Page 201 - IJB-9-6

International Journal of Bioprinting Attractiveness of 4D printing in medical field

used thermal expansion to model the temperature- was printed to analyze the shape memory behavior .
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responsive hydrogel, and the percentage error between Bodaghi et al. (2018) produced adaptive structures with a
the theoretical and experimentally measured folding dual and triple SME by creating hot–cold programming
angle was about 5%. Also, it improved the design, of SMPs, whose self-bending behavior was experimentally
control, and prediction of 3D-printed stimuli-responsive demonstrated .
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shape-morphing structures that have applications in The second trend concerns research on innovative
biomedical devices . Inverardi et al. (2021) proposed materials and processes to fabricate reversible structures.
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an experimental/computational method to design shape As Lee et al. (2020) explain, while one-way shape
memory devices fabricated by hot processing . First, a deformation is one-directional, two-way memory provides
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thermal, mechanical, and shape memory characterization reversibility through two persistent states (original and
under different testing conditions with different samples deformed) according to the stimulation conditions applied
was realized. Then, a prototype was fabricated, temporally and with no physical contact . They created a contactless
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deformed, and tested to compare the simulation with shape mechanism to enhance reversible 4D printing
the obtained results . Wagner et al. (2017) designed a using a combination of stimuli to overcome challenges
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3D-printed auxetic metamaterial that can be programmed associated with low response, shape morphing, and other
into flexible shapes and recover its initial shape . This limitations of SMP-based materials. Their research showed
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material was utilized to construct a beam model to predict the potential of reversible 4D printing for soft robotics .
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forces and deformations of a complex structure. A great Additionally, Lee et al. (2017) exhibited an important
correlation was established between the finite element research opportunity involving the effect of TWSME in
simulation and experimental data from a bending test. A metals and metal alloys, which are mainly stimulated by
second complex shape was built and programmed into a methods such as thermomechanical (heating and cooling
random shape, and its shape was recovered as predicted. to contract or expand their shape) and electrochemical
The second trend focuses on the utilization of algorithms hydrogenation; however, they still have limitations, but
and statistical models for batch optimization and improving their performance can be useful for applications
deformation . Suryavanshi et al. (2023) used experimental in robotics, aerospace, and biomedical industries .
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data of a new thermo-responsive self-folding feedstock to Moreover, they also indicated combining two or more
train machine learning algorithms for batch optimization, stimuli to achieve reversibility is one of the future research
which was later used for drug delivery applications . directions . Recently, Parimita et al. (2023) studied a
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Ren et al. (2023) created theoretical deformation models chitosan hydrogel ink that showed a displacement field
using machine learning methods to acquire information caused by a concentration gradient after the edge of the
on the stiffness deformation and pressure of the material structure was dipped inside a solvent . The concentration
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at different temperatures . This model was applied in gradient between the hydrophilic chitosan and hydrophobic
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a cardiac-mimicking actuator showing the promising silane layers of the material caused a bending behavior in
applicability in medical assistive devices, artificial muscles, the printed structure that can only be reversed by soaking
and soft robotics, among others . the structure in ethanol in order to lower the concentration
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gradient . On the other hand, Wu et al. (2018) proposed
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With respect to the interaction mechanisms category,
two trends were identified. The first one is about the use of a 4D printing method that used a grayscale pattern to
administer the light power distribution of a UV projector in
the SME for folding and bending behaviors. Großmann et al. digital light processing . This method generated reversible
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(2022) investigated the use of shape memory behavior to self-folding structures with different curing angles and
fold and contain objects fabricated from thermoplastic crosslinking densities at different locations. The bending
polyurethane filaments in water-soluble hard gelatin behavior of these structures can be induced due to volume
capsules; later, the unfolding time and dimensional recovery shrinkage after uncured oligomers are removed from the
were examined as functions of material properties and crosslinked network. This behavior can be reversed, and the
shape . Diverse flexible dosage forms were designed to structure can swell by the absorption of acetone. According
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make the unfolded size suitable for gastric retention, showing to the authors, this method has huge potential in the
different behaviors depending on the shape and material . fabrication of smart structures and endovascular stents .
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On the other hand, Pandey et al. (2022) examined the SME
of PLA and polycaprolactone (PCL) polymers, using PLA 4.2.2. Applications
like an unchangeable phase of the polymers to memorize Regarding the applications category, three trends were
the original shape and PCL as a reversible phase to promote identified. The first trend involves the development of drug
the transformation and fixation to a non-permanent shape delivery devices designed in a compact shape, which can
when thermal stimulus was applied . A tracheal scaffold expand subsequently after the stimuli is applied.
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Volume 9 Issue 6 (2023) 193 https://doi.org/10.36922/ijb.1112