Page 584 - IJB-10-3

International Journal of Bioprinting 4D printing & simulation for biomedicine

2.8. Shape-memory effect and experiment transitions into a glassy state and can maintain its
for simulation programmed shape. 24-26 Therefore, DSC was used to
The shape-memory characteristics of the 4D-printed determine the T range of the SMP, which yielded T
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polymer processed with a 3D printer were examined. The values of 59.1°C for PLA, 36.2°C for PLA+PEG 10 phr,
experiments were carried out over a temperature range of and 34.0°C for PLA+PEG 20 phr (Figure 2a). It was
40–55°C, which exceeded the material’s T . confirmed that T was established within a range similar
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The experiments were conducted as follows. A to the range of body temperature for both PEG 10 phr
cylindrical column was fabricated with an inner diameter and PEG 20 phr compositions of PLA+PEG.
of 8.45 mm, thickness of 0.80 mm, and height of 5.22 mm. The range of thermal degradation, when heat was
The original shape, which represented the memorized applied to the SMP, was assessed by TGA (Figure 2b). In
shape, was exposed to a temperature exceeding the T (high FDM printing, which processes the polymer by melting,
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temperature), and an external force was applied to induce a it is possible to identify the temperature range when
temporary shape change. The external force was sustained thermal degradation does not occur during printing.
for 5 min while maintaining the high temperature. The degradation temperature range was confirmed based
Subsequently, the temporary shape was allowed to remain on a weight reduction of 1.0%. The results indicated that
in a free state without any external force applied for 24 h degradation occurred at a temperature of 336.8°C for PLA,
at room temperature (low temperature). With no external 306.9°C for PLA+PEG 10 phr, and 289.4°C for PLA+PEG
force applied, the temperature exceeding the T (high 20 phr. With the addition of PEG, the degradation
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temperature) was applied, and the recovery process was temperature decreased, indicating a tendency to become
maintained for 5 min. Throughout these stages, the inner more vulnerable to thermal decomposition.
diameter, thickness, and height of the structure in each
state were examined. Next, using DMA, we confirmed the mechanical
properties at each temperature relative to varying PEG
A rigid-body hinge was fabricated by stereolithography concentrations. Analysis of temperature-dependent
(SLA) with a 3D printer (Objet30; Stratasys, USA). A behavior displayed a typical amorphous thermoplastic
hollow square shape was produced to match the 3-mm polymer in all groups. The mechanical strength of the
height of the hinge made of SMP. A hinge made of SMP was materials began to drop at higher temperatures, as
inserted into a rigid body to verify the shape-memory effect indicated by the storage modulus (Figure 2c). Specifically,
according to a method similar to that described above. PLA exhibited high brittleness and susceptibility to

2.9. Statistical analysis breakage at temperatures < 10.00°C, necessitating
All of the quantitative data are presented as the mean ± measurements to be conducted at room temperature. The
standard deviation. The results were analyzed using a one- storage modulus tended to decrease with increasing PEG
way analysis of variance, followed by Tukey’s post hoc test. content. The peak loss modulus refers to the region where
Statistical analysis was conducted using Origin (Origin 8.6 the molecular motion undergoes a significant change.
ver., OriginLab Corporation, USA). Large segments of the polymer could move cooperatively,
leading to increased energy dissipation. Simultaneously,
3. Results and discussion the material began to deform more easily. 27,28 In each
group, the loss modulus also tended to decrease with
3.1. Thermal and mechanical properties of shape- increasing PEG content, and the peak was confirmed to
memory polymers for 4D printing occur at low temperatures (Figure 2c). The peak of the
SMPs generally retain their programmed shape and can tangent delta is the transition region where the material
recover their original shape in response to environmental exhibits the most pronounced viscous response to
stimuli. In medical applications, they offer the advantage deformation. From these results, it was confirmed that
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of accommodating large deformation, making them well- all groups maintained the glassy state at temperatures
suited for addressing the effects of minor invasions or < 23.42°C (Figure 2d). In particular, with PLA+PEG 10
changes in tissue. phr and PLA+PEG 20 phr, the flow region was reached
Specifically, temperature-responsive SMPs, at a temperature > 67.60°C. The produced SMP could
characterized by an amorphous network, typically be expected to be printed smoothly at temperatures
exhibit shape-memory behavior in proximity to the T . higher than the temperature range after reaching the flow
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In the shape-memory cycle, significant deformation region. Therefore, considering the characteristics of TGA
can occur even under low stress due to rapid changes and DMA, the temperature range for printing could be
in material stiffness above T . Below T , the material expected to be approximately 67.60–250°C.
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Volume 10 Issue 3 (2024) 576 doi: 10.36922/ijb.3035