Page 472 - IJB-10-5

International Journal of Bioprinting 3D-printed post-otoplasty ear retainer

of 0.2–0.3 m. Subsequently, the data was automatically cover for the retainer to ensure proper alignment. The
imported and manually processed in the software. The cover is connected to the outer shell (protective shell) using
point-clouds data were aligned and fused to construct a a fixture. Both the positioning cover and outer shell were
3D digital model of the ear. The digital model was then printed using BioMed Clear Resin (Formlabs, USA). The
refined with data smoothing and defect repairing. Excess restriction band was then tied around the patient’s head to
points that were not functional in subsequent processes apply external pressure on the protective shell, effectively
were removed to reduce the computational load. The final preventing movement. This device helps maintain the
3D scan was rendered by the software algorithm. The correct shape of the ear, ensuring the effectiveness of the
geometric model of the human ear structure obtained corrective surgery.
from 3D reconstruction is relatively rough, represented
as a triangular mesh model. It may exhibit structural 2.3. 3D printing of post-otoplasty morphology
issues such as deformations, distortions, and overly rough retainer and relative constructs
surfaces. The human ear (in standard tessellation language The design of the maintainer was exported as an STL file
[STL] file format) was imported into Geomagic Studio and imported into PreForm software (3.21.0; Formlabs,
2014 (Raindrop Company, United States of America USA). All prints were manufactured using a Form3B+
[USA]), where it undergoes surface fitting and smoothing printer (Formlabs, USA) with a resin having a Shore
processes. Through processes like precise surfacing, hardnesses of 80 A (BioMed Flex 80A Resin; Formlabs,
additional structures such as ear retainers and 3D-printed USA). The orientation, supportive material, and layout
hard shells are integrated. Finally, the finite element model were automatically generated by the software. After
of the ear retainer was assembled and exported (in STL file printing, the part was removed from the platform using
format) as a reference model. a scrapping tool and subjected to post-processing. The
parts were immersed in 99% isopropyl alcohol (IPA) for
2.2. Design of the retainer based on the 3D scanning 20 min, removed by gentle pulling, and washed again for
Corrective surgery for ear malformation and its 10 min. After washing, the parts were dried fully for 1 h at
morphological changes are closely related to the anatomical ambient temperature. The dry parts were then placed in
structures of the auricle (Figure 1A). A typical case of a glass beaker and submerged in water to polymerize the
constricted ear deformity (cup ear) with mild resurgence parts for 30 min at 70° in a UV-polymerization unit (Form
one year after surgery is displayed in Figure 1B–D. Cure; Formlabs, USA), according to the manufacturer’s
The digital model was designed using Rhinoceros instructions. After the water had reduced to room
(McNeel Europe, Spain). Based on the largest percentile of temperature, the parts were dried with a paper towel. No
human ear dimensions, the main part of the retainer was additional post-processing procedures were performed.
designed with dimensions of 65 × 40 mm. The scanned 2.4. Mechanical tests
digital model of the ear was placed within this range, and To compare the mechanical properties of two biocompatible
the ear and surrounding areas were trimmed. Along the resins, BioMed Flex 80A Resin and BioMed Elastic 50A
outline of the outer ear helix and earlobe, a kidney-shaped Resin, we conducted tensile, three-point bending, and
surface was created. This surface was offset outward to the compression tests on both materials using a universal
dimensions of 65 × 40 mm, creating a closed surface that testing machine (Instron 5967; Instron, USA).
forms the soft rubber shell model, which was printed with
BioMed Flex 80A (Formlabs, USA) (Figure 1E). To thoroughly assess the mechanical properties (i.e.,
resistance to deformation) of BioMed Flex 80A Resin,
Using Boolean tools, the ear model was subtracted a series of tests were performed, including uniaxial
from the main part of the model to obtain the preliminary tensile, equal biaxial tensile, plane tensile, and volumetric
completed soft rubber model. The resulting STL model compression tests, to measure their response to tension
was converted to a subdivided surface, and a flexible and pressure.
modification tool was subsequently employed to suitably
raise the height, thereby accentuating key features like the For the uniaxial tensile test, the samples were processed
concha and triangular fossa of the auricle. This adjustment into dumbbell-shaped with a length of 25 mm and a width
was aimed at improving the retainer’s performance in of 2 mm in the middle narrow section. The samples used
these deeper anatomical regions. Additionally, for ease in the equal biaxial tensile test were round-shaped with a
of wearing, we divided the retainer into two parts at the diameter of 60 mm and a thickness of 2 mm. The plane
auricular concha and fully aligned them using external tensile test was performed using rectangular samples with
fastening devices. To effectively secure the ear retainer, a length of 150 mm, width of 10 mm, and thickness of
we have innovatively developed a 3D-printed positioning 2 mm. The experiments utilized a slow cyclic time-strain

Volume 10 Issue 5 (2024) 464 doi: 10.36922/ijb.3986