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Dhakshinamoorthy Sundaramurthi, Sakandar Rauf and Charlotte A. E. Hauser

containing a mixture of islets of Langerhans and algi- terning. Though, this field is in its infancy, 4D bio-
nate. This construct showed sufficient oxygen and printing may help to overcome some challenges in 3D
nutrient permeability due to the suitable porosity of bioprinting [117] .
the printed construct. The islets in the bioprinted con- Vasculature is one of the important factors that de-
struct were found to be viable and also showed native termine the success of an organ transplant since it is
morphology [114] . This bioprinted hydrogel may be used responsible for nutrients delivery and oxygen supply.
as islets carrier for transplantation [114] . Though several researchers have been focusing on
In vivo bioprinting is another emerging and prom- developing vascularized constructs using bioprinting,
ising technology that may bring improvements in the further developments are required in this area of re-
field of regenerative medicine. In vivo bioprinting is search. Simple handheld bioprinters can also be fabri-
thought to be an alternative to the existing in vitro bi- cated in the future to address various clinical chal-
oprinting methods [115,116] . In vivo bioprinting technol- lenges. Bioinks and fabrication technologies could be
ogy is a medical intervention to directly print new further improved to generate fully functional tissues/
tissue constructs at the defect site. During surgical organs for regenerative medicine applications in the
procedures, the probe of the bioprinter is inserted (mi- future.
nimally invasive) into the defect site to reconstruct the
damaged tissues in vivo by printing relevant structures. Authors' Contributions
Keriquel et al. [116] have recently shown a proof-of- All authors have equal contribution in the preparation
concept study to repair osteochondral bone in a mouse of the manuscript.
model using in vivo bioprinting of n-hydroxyapatite
into the defect region. Conflict of Interest and Funding

8. Conclusions and Future Directions No conflict of interest was reported by all authors. The
research reported in this publication was supported by
Bioprinting is one of the tools for rapid prototyping to funding from King Abdullah University of Science
develop 3D constructs for clinical applications. The and Technology (KAUST).
main goal of 3D bioprinting is to develop 3D organs
that fully mimic the native tissue architecture and References
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