Wednesday, 17 Jul 2019

Organic printing inks may restore sight to blind people

Fabricated using cheap and widely-available organic pigments used in printing inks and cosmetics, it consists of tiny pixels like a digital camera sensor on a nanometric scale

Linköping University - An array of semitransparent organic pixels on top of a ultrathin sheet of gold

2 May 2018 | Editor

Researchers from the Laboratory of Organic Electronics, Linköping University led by Eric Glowacki, principal investigator of the organic nanocrystals subgroup have developed a tiny, simple photoactive film that converts light impulses into electrical signals.

Fabricated using cheap and widely-available organic pigments used in printing inks and cosmetics, it consists of tiny pixels like a digital camera sensor on a nanometric scale. Researchers hope that it can restore sight to blind people.

These signals in turn stimulate neurons (nerve cells). The research group has chosen to focus on a particularly pressing application, artificial retinas that may in the future restore sight to blind people.

The Swedish team, specialising in nanomaterials and electronic devices, worked together with researchers in Israel, Italy and Austria to optimise the technology. Experiments in vision restoration were carried out by the group of Yael Hanein at Tel Aviv University in Israel.

The results have recently been published in Advanced Materials.

The retina consists of several thin layers of cells. Light-sensitive neurons in the back of the eye convert incident light to electric signals, while other cells process the nerve impulses and transmit them onwards along the optic nerve to an area of the brain known as the "visual cortex".

An artificial retina may be surgically implanted into the eye if a person's sight has been lost as a consequence of the light-sensitive cells becoming degraded, thus failing to convert light into electric pulses.

The artificial retina consists of a thin circular film of photoactive material, and is similar to an individual pixel in a digital camera sensor. Each pixel is truly microscopic - it is about 100 times thinner than a single cell and has a diameter smaller than the diameter of a human hair. It consists of a pigment of semi-conducting nanocrystals. Such pigments are cheap and non-toxic, and are commonly used in commercial cosmetics and tattooing ink.

"We have optimised the photoactive film for near-infrared light, since biological tissues, such as bone, blood and skin, are most transparent at these wavelengths. This raises the possibility of other applications in humans in the future"

Eric Glowacki

Eric describes the artificial retina as a microscopic doughnut, with the crystal-containing pigment in the middle and a tiny metal ring around it. It acts without any external connectors, and the nerve cells are activated without a delay.

"The response time must be short if we are to gain control of the stimulation of nerve cells"

"Here, the nerve cells are activated directly. We have shown that our device can be used to stimulate not only neurons in the brain but also neurons in non-functioning retinas."

David Rand, Postdoctoral researcher at Tel Aviv University

Eric Glowacki and his research group work at the Laboratory of Organic Electronics in Norrkoping, Sweden. The research group is part of a larger research initiative called the Wallenberg Center for Molecular Medicine, WCMM, at Linköping University. This initiative has created the unique environment necessary to develop this technology in a collaboration between nanomaterials scientists, biomedical engineers, and biologists. https://liu.se/en/research/wallenberg-centre-for-molecular-medicine

Direct Electrical Neurostimulation with Organic Pigment Photocapacitors

David Rand | Marie Jakešová | Gur Lubin | Ieva Vėbraitė | Moshe David‐Pur | Vedran Đerek Tobias Cramer | Niyazi Serdar Sariciftci | Yael Hanein | Eric Daniel Głowacki

First published: 2 May 2018 | https://doi.org/10.1002/adma.201707292


An efficient nanoscale semiconducting optoelectronic system is reported, which is optimized for neuronal stimulation: the organic electrolytic photocapacitor. The devices comprise a thin (80 nm) trilayer of metal and p–n semiconducting organic nanocrystals. When illuminated in physiological solution, these metal–semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to electrically stimulate neurons with safe light intensities. The devices are freestanding, requiring no wiring or external bias, and are stable in physiological conditions. The semiconductor layers are made using ubiquitous and nontoxic commercial pigments via simple and scalable deposition techniques. It is described how, in physiological media, photovoltage and charging behavior depend on device geometry. To test cell viability and capability of neural stimulation, photostimulation of primary neurons cultured for three weeks on photocapacitor films is shown. Finally, the efficacy of the device is demonstrated by achieving direct optoelectronic stimulation of light‐insensitive retinas, proving the potential of this device platform for retinal implant technologies and for stimulation of electrogenic tissues in general. These results substantiate the conclusion that these devices are the first non‐Si optoelectronic platform capable of sufficiently large photovoltages and displacement currents to enable true capacitive stimulation of excitable cells.


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Source: Linköping University

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