In space it is almost impossible to put drops in the eyes: liquids do not flow downward in weightlessness, and standard drops rely on gravity. Researchers from the Korea Advanced Institute of Science and Technology (KAIST) led by Professor Ki-Hun Jeong, together with a team led by Professor Se Joon Woo of Seoul National University Bundang Hospital, have proposed a flexible patch that delivers eye drops without the help of gravity. The work was published in the journal Sensors and Actuators B: Chemical.
On long space flights it is important for cosmonauts to be able to take care of their health themselves without constant help from medics. In weightlessness body fluids shift toward the head, which can change the structure of the eyes and vision. The usual method of instilling drops does not work there without modification.
Instead of gravity, the scientists used gas pressure. A single flexible patch combines microchannels for liquid and a chamber where a chemical reaction takes place. When a person presses the activation zone, the gas formed inside pushes the drop along the microchannel toward the eye. The reaction is based on the interaction of vitamin C (ascorbic acid) and baking soda (whose main component is sodium bicarbonate): on contact with water they release carbon dioxide. Its pressure propels the medicine.
A filter stands between the reaction chamber and the chamber with the drops: it lets gas through but retains liquid. Thus the reagents do not mix with the medicine, while the pressure is transmitted. The patch needs no external pump or electrical power, so it is suitable for conditions with limited equipment.
On Earth the researchers verified that the patch releases drops evenly even when the direction of gravity changes. In tests on volunteers it delivered the drug in roughly the same way as conventional drops. This shows the potential of the method, which does not depend on the direction of gravity. However, the results were obtained only in ground experiments with different directions of gravity and in people; further checks are needed for real space.
The technology could also be useful on Earth - for example, for people with hand tremor or other physical limitations that make it difficult to aim a bottle at the eye. Among possible users the authors name patients with Parkinson's disease.
"The flexible eye-drop patch developed in this study is a wearable platform capable of delivering medicine without complex additional equipment, and we hope it will find application in space medicine and other fields," KAIST's press service quoted Professor Jeong as saying.