3D-printing human corneas

The article was originally published on thechemicalengineer.com

HUMAN corneas have been 3D-bioprinted using a specially designed bio-ink containing corneal cells.

The cornea serves a vital role as the protective outer layer of the eye, but if it becomes scarred by burns or lacerations it can lead to blindness. The cornea is also susceptible to damage from the infectious disease trachoma, and around 15m people worldwide suffer from blindness due to trachoma or scarring. Corneas can be transplanted, but there is a significant shortage of corneas available, leading scientists to seek methods of fabricating them using bioprinting.

In 3D bioprinting, cells are combined with a biomaterial and deposited layer by layer to build tissue constructs. This layer by layer printing is advantageous when trying to recreate a human cornea because the stroma – the thick, transparent middle layer in the cornea – is composed of around 250 layers known as lamellae. The lamellae are made of collagen and are responsible for maintaining the strength and shape of the cornea. Reproducing the exact curvature of the cornea is also an important part of the process as the cornea is responsible for refracting some of the incident light so that the lens can focus a clear image on the retina behind.

Researchers at Newcastle University, UK, have developed a method for bioprinting human corneas using a specially designed bio-ink and a low-cost 3D bioprinter. The bio-ink is a composite of sodium alginate and collagen, and human corneal stromal cells from a healthy donor cornea can be incorporated into the bio-ink.

The cell-laden bio-ink can be 3D printed into the shape of a cornea with the help of a gel. The researchers used a method known as freeform reversible embedding of suspended hydrogels (FRESH). The FRESH method is a gel-in-gel approach that prints soft biomaterials inside a thick slurry of gelatine. The gelatine acts as a support so that the soft biomaterial, in this case bio-ink, can be printed layer by layer. The gelatine is then aspirated, leaving behind a stable construct.

"Many teams across the world have been chasing the ideal bio-ink to make this process feasible,” said Che Connon, professor of tissue engineering at Newcastle University, who led the work. “Now we have a ready to use bio-ink containing stem cells allowing users to start printing tissues without having to worry about growing the cells separately."

The cornea was formed by printing the bio-ink in concentric circles and the printing process only took ten minutes. Printing paths can be determined from models based on CT and MRI scans, making it possible to print unique corneas for individual patients.

The printed corneas still need further testing and it will be several years before they could be used for transplant, however establishing that 3D bioprinting is a feasible method is an important step towards curing blindness in millions of people.