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A Review on Bioinks and their Application in Plant Bioprinting
4.1.4. Chitosan 4.1.7. Silk

Chitosan is a polysaccharide that forms naturally when Silk fibroin (SF) is a highly versatile natural protein
chitin is deacetylated [80,81] . Chitosan is normally insoluble derived from silkworms [3,87,88] . In tissue engineering, SF is
in water, although it can be dissolved in solutions with quite valuable because of its mechanical characteristics,
pH 6.2 or lower solutions. Chitosan is also biodegradable, biocompatibility, and easily regulated degradability.
bio adhesive, non-toxic, renewable, and biocompatible; Shear thinning qualities also make this natural fibrous
however, it also has low mechanical strength, which polymer perfect for extrusion bioprinting . SF is an
[89]
limits its use in the production of hard tissues such as appealing natural hydrogel component because it can be
cartilage [80,81] (Figure 8). physically crosslinked, eliminating the requirement for
harsh crosslinking chemicals, and it can allow chemical
4.1.5. Collagen interactions beyond simple covalent interactions
[90]
Collagens are the most widespread proteins found in (Figure 11).
mammals, accounting for roughly 30% of the average total There are a number of other biomaterials used in
protein mass in mammals . Collagens are hydrophilic the bioprinting process, such as fibrin, dextran, gelatin,
[83]
proteins that play significant structure roles in the ECMs HA, Matrigel, Gellan gum, and more; however, the seven
of cells [34,83] (Figure 9). Collagens feature triple helical biomaterials discussed above are the most commonly
[15]
domains composed of three polypeptide chains. Collagens used . A summary table is provided below to highlight
come in 28 different varieties, each with a unique additional information about these biomaterials (Table 2).
number of triple helices and chain combinations [34,83] .
Collagens possess integrin-binding domains that enhance 4.2. Synthetic biomaterials
proliferation, cell adhesion, and attachment, and they are Natural polymers or hydrogels are able to directly
immunologically inactive, meaning they do not exhibit mimic the native ECM and providing the appropriate
immune responses . micro-environment for cell adhesion and proliferation
[37]
with limited adjustable capabilities . As a result, these
[56]
4.1.6. dECM
natural polymers are merged with synthetic polymers or
Decellularization of tissues by several physical and other natural polymers to form more stable, customizable
chemical processes such as detergents, enzymatic agents, 3D bioprinting structures . Unlike natural polymers,
[3]
freeze-thaw cycles results in the formation of dECMs . synthetic polymers neither facilitate nor promote cellular
[85]
The purpose of tissue decellularization is to eliminate adhesion. Because of this ability, they are promising
tissue’s cellular components while maximally conserving options for modifying features including mechanical
the structure and substance of the ECM (Figure 10). qualities, printability, and cross-linking, and so on.
[15]
The retention of the properties of the ECM has several Pluronic and poly(ethylene glycol) (PEG) are the most
advantages with respect to use as a bioink component, often utilized synthetic polymers within the field of 3D
and as a means of removing crosslinkers . bioprinting [105] . Polyethylene (glycol) diacrylate (PEGDA)
[85]

Figure 7. Diagrammatic representation of the printing process using nanocellulose based bioinks (from ref. licensed under Creative
[79]
Commons license.
180 International Journal of Bioprinting (2022)–Volume 8, Issue 4