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3D bioprinting technology for regenerative medicine applications

[3]
instructions to develop biological constructs . Bio- puter-aided design techniques to make structures that
printing can be defined as the use of materials science closely mimic the anatomical structures of organs/
and fabrication techniques to build biological con- tissues. Based on its ability to produce organ con-
structs containing tissues, cells and biomolecules with structs with native tissue biology, bioprinting has re-
[4]
a particular organization and biological function . ceived enormous attention in the field of regenerative
Bioprinting techniques have been recently explored medicine. Even though bioprinting of a whole organ,
for different biological applications due to their poten- suitable for transplantation, is yet to be achieved, this
tial to overcome most of the problems associated with technology is moving fast and could soon satisfy
[5]
the classical tissue engineering methods . Classical hopes to solve the shortage of organs for transplanta-
tissue engineering involves the combination of scaf- tion in the future.
folds, cells and compounds, such as growth factors [5,6] . In this review article, we will first describe different
Scaffolds are seeded with the cells and compounds bioprinting methods such as extrusion-based printing,
that promote tissue regeneration. Tissue engineering cellular inkjet printing, laser-assisted printing, inte-
strategies have been utilized for the regeneration of grated tissue organ printing (ITOP) and robotic bio-
various organs such as skin, trachea, bone, esophagus printing used to develop scaffolds and other biomedical
[5]
and myocardium . Though tissue engineering ap- constructs. Secondly, we describe the bioinks available
proaches have been shown to be clinically effective, for bioprinting and the challenges involved in devel-
all scaffolds up-to-date lack complex and intricate oping a suitable bioink that satisfies the critical re-
[7]
structures of the native tissue . In addition, the tissue quirements for printing. Finally, the key applications of
engineered scaffolds do not mimic the native archi- bioprinting in regenerative medicine are summarized,
tecture of the tissues [8,9] . and its future directions are outlined.
The key requirements of a tissue engineered scaf-
fold are (1) biocompatibility; (2) biodegradability; (3) 2. Methods for Bioprinting Tissue/Organs
adequate porosity; (4) mechanical strength; 5) biomi- Bioprinting of a tissue or an organ is a complex
[6]
metic structure and (6) therapeutic activity . Various process which depends on the inherent properties of
fabrication methods such as electrospinning, freeze- the bioinks, printing techniques and cellular systems
drying, phase separation, gas foaming, particulate used for printing. Furthermore, the resolution of the
leaching and solvent casting have been developed to printed structure is controlled by the parameters such
produce tissue scaffolds [10] . However, tissue engineer- as needle orifice size, surface tension and viscosity of
ed scaffolds do not completely mimic the native ar- the bioink, temperature, and humidity [14–16] . A typical
chitecture of the tissues, have difficulties to support bioprinting system can dispense bioinks onto a suita-
the growth of cells in 3D and have problems to depo- ble substrate of choice using a cartridge or a syringe.
sit different cell types in the scaffolds at specified lo- More advanced bioprinting systems contain multiple
cations [8,9,11,12] . Besides, many of these fabrication print heads, and each one can be loaded with the same
methods involve the use of organic solvents which or different bioinks [17] . Printing patterns can be gener-
impair the cellular growth [13] . Further, tissue engi- ated, modified and printed using computer-aided
neered scaffolds do not completely fulfill all the ideal software such as CAD (Computer Aided Design). The
requirements needed for tissue regeneration as dis- turnaround time taken for making modifications in the
cussed above. On the other hand, bioprinting offers an CAD files is just seconds to minutes making this
alternative approach solving most of the problems process easy and user-friendly [18] . This is advanta-
associated with the current tissue engineering methods. geous to bioprint custom made structures such as tis-
Tissue engineering strategies are mainly involved in sues and organs for transplantation. The prerequisites
the development of scaffolds to promote regeneration/ to develop a bioprinting process comprise characteris-
repair of tissue defects. While 3D bioprinting methods tics, such as CAD, high resolution to obtain the mi-
can also be used to develop whole or parts of organs, cro/nanoarchitecture and high-precision to localize
the main advantage is its potential to print whole or- cells in a 3D environment. With these design strategies
gans for transplantation purposes. Bioprinting can be in mind, bioprinting is using biomimicry and 3D tis-
used to fabricate biological constructs with defined sue generation. The biomimicry approach enables the
micro/nano architectures combining scaffolds with fabrication of constructs with features that mimic the
cells, and bioactive molecules. Bioprinting uses com- native architecture of the tissue as close as possible [19] .

10 International Journal of Bioprinting (2016)–Volume 2, Issue 2