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International Journal of Bioprinting 3D bioprinting techniques & hydrogels materials

large printer, making it more convenient, but the printing methods for creating heterogeneous tissues, such as
speed is relatively slow. During the printing process, the osteochondral tissue and bone.
planar configuration of each layer is determined by the
projected light, and the 3D structure can be manipulated 3. 3D-bioprinted hydrogel system for
via a light absorber that attenuates the light, resulting in osteochondral integration repair
high resolution. 105,106 Furthermore, since the entire layer
of bioresin can be polymerized immediately, SLA results In this section, we summarize the application of 3D-printed
in higher printing speeds compared to both nozzle- hydrogel systems in osteochondral integrated repair
related and nozzle-free methods. 107,108 from three aspects: scaffold, cells, and bioactive factors.
Hydrogels are the most commonly used materials in 3D
Digital light processing (DLP) printing is predicated bioprinting due to their ability to control printability and
on the local photopolymerization of liquid monomers or viscosity and mimic native tissues. 118,119 As hydrogels alone
oligomers triggered by ultraviolet light in the presence of also promote cell differentiation and tissue regeneration
photoinitiators, which involves the utilization of a DMD in vivo, this review will give an overview of hydrogel
to project the entire optical pattern plane onto the optical substrates in the stent section and then summarize the
polymer solution for concurrent printing, accelerating application of composite hydrogels.
the printing process. 109-111 Furthermore, the continuous
updating of the projected optical pattern enables the 3.1. Hydrogel substrates
movement of the platform carrying the printed object, 3.1.1. Alginate-based hydrogels
thereby facilitating the printing of smooth 3D objects Alginate contains two distinct guluronic acids that are
without artificial interfaces. The greatest advantage of found naturally in the cell walls of algae and the capsules
112
DLP technology is its high printing speed and geometric of Azotobacteria and Pseudomonas, and can thus be
resolution (up to the nanoscale). 113,114 Thus, it is more produced from brown seaweed and bacteria. 120,121 Owing
appropriate for printing large structures at the micron level to its excellent biocompatibility, degradability, and ability
than SLA. to form gels, it is widely used in tissue engineering. In
122
The 2PP system is capable of fabricating high-resolution osteochondral repair, alginate hydrogels are commonly
arbitrary 3D microstructures at the nanoscale through employed as bioinks to fabricate scaffolds via 3D printing.
the utilization of a near-infrared laser femtosecond light Chawla et al. fabricated an alginate scaffold that is
source. The femtosecond laser is focused precisely onto compatible with blood and cells and facilitates the survival
115
the bioresin, and its movement is governed by an oil- and proliferation of osteoblasts in vitro, verifying its
immersed objective. Moreover, the polymerization process biological activity. Moreover, they also demonstrated that
is initiated by two-photon absorption. The system can be the solution formulated with 2.5% alginate and 5% gelatin
accomplished within a remarkably short period of time. exhibited optimal viscosity. 123
Nevertheless, the application of this system is restricted by Despite these benefits, poor cellular adhesion,
material degradation and bubble damage caused by high migration, and viability may affect cell proliferation and
laser power. 57 survival. In addition, its weak mechanical properties
124
2.5. Tomographic volumetric printing may compromise its shape fidelity and integrity after
Tomographic volumetric printing (TVP) is an emerging printing. To address these shortcomings, alginate has
printing approach that constructs entire 3D objects by been incorporated with a variety of bioactive molecules,
projecting light patterns from various angles, rather such as bioactive proteins (collagen and fibrin) and cell-
than through iterative layer-by-layer polymerization, adhesion peptides (arginine-glycine-aspartic acid), to
125-127
and the method features a resolution of up to 80 µm. improve its ability to promote cell proliferation.
116
As TVP technology advances, it becomes feasible to Additionally, some bioactive inorganic materials
build structures that accommodate arbitrary cells. The (calcium carbonate) and polymers (chitosan) are
117
high cost and complexity are the main limitations of its employed to enhance the mechanical properties of these
128-130
application. Additionally, continuous chaotic printing has materials. Furthermore, Chawla et al. reported that
been developed to fabricate layered structures. A print loading cells in alginate hydrogels also increased their
123
head equipped with a static mixer is utilized to generate mechanical strength, as the cells secreted matrix.
a mixed bioink, and a defined internal layer is extruded to Owing to the inherent defects of alginate gel, 3D-printed
exponentially expand the interface area between adjacent pure alginate hydrogels may not meet the requirements
bioinks. These approaches could provide efficient of osteochondral repair, warranting further research into
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Volume 10 Issue 6 (2024) 73 doi: 10.36922/ijb.4472