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

favorable for cell adhesion and proliferation. Several We also summarize the latest approaches in the 3D
types of hydrogels have been studied for biomedical (bio)printing of magnetic hydrogels, highlighting their
applications based on the desired functional outcome, most promising results aiming at in vitro organ generation.
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5,6
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with applications in cartilage, bone, muscle, and Recent studies focused on the injectability of this type of
neural tissue engineering, among others, as well as in hydrogels are also reviewed, given the importance of this
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anticancer therapies. 8,9 feature for their use in 3D (bio)printing applications, more
specifically following extrusion approaches. Finally, we
Recently, interest has been shown in the incorporation
of magnetic components into these polymeric matrices in discuss the current limitations of these strategies and how
order to produce magnetic 3D constructs for biomedical they can be overcome, and envision the applications of this
applications. Magnetic materials have shown great technique in tissue and organ engineering.
promise in this field due to their biocompatibility, both 2. Formulation of magnetic nanoparticles
in vitro and in vivo; their remote controllability through
the use of an external magnetic field, which reduces the The incorporation of magnetic particles into a polymeric
need for invasive procedures and the associated risk in matrix is the main strategy used when developing
clinical setting; and their high adsorption capacity to magnetic hydrogels for 3D (bio)printing applications. The
the polymeric matrix, with applications in anticancer application of an external magnetic field produces forces
hyperthermia treatments and as contrast agents for and torque in these particles, which then causes them to
medical imaging. Furthermore, there have been move, translationally or rotationally, dissipating energy.
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reports of this type of approach being used as a tool to MNPs can be applied in the biomedical field as tools
enhance the angiogenic potential of human umbilical for drug delivery, 15-17 cancer therapy, 15,18,19 and medical
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vein endothelial cells (HUVECs), by triggering higher imaging, among others. Therefore, in this section,
secretion of vascular endothelial growth factor (VEGF) particular attention will be given to MNPs formulation and
by mesenchymal stem/stromal cells (MSCs) embedded current applications.
in a magnetically-responsive scaffold. MSCs have also MNPs have been drawing attention from the biomedical
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been shown to overexpress VEGF after internalizing community due to their large surface-to-volume ratio,
magnetic nanoparticles (MNPs)-laden liposomes in a small size, good tissue diffusion, and easy manipulation via
mouse hind-limb ischemia model, resulting in higher an external magnetic field. Several different compositions
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revascularization, as well as on their own when exposed have been studied, with the most reported and applied being
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to high-intensity pulsed electromagnetic fields. Thus, the iron oxides magnetite (Fe O ) and maghemite (γ-Fe O )
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3
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the use of magnetic fields and components might due to their biocompatibility, superparamagnetism, and
have great implications in organ/tissue engineering, chemical stability at room temperature, features that
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since vascularization is a major limitation in this field. are advantageous for tissue engineering applications.
Furthermore, the incorporation of magnetic components Despite those properties, MNPs tend to aggregate due
within an ink and 3D printing under external magnetic to their small size, in order to minimize their surface
stimulation can be instrumental to obtain specific energy; thus, different approaches have been proposed
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microarchitectures, potentially leading to a close for the functionalization of these particles to improve their
mimicking of native tissues’ structure and properties, stability. 6,9,22-28 Moreover, unlike organic nanoparticles,
namely allowing for collagen fibers orientations MNPs present superior hyperthermic capabilities and
resembling the ones found in native cartilage. 14 can be easily visualized by magnetic resonance imaging
In this review, we provide an overview of recent techniques, making them ideal tools for medical imaging
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studies performed on the field of magnetic hydrogels, and applications in diagnosis. Moreover, while gold
with special emphasis on their manufacturing by 3D (bio) nanoparticles (AuNPs) also present hyperthermic
printing toward tissue engineering applications, which, capabilities and can be used for imaging, MNPs still have
to the best of our knowledge, has not yet been addressed the unique capability of being easily controlled remotely by
in the literature. Firstly, we address the most commonly the application of external magnetic fields.
used techniques to fabricate MNPs and how they are MNPs production process includes a first step, where a
incorporated into the hydrogels’ matrices. As a result of the short nucleation burst occurs due to the sudden addition
growing use of extrusion-based 3D (bio)printing strategies of reagents and consequent reaction, which causes solution
for the fabrication of magnetic hydrogels with complex supersaturation and, thus, particle nuclei formation.
microarchitectures, the basic concepts of this manufacturing Afterward, a second particle growth step takes place by
technology are also detailed. continuous reaction of precursors with the existing particle

Volume 10 Issue 1 (2024) 2 https://doi.org/10.36922/ijb.0965