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International Journal of Bioprinting Bioprinted organ-on-a-chip with biomaterials

structure containing cells—has found widespread use 2.2.2. Inkjet bioprinting
across various fields of bioengineering. This method has Inkjet bioprinting system is a non-contact technique that
been developed using a range of engineering techniques. delivers controlled droplets of cells or biomaterials using
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Among the most used 3D bioprinting technologies are various methods, including electrically heated bubbles,
inkjet, extrusion-based, and laser-assisted bioprinting. valve-controlled pressure pulses, and piezoelectric
Each of these technologies is classified based on the method actuators (Figure 2B).
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of releasing cells and biomaterials, and each method comes The printhead of a thermal inkjet printer is electrically
with its distinct advantages and disadvantages. The heated to create a pressure pulse that pushes the droplet
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following is a brief description of these technologies, and out of the nozzle. The maximum heating temperature of a
Table 2 provides a summary of 3D bioprinting methods thermal printer is as high as 300°C; however, the duration
along with bioink requirements.
is relatively short, so it does not adversely affect cell survival
2.2.1. Extrusion-based bioprinting or biomaterial denaturation. Thermal inkjet printing offers
An extrusion-based bioprinting system applies specific advantages such as low cost and high printing speed.
pressure to the syringe nozzle, depositing viscous However, it does have limitations in controlling the size or
biomaterial to form a continuous liquid bead (Figure direction of the droplets. Additionally, mechanical stress
2A). As the extrusion head or stage moves along the on the cells and frequent nozzle clogging are encountered. 80
z-axis, the next layer is sequentially stacked on top of A valve-controlled pressure pulse inkjet printer
the previously deposited layer, resulting in the creation applies a specific pressure and controlled pulsed voltage
of a 3D biological structure. Control over the amount to the liquid in the printhead and then opens and closes
of extruded biomaterial is achieved by adjusting the the electromechanical valve to form droplets. Compared
pneumatic or mechanical pressure, nozzle size, or nozzle with other inkjet printing methods, this approach has
speed along the x- or y-axis. 23,75,76 The composition of an the advantage of enhanced cell deposition and viability
extrusion-based bioprinting system is relatively simple because it does not use heat. 81
compared with other bioprinting systems, rendering it
a cost-effective option. Extrusion-based bioprinting is A piezoelectric inkjet printer has a piezoelectric
a commonly used method for fabricating biological 3D crystal that generates sound waves inside the printhead
structures due to its capability to process biomaterials in response to a controlled voltage. These sound waves
of various viscosities and produce high-density cell divide the liquid biomaterial in the printhead into several
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structures or large-scale 3D structures. However, droplets and enable them to be ejected at a constant speed.
extrusion-based bioprinting systems face challenges When a softer sound field is formed, the droplets exhibit
high precision and directionality, leading to enhanced cell
in extruding biomaterials with very low viscosities, survival. 82,83
rendering it difficult to maintain the shape of a 3D
structure. Additionally, issues such as nozzle clogging These inkjet printing methods are widely employed
or cell survival concerns may arise when extruding because they can be used for printing low-viscosity
biomaterials with high viscosities, leading to potential biomaterials and exhibit high cell viability. Additionally,
challenges associated with high shear stress. 78 inkjet printing is advantageous for manufacturing small

Table 2. Conventional 3D bioprinting methods and bioink requirements
Bioink requirements Conventional 3D bioprinting methods
Extrusion-based Inkjet Laser-assisted
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Bioink viscosity 30–6 × 10 mPa⋅s <10mPa⋅s 1–3 × 10 mPa⋅s
2

Cell concentration High Low Medium
6
(<10 cells/mL) (~10 cells/mL)
8
Resolution 200–1000 μm 10–50 μm 10–100 μm
Cell viability ~90% ~85% ~95%
Advantages Wide choice of materials; simple High speed; low cost High cell viability; high repeatability;
process; good printability and fidelity high efficiency
Disadvantages Nozzle blockage; long printing time Few materials; low printing accuracy; Requirement of the laser source;
small structure complex workstation
Reference 184 185 186

Volume 10 Issue 1 (2024) 26 https://doi.org/10.36922/ijb.1972