For instance, one type of artificial cornea currently marketed under the name AlphaCor is also based on a hydrogel. Yet the material contains only half the amount of water as the Stanford implant. As a result, it can’t support the growth of epithelial cells, which many researchers say could explain AlphaCor’s high failure rate.
Because the Stanford hydrogel is inert, cells don’t normally stick to it. So, with the help of Stanford bioengineer Jennifer Cochran, the researchers devised a way of tethering collagen to the artificial cornea’s surface. The collagen, in turn, binds to the epithelial cells. Cochran is working on incorporating growth factors and other components of the cell’s natural environment into the material.
Using photolithography, Frank’s team can also create patterns of microscopic pores around the edges of the implant. That way, he says, when the cornea is implanted in the patient’s eye, cells will migrate through the pores, anchor the cornea, and help integrate the material with the native tissue. This will also reduce the number of sutures required to keep the artificial cornea in place, says Frank.
Shen, who was not involved in the Stanford effort, says that the development of new artificial corneas will be important for solving a critical health problem. However, she wonders whether the design of these new implants is well suited for use in the developing world. For instance, hydrogel-based implants might require relatively complicated surgery. “That could be difficult in terms of training surgeons abroad,” Shen says. She is also concerned about the potentially high cost of the materials, whether they can be applied to large populations, and whether they will require a lot of follow-up care.
So far, the Stanford group has shown that the diffusion of glucose across the material is equal to that of the human cornea, and preliminary studies in rabbits show that implants can support the growth of epithelial cells. The researchers say that studies in human patients are still several years away.