Page 366 - IJB-9-5

International Journal of Bioprinting Multifunctional hydrogel surgical training model

2.3. Mechanical property tests the force and displacement data were recorded from the
The hydrogel samples were tested by Instron Model 5576 beginning of the first sample to the end of the second
(USA) universal material testing machine with a 10 kN sample.
load cell. Dumbbell samples (25 × 4 × 2 mm) for tensile
experiments were tested at the tensile rate of 100 mm/ 2.8. Ultrasonic scalpel cutting tests
min, and cylindrical samples (d = 8 mm, h = 6 mm) for Hydrogel models of different substantial organs, such as
compression experiments were tested at the compression liver and kidney, were prepared separately. The surgical
rate of 5 mm/min. The Young’s modulus of the hydrogel cutting process of real tissues was simulated using
was calculated from the slope of the stress–strain curve, ultrasonic scalpel instruments to evaluate the smoothness
ranging from 10% to 20% of the strain. and realism of the models in the cutting process. The
vibration frequency of the blade head of the ultrasonic
2.4. Electrical conductivity tests scalpel was set to 55 kHz.
The conductivity of the hydrogels was measured by a digital
four-probe tester (RTS-9, 4 PROBES TECH) with a current 2.9. In vitro vascular clotting and hemostasis study
of 10 μA and a linear probe tip (1.0 mm spacing). Each Hydrogel blood vessel models with different diameters
sample was tested 10 times and averaged. All hydrogels of 1, 2, and 3 mm were designed, respectively. They were
were washed with deionized water, and residual water was placed in molds in advance, and the prepared hydrogel
removed from the hydrogels using filter paper. liquid was poured into the molds for curing to obtain the
samples containing vascular channels inside. To simulate
2.5. Thermal conductivity tests the surgical scenario more realistically, the low power
The thermal conductivity of the prepared hydrogel samples grade of the ultrasonic scalpel was chosen to coagulate the
was measured at room temperature by the transient vessels separately to avoid possible thermal damage to the
planar heat source method using a Hot Disk thermal tissue. In addition, the blood flow process was simulated
constant analyzer (TPS 2500 S, Hot Disk, Sweden). All by connecting a pressure-adjustable circulation pump
measurements were performed three times. system to the outside world to simulate the coagulation
and hemostasis of the ultrasonic scalpel in an accidental
2.6. Rheology testing bleeding scenario during surgery.
The viscoelasticity of all hydrogels was evaluated by an
advanced expanded rheometer (MCR302, Anton Paar) 2.10. Microwave ablation study of tumors
with a parallel plate with a diameter of 25 mm. Hydrogel The sample with the tumor simulant was prepared first,
sheet samples of 25 mm diameter and 1.2 to 1.8 mm and the power parameters could be set to vary from 50 to
thickness were placed under the top plate. 80 W, and the time could be set from 2 to 5 min depending
on the size of the tumor and the treatment situation. In this
Dynamic sweep tests (from 0.1 to 100 rad/s) were first experiment, we prepared an ellipsoidal tumor sphere with
performed at constant strain (ε = 0.1%) to determine the a long axis of about 2.5 cm and a short axis of about 1.5 cm,
viscoelasticity (tan δ, G’’/G’), where G’ and G’’ are the which was implanted in a sample simulating the liver
storage modulus and loss modulus, respectively. Next, parenchyma for anatomical photography. The ablation
the variation of the friction coefficient with time under needle of a microwave ablation therapy instrument (KY-
constant normal force (F = 5 N, ω = 0.5 rad/s) was tested 2000A, Kangyou Medical Devices Co. Ltd., China) with a
for 15 min with a friction coefficient μ = 4T/3RF (where power of 65 W and a time of 3 min was inserted into the
T is the torque and R = 12.5 mm). It is worth mentioning tumor mimic. Then the instrument was started to observe
that during the friction test, the tissue-like soft hydrogel the changes in the tumor during ablation. This process can
was dripped with an appropriate amount of deionized be completed under the guidance of ultrasonic devices.
water to prevent the sample from becoming dehydrated
and dry. 2.11. Ultrasonic image tests
The internal structure of the model with tubes was
2.7. Surgical needle suturability study observed by the Welld full digital ultrasound (Shenzhen
The test was performed by an Instron Model 5576 (USA) Welld Medical Electronics Co. Ltd., China) after the model
universal material testing machine connected to a 500 N was passed into the fluid and discharged from the air.
load cell. A 0.6 mm diameter straight needle was manually The ultrasound frequency could be selected in a low- or
held by a clamp, and the sample was punctured at a speed high-frequency mode according to training needs. A little
of 60 mm/min, during which force and displacement data ultrasonic coupling agent was applied to the surface of
were recorded. Two samples with different stiffnesses the observed object so that the ultrasonic probe and the
were also pierced continuously at the same feed rate, and observed object could be closely combined, thus reflecting

Volume 9 Issue 5 (2023) 358 https://doi.org/10.18063/ijb.766