Table 6.

Characteristics of most useful natural polymers (protein- or polysaccharide based) used to fabricate 3D hybrid scaffolds.

	Characteristics	Advantages	Disadvantages	References
Collagen	-Animal-derived fibrous glycoproteins -Most abundant protein in the human body -Fibrous morphology -Primary component in bone -Collagen type I is prevalent in skin, tendon, and bone, while type II is prevalent in cartilage	-Biocompatible -Biodegradable -Mimic native bone -Rich in surface-binding sites for cells -Stimulates -cell adhesion, proliferation, and differentiation	-Low stability/degradation -Difficult processing -Viral and prion contamination -Poor mechanical properties	[120,124,141,142]
Gelatin	-Derives from hydrolysis of collagen -Producing hydrogels with excellent thermostability	-Biocompatible -Biodegradable -Good cell recognition -Easy to mould -Low antigenicity -Good adhesion, proliferation, and differentiation of cells	-Chemical cross-linking needed -Poor mechanical properties -Low stability	[143,144,145,146]
Silk fibre	-Protein fibre secreted by arthropods -Consists of two main proteins, sericin, and fibroin	-Biocompatible -Biodegradable -Slow degradation -High mechanical properties -High thermal stability -High mechanical strength	-Low availability -Residues of contaminants -Brittleness	[147,148,149]
Chitosan	-Natural polysaccharide deriving from chitin (a component of crustacean exoskeleton) -Cationic nature -Relevant -vector for non-viral gene delivery	-Biocompatible -Biodegradable -Biologically renewable -Antibacterial properties -Highly availability -Fast degradation	-Low mechanical strength -Long delay in bone formation -Weak stability -Immunogenicity	[150,151,152]
Alginate	-Natural polysaccharide deriving from brown seaweed or produced by some bacteria -Most abundant marine biopolymers	-Biocompatible -Biodegradable -Easy functionalisation -Resistance to acid conditions -Negatively charged -Form soft hydrogels	-Low mechanical properties -Uncontrolled degradation -Difficult of handling	[153,154,155]
Cellulose	-Natural polysaccharide consisting of a linear chain -Structural component of the primary cell wall of green plants, many forms of algae, and oomycetes	-Biocompatibility -Bioactivity -Biomechanics -Easily converted into derivatives	-Low degradability -High retraction of cellulose hydrogels upon dehydration	[136,145]