Using organic semiconductors to restore vision

Diseases like retinal pigmentosa and macular degeneration cause eye photoreceptors to degenerate, leading to vision loss. However, because the optical neural network remains functional, artificial stimulation of the neurons can restore partial vision.

Prevailing prosthetics that artificially stimulate the retinal neurons require either an external power source or are rigid and non-biocompatible. Organic semiconductors, particularly bulk heterostructure junctions (BHJs), can function without any external power source, be coated onto flexible substrates, and are lightweight, patternable, and biocompatible. Krishnan et al. use a novel polymer BHJ to restore vision to a developing blind chick retina.

In a healthy retina, photoreceptors absorb light and transform it into electrical signals that are sent to retinal ganglion cells (RGCs), which send information about the visual scene to the brain. Damaged photoreceptors can be replaced with organic BHJs with absorption spectra spanning the visible range, about 380-750 nm, allowing them to absorb light and send electrical signals to the RGCs.

“Our polymer blend has an absorption peak around 750nm, making it suitable for vision restoration,” said author K S Narayan. “We found that the responsivity measurements of the BHJ matched the absorption profile peaking at 700nm.”

Despite the stellar BHJ performance, the retina was not always receptive. The authors found it could not be stimulated by wavelengths greater than 630 nm.

“We realized that spectral attributes of the BHJs may not be the only criteria for initiating retinal signaling, opening up questions regarding the mechanism of the polymer retina interactions,” said Narayan. “Our next projects will involve unearthing this interaction mechanism through specific experiments aimed at understanding capacitive, Faradaic, and thermal components.”

Source: “Investigations on artificially extending the spectral range of natural vision,” by Abhijith Krishnan, C. S. Deepak, and K. S. Narayan, APL Bioengineering (2023). The article can be accessed at https://doi.org/10.1063/5.0156463 .

This paper is part of the Implantable Bioelectronics Collection, learn more here .