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International Journal of Bioprinting Bioprinting of exosomes

host vasculature upon transplantation in vivo. Moreover, heterogeneous tissues for the restoration of biological
the gradient distribution and controlled release of multiple function. Secondly, the choice of bioink is another
EXO types from bioprinted scaffold encapsulating various important factor that needs to be considered, as it should
cell types can be utilized for the guided development of not negatively impact the physical, chemical, or biological
heterogeneous tissues in numerous regenerative medicine attributes of encapsulated EXOs. The selected bioink
applications (Figure 1D). However, one important aspect should provide a compatible microenvironment that is
that needs to be considered for the sustained release of conducive for maintaining the stability and preservation of
EXOs from bioprinted scaffolds is the dosage of EXOs the intended biological function of EXOs. For example, the
at the target site, which should produce the intended selection of an appropriate shear thinning bioink is favored
therapeutic effect over a sustained period of time. In this for extrusion-based bioprinting, as it will significantly
context, several studies have revealed that the desirable reduce the magnitude of shear stresses exerted on EXOs
time course of action for therapeutic EXOs depends on the during the printing process, which might otherwise
end clinical application. To cite an instance, EXOs released adversely affect its biological activity.
from engineered hydrogels over a duration of 4–21 days From the viewpoint of EXOs, few considerations
induced angiogenesis, stimulated re-epithelialization, and remain for successful translation and clinical application of
promoted wound closure in chronic diabetic wounds [78-80] . cell-derived EXOs as regenerative therapeutics . Firstly,
[83]
In a similar situation, the sustained release of stem cell- or the source of producer cells for EXO production should be
progenitor cell-derived EXOs from hydrogel scaffolds over carefully examined because the choice of cells determines
a period of 21 days promoted myocardial regeneration in the quantity, functional activity, and target clinical
infarcted hearts [58,59,81] . application of EXOs. For instance, EXOs derived from
corneal stromal stem cells have been shown to be enriched
5. Future perspectives with anti-angiogenic factors, and thus can be used to
[84]
Bioprinting presents a unique opportunity to spatially and engineer avascular tissues, such as the cornea , whereas
temporally pattern cell-derived EXOs at high resolution EXOs derived from BMMSCs or AdMSCs have been
for engineering biologically relevant tissues. Additionally, shown to contain high levels of pro-angiogenic factors that
[85]
this approach yields scaffolds with gradient release profiles can be used for vascular tissue repair and regeneration .
of different exosomal types that can be used for the Likewise, MSC-EXOs derived from different tissue sources,
synchronized development of complex tissues composed including bone marrow, umbilical cord, menstrual blood,
of various cell types. This is critical for the fabrication and chorion, promote neurite outgrowth in varying
[86]
of heterogeneous tissues with desired phenotype and degrees . Furthermore, the age and physiological state of
function. However, despite the promising potential of the cells should also be considered to ensure reproducible
3DBP, there are several challenges to be addressed in EXO quality (cargo composition) with minimal batch-
printing EXO-laden bioink formulations to form scaffolds to-batch variability. Besides, the choice of the bioreactor
for tissue engineering applications. Firstly, the appropriate system, be it the stirred tank bioreactor or hollow fiber
selection of bioprinting technique is crucial for the optimal bioreactor, plays a crucial role in the large-scale production
bioprinting of EXOs. For instance, 3DBP approaches of EXOs for clinical use, which is still in its infancy; this
such as stereolithography and selective laser sintering are is attributed to the influence of cell culture parameters on
[83]
often excluded, as they are associated with high operating EXO yield and cargo composition . Particularly, through
[87]
temperatures, hazardous chemical solvents, and extended the application of fluid shear stress or hypoxic culture
[88]
use of high-intensity ultraviolet (UV) irradiation , all of conditions , physical stimulation has been shown to
[82]
which might significantly affect the biological function of increase EXO quantity and confer enhanced therapeutic
bioprinted EXOs. On the other hand, extrusion, inkjet, or attributes, such as pro-angiogenic, immunomodulatory,
laser-assisted bioprinting approaches are often employed and neuroprotective effects, which are advantageous for
for bioprinting of growth factors and cell modulators, promoting vascularization in tissues in vivo.
as they are relatively gentle and do not compromise on Additionally, careful consideration needs to be given
the bioactivity of encapsulated biotherapeutics [65,82] . The to the isolation, purification, and characterization of
preferred 3DBP technique should be capable of achieving EXOs for the production of clinical grade EXOs. Although
high printing resolution to systematically create defined there is no consensus or standardized protocols for these
exosomal gradients within the scaffold. This is essential for methods, the International Society of Extracellular Vesicles
the spatial presentation and modulation of different EXO has laid out the minimal set of information required for
release kinetics to induce neotissue formation, which can studies on EXOs . With regard to this, ultracentrifugation
[89]
effectively mimic the complex microarchitecture of native (UC), wherein centrifugal forces of 100,000–200,000 × g

Volume 9 Issue 2 (2023) 460 https://doi.org/10.18063/ijb.690