industry. 3D printing had entered the medical field by the late 1990s, with surgeons

printing dental work, custom prostheses, and renal sacs. As a result, the term ‘3D

bioprinting’ was coined to describe the 3D printing of living organisms, materials

science, or active molecules using a material known as ‘bioink’. As with additive

manufacturing, ‘3D bioprinting’ utilizes layer-by-layer deposition of bioink to create

3D structures such as tissues and organs (Gu et al. 2020).

There are three types of 3D bioprinting: ‘extrusion droplet bioprinting’, ‘inkjet-

based bioprinting’, and ‘laser-based bioprinting’. Extrusion-based biomimetic

deposits ‘bioinks’ in filaments via pneumatic, hydraulic, or solenoid sprayer

systems, whereas inkjet-based bioprinting generates ‘bioink’ droplets via heat

energy,

microvalve,

or

electrodes.

Structures

are

3D

printed

using

a

photopolymerization

hypothesis

in

laser-based

bioprinting

methods

like

stereolithography (SLA). In laser direct-write and laser-induced forward energy

transfer, it can also be used to precisely position cells (LIFT). Each of these

bioprinting techniques necessitates a different set of ‘bioinks’ with different viscos-

ity, flowability, crosslinking chemical properties, and bioactivity. Shear-thin bioinks

are required for extrusion-based bioprinting, whereas low viscosity funds are needed

for inkjet bioprinting. To meet the growing demand for new ‘bio-printable’

materials, ‘bioink’ layout and synthesizing have advanced significantly in recent

years. Making 3D structures with low viscosity ‘bioinks’, for example, has always

been tricky. These ‘bioinks’ can now be compacted into a granular structural with

strain rate hydrogels. These hydrogels harden around the extruded structure, trying

to prevent it from collapsing and thus fixing the issue. Bioprinting is used to create

in vitro tissue designs for drug test, clinical diagnostics, and a variety of other in vitro

applications, in relation to printing organs (Ashammakhi et al. 2019).

In case of use of 3D bio-printed organs in regenerative medicine and tissue

engineering, Kim et al. described a tubular tracheal graft made of two layers of

polycaprolactone that was 3D printed. This tracheal graft seeded with induced

pluripotent stem cell (iPSC)-derived mesenchymal (MSCs) and chondrocyte stem

cells assisted the regeneration of tracheal mucosa and cartilage in a rabbit model of a

segmental tracheal defect (Kim et al. 2020). Galarraga et al. used a norbornene-

modified hyaluronic acid (NorHA) macromer as a symbolic bioink for cartilage

tissue engineering. Printed structures containing MSCs increased compressive

moduli and expressed biochemical content like native cartilage tissue after long-

term culture (Galarraga et al. 2019). Vidal and his team used 3D printed adjustable

calcium phosphate scaffolds with and without a vascular pedicle to treat large bone

defects in sheep. To model the microenvironment of the oesophagus (Vidal et al.

2020). Nam et al. used a bioink made of decellularized matrix from the mucosal and

muscular layers of native oesophageal tissues. Using gelatin-based bioinks. Leucht

et al. investigated vasculogenesis in a bone-like microenvironment (Nam et al. 2020;

Leucht et al. 2020). To resemble the different layers of osteochondral tissue, Kilian

in his lab used a calcium phosphate cement (CPC) and an alginate-methylcellulose-

based bioink containing primary chondrocytes. In case of drug testing and drug

discovery, ‘liver-on-a-chip’ was used successfully to assess the drug-drug interac-

tion and cytotoxic analysis of acetaminophen (Kilian et al. 2020). The results

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G. Aggarwal et al.