the initial pattern where they are
through a vacuum cycle, which helps to improve placed, and the spatial reference on the specimen is even if
steam penetration. This stage lasts for 2–5 min. there is a lot of deformation.
• Steam injection: Steam is injected into the The painting did not affect the results of the tests since
autoclave and the pressure and temperature begin the painting was finished before the test was performed;
to rise. This stage lasts for 5 min. therefore, no chemicals from the paint could influence
the samples. Samples were manually placed on the testing
(2) Holding time: The temperature and pressure are machine, and the tests were performed at 3 mm/min speed
maintained around 134°C and 2.5–3 atm, respectively, for all the materials.
for 4–5 min. This is the time required for the steam to
penetrate and kill any microbial organisms. 2.5. Shore hardness
(3) Depressurization: The pressure inside the autoclave Hardness tests were only performed on soft materials
is reduced back to atmospheric pressure. This step with cylindrical specimens because the hardness of these
lasts for 10 min. materials could vary due to sterilization. The durometer
always produced the highest value when the hardness of
(4) Drying: The items inside the autoclave are dried. rigid materials was being measured. In terms of the Shore
This stage lasts for 15 min. hardness test, the ATSM D2240—Durometer Hardness
The maximum pressure reached is 2.5–3 atm and the method was carried out. For that, the Shore durometer
temperature reached during the cycle is 134°C. type A (Baxlo, Instrumentos de medida y precisión S.L.,
Spain) was used for measuring the hardness of the different
2.4. Tensile testing samples. To obtain more accurate results, a stand arm
The tensile tests were performed for the rigid materials with was used, and a durometer support was designed and
Instron 4507 at the EEBE-UPC (School of Engineering of fabricated. The hardness value was always measured at the
Barcelona East, a UPC facility) using 3D-printed samples same level of the stand arm, and three measurements were
following the ISO 527 type IA. Three control tensile tests taken from each sample.
and three tensile tests for each sterilization process and 2.6. 3D printing accuracy
each material were performed. Deformation measurements For the rigid materials, surface comparison of tensiles
were made by Digital Imaging Correlation (DIC) with the between the different groups (sterilized and control) was
Vic-Gauge 2D/3D software. It uses optimized 2D and performed to analyze the dimensional changes since in
3D correlation algorithms for providing the real-time some tensiles; potential dimensional and geometrical
displacement and deformation data for mechanical testing. deformations were detected once they were subjected to
This can be seen as a set of virtual strain gauges in which sterilization at high temperatures or pressures.
data can be obtained for various points and plotted in live
versus analog load inputs. Then, results were saved for each A CT scan of all tensiles was performed using a 1.5 T
point examined, and complete images stored for analysis in System MR-Philips in HSJD to obtain the 3D digitalized
both Vic-2D and Vic-3D (Figure S1). model of each printed tensile. Once the CT scan was
acquired, the resulting DICOM (Digital Imaging and
Four digital gauges (rosette gauges) were used for the Communications in Medicine) images were segmented to
tests, with varying distances between the gauges according obtain the STL (Standard Tessellation Language) model
to the material deformation, and were placed in the test for each tensile. Using 3-Matic from Materialise®, every
zone of the specimen. To take the images and measure the 3D mesh of each sterilized tensile was aligned to a control
deformation, a Basler camera was used. For that, Fujifilm tensile mesh (Figure 2) and the point cloud were compared
lenses of 50 or 35 mm were used and varied according by a point cloud-based analysis.
to the deformation of the material (because if it deforms The point-based evaluation of the 3D cloud meshes
too much, it comes out of the camera). The samples involved analyzing individual points within the mesh in the x,
were prepared as per the steps in the following: (i) a y, and z coordinates. The following steps outline the process:
visual inspection was made; (ii) with a micrometer, the
measurements of the specimens were taken (see Table S1 (1) Obtain the 3D point cloud mesh data which includes
in Supplementary File); and (iii) to place the gauges and the x, y, and z coordinate values for each point.

Volume 9 Issue 5 (2023) 150 https://doi.org/10.18063/ijb.756