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Microscopic solar cells could give vision to blind

Postdoc Rasmus Schmidt Davidsen conducts research into optimizing solar cells. Now, with the help of micro-sized photovoltaic cells, he will restore sight to the blind.

Over two million people worldwide are blind because the photoreceptors in their eyes do not function properly. Photoreceptors are special types of cells whose function is to absorb light and transmit electrical signals to the brain. When the brain does not receive impulses from the photoreceptors, the patient experiences being blind. This is the situation Rasmus Schmidt Davidsen from DTU Nanotech hopes to rectify with the aid of artificial vision.

“We are working to develop an implant with several thousand tiny isolated solar cells, to be inserted behind the retina of blind patients,” says Rasmus Schmidt Davidsen.

Rasmus Schmidt Davidsen explains how the technology works:

Solar cells implanted in the eye’s retina can replace a small part of the photoreceptors that do not work.

Solar cells (the grey squares) are affected by the light which enters the eye, produces a current, and sends impulses to the optic nerve.

“The eye’s photoreceptor actually behaves in much the same way as solar cells and when we saw this, we got the idea of using some of my solar cell developments to create a chip for blind patients. Each solar cell will correspond to a pixel of artificial vision that we will try to create, and naturally, we’ll try to maximize the number of pixels to achieve the best possible result.”

One of the first challenges is to produce sufficient electricity using ambient light, explains Schmidt Davidsen.

“Even with the best solar cells, we can’t create a solar cell that produces enough electricity using visible light. We are also limited to a solar cell surface area of 3 x 3 millimetres for surgeons to be able to insert the chip. And we can’t even utilize the entire area because there has to be room for electrodes and holes, so tissue fluid can flow freely inside the eye.”

Fortunately, other research groups have solved the problem of insufficient light. The light source can be located inside a glasses frame along the lines of Google Glass.

“Using a similar technology, we can transmit light of an appropriate wavelength so that it hits the retina at the point where we have inserted our chip—so we’re not too worried about it,” says Rasmus Schmidt Davidsen.

Beneficial collaboration
That said, there are some biological challenges that the young postdoc has recently become aware of, which is why he is delighted to be working alongside Toke Bek—Senior Consultant and Clinical Professor at the Department of Ophthalmology at Aarhus University Hospital. In addition to providing medical expertise, the project also benefits from a special agreement with a major Danish company.

“We’re conducting lots of research into eye diseases and have an excellent working arrangement with Danish Crown, which supplies fresh porcine tissue,” explains Toke Bek. “We receive fresh eye tissue in under an hour. We place our order the day before and receive 30-35 refrigerated pig eyes every morning.

The 40 micrometre-high polymer columns on the solar cell are electrically active and have contact with the underlying solar cell implant, enabling them to conduct the current away from the nerve cells in the eye tissue. Over time, the nerve cells grow down into the ‘grooves’ between the columns.

The fresh pig eyes give Toke Bek and Rasmus Schmidt Davidsen a unique opportunity to test the solar cell implant on living tissue similar to that of the project goal—namely the human eye.

However, it will be a long time before this kind of procedure can actually be performed on humans. The implant will never be able to give the patient normal eyesight, but for the completely blind person, it will make a huge difference.

“Right now we’re working on the first prototype of the implant. Going forward, it remains to be seen whether we can detect a reaction in the pig eye nerve cells. We have to position the implant as close to the tissue as they would in an actual operation and then shine light on it to see how much electricity it produces.”

Consultant Toke Bek has high hopes for the project, but also sees major challenges.

“One of them is biocomplexity. There is a high probability that the tissue will reject foreign bodies—in particular in the eye. However, nanoscientists can encapsulate the implant inside materials, which the tissue finds harder to reject—and they can render it extremely small. The utility value of the solar cells is also very high—they exploit almost 100 per cent of the light—all of which speaks in favour of continuing with the project. There are some great technological advantages of collaborating with DTU.”

Source: DTU

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