Page 590 - IJB-10-3

International Journal of Bioprinting 4D printing & simulation for biomedicine

USA). For detailed information on finite element analysis data in Supplementary 2 assumed of a conventional
(FEA), the solutions and numerical programming were PLA polymer, rather than a shape-memory polymer. It
reported previously. 22 illustrates the temperature-dependent stress–strain curve

The shape-programming and recovery processes of and the structure of thermoplastic polymers. In this
the SMP were simulated using COMSOL Multiphysics instance, the memory effect is excluded, depicting the
(COMSOL Inc., Sweden). During the cooling step, the immediate return to the original state.
rubber phase changed to a glass phase, and the inelastic Shape-memory polymers that respond to body
strain (ε ) calculated using MATLAB was stored in the temperature can be used in a variety of applications. It has
in
SMP material. This strain storage was proportional to been confirmed that the shape-memory effect transitions
η based on the rubber phase strain. In simulations of through the stages of original shape, temporary shape,
g
the heating step, the stored strain was gradually released and recovery shape within the range of body temperature
proportional to η with respect to the previous glass phase (Figure 6a). Using 3D printing, these polymers can be
g
and strain storage. Here, there were 600 temperature steps fabricated in appropriate sizes and diverse shapes (Figure
during cooling and heating. 6b and c). It could demonstrate the polymer’s ability
to maintain complex geometries through the memory
3.6. Comparing the experimental and simulated effect. Additionally, it has been demonstrated that shapes
behaviors of the shape-memory polymer incorporating rigid bodies can function as hinges, further
A cylindrical column was used to investigate for confirming the potential for these materials to act as
experimental behavior of the SMP (Figure 5a and b). It actuators (Figure 6d).
was initially fabricated with an inner diameter of 8.45
mm, a thickness of 0.80 mm, and a height of 5.22 mm, 4. Conclusion
representing its original shape (the “a” point in the
temperature-dependent stress–strain curves in Figure 5c). 3D printing is used to develop patient-specific
By subjecting it to temperatures above T , it transitioned biomedical applications, such as regenerative medicine
g
to the “b” point state. Applying an external force and tools, drug delivery devices, and implants, leveraging its
cooling resulted in the “c” point state, with a cooling ability to mimic physiological geometry. However, the
shape having an inner diameter of 10.08 mm, thickness dynamic nature of the human body presents a challenge,
of 0.70 mm, and height of 4.90 mm. Upon removal of the prompting the emergence of 4D printing, a concept in
external force to achieve the free state, it had a diameter which the time domain is added to 3D printing, thus
of 10.00 mm, thickness of 0.73 mm, and height of 4.90 enabling shape or function changes over time in response
mm, representing the “d” point state. When T reverts to to specific stimuli.
o
the memorized shape, raising the temperature led to the In this study, the SMP was newly developed for 4D
recovery shape (“a ” point), experimentally confirmed to bioprinting in the biomedical field. The thermal and
0
have a diameter of 8.94 mm, thickness of 0.79 mm, and physical properties of the manufactured SMPs were
height of 5.12 mm. analyzed, and the results confirmed a suitable T range
g
Figure 5c shows the FAE COMSOL Multiphysics for PLA+PEG 10 phr and PLA+PEG 20 phr to react at
simulation results of SMP. The original shape was 8.45 human body temperature. Thermal stability was verified,
mm in diameter, 0.80 mm in thickness, and 5.25 mm in confirming an appropriate processing temperature of
height, and was maintained at 10.08 mm in diameter, 0.73 200°C for FDM printing. DMA analysis displayed that
mm in thickness, and 4.94 mm in height when cooling higher PEG content led to lower storage and loss modulus
from a high to low temperature. In the free state with the values and the transition from a glass to a viscous state at
applied external force removed, the shape had a diameter lower temperatures. PLA+PEG 20 phr was suggested to
of 9.46 mm, thickness of 0.74 mm, and height of 5.00 be suitable for printing based on thermal and mechanical
mm, and after the temperature was raised again to a analyses, and the results were used as data for SMP
higher temperature, the recovery shape had a diameter simulation. Printability conditions were determined
of 8.5 mm, thickness of 0.8 mm, and height of 5.25 mm with optimal results achieved at a temperature of 200°C,
(Figure 5b and c). The results calculated with this FE pneumatic pressure of 200 kPa, and feed rate of 420 mm/
solution were in good agreement with those measured min. Hydrolytic degradation confirmed biodegradability,
in the experiments, indicating that they could be resulting in weight loss for 49 days. Biocompatibility
analyzed with COMSOL Multiphysics from a numerical was analyzed based on cell viability and proliferation.
perspective when verifying or predicting the memory FE solution was used to predict the shape of the printed
phenomena observed in 4D printing samples. And the SMP. A two-phase model, consisting of rubber and glass

Volume 10 Issue 3 (2024) 582 doi: 10.36922/ijb.3035