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International Journal of Bioprinting 3D bioprinting for musculoskeletal system

bioprinting methods are inkjet bioprinting, extrusion- the printed structure and lower-viscosity materials are
based bioprinting, and light-based bioprinting. Briefly, beneficial for maintaining cell survival and function. The
inkjet bioprinting typically involves spraying low-viscosity trade-off between printability and cell viability needs to
bioinks onto a substrate in discrete droplets, while be considered in the selection of bioinks. Bioinks with
extrusion-based bioprinting extrudes viscous bioink different ranges of viscosity (30 to over 6 × 10 mPa·s) for
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into continuous filaments. The bioinks for light-based use in extrusion-based bioprinting have been reported.
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bioprinting are composed of photoresponsive materials, Extrusion-based bioprinting is the most common printing
which are solidified by light irradiation. method for musculoskeletal tissue engineering, mostly
because of its advantages, including a wide selection of
2.1.1. Inkjet bioprinting available bioinks, ease of operation, fast printing, and
Inkjet bioprinting is the earliest developed 3D bioprinting ability to create large and complex constructs.
technology and its concept is the same as that of traditional
2D inkjet printing. The technology, also known as drop- 2.1.3. Light-based bioprinting
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on-demand bioprinting, uses various energy sources to Light-based bioprinting is an additive manufacturing
allow for pattern deposition of discrete droplets onto technology with very high resolution and accuracy. The
a substrate layer. The system achieves the deposition technology uses a tuned light source to solidify or deposit
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of droplets by applying pressure pulses to overcome bioinks. The printed structure supports higher cell survival
the surface tension of the materials. By adjusting the (85%–95%) due to the absence of high temperature and
energy parameters, the density, shape, and size of the extrusion shear force damage. Stereolithography (SLA)
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droplets can be controlled. These droplets can be ejected and digital light processing (DLP) are typical light-based
to predetermined positions to create a 3D construct bioprinting technologies that could crosslink polymer
with different concentration gradients. Inkjet printers solutions based on the light pattern on each layer to fabricate
with a reservoir connected to multiple nozzles enable desired constructs. The samples printed by these methods
simultaneous printing of different cells and biological usually present high precision and smooth surfaces.
components. Moreover, this technology has relatively Another common light-based bioprinting method is laser-
fast printing speed and is ideal for printing structures for assisted bioprinting (LAB), which does not depend on
soft tissue regeneration. However, it is limited by several printheads, and the structures printed by this method can
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disadvantages. Due to the low driving force of inkjet support high cell viability (>95%). For LAB, laser pulses
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printers, bioinks with a higher viscosity are not suitable for are manipulated to induce the bioink droplets to transfer
inkjet printing, narrowing the selection range of printable from the donor layer to the collecting substrate and form
materials. The use of lower-viscosity bioinks results in 3D structures. Volumetric bioprinting has recently become
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poor mechanical strength of scaffolds, which fail to meet a potent tool because of its ability to quickly fabricate tissue
the requirements of in vitro culture and transplantation. In constructs. 22,23 The bioinks polymerize and form expected
addition, it is difficult to print constructs with physiologic structure when exposed to a specific light source. The
cell density because of the nozzle clogging caused by high process can be completed in seconds without the need for
cell density bioinks. support and sacrificial materials, significantly improving the
suitability of biomaterials. Compared with the traditional
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2.1.2. Extrusion-based bioprinting extrusion-based and laser-assisted bioprinting technologies,
Currently, extrusion-based bioprinting has become one volumetric bioprinting has obvious advantages in accuracy,
of the most popular technologies of 3D bioprinting due resolution, and cell viability, opening new possibilities for
to its versatility and affordability. This method usually musculoskeletal regeneration and disease modeling.
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fabricates a 3D construct by utilizing mechanical forces Overall, the major advantage of light-based bioprinting
driven by air pressure or a motor to extrude viscous technologies is their capacity to fabricate complex designs
cell-laden bioinks through a nozzle in a controlled with high resolution and instantly print structures without
and filamentous manner. The precision of the printed supporting materials. Despite these advantages, there are
construct can be adjusted by controlling the printing also some limitations, such as high cost and limited choice
speed, extrusion speed, printing temperature, nozzle of photopolymerizable bioinks.
size, and other parameters. Extrusion-based bioprinting
allows successful fabrication of constructs with high cell 2.2. Bioinks
density (>10 cells per mL). Another major advantage In 3D bioprinting, living cells encapsulated in bioinks are
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for extrusion-based bioprinting is that any materials with used and printing parameters are adjusted in the fabrication
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sufficient viscosity can be used as candidates for bioinks. process of living tissues. The printability of bioinks is defined
Higher-viscosity materials provide structural support for as the capacity to generate 3D structures with good fidelity

Volume 10 Issue 1 (2024) 77 https://doi.org/10.36922/ijb.1037