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International Journal of Bioprinting 3D bioprinting for corneal regeneration

Figure 2. Types of mold used in corneal bioprinting.

of individual droplets in the scaffold. The difference monochromatic light beams—to print individual bioink
among these techniques lies in the methods used for droplets. The equipment consists of a laser passing
droplet production, such as a heat actuator in thermal through a focusing system, heating a quartz glass plate
inkjet printing, a pressure plate in electrostatic inkjet coated with an absorption metal layer (such as gold) at
printing, and an electric field in electrohydrodynamic a specific point. The opposite side of the plate contains
printing. Each technique has its drawbacks. In thermal a hydrogel coating. The laser induces the formation
inkjet printing, the hydrogel must be subjected to high of droplets at a designated point, which then lands
temperatures (200–300°C) for droplet formation, which on a surface equipped with a receiving substrate. One
can potentially harm the cells inside the print head and advantage of this technique is the absence of print head
inactivate biologically active proteins in the hydrogel. clogging, allowing for a wide viscosity range during
Maintaining appropriate viscosity is another challenge, printing. High cell density can be achieved without
as overly viscous materials may not form droplets compromising cell viability. However, the disadvantage
effectively and can clog the print head, while excessively is the potential introduction of particles from the metal
thin hydrogel may flow out of the print head without layer into the sample during printing, and the method
proper binding. Certain types of 3D printing methods incurs a high material cost. This technique is applicable
may be suitable for corneal printing, such as the reactive for printing various tissues and organs, including the
inkjet method (RIJ) based on inkjet technology. Duffy cornea. Techniques based on the resin polymerization
et al. utilized RIJ to construct a cornea based on poly- method include stereolithography (SLA), digital light
51
ε-lysine and gellan gum hydrogel. This inkjet printing processing (DLP), and two-photon polymerization
method employs two print heads, each containing (2PP). In these methods, a photoactive or light-binding
different components of the hydrogel. While each bioresin is used and bound layer by layer with an LED or
component is inactive on its own, their simultaneous laser-based light source. SLA and DLP are very similar,
printing on a special substrate results in binding through with SLA employing a UV laser or visible light source
physical or chemical reactions in situ. 36,47,51-53
focused on a movable platform to bind the bioresin
6.3. Light-based methods through laser scanning. In contrast, DLP focuses the
Among the 3D printing methods using light, two image of the pattern to be printed in the resin using
categories can be distinguished: laser-induced a complex mirror system, allowing for the creation of
forward printing (LIFT) and methods based on resin entire layers at once. Two-photon polymerization is a
polymerization. LIFT uses laser pulses—collimated, method in which a resin molecule absorbs two photons.

Volume 10 Issue 2 (2024) 115 doi: 10.36922/ijb.1669