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Recent cell printing systems for tissue engineering

Figure 3. Temperature-controlled 3D cell printing process, (a) increasing temperature-controlled (from 4 to 37°C) printing using
ECM-based bioinks [48, 49] and (b) low-temperature (−10°C) cell printing process [50] .

shaping ability. It also revealed the successful fabrica- nozzle and reduced the damage of the cells in the
tion of multi-layered scaffold with significantly en- printed bioink [52] . Moreover, the electric field en-
hanced mechanical properties (10 ± 2.2 MPa of You- hanced the printing stability and resolution of the dis-
ng’s modulus). For further development, initial cell pensed struts since the electric force pulled down
viability can be improved, and various types of bioink the bioink and resulted in an increase in the cohe-
can be used for low-temperature cell printing. rence between the layers and a decreased strut size.
However, there was potential cell damage when the
3.3 Electric-field Assisted 3D Cell Printing
high electric field was used, and they reported that the
Recently, the application of an electric field in cell pri- limitation of the applied voltage with their experi-
nting was proposed. Yeo et al. [51] combined elec- mental conditions was less than 2 kV.
tric-filed assisted 3D cell printing and aerosol cros-
slinking process to fabricate a 3D hybrid cell-laden 3.4 Hybrid Systems for Mechanically Stable 3D Cell-
laden Structures
scaffold. The osteoblast-like cell-laden fibers were
deposited with 0.16 kV on 3D lattice PCL struts As the 3D cell printing was derived from the conven-
(Figure 4a). The initial cell viability was reasonable tional 3D printing technology, some researchers have
(above 80%), and the cells could proliferate for pro- tried to apply the conventional 3D printing methods to
longed culture period. The fibers maintained their the 3D cell printing process. Several papers reported
shape without dispersion on the hybrid scaffold with a that the melt-plotting method, one of the most com-
significant increase in tensile modulus (4.9 ± 0.6 MPa) mon methods among non-cell printing processes, was
compared to alginate mat. Also, Yeo et al. [51] applied combined with the cell printing techniques to fabricate
an electric field to the extrusion-based cell p rinting and strengthen a cell-laden 3D structure by providing
that pneumatically printed alginate-based bioink with a firm frame or support for the soft cell-laden bio-
human adipose stem cells with the electrical field inks [48,53–56] . In 2012, Shim et al. [53] used the melt-
(Figure 4b). This reduced the wall shear stress in the plotting method with a s ynthetic polymer, poly (ε-
34 International Journal of Bioprinting (2017)–Volume 3, Issue 1