From Singularity Hub: "In order to work in the human body, an artificial cornea has to meet some rather stringent requirements. First, it has to bond to the human eye around its edge, but stay unclouded by cells in its center. To that end, [researchers] took a widely used opthalmological polymer (found often in intraocular lenses) and adapted it with other special polymers around the edges. Combined with the application of a growth factor protein, the modified edge promoted cell growth around the periphery of the implant and secured it in place using the body's own cells. The center of the artificial cornea, however, does not promote cell growth and remains clear so that it can be seen through. The artificial cornea also has to move freely with the eyelid and balance moisture on its faces. The polymer [researchers] chose is hydrophobic, allowing tears to lubricate the surface and provide the correct moisture on both of its sides. ... The artificial cornea has passed clinical trials and is ready to see expanded use in patients this year."

Link: http://singularityhub.com/2010/06/02/germanys-artificial-cornea-getting-ready-to-restore-sight-to-thousands/