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International Journal of Bioprinting Magnetic (Bio)inks for tissue engineering

In a study targeting neural tissue engineering, agents and in tumor ablation strategies. Moreover, it
Ghaderinejad et al. developed an alginate hydrogel is expected that magnetic hydrogels will be employed
containing magnetic short polycaprolactone (PCL) as smart advanced biosystems in emerging fields such
nanofibers (MSNFs) aiming to induce neuronal as soft robotics. Furthermore, 3D (bio)printing of
differentiation in olfactory ectomesenchymal stem cells these stimuli-responsive materials will allow for the
(OE-MSCs). The MSNFs were proven to be orientable scalable and reproducible fabrication of constructs with
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by an external magnetic field within the magnetic complex structures able to mimic the properties of the
hydrogel, as in the previous study, and the storage native tissues and to be externally stimulated to foster
modulus of the bioink was found to be in the range of regenerative processes. Additionally, the incorporation
the values reported for the brain tissue (100–1000 Pa). of magnetic particles into hydrogels also allows a better
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Additionally, the results showed that the hydrogels modulation of the hydrogels’ features, since an external
containing MSNFs were able to promote the OE-MSCs magnetic field can control the positioning of the MNPs
neuronal differentiation. within the scaffold, conferring different properties
to different locations of the scaffold, which might
Another biomedical application of magnetic hydrogels contribute to the recapitulation of highly heterogeneous
is their use in hyperthermia anticancer therapies. This tissues.
type of therapy takes advantage of an external alternating
magnetic field to stimulate the magnetic nanoparticles However, there are still some issues that need to be
present within the hydrogel. When this stimulus is applied, further optimized for their effective implementation.
the MNPs dissipate heat through relaxation losses and Regarding the use of 3D-(bio)printed magnetic hydrogels
hysteresis, and this heat then causes the death of the for tissue engineering applications, there have been
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surrounding cancer cells. Given that this heat release can conflicting reports concerning the effect of the introduction
cause unwanted damage to cells neighboring the tumor, it of MNPs within the hydrogel matrix. Some studies have
is crucial for the hydrogel to be accurately injected into the reported the improvement of mechanical properties,
desired location. For this purpose, Qian et al. constructed which translate to increased stiffness and higher Young’s
an injectable silk fibroin hydrogel (FSH) with confined modulus, due to the interaction of these particles with the
polyethylene glycol stabilized hydrophilic iron oxide polymer chains. However, other works claimed that the
nanocubes (IONCs) and evaluated its effectiveness in the introduction of MNPs disturbs the bonds between chains
targeting and ablation of tumors. The scaffolds showed within the hydrogel, thus decreasing their mechanical
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good injectability and a quick response to an external performance. Therefore, further research is needed to
magnetic field. Furthermore, its self-healing behavior was define, more specifically, how these particles interact with
tested and proven, which is crucial for the recovery of the their surrounding matrix, in order to accurately tune the
gel state following injection. Finally, after implantation in scaffolds features.
mouse and rabbit models, its hyperthermic effects were MNPs—more specifically magnetite and maghemite—
observed. have been shown to be cytocompatible in several in vitro
and in vivo animal studies. Nevertheless, given that the
Extensive research has been made regarding the
injectability of hydrogels and its applicability in several human body consists of several complex systems whose
interaction is not accurately represented by these models,
domains of research. 86,87 Besides its applications in the it is crucial that magnetic hydrogels can be tested in more
local delivery of hydrogels in a highly precise manner and advanced in vitro humanized models and in clinical trials in
through non-invasive methods, we reckon that the results order to move toward the final goal of their implementation
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of these works can show whether a bioink formulation into clinical practice.
possesses the right mechanical and rheological features
to manufacture a solid 3D structure via a 3D (bio) Finally, 3D (bio)printing of cell-laden bioinks has not
printing process. This demonstrates the current potential been very extensively explored. The incorporation of cells
of injectable magnetic hydrogels and its potential to be in the bioink allows for a more uniform dispersion of cells
applied in 3D (bio)printing approaches. within the hydrogel while still allowing the precise definition
of its shape and structure. Nonetheless, these magnetic
6. Conclusion and future perspectives bioinks must have characteristics that are compatible with

With a broad spectrum of applications, magnetic cell viability—such as a shear-thinning behavior.
hydrogels are used not only in several branches of tissue Overall, we envision that magnetically-responsive
engineering, for example, neural, muscle, cartilage, systems will have a great impact on tissue and organ
and bone tissue regeneration, but also as antibacterial engineering due to their unique characteristics that allow

Volume 10 Issue 1 (2024) 14 https://doi.org/10.36922/ijb.0965