Alginate in corneal tissue engineering

Corneal blindness is the major cause of vision impairment and the fourth-largest leading cause of blindness worldwide. An allograft corneal transplant is the most routine treatment for visual loss. Further complications can occur, such as transplant rejection, astigmatism, glaucoma, uveitis, retinal detachment, corneal ulceration due to reopening of the surgical wounds, and infection. For patients with autoimmune disorders, allografting for chemical burns and infections is contraindicated because of the risk of disease transmission and further complications. Moreover, corrective eye surgery renders the corneas unsuitable for allografting, further increasing the gap between donor tissue demand and supply. Due to these challenges, other therapeutic strategies such as artificial alternatives to donor corneal tissue are being considered. This review focuses on the use of alginate as a building block of therapeutic drugs or cell delivery systems to enhance drug retention and encourage corneal regeneration. The similarity of alginate hydrogel water content to native corneal tissue makes it a promising support structure. Alginate possess desired drug carrier characteristics, such as mucoadhesiveness and penetration enhancing properties. Whilst alginates have been extensively studied for their application in tissue engineering (TE), with many reviews being published, no reviews exist to our knowledge directly looking at alginates for corneal applications. The role of alginate in drug delivery to the surface of the eye and as a support structure (bioinspired tissue scaffold) for corneal TE is discussed. Biofabrication techniques such as gel casting, electrospinning, and bioprinting to develop tissue precursors and substitutes are compared. Finally, cell and tissue encapsulation in alginate for storage and transport to expand the scope of cell-based therapy for corneal blindness is also discussed in the light of recent applications of alginate in maintaining the function of biofabricated constructs for storage and transport.