Scientists create model of eye with 3D printer

By Mark Waghorn via SWNS

Scientists have created a model of an eye...with a 3D printer.

Using patient stem cells, the tissue represents the outer blood-retina barrier.

It opens the door to developing new treatments for age-related macular degeneration (AMD) - the leading cause of blindness.

Lead author Dr. Kapil Bharti, of the National Eye Institute, Maryland, said: "We know AMD starts in the outer blood-retina barrier.

"However, mechanisms of AMD initiation and progression to advanced dry and wet stages remain poorly understood due to the lack of physiologically relevant human models."

The technique described in Nature Methods also provides a platform for studying other diseases that affect vision.
 
The outer blood-retina barrier consists of the retinal pigment epithelium (RPE) which is separated by a membrane from a blood-vessel-rich layer of capillaries.

The membrane regulates the exchange of nutrients and waste. In AMD, fat deposits called drusen form outside, impeding its function.

Over time, the RPE breaks down leading to photoreceptor degeneration and vision loss. 
The macula is part of the retina and responsible for central vision and fine detail.

In AMD, retinal cells die and are not renewed. Risk increases with age. Most affected patients have dry AMD. The decline in sight is gradual and can take many years.

Wet AMD can develop suddenly and lead to rapid vision loss but can be treated if caught quickly.

The team combined three immature cell types in a hydrogel - pericytes and endothelials which form capillaries and fibroblasts which add structure.

They then printed the gel on a biodegradable scaffold. Within days, the cells began to mature into a dense capillary network.

After nine days, the scientists seeded retinal pigment epithelial cells on the flip side of the scaffold. The printed tissue reached full maturity on day 42.

Analyses showed the printed tissue looked and behaved similarly to the native outer blood-retina barrier.

Under induced stress, it exhibited drusen deposits underneath the RPE and progression to late dry-stage AMD, where tissue degradation was observed.

Low oxygen-induced wet AMD-like appearance. Drugs used to treat AMD suppressed this vessel overgrowth and migration and restored tissue shape. 

Dr. Bharti said: "By printing cells, we’re facilitating the exchange of cellular cues that are necessary for normal outer blood-retina barrier anatomy.

"For example, the presence of RPE cells induces gene expression changes in fibroblasts that contribute to the formation of Bruch's membrane - something that was suggested many years ago but wasn't proven until our model."

Nearly 20 million people in the United States are living with some form of AMD.

Co-author Dr. Marc Ferrer said: "Our collaborative efforts have resulted in very relevant retina tissue models of degenerative eye diseases. Such tissue models have many potential uses in translational applications, including therapeutics development."

The researchers are now using printed blood-retina barrier models to study AMD. They are experimenting with adding additional cell types to the process.