Researchers use 3D bioprinting to create eye tissue

Scientists created eye tissue using patient stem cells and 3D bioprinting, which will help them understand the processes of blinding illnesses. The National Eye Institute (NEI), which is part of the National Institutes of Health, printed a mixture of cells that comprise the outer blood-retina barrier, which is eye tissue that supports the retina's light-sensing photoreceptors. The approach allows researchers to examine degenerative retinal illnesses such as age-related macular degeneration with a theoretically infinite supply of patient-derived tissue (AMD).

"We know that AMD begins at the outer blood-retina barrier," said Kapil Bharti, Ph.D., chair of the National Eye Institute's Section on Ocular and Stem Cell Translational Research. "However, because to a paucity of data, mechanisms of AMD onset and development to advanced dry and wet phases remain poorly understood."

The outer blood-retina barrier is made up of the retinal pigment epithelium (RPE), which is separated from the blood-vessel-rich choriocapillaris by Bruch's membrane. Bruch's membrane mediates nutrition and waste exchange between the choriocapillaris and the RPE. Lipoprotein deposits known as drusen grow outside Bruch's membrane in AMD, impairing its function. The RPE degrades with time, resulting in photoreceptor degradation and visual loss.

Bharti and colleagues used a hydrogel to mix three immature choroidal cell types: pericytes and endothelial cells, which are important components of capillaries, and fibroblasts, which give tissues shape. The gel was then printed on a biodegradable scaffold by the scientists. The cells began to grow into a dense capillary network within days.

On the ninth day, the researchers implanted cells from the retinal pigment epithelium on the other side of the scaffold. On day 42, the printed tissue was fully developed. The printed tissue resembled the natural outer blood-retina barrier in appearance and behaviour, according to tissue investigations, genetic tests, and functional analysis. Under conditions of generated stress, printed tissue displayed early AMD characteristics, such as drusen deposits under the RPE, and advanced to late dry stage AMD, where tissue deterioration was seen. Low oxygen levels caused a wet AMD-like look with choroidal vascular hyperproliferation that moved into the sub-RPE zone. When used to treat AMD, anti-VEGF medications slowed the formation and migration of blood vessels while also improving tissue shape.

The interchange of cellular cues required for typical outer blood-retina barrier architecture is made possible by cell printing, according to Bharti. For instance, the presence of RPE cells causes fibroblasts to express different genes, which helps to build the Bruch's membrane. This was predicted many years ago but wasn't confirmed until our model.

Creating an appropriate biodegradable scaffold and obtaining a consistent printing pattern were two technological issues that Bharti's team tackled. They developed a temperature-sensitive hydrogel that produced distinct rows while the gel was cold but disintegrated when the gel warmed. A more exact technique of assessing tissue architecture was made possible by good row consistency. Additionally, they adjusted the proportion of fibroblasts, endothelial cells, and pericytes in the cell combination.

The outer blood-retina barrier tissues were biofabricated "in-a-well" by co-author Marc Ferrer, Ph.D., director of the 3D Tissue Bioprinting Laboratory at the National Center for Advancing Translational Sciences of the National Institutes of Health. His group also provided analytical measurements that allowed for drug testing.

According to Ferrer, "our combined efforts have produced extremely pertinent retina tissue models of degenerative eye disorders." Such tissue models offer a wide range of possible translational applications, including the creation of medicines.

To further mimic genuine tissue, Bharti and colleagues are experimenting with adding additional cell types to the printing process, including as immune cells. These models of the blood-retina barrier will be used to research AMD.