Page 586 - IJB-10-3

International Journal of Bioprinting 4D printing & simulation for biomedicine

3.2. Fixation and recovery rate of a comparable size range (within ± 10%) were identified
shape-memory polymers (Figure 3a). Validation experiments reported that increased
The fixation and recovery rates, which are key pressure resulted in thicker strands, while higher feed rates
characteristics of SMPs, were examined. The fixation yielded thinner strands. Notably, excessively fast feed rates
rate refers to the ability of SMP to maintain its shape led to strand movement before proper layer accumulation,
after being subjected to an external force, retaining the resulting in a wavy shape. Based on these observations
deformed shape. The recovery rate refers to the ability of (Table S1 in Supplementary File), subsequent printing was
SMP to return to its initially programmed shape (original performed with the pressure set to 200 kPa and the feed
shape) after a specific stimulus is applied. For the rate set to 420 mm/min.
application of SMP in medical devices, the fixation and Biodegradable materials are substances whose
recovery rates for two representative motions, bending molecular weight decreases through the disruption of
and linear motion, were studied. The structures for the chemical bonds within the human body. Specifically, for
bending motion were designed in the form of a hinge, applications in the medical field, these materials must
while the structures for the linear motion were designed facilitate tissue regeneration during the period of use and
as a thin sheet (Figure 2e). Furthermore, the fixation and assume structural functions within the human body once
recovery rates were investigated based on the content of tissue regeneration has stabilized. The SMP developed in
PEG in the SMP composition.
this study was a biodegradable composite polymer based
Fixation and recovery rates exceeding 90% were on PLA and PEG. Biodegradability is widely assessed using
observed across all motions and PEG contents. It was hydrolytic degradation. Two techniques for evaluating
noted that bending motion exhibited slightly lower values biodegradability through hydrolytic degradation include
compared to linear motion. Additionally, it was observed a method using a neutral solution and another for
that the fixation and recovery rates tended to decrease accelerated decomposition. In this study, the accelerated
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with higher PEG content. Specifically, for PLA+PEG 10 decomposition method, particularly the weight
phr, the fixation rates for the bending and linear motions loss measurement method using alkaline solution,
were 97.44% (±1.67) and 99.08% (±0.57), respectively. was employed.
For PLA+PEG 20 phr, the fixation rates for the bending
and linear motions were 93.66% (±1.16) and 97.64% The experiment was conducted with an initial weight
(±0.34), respectively (Figure 2f). For PLA+PEG 10 phr, of 0.2 g, and the extent of weight loss was assessed after
the recovery rates for the bending and linear motions decomposition for 0, 7, 14, 21, 35, and 49 days (Figure 3b).
were 97.25% (±0.96) and 99.16% (±0.41), respectively. For The degree of weight loss increased over time: 7.723% at 7
PLA+PEG 20 phr, the recovery rates for the bending and days, 20.837% at 14 days, 39.357% at 21 days, 59.676% at
linear motions were 93.97% (±3.63) and 99.16% (±1.76), 35 days, and 79.174% at 49 days. Both the overall sample
respectively (Figure 2g). size and strand size decreased in proportion to weight
loss as the polymer decomposed. In addition, SEM
Both the fixation and recovery rates for the two images revealed an increase in surface roughness with the
motions were close to 90–100%, indicating that the SMP progression of decomposition (Figure 3c).
effectively maintains the desired structure during cooling
and returns to its original shape upon heating. This Biodegradability through hydrolysis is known to occur
highlights its suitability for medical applications. by breaking the ester links of the polymer chain when
reacting with water. Decomposition typically begins in the
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3.3. Printability and degradability of shape-memory amorphous region, which is the more flexible segment of
polymers for 4D printing the polymer and is more susceptible to the effects of water.
Considering its thermal properties, a body temperature- Moreover, the decomposition mechanism of hydrolysis
responsive SMP was designed for 4D printing utilizing varies based on the solution used. In neutral or acidic
PLA+PEG 20 phr. FDM printing, a method involving solutions, hydrolysis destroys the ester linkages through
melting and extrusion, was used to fabricate SMP at 200°C, protonation as water is added. Conversely, in alkaline
which was below the thermal decomposition temperature solutions, decomposition occurs through a mechanism
of the material. Printability was confirmed by adjusting that breaks the ester linkages as a hydroxyl ion is added to
variables, such as the pressure pushing the molten SMP and the carbon of the carbonyl group. 31,32 This study confirmed
feed rate, which is the speed of the printing head (Figure 3a). the biodegradable properties of PLA- and PEG-based
A printing nozzle with a diameter of 400 μm was used, SMPs using a weight loss measurement method with an
and printing conditions ensuring strand thickness within alkaline solution.

Volume 10 Issue 3 (2024) 578 doi: 10.36922/ijb.3035