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Recent cell printing systems for tissue engineering

printing materials at a size of 50 µm using an ink-jet devoted to developing the technology using numerous
printer. The printed cell-laden bioinks showed self- trials and innovative methods. Primarily, they ha-
assembling characteristics between the cell-aggregates ve been modified from conventional 3D-printing me-
and formed tissue-like structures during culturing time. thods, and adapting them for cell culture. The 3D cell
The results provided the basis for the fabrication of printing techniques are mainly classified into three te-
desired tissues or organs by printing and culturing chniques: (1) laser-assisted, (2) inkjet, and (3) extrusion
cells at the required sites. cell printing [14–16] . However, unfortunately, the current
Owing to the strengths of 3D cell printing techno- cell printing processes have not successfully designed
Oogy for tissue regeneration, many studies have been or fabricated 3D porous cell-laden structures (Table 1).

Table 1. Advantages and disadvantages of basic 3D cell printing techniques.
Techniques Laser-assisted Inkjet Microextrusion
Advantages Single cell manipulation High cell viability High mechanical properties
Nozzle free Noncontact nozzle Short fabrication time
Usage of high viscosity bioink Printed cell patterns using different cell types Printing of various types and viscosities
High resolution Multicell heterogeneous constructs of bioink
High accuracy High throughput Wide range of biocompatible materials
High gelation speed High gelation speed
Disadvantages Low mechanical properties Low mechanical and structural integrity Low cell viability due to nozzle wall
Long fabrication time Long fabrication time shear stress and mechanical stress
Damage cells due to heat generated Low upper limit for viscosity of bioink Low accuracy
from laser energy Low reproducibility Cell death due to changes in dispensing
Aggregate in the final tissue construct Cell aggregation pressure and bioink concentration
Clogging of the nozzle orifice
References [18–21] [23–27] [29–33]

In this mini-review, we present the basic cell print- significantly increase if a scaffold is built in larger
ing technologies and show several modified cell scale. In addition, the potential cell damages
printing systems, which can overcome the limitations caused by the thermal energy of the laser is another
of the current cell printing processes, with a focus on a factor to be concerned [17,22] . Therefore, the integra-
mechanically modified 3D cell printing process (Table tion of techniques, such as fast gelation of droplets
2). In addition, since, in many cases, modified cell or bio-papers, are actively attempted to overcome
printing systems are closely related to hydrogel-EDVHG the existing limitations.
bioinks, we mention various bioinks.
2.2 Inkjet 3D Cell Printing Technique
2. Basic Techniques of 3D Cell Printing
In the early generation of 3D cell printing, the inkjet
2.1 Laser-assisted 3D Cell Printing Technique cell printing technique was devised to print biomate-
rials in a 3D structure by remodeling the existing in-
Laser-assisted cell printing is a 3D printing method to
pattern and assemble bioinks by direct writing using kjet printers. Inkjet cell printers were designed to use
laser. It has been rise to be an automated system that three general methods: thermal, piezoelectric, and
prints the cell-laden bioinks with a high resolution, acoustic inkjet printers using heat, piezoelectric, and
accuracy, and precision [17] . As the lasers is beamed on acoustic wave actuators, respectively, to dispense
[23–27]
the absorbing layer, the bioink is deposited in mi- cell-embedded microdroplets (Figure 1b) . This
cro-sizes by controlling scanning mirrors and focusing technique is widely used for its high cell viability and
lens in x and y-axis (Figure 1a) [18–21] . This nozzle-free resolution in microscale structures. In addition, it is
fabrication prevents cell o r material clogging often easily accessible and inexpensive. However, the inkjet
found in extrusion-based 3D cell printing tech- printers can only use comparatively low viscosity ma-
niques [16] . However, despite of these advantages, it is terials with a low cell density. This is a critical draw-
difficult to print macroscale 3D porous structures back for a stable 3D cell printing process [25,27] . To
using laser-assisted cell p rinting. Owing to a r ela- overcome this problem, many approaches, such as
tively low flow rate, the vaporization of cell-la- developing a crosslinking method, are being studied
den bioink and possibility of cell contamination can and examined. Although inkjet 3D cell printing has

28 International Journal of Bioprinting (2017)–Volume 3, Issue 1