Pig collagen helped restore eyesight in people who were blind — study
As far as transplants go, corneas are hard to come by. Bioengineering synthetic ones might change that.
Across the globe, there are about two billion people living with some level of vision loss. For half of those individuals, the loss of sight can be mitigated, to some extent, with the help of corrective lenses, surgery, or other rehabilitative treatments.
But not everyone has access to available or affordable eye care. And for individuals living in resource-strapped regions of the world whose vision loss is due to a damaged or diseased cornea — the transparent layer of tissue enveloping the eye — getting a transplant can be even harder to come by.
But a group of Swedish researchers aims to change that with a little help from a porky friend. In a study published Thursday in the journal Nature Biotechnology, bioengineers at Linkӧping University fashioned an implant resembling a human cornea using collagen from pig’s skin. They also developed a minimally invasive, stitchless method that could make it easier to treat keratoconus, a progressive condition that occurs when the cornea thins out and bulges into a cone versus its usual spherical shape. Among 20 people who underwent the cornea-swapping surgery, all saw their vision restored, albeit not to a perfect 20/20.
“The results show that it is possible to develop a biomaterial that meets all the criteria for being used as human implants, which can be mass-produced and stored up to two years and thereby reach even more people with vision problems,” Neil Lagali, the study’s co-author and professor in experimental ophthalmology at Linkӧping University, said in a press release.
“This gets us around the problem of shortage of donated corneal tissue and access to other treatments for eye diseases.”
How they did it — Using collagen-based hydrogels — materials that absorb rather than dissolve in water — to regenerate corneas and other tissues isn’t a novel idea, says Brian Aguado, a professor of bioengineering at the University of California San Diego, who was not involved in the study.
“Porcine skin collagen is a byproduct already used in FDA-approved wound dressings,” he writes in an email to Inverse. But what is novel is how the researchers molded the pig collagen to make their implant using a “double crosslinking” method.
The cornea is chock full of collagen linked together in a pattern reminiscent of a cross-linked chain fence. In diseases like keratoconus, these collagen cross-links falter and weaken, which is why the cornea loses its shape and stability.
Molding pure collagen in the lab by itself can be hard to do — it’s a soft, squishy material prone to breakdown. In order to give it shape and stabilize it, the researchers replicated this crosslinking twice over by treating highly purified collagen harvested from pig skin with chemicals and laser beams.
After testing its mechanical and optical properties, including making sure it was compatible with human skin (it didn’t cause any obvious reactions), non-toxic (appears so), and had a reliable shelf life (up to two years), the researchers go to work testing out their porcine-derived corneas in humans.
Pooling a pilot study of 20 individuals in India and Iran (keratoconus affects 2.3 and 4 percent of the rural population, respectively), two countries where lack of access to medical care makes cornea transplants extremely limited. Working with local surgeons, the Linkӧping team employed a technique that didn’t require cutting off the entire bulge of the cornea laying atop the iris (the eye’s colored part). Instead, they created a small incision pocket in the old cornea and tucked the new implant right in. (The researchers first tested out this technique in pigs before trying it out in humans.)
Fourteen of the 20 folks operated on were mostly blind. When they were followed up over a two-year period, all former keratoconus sufferers had a vast improvement in their sight: about 20/26 vision for the Indian cohort and 20/58 for the Iranian one (this isn’t perfect vision, of course, but fairly close). Their corneal thickness and curvature were also, much to the researchers’ surprise, restored to normal.
Why it matters — To emphasize, corneas are in high demand in regions of the world where corneal problems are the fourth leading cause of blindness after glaucoma, cataracts, and age-related macular degeneration. It’s estimated that only one out of 70 patients is lucky enough to get a cornea transplant.
Even when someone is able to get the surgery, it carries with it a 10 percent risk of rejection down the road, according to the Mayo Clinic. Since all twenty operated on exhibited no complication for the two years they were followed, this new pork collagen transplant may offer a survival advantage free from the immune system’s interference.
Beyond corneas, the new technology could prove useful in other areas of regenerative medicine such as recreating or repairing bone, cartilage, or nerves.
“Stabilization of implanted materials is certainly of interest for generating robust tissue replacements depending on the application,” explains Aguado. “I believe the hydrogel stabilization technique used in this contribution can be used for a wide variety of cell-free tissue engineering applications.”
Digging into the details — Aguado says it’s a good sign that the transplants were able to restore sight to keratoconus sufferers but in a small study without controls (which the researchers also acknowledge as a limitation to their study), the full therapeutic value of the new tech still needs parsing out.
“The results are from a pilot study, so more patients will be required for a future randomized clinical trial comparing the new hydrogel material with patients receiving human donor corneas as controls,” he says.
What’s next — The Linkӧping team is planning a much larger clinical study in Europe this time for potentially treating presbyopia, an age-related condition where the eye’s lens loses flexibility and its ability to change shape. Presbyopia affects over one billion people in the world with the highest prevalence among adults age 35 and older in Latin America.
“We’ve made significant efforts to ensure that our invention will be widely available and affordable by all and not just by the wealthy,” Mehrdad Rafat, the paper’s lead researcher and associate professor of tissue engineering at Linkӧping University, said in a press release.
“That’s why this technology can be used in all parts of the world.”