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Synthetic Retina Developed with Natural Materials

Bio-pixel array

Bio-pixel array (University of Oxford)

5 May 2017. A chemistry lab in the U.K. developed a synthetic retina made of natural materials resembling human tissue that in lab tests detects static, moving, and grey-scale images. The team from University of Oxford, led by doctoral candidate Vanessa Restrepo-Schild, published its findings in the 18 April issue of the journal Scientific Reports.

Restrepo-Schild and colleagues in the chemical biology lab of Hagan Bayley are seeking better options for people needing retinal implants to treat degenerative eye disorders, such as retinitis pigmentosa. The retina is a layer on the back of the eye with light-sensitive cells that convert light into neural signals, carried into the brain by the optic nerve. Retinitis pigmentosa is an eye disease caused by genetic defects that damages cells in the retina affecting night vision, and sometimes peripheral and central vision, leading to blindness. The condition affects 1 in 2,700 people, or about 100,000 in the U.S.

Current retinal implants, like the Argus II device reported in July 2016 by Science & Enterprise, can help restore perceptions of light and movement, but not full eyesight, for people with retinitis pigmentosa. These devices use microelectronics, with tiny camera cells and chips, made with hard, rigid materials. The Oxford team designed and tested an alternative retinal implant technology with materials better resembling natural human tissue.

The researchers developed the photosensitive device using a layer of hydrogel, a water-based biocompatible polymer gel material, topped with photo-sensitive droplets. These droplets, made with lipids or natural oils and water, are arrayed on the hydrogel, with each droplet containing a protein known as bacteriorhodopsin produced by a well-studied desert bacteria. Bacteriorhodopsin reacts to light energy by pumping out protons, which in the Oxford technology, provides the sensitivity to light.

The device’s hydrogel surface acts both as a structure for the light-sensitive protein droplets, called bio-pixels, and a medium to conduct the energy they produce. The protons produced by the bio-pixels travel across the hydrogel layer, where they are converted into electrical signals. These signals are then amplified and captured, creating patterns from the bio-pixels that can be recorded and measured, in an integrated system.

The team tested 16 bio-pixels in a 4×4 array, connected to electrodes and displayed on a corresponding output grid. The first tests captured static images, produced by photomasks of lines and box patterns of tiny squares, with one square for each bio-pixel. The second group of tests captured moving images, created with photomasks of tiny squares in different shapes moving across the array of bio-pixels, resembling a simplified Tetris game.

A third set of tests assessed the system’s ability to detect grey-scales in static images. In these tests, photomasks of tiny squares produced crossed-line patterns, with different degrees of transparency in the squares, creating a variety of different grey-scale shades. The authors report in all tests, the bio-pixel array accurately captured these images.

The initial tests reported in the paper, say the researchers, proved the technology’s concept, and in the next steps they plan to produce and test an implant device. The team also expects to expand the bio-pixel array to enable the recognition of colors and more complex shapes and symbols. The university filed a patent for the technology.

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