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tissue repair potential, not only showing excellent anti- With the advancement in biofabrication technology,
inflammatory ability but also facilitating the migration particularly 3D bioprinting, bone organoids with bone-
of SCs and the CGRP secretion of DRG neurons, thus like microstructure and osteogenic microenvironment
contributing to an elevated osteogenic differentiation features can be fabricated by cell-laden 3D bioprinting, as
efficiency of MSCs. 120 well as multicellular 3D bioprinting, characterized by not
Different from the bioactive inorganic minerals and only an assembly of osteoblast spheroids into a larger-scale
the neurotrophic factors, the exosome-mediated nerve– bone microtissue but also integration between osteocytes,
bone crosstalk features intricate interaction mechanisms vascular endothelial cell, and neural cells with more close
underlying bone regeneration, as well as diverse release contacts. The bioinks serving as extracellular matrices of
approaches of neuroactive substances. On the one the 3D-bioprinted osteo-organoids should provide the
hand, the NGFs released from the exosomes bind to the biochemical or biomechanical cues mentioned above for
surface receptors on osteocytes, neural cells, and vascular facilitating neural growth inside the bone microtissues.
endothelial cells and activate the corresponding signaling In this section, the recent advances of the 3D-bioprinted
osteo-organoids
emphasized,
are
and
reviewed
pathways. On the other hand, the exosomes also can highlighting, especially, the activation of innervation
be endocytosed into the targeted cells, and the loading by 3D-bioprinted scaffolds and the development of
microRNA can be translocated toward nucleus regions multicellular 3D-bioprinted bone microtissues with
for regulating protein synthesis and cell differentiation. enhanced nerve–bone crosstalk.
Therefore, the exosomes often exhibit long-term bone
regeneration with a delayed release period and abundant 4.1. Cell-laden 3D bioprinting for promoting skeletal
target pathways. Moreover, Lian et al. modified the nerve restoration and bone regeneration
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MSC-derived exosomes by stimulating MSCs with the
NGF, and the modified exosomes show an excellent 3D bioprinting, also called additive manufacturing,
is a promising approach for the fabrication of tissue-
potential in accelerating neurogenesis and osteogenic engineered osteo-organoids, benefitted from its abilities
differentiation, representing a unique strategy to in rapid prototyping, high-density cell integration, and
improve therapeutic outcomes in comparison with heterogeneous architecture manufacturing. Recent studies
bioactive inorganic minerals and neurotrophic factors.
Meanwhile, the intricate interaction mechanisms of the have presented the 3D bioprinting strategies and therapy
exosome-mediated nerve–bone crosstalk are still not fully applications of tissue-engineered bone microtissues; among
understood, presenting huge challenges to further clinical them BMSC-laden 3D-bioprinted constructs represent a
translation. common choice for tissue-engineered bone transplantation
and regeneration. Wang et al. have fabricated
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125
4. Fabrication of bone organoids with microfilament-based scaffolds with different geometric
enhanced nerve–bone crosstalk structures using 3D electrostatic printing and found the
preferred microfilament patterns with an angle of 90° not
Bone organoids, mainly containing stem cell spheroids only promoted osteogenic differentiation of BMSCs but
and their extracellular matrixes, represent a promising also stimulated expression of vascular and neural growth
regeneration therapy for healing refractory bone defects, factors for neovascularization and innervation formation.
whereas vascularization and innervation formation Another study also observed the enhanced vascularized,
constitute an uphill battle for osteo-microenvironment neurogenic, and osteogenic marker expression in a rabbit
remodeling in the osteo-organoid technology innovation femoral defect model after implantation of a 3D-printed
and clinical translation. Responding to these challenges, polyhedron-like bioceramic scaffold, demonstrating
the 3D co-culture of osteoblast, osteoclast, hematopoietic- the superiority of 3D bioprinting over traditional tissue
associated, and other cells is often preformed for osteo- engineering approaches. However, newborn tissues
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organoid formation through intramembranous or arising from the BMSCs encapsulated in the 3D-bioprinted
endochondral osteogenesis processes, thus customized constructs are subject to inadequate metabolism due to lack
into diverse organoid types, such as callus organoids, of vascularization, and their osteogenic differentiation is
woven bone organoids, and trabecular bone organoids. also limited due to neurotrophic factor stimulus constraints.
Although restricted in a microscopic space, the 3D culture As mentioned above, both the activation of sensory neurons
of cell spheroid-based bone organoids still presents and the inhibition of sympathetic nerve activity contribute
the robust osteogenetic ability under biochemical and to the enhanced osteogenic differentiation of BMSCs
biomechanical stimuli; 121,122 for instance, dental pulp and bone fracture healing. It has been demonstrated
stem cells prefer to form spheroid-like microtissues that the sensory nerve stimulators (NGF, CGRP) and the
on an agarose gel substrate and differentiate toward sympathetic nerve inhibitors (nifedipine and propranolol)
osteoblast lineage with cannabidiol treatment. can be loaded in and released from 3D-bioprinted gelatin/
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Volume 1 Issue 1 (2025) 10 doi: 10.36922/OR8294