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International Journal of Bioprinting Application and prospects of 3D printable microgels

Figure 1. Gravity-assembled microgels. (A) Microgels have unique features, including injectability, heterogeneity, and porosity, which allow for
passage through the structure. Interlinking between particles further stabilizes the structure. [from ref. licensed under Attribution-NonCommercial-
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NoDerivatives 4.0 International (CC BY-NC-ND 4.0)]. (B) Jammed microgel ink fabrication, rheological properties, and extrusion. (a) The process of
microfluidic preparation of microgels. (b) Representative fluorescent images of suspended microgels (left) fabricated from 2 wt% NorHA that are jammed
through vacuum filtration into a solid (right) that can be extruded from a syringe. (C) Rheological characterization of jammed NorHA microgel inks
showing (i) decreased viscosity with continuously increasing shear rates (0–50 s ), (ii) shear-yielding with increase in strain (0.037%–1000%, 1 Hz), and
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(iii) shear-thinning and self-healing through low (unshaded, 1% strain, 1 Hz) and high (shaded, 500% strain, 1 Hz) strain cycles. [(from ref. licensed
[61]
under Creative Commons Attribution 4.0 license)].
relatively fast reaction rate, and the resulting microgel action have typically been found to possess self-healing,
have good biocompatibility. For example, Li et al. used shear thinning, and injectability, but tend to have lower
N-hydroxycarbamyl-amine coupling to assemble water- mechanical strength compared to those assembled through
based micromicrogel containing human bone marrow chemical action.
mesenchymal stem cells (MSCs). In this crosslinking
process, the microgel also had the potential to rapidly The self-assembly of microgel through host–guest
bond with tissue models, which could be useful in the interactions refers to the formation of specific polymers
implementation of in situ printing . through the self-assembly of monomer molecules based
[68]
on the recognition characteristics between the host and
3.3. Physical effect guest . For example, by using cyclodextrin as the host and
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Through physical interactions between microgels, typically adamantyl as the guest in the self-assembly of microgels,
non-covalent interactions, the assembly of water-based different microgels can be selectively assembled by altering
microgels can be achieved (Figure 2B). Common physical the size and shape of the host and guest components.
interactions include host–guest interactions, electrostatic Overall, the assembly of microgels through the interaction
interactions, hydrogen bonding, and biotin-streptavidin between main and secondary objects occurs at a fast rate,
conjugation . Microgels formed through physical resulting in microgels with strong biological compatibility.
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Volume 9 Issue 5 (2023) 90 https://doi.org/10.18063/ijb.753