Page 274 - IJB-10-4

International Journal of Bioprinting 3D printing prosthesis for palatal fistula

2. Materials and methods bone and soft tissue of the palate defect, creating a high-
precision and highly compatible prosthesis model.
2.1. Materials and reagents
PTMEG (Mn = 650 g/mol), PTMEG (Mn = 1000 g/mol), The prosthesis developed based on the models
PTMEG (Mn = 2000 g/mol), tetrahydrofuran (THF), described above was adjusted and assembled. The upper
2-hydroxyethyl methacrylate (HEMA), isophorone airway models before and after repair were imported into
diisocyanate (IPDI), 2-ethylhexyl acrylate (2-EHA), and the Ansys 2021 software (Ansys, USA) to divide the CFD
dibutyltin dilaurate (DBTDL) were supplied by Macklin model mesh. This step effectively improved the similarity
Biotechnology Co., Ltd. (Shanghai, China). Dulbecco’s and accuracy of the model. The mesh quality was required
modified Eagle’s medium (DMEM) medium, fetal bovine to be more than 0.35.
serum (FBS), and Dulbecco’s phosphate-buffered saline
(DPBS) were purchased from GIBCO (California, USA). Live/ 2.3.2. Numerical simulation and boundary condition
Dead Viability Kit and Alamar Blue Cell Viability Assay Kit definition of CFD analysis
were obtained from Thermo Fisher Scientific (Massachusetts, We used the computational software FLUENT 21.0 in this
USA). Milli-Q grade water was used in all experiments. experiment, and the computational domain covered regions
from the anterior nostril to the pharynx. The pressure and
2.2. Establishment of the animal model of palatal velocity fields were solved, and the momentum equation
fistula and 3D reconstruction was discretized with second-order accuracy. The medium
3
The experimental protocol was approved by the Laboratory was air, the density was ρ = 1.225 kg/m , and the dynamic
-5
Animal Welfare and Ethics Committee, Southern Medical viscosity coefficient μ = 1.7894 × 10 kg/m·s.
University, in accordance with the Guide for the Care and Under normal circumstances, the tidal volume of rabbits
Use of Laboratory Animals (SMUL2022312). Under general is 20 mL per breath, about 46 breaths per minute, and about
anesthesia by 3% (w/v) pentobarbital at a dose of 50 mg/kg 1.3 seconds per cycle. In this experiment, the adequate
administered at the midline of the upper palate of 6-month- ventilation volume was 20 mL, and the respiratory rate
old male New Zealand white rabbits to the right, the was 46 breaths per minute; one respiratory cycle was 1.3 s
mucosa and hard palate bone plate were cut to establish an (t = 1.3 s). Broadly, one can view the respiratory wave as a
oval fistula connecting the mouth and nasal cavity; the size sine wave with a 1:1 ratio of expiratory to inspiratory time.
of the fistula was about 8 mm × 6 mm. Suturing absorbable
sutures connect the palatal mucosa and nasal floor mucosa. To eliminate the influence of the boundary effect on
After 1 week, we examined the fistula and conducted a cone the experimental results, during inspiration, the anterior
beam computed tomography (CBCT) scan to confirm the nostril of the upper respiratory tract was defined as the
successful establishment of the animal model. inlet. The lower edge of the throat was set as an outlet.
To define exhalation, the position of the inlet and outlet
CBCT data for the 3D reconstruction of the palatal to be changed was set, and the position of the outlet and
defect model were imported into the Mimics 21.0 software inlet for defining inhalation is opposite to that of the
(Materialise, Belgium). Based on the original CT image, exhalation defining process. In the formula, the wall of
thresholding was performed to obtain the initial upper the upper airway was regarded as a non-slip boundary
airway model before repair, which incorporates the (V = 0 m/s), and the upper airway was regarded as an
anatomical structure of upper airway and dead space. The instantaneous rigid body. The internal fluid is regarded as
model was then edited to remove irrelevant structures an incompressible fluid with steady flow. In the simulation
like frontal, sphenoid, and ethmoid sinus. Based on the process, we considered the influence of gravity but ignored
gray value, a separate mask was established, smoothed the effects of temperature field change, mucous cilia, and
to generate a 3D geometric model, and exported in STL maxillary sinus cavity. We treated the flow as steady and set
format. Subsequently, the STL format model was fed into the upper airway wall as a no-slip boundary (V = 0). This
Geomagic 2017 (Geomagic, USA) for noise reduction and study used the standard k-ε turbulence model to simulate
optimization of model features. The 3D solid model in step the airflow changes in the upper airway before and after
format was then exported. repair in a complete respiratory cycle under a set flow rate.

2.3. Design of prosthesis and CFD 2.3.3. CFD post-processing analysis
analysis-guided design After assembling the prosthesis, we obtained the repaired

2.3.1. Design of the prosthesis and the division of upper airway model again. Through calculating the
the mesh transient solution of the corresponding breathing process
We utilized the SolidWorks 2017 software to perform by computer, CFD post-processing analysis yielded
reverse engineering on the upper airway model and the gas flow data under the breathing state: 3D flow trace

Volume 10 Issue 4 (2024) 266 doi: 10.36922/ijb.2516