NIH researchers use 3D bioprinting to create

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Thursday, December 22, 2022, 11 a.m. ET

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Dustin Hays
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NIH researchers use 3D bioprinting to create eye tissue
The technique provides a model to study the genesis of age-related macular degeneration and other eye diseases

Scientists have used patient stem cells and 3D bioprinting to produce eye tissue that will provide insight into the mechanisms of blinding diseases. The National Eye Institute (NEI) research team, part of the National Institutes of Health, has printed a combination of cells that form the outer blood-retinal barrier, an eye tissue that supports light-sensitive photoreceptors in the retina. The technique provides a theoretically unlimited supply of patient-derived tissue to study degenerative retinal diseases such as age-related macular degeneration (AMD).

“We know that AMD starts in the outer blood-retinal barrier,” said Kapil Bharti, Ph.D., who directs the NEI Section on Translational Eye and Stem Cell Research. “However, the mechanisms of AMD initiation and progression to the advanced dry and wet stages remain poorly understood due to the lack of physiologically relevant human models.”

The outer blood-retinal barrier consists of the retinal pigment epithelium (RPE), separated by Bruch’s membrane from the blood vessel-rich choriocapillaris. Bruch’s membrane regulates the exchange of nutrients and waste between the choriocapillaris and the RPE. In AMD, deposits of lipoproteins called drusen form on the outside of Bruch’s membrane, impairing its function. Over time, the RPE breaks down, leading to degeneration of photoreceptors and loss of vision.

Bharti and colleagues combined three types of immature choroidal cells in a hydrogel: pericytes and endothelial cells, which are key components of capillaries; and fibroblasts, which structure tissues. The scientists then printed the gel onto a biodegradable scaffold. Within days, the cells began to mature into a dense capillary network.

On the ninth day, the scientists seeded retinal pigment epithelial cells on the back of the scaffold. The imprinted tissue reached full maturity on day 42. Tissue analysis and genetic and functional testing showed that the imprinted tissue looked and behaved similarly to the native outer blood-retinal barrier. Under induced stress, the printed tissues exhibited patterns of early AMD such as drusen deposits under the RPE and progression to late stage dry AMD, where tissue degradation was observed. Wet AMD-like appearance induced by low oxygen, with hyperproliferation of choroidal vessels that have migrated into the sub-RPE area. Anti-VEGF drugs, used to treat AMD, suppressed proliferation and migration of these vessels and restored tissue morphology.

“By printing cells, we facilitate the exchange of cellular signals necessary for the normal anatomy of the outer blood-retinal barrier,” Bharti said. “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 has not been proven. up to our model.”

Among the technical challenges Bharti’s team faced were generating a suitable biodegradable scaffold and achieving a consistent print pattern through the development of a temperature-sensitive hydrogel that achieved rows distinct when cold but dissolving when the gel warmed. Good row consistency allowed for a more accurate system of quantifying tissue structures. They also optimized the cellular mixing ratio of pericytes, endothelial cells and fibroblasts.

Co-author Marc Ferrer, Ph.D., director of the 3D Tissue Bioprinting Laboratory at the NIH’s National Center for Advancing Translational Sciences, and his team provided expertise for the biofabrication of outer blood-retinal barrier tissue” in a well,” as well as analytical measures to enable drug testing.

“Our collaborative efforts have resulted in highly relevant retinal tissue models of degenerative eye disease,” Ferrer said. “These tissue models have many potential uses in translational applications, including therapeutic development.”

Bharti and his collaborators are using printed models of the blood-retinal barrier to study AMD, and they are experimenting with adding additional cell types to the printing process, such as immune cells, to better recapitulate native tissues.

Reference:
The 3D outer retinal barrier reveals the RPE-dependent choroidal phenotype in advanced macular degeneration. Natural methods. https://www.nature.com/articles/s41592-022-01701-1. DOI:10.1038/s41592-022-01701-1.

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