**4.8 Corneal**

 Diseases of the cornea have a significant impact on visual health worldwide. Corneal opacity is the fourth leading cause of bilateral blindness globally [78, 79]. A total of approximately 50,000 corneal transplantations were performed in the United States in 2013 [80–82], yet drawbacks to this procedure include a reduced quality of visual recovery due to an early endothelial cell loss, detachment of the posterior lamellar grafts and vascular in-growth into the lamellar plane [79]. Using sodium alginate and methacrylated type I collagen mixed with corneal keratinocytes, Isaacson et al. extruded corneal scaffolds [83]. To produce a concave structure, gelatin was used as a support material and had a hollowed out shape. Cell viability of cornel keratinocytes were 90% after 1 day post-fabrication which dropped to 83% after 7 days.

The limbus borders the cornea and provides it with limbal epithelial stem cells (LESCs) for regeneration. Damage caused to it by disease or injury can impair a person's vision [84]. Using laser-assisted bioprinting Sorkio et al. printed human embryonic stem cell derived limbal epithelial stem cells (hESCs-LESCs) and hASCs for the repairing of the limbus [85]. *Ex vivo* assessment of the structures was performed on porcine corneal tissue, with results compared to commercially available acellular Matriderm® sheets as a control. The bioprinted scaffolds exhibited strong adhesion with the host tissue enabling hASCs migration, while control group had a more limited response.
