Table 2.

Tissue engineering applications of natural hydrogels in heart, nervous system, and bones.

	Hydrogel	Approach	Outcome	Ref
Cardiac Tissue Engineering	GelMA	Nanofunctionalization with CNTs, GO, and rGO	Good electrophysiological properties, electrical conductivity, proper mechanical stiffness, and maturation of CMs	[149]
		3D Bioprinting + Fibronectin	Enhanced CM survival and spreading	[150]
		3D Bioprinting + GNRs	Spreading of CMs and GNRs provided propagation of electrical signal	[139]
		Nanofunctionalization with GNW	Contractile behavior of CMs and enhanced maturation	[151]
	Chitosan	Nanofunctionalization with AuNPs and GO	Desirable degradation, CM maturation, increased electrical conductivity. In vivo, improved heartbeat and conductivity	[152]
	Collagen	Nanofunctionalization with AuNPs	Increased CM maturation, recovery of infarcted myocardium, reduced scar size	[153]
		Nanofunctionalization with CNTs	Supporting cardiac function with improved contraction	[154]
	Alginate	Injection	Promising results for cardiac regeneration	[155]
		Nanofunctionalization with peptides	Improved CM attachment and maturation and alignment	[156]
Neural Tissue Engineering	Collagen	Collagen tubes	Nerve regeneration in mice was observed, formation of neurites, and proper electrical behavior	[157]
	Collagen and fibrin	In vivo transplantation of scaffold	Enhanced axonal count	[158]
	Fibrin	Nanofunctionalization with MWCNTs and PU	Increased conductivity and neuronal regeneration	[159]
	Gelatin	Electrospinning	Schwann cell alignment and axon organization	[160]
		Electrospinning with dECM	Increased cellular function and proliferation	[161]
	Gelatin + Chitosan	Nanofunctionalization with PEDOT	Increased conductivity, neurite growth, neuronal regeneration and synapse formation	[162]
	GelMA	3D bioprinting	Cell proliferation and survival and neuronal differentiation	[163]
	Alginate	Nanofunctionalization with graphene and PVA	Increased material stiffness and electrical conductivity, PC12 cell attachment and spreading	[164]
		Nanofunctionalization with CAFGNs	Electroactive hydrogel with increased cell proliferation and improved neurite formation. In vivo implantation decreased inflammation	[165]
	Chitosan + HA	In vivo implantation	Increased formation of myelinated nerve fibers and increased myelin sheet thickness	[166]
	Silk fibroin	Electrospinning	Enhanced cell survival and neuron differentiation	[167]
		Electrospinning + Melanin	Improved signal propagation, improved cell differentiation	[168]
Bone Tissue Engineering	Collagen	Cryostructed porous scaffold	Mimicking of bone ECM with attachment of hMSCs. In vivo implantation showed promising results for meniscus regeneration	[169]
		Functionalization with HA by freeze-drying	Gradient mimicked bone structure and showed good bone functionality, osteogenic differentiation, and ALP activity	[170]
	Gelatin	Functionalization with BMP-2 and HA	Increased cell proliferation, osteogenic differentiation, and ALP activity	[171]
	GelMA	Nanofunctionalization with AuNPs and 3D bioprinting	Cell attachment, osteogenic potential, calcium deposition, ALP activity, enhanced X-ray attenuation	[172]
		3D bioprinting	High cell viability, calcium deposition, osteogenic gene expression	[173]
		3D Bioprinting and Nanofunctionalization with VEGF and silicate nanoplatelets	Mimicking of blood vessel with HUVEC incorporation. Osteogenesis and calcium deposition, as well as osteogenic gene expression	[174]
	Alginate	Nanofunctionalization with RGD-sequences	Promotion of osteogenesis and osteogenic differentiation of MSCs	[175]
	Silk fibroin	Calcium phosphate Nanofunctionalization	Self-healing properties promoting osteogenesis and formation of new bone tissue after 8 weeks in vivo.	[176]