Table 2.

Current studies of 3D bioprinting for retina tissue engineering.

3D Bioprinting Technique	Materials of the Bio-Inks and Inks	Cells	Scaffold Function/Study Objective	In Vivo	Most Relevant Results	Ref.
Laser assisted 3D bioprinting	HA-GM (hyaluronic acid with methacrylation by glycidyl-hydroxyl reaction) and PEG-RGDS (Arg-Gly-Asp-Ser peptide)	Retinal pigment epithelial cells (RPE) Human fetal retinal progenitor cells (fRPCs)	Tissue equivalent replication. Retina made up of two layers	No	Development of a structure of two layers: one assembling the retina (using fetal retinal progenitor cells (fRPCs)) and the other assembling the pigment epithelium (using RPE) Good cell viability Differentiation of fRPCs to PRs (photoreceptor cells) within the scaffold	[76]
Piezoelectric inkjet bioprinting	DMEM (Dubelcco’s Modified Eagle’s Medium) (not structural function)	Retinal ganglion cell (RGCs) neurons Retinal glial cells.	Study the effect of piezoelectric inkjet bioprinting in the viability of the printed cells.	No	Piezoelectric inkjet allows printing of retinal cells with similar survival/regeneration properties to controls Printed glial cells retain their growth promoting capability when used as substrate Cell sedimentation occurred in the nozzle area	[74]
Microvalve-based inkjet bioprinting	DMEM:F12 (not structural function) Alginate and Pluronic	Human retinal pigmented epithelial cell line (ARPE-19) Human retinoblastoma cell line (Y79)	Tissue replication. Retina made up of two layers.	No	Development of a structure formed by a monolayer with ARPE-19 cells (representing the Brunch’s membrane and the RPE monolayer) and a second with a human retinoblastoma cell line (Y79) The obtained structure is stable Viability is not compromised and cell density increases with time	[24]
Two-photon lithography	Indium tin oxide (ITO)-coated glass	Human induced pluripotent stem cell (iPSC)	Development of scaffolds to deliver correctly oriented retinal progenitor cells	No	Establishment of the best parameters to print scaffolds using two-photon lithography with adequate and reproducible characteristics Differentiation of iPSCs to retinal progenitor cells and incorporation of these last into the scaffold The retinal progenitor cells formed neural structures parallel to the vertical pores of the scaffolds	[57]
Thermal inkjet 3D bioprinting combined with electrospinning	Alginate and culture Medium for 3D bioprinting Polylactic acid (PLA) dissolved in 1,1,1,3,3,3 hexafluoro-isopropanol (HFIP) and matrigel for electrospinning	Retinal ganglion Cells (rgcS)	Development of scaffolds to deliver correctly oriented retinal progenitor cells	No	Determination of printing parameters, materials and cell density in order to print a pattern with an organization similar to that of the human retina Good cell viability, adequate orientation of the cells in the pattern and correct guidance of the axons within the scaffold The cells maintained their functional electrophysiological properties after being printed	[60]