Table 2. Hydrogel Fiber-Based Biofabrication Methods for SMTE.

hydrogel-based fiber biofabrication technique	hydrogel	muscle cells	cell-seeded/cell-laden	external stimulation	fiber diameter	in vitro/in vivo main outcomes	ref
molding	alginate/fibrinogen	C2C12	cell-seeded		∼20 μm	freestanding hydrogel fibers	(103)
						C2C12 myoblasts remained adhered after the dissolution of the sacrificial layer used as a substrate
						C2C12 myoblasts aligned along the microfiber direction after 3 days of culture
molding	GelMA	C2C12	cell-laden	mechanical stretching	∼400 μm	formation of 10 cm-long microfibers	(72)
						differentiated myotube after static unaxial mechanical stimulation (35% strain)
direct electrospinning	alginate/PEO/fibrinogen	C2C12	cell-seeded	mechanical stretching	∼10 μm	aligned hydrogel microfibers bundle mimicking muscle structure	(112)
						densely aligned MHC-positive myotubes after uniaxial mechanical stimulation (static and cyclic)
hybrid electrospinning	alginate/PEO/	C2C12	cell-seeded		∼0.2 μm	fabrication of a hierarchical scaffold with hydrogel nanofibers deposited onto a PCL structure	(120)
						generation of topographical cues obtained by leaching process
						aligned and differentiated myotubes after 21 days of culture
direct electrospinning	alginate/PEO	C2C12	cell-laden		∼60 μm	defined and bead-less hydrogel electrospun microfiber with high cell viability (>80%)	(122)
						elongated and differentiated myoblasts after 7 days of culture
hydrogel casting on polymeric nanofibers	alginate/gelMA	C2C12	cell-laden		∼400 μm (core)	generation of composite core–shell microfibers	(128)
					∼200 μm (hydrogel thickness)	C2C12 myoblasts homogeneously distributed and aligned along microfiber direction after 2 days of culture
						improved electroconductivity and enhanced myogenic gene expression in microfibers coating with rGO
indirect 3D bioprinting	fibrinogen/gelatin/hyaluronic acid	hMPC	cell-laden		∼300 μm	82% of functional skeletal muscle recovery after 8 weeks of in vivo implantation in TA defect of a rodent model	(145)
						regeneration of highly organized muscle structure in the defect site
						innervation and vascularization in vivo
microfluidic-assisted 3D bioprinting	monoacrylated-PEG fibrinogen/alginate	C2C12	cell-laden		∼250 μm	high-resolution 3D bioprinted cell-laden hydrogel filaments	(7)
						formation of completely striated myofibers exhibiting spontaneous contraction
						formation of an organized and mature muscle-like structure after 28 days of in vivo implantation
direct 3D bioprinting	collagen	C2C12	cell-laden	electrical	∼350 μm	alignment of GNWs embedded into collagen-bioink using optimal 3D printing pressure and nozzle moving speed	(197)
						alignment of C2C12 myoblasts along the printing direction
						enhancement in cell alignment and MHC expression after electrical stimulation
hybrid 3D bioprinting	alginate/PEO	C2C12	cell-laden			homogeneous cell release onto thermoplastic 3D printed structure	(159)
						generation of a cylindrical bundle-like structure obtained by rolling the 3D printed scaffold
						cell alignment along the microfiber longitudinal direction
extrusion	fibrinogen	C2C12	cell-seeded		∼60–80 μm	aligned superficial microgrooves obtained by MES-based chemical treatments	(165)
						cell alignment along the microgroove direction
extrusion	GelMA/PEGMA	C2C12	cell-laden	mechanical stretching	∼100−300 μm	fabrication of microfiber with different diameter by changing sieve pore size	(167)
						high cells viability (<90%)
						MHC-positive myotubes under static mechanical stimulation
microfluidic spinning	GelMA	C2C12	cell-seeded		∼500 μm	fabrication of microgrooved microfibers	(186)
						C2C12 myoblasts alignment along the microgrooves after 3 days of culture
microfluidic spinning	alginate/collagen	C2C12	cell-laden	mechanical stretching	∼150 μm	differentiated C2C12 myoblasts after 2 days of cyclic mechanical stretching	(195)