Table 3.

Bioprinting scaffolds.

Bioink type	Hydrogels	Synthetic	Natural
Description	Composed of hydrophilic polymers crosslinked either through covalent bonds or held together via physical intramolecular and intermolecular attractions1	Derived from synthetic and natural sources e.g. polyethylene glycol (PEG)-based materials such as PEG diacrylate (PEGDA) and polyacrylamide (PAAm)-based gels	Made with biological material e.g. collagen, fibrin, hyaluronic acid
Advantages	Hydrophilicity allows for easy exchange of gases and nutrients, highly biocompatible, easily modified	Easily modified e.g. Easily tailored functional groups, non-immunogenicity	Highly biocompatible
Disadvantages	Poor cell seeding, poor mechanical properties1	No cellular attachment sites2	Limited modification, shear thinning2
Viscosity	Adjustable3	PEG: low Pluronic-acid: high2	Gelatin and Fibrinogen: low Hyaluronic Acid: high (up to 1000 Pa s) Silk: high2