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International Journal of Bioprinting Robotic in situ bioprinting

2. In situ bioprinting modalities The aforementioned methods are the most common
modalities in bioprinting. Their derivatives, which include
2.1. Extrusion-based bioprinting acoustic droplet ejection , direct-write assembly , fused
[24]
[25]
[26]
[27]
Extrusion-based bioprinting involves the continuous deposition modeling , and powder printing , have also
deposition of bio-ink through syringes or nozzles to been developed recently. These printing modalities can be
construct 3D tissues or organs . Applied pressure, further applied to a variety of printers (or end effectors)
[21]
piezoelectric effect, and solenoid dispensing have been mounted on robotic arms for dexterous and precision
employed by bioprinters of this type. Extrusion-based biofabrication.
bioprinting generally offers gentle fabrication with high 3. Bioprinting robots
regard for cell viability. One of the most promising features
of this technology lies in the fact that multiple cells and Robots and handheld devices are commonly employed to
biocompatible materials can be simultaneously applied achieve in situ fabrication of 3D structures with complex
[15]
through different nozzles. Furthermore, it is regarded as shapes and curved surfaces . Robotics can facilitate
the most mature solution for in vivo clinical applications, bioprinting tasks with high accuracy and automation level
owing to its decadal recognition in arthroscopy repair. without exhaustion. Robots have been routinely used in
[28]
Commercial bioprinters that are based on this technology minimally invasive surgical settings , thereby paving
[29]
have been successfully developed. the way for in situ bioprinting . Robot configurations
determine the working space, deposition flexibility, and
2.2. Inkjet bioprinting operational precision of bioprinting, of which Cartesian
In inkjet bioprinting, bio-ink is sprayed onto the deposition coordinate, articulated, and parallel robots are the main
[30]
substrate via droplet or continuous ejection to establish 3D configurations . The typical robotic-assisted bioprinting
living constructs . Similar to traditional inkjet printing, process is shown in Figure 2.
[22]
this technology has certain merits, including a broad 3.1. Configurations
selection of commercial apparatus due to the low cost of
machine modification. Ease of multiple printer heads 3.1.1. Cartesian coordinate robots
installation facilitates heterogeneous architectures of Conventional 3D printers deposit materials layer-by-
tissue or organ and ensures a sound printing resolution. layer along the vertical direction (Figure 3A) using the
An ability to keep integrity is critical as newly printed axis-aligned slicing method. A planar surface is often
cells are expected to have long-term survival in the in vivo needed to support the printed structure. Adopting this
environment. A prompt establishment of mechanical mechanism allows for individualized modeling and
properties through supporting biomaterials is valuable. rapid fabrication. The procedure involves 3D computer
Since the printing conditions and size are limited, inkjet model design and slicing followed by layer deposition of
bioprinting is merely practical for in vivo repair or biomaterials through force, sound, light, electricity, and
fabrication of exterior structures, such as skin. heat. Extrusion-, inkjet-, and optics-based methods can
be readily combined with Cartesian coordinate robots.
2.3. Laser-assisted bioprinting
The advantages of this technology for bioprinting include
Laser-assisted bioprinting employs a laser to polymerize low cost, technology transferability from conventional
bio-ink into solid structures . Laser direct-write 3D printing, and a high degree of stiffness of the
[23]
techniques have been widely used in this approach. By printing platform, whereas the challenges are evident
laser pulses, living cells are selectively transferred from in anisotropic bioprinting . Since body tissues are
[31]
the supply container to defect locations. Stereolithography anisotropic, different anisotropic material properties
can also be used for in vivo bioprinting to allow precise along an axis are needed. Moreover, the stair-step effect is
fabrication of structures with micro or nanoscale resolution. non-negligible . During the fabrication of each layer, the
[32]
The fact that the heat generated by the laser or exposure motion of the nozzle is restricted to a two-dimensional
to ultraviolet lights may impair cell viability should be plane along the direction of gravity. This inevitably
considered. Moreover, laser or stereolithography-based results in the staircase effect, where surface distortion
techniques may be unsuitable for in vivo scenarios due to occurs between neighboring layers. To improve printing
the machine size. Although the advantage of optics-assisted flexibility, Edward Shi et al. proposed a method combining
bioprinting in ultrahigh resolution and precision to meet Cartesian and curvilinear printing head motion for in
the requirements of clinical settings, there is still room for vivo bioprinting. A biomimetic “tendon cable” soft robot
improvement in terms of photocrosslinkable biomaterials arm was added to a conventional Cartesian three-axis
and photonics techniques. 3D printer to facilitate motion along six independent

Volume 9 Issue 1 (2023) 100 https://doi.org/10.18063/ijb.v9i1.629