Table 1.

Details of various nanostructures and their morphologies for targeting specific tissues or cells for retinal regeneration.

Nanostructure	Nanomaterial	Size Range (nm)	Target Tissue/Cells	Ref.
Nanoparticles	Gold (Au) (diameter)	3–5	Choroidal and retinal endothelial cells	[42]
		10–12	Retina of rabbit	[43]
		10–20	Photoreceptor precursor transplantation	[44]
		80	Retinal cells	[45]
		20–80	Nucleus and mitochondria of retinal cells	[46]
		5–20	Blood–retinal barrier	[44,47,48]
	Gold (Au) nanodisk	Thickness: 20 Diameter: 160	Retina	[47]
	Silver (Ag) (diameter)	20–80	Bovine retinal endothelial cells	[49]
		40–50	Porcine retinal endothelial cells	[50]
	Superparamagnetic iron oxide nanoparticles	Diameter: 5–20	Retina	[51]
	Magnetite	10	Retina and cells	[52,53]
NWs	Poly (ε-caprolactone) (PCL) membranes	Length: 2500	Implantation into subretinal space	[54]
	Gallium phosphide (GaP)	Length: 500–4000	Retinal cells	[55]
	n-type silicon	Length: 4400	Retinal cells	[56]
	Gold (Au) nanorods	Thickness: 10–35	Retinal cells and photoreceptors	[57]
Hybrid nanostructure	Gold NPs coated over titania (TiO2) NWs	Au NP diameter: 5–15 TiO2 NW length: 2000	Artificial photoreceptors	[54,58,59,60,61]
	Gallium phosphide (GaP) rod and cone	Length: 20–2500	Ganglion cells, and bipolar cells	[55]
	Gold NPs coated over silicon NWs	Au NP diameter: 5–10 NW length: 500–2500	Artificial photoreceptors	[62,63]
	Thin film functionalized with the NPs	Diameter: 5–50	Photoreceptors	[64,65]
	p–n junction silicon NWs	NW length: 10–120	Membranes of live bipolar cells	[66]
	Au-coated carbon nanotube (Au-CNT)	Au NP diameter: 5–20 CNT length: 500–2500	Subretinal space of mice	[67]
	Iridium oxide (IrOx) combined with reduced graphene oxide	IrOx diameter: 2–25 CNT length: 2–2500	Subretinal implant into live mice	[68]
	Iridium oxide (IrOx) coated with CNT	IrOx diameter: 5–25 CNT length: 500–2500	Retinal cells/tissues	[52,69,70,71,72]
	Core–shell-structured β-NaYF4:20%Yb, 2%Er@β-NaYF4 nanoparticles	Diameter: 30–40	Subretinal space of mice	[15]
Nanoscaffolds	Natural polymer: gelatin, fibrin, chitosan, laminin, and hyaluronic acid	Diameter/porosity: 100–200	Extracellular matrix and cell attachment	[73,74,75,76,77,78]
	Synthetic polymer: poly (lactic-co-glycolic acid) (PLGA), poly (ε-caprolactone) (PCL), poly (L-lactic acid) (PLA), polyimide, and poly (l-lactide-co-ε-caprolactone)	Diameter/porosity: 50–500	RPE, biological activity, extracellular matrix, and cell attachment	[79,80,81,82]
	Biohybrid: nanofibers of Bruch’s membrane	Diameter/porosity: 100–200	RPE and biological activity	[83]