Page 78 - IJB-10-6

International Journal of Bioprinting 3D bioprinting techniques & hydrogels materials

material, and a variety of crosslinking methods, such waste through the targeted spraying of ink droplets, led to
as covalent bonding, thermogelation, cryogelation, and its widespread adoption. 63,64 In order to meet the electronic
other noncovalent bonding methods, have been widely control requirements of inkjet printing equipment, inkjet
used in the 3D bioprinting of hydrogels. Furthermore, bioinks must possess a certain level of conductivity. In
54
novel preparation methods, such as photo-crosslinking addition, due to the small deformation at the outlet of the
and click chemistry, can be used to fabricate hydrogels inkjet print nozzle, inkjet printing is not suitable for high-
with adjustable mechanical strength and degradability. 55,56 viscosity bioinks with high cell density because the high
However, synthetic hydrogels are limited by poor viscosity can cause frequent clogging of the print nozzle. 65,66
biocompatibility, toxic degradation products, and loss of
mechanical properties during degradation. 2.2. Extrusion printing
Extrusion printing technology, which has high precision
Owing to the significant potential of 3D-bioprinted and accessibility, is the most commonly utilized method for
hydrogel materials in osteochondral repair, we conducted creating 3D scaffold structures by extruding or dispersing
a review of its related applications. Firstly, we summarize continuous biomaterial strands or fibers layer-by-layer. 49,67,68
the diverse 3D printing approaches and analyze their It is widely used in the field of biomanufacturing and can
advantages and defects. Secondly, the current clinical be applied to almost all types of hydrogel polymer solutions
applications are summarized in accordance with the with different viscosities, as well as bioinks encapsulated
three segments of tissue engineering: scaffolds, cells, with high cell density. 66,69 Generally, materials with higher
and bioactive factors. Finally, this review discusses the viscosity are utilized to offer structural support, whereas
development prospects and current challenges regarding materials with lower viscosity establish critical conditions
the 3D bioprinting hydrogel system. to preserve cell viability and function. The main advantage
of this technology is that it can utilize a variety of materials
2. 3D printing methods and cell types to fabricate tissue scaffolds. In addition, it
70
The field of osteochondral repair features a variety of 3D is able to deposit biological materials with physiological
71
printing technologies, each with its own advantages and cell density layer-by-layer in a designed way. However,
disadvantages. In this section, we provide a comprehensive the high pressure and shear stress generated by the nozzle
overview of the advantages and disadvantages associated during printing may cause a decrease in cell viability; thus,
with traditional 3D printing technology as well as its it is crucial to balance printability and cell viability, which
latest advancements (Table 2; Figure 1). 7,57,58 Moreover, may require the incorporation of various bioinks with
bioinks are essential for the successful printing of tissue special rheological properties to prevent cell damage. 72-75
and organ structures. Different 3D printing technologies Moreover, the limited strand resolution (typically greater
have distinct requirements for bioinks based on their than 100 µm) is another inadequacy. 76,77
59
respective principles. Thus, we have also summarized the Fused deposition modeling (FDM) is a special
adaptability of 3D bioinks. extrusion technology, in which the material is melted
at high temperatures to transform it into a liquid state,
2.1. Inkjet printing extruded through a printer nozzle, cured, and easily used
Inkjet 3D printing technology is an advancement of to fabricate scaffolds with excellent structural integrity.
78
traditional inkjet printing that uses microtriggers in the The main drawback of this technology is the lack of suitable
print head to precisely control the spray and solidification biocompatible and bioactive materials. In addition, the
speed of ink to achieve 3D printing. This non-contact printing parameters of the bone scaffold that produces
printing method offers high precision and efficiency in the strongest mechanical properties remain unknown.
79
depositing various materials, making it one of the most Currently, in the field of FDM, traditional prototype
widely used forms of 3D printing. 60,61 Based on the ink printing methods, such as the use of semi-molten polymers
droplets formed in printers, inkjet printing can be divided and hydrogels, are gradually being developed for high-
into two types: continuous inkjet (CIJ) printing and drop- performance composite material fabrication to improve
7
on-demand inkjet (DOD) printing. In CIJ printing, material function. 80,81 Moreover, Junqueira et al. created
the bioink is forced through the nozzle under pressure, personalized drug dosage forms by combining FDM with
causing the nozzle to extrude into a stream of droplets inkjet printing. FDM is becoming one of the most widely
82
due to Rayleigh-Plateau instability. However, the use of used AM technologies.
62
CIJ printing is severely limited due to the complexity of its
equipment, bioink wastage, and potential contamination of 2.3. Laser-assisted printing
biomaterials. In DOD printing, its simplicity, precision, Laser-assisted printing, also known as laser-induced
63
and equipment efficiency, as well as the ability to minimize forward transfer, uses laser pulses to vaporize the

Volume 10 Issue 6 (2024) 70 doi: 10.36922/ijb.4472