So far, most diabetics have had to measure their blood sugar level with a prick in their fingers. In the future, however, a newly developed contact lens could possibly take on this task – and even release the right dose of a corresponding medication directly. This is made possible by a biosensor integrated into the edge of the lens, which measures the glucose content of the tear fluid, and an ultra-thin drug reservoir that opens remotely. In initial tests with rabbits, this multi-purpose contact lens has proven to be compatible and functional, as researchers now report.
Our body normally regulates blood sugar itself: if the levels in the blood increase after a meal, cells in the pancreas release the hormone insulin, which ensures that sugar is absorbed into the cells. However, in people with type 1 diabetes and severe type 2 diabetes, the insulin-producing cells no longer function properly. These patients must therefore measure their blood sugar themselves and inject the required amount of insulin. For those affected, this means that they regularly have to prick their fingertips and then have to give themselves an injection – this is painful and costs overcoming. That is why scientists have long been looking for alternative methods for measuring blood sugar and applying insulin. The first prototypes of sensor patches with microneedles or “intelligent” gels are already available, which only release the active ingredient when needed.
Contact lens is a sensor and applicator in one
Do Hee Keum from Pohang University in South Korea and his colleagues have now taken a different approach. You have developed a contact lens that determines the blood sugar level based on the tear fluid in the eye and can release the corresponding active ingredients. “The surface of the cornea represents a practical and non-invasive interface to the physiology of the human body,” the researchers explain. That is why the eye can also serve as a window into the body, especially for diabetics. We know from previous studies that changes in blood sugar levels are also reflected in the tear fluid. The new contact lens consists of five components: a biosensor for glucose, an active substance reservoir with controlled release, a microchip, an inductive power supply and a wireless communication module. All parts are so miniaturized and flat that they can be integrated into the edge of a normal contact lens, as the scientists report.
The biosensor integrated in the contact lens measures the sugar content of the tear fluid using a hydrogel, which changes its conductivity when it reacts with sugar. These changes are registered by two platinum electrodes, evaluated and transmitted by the microchip. Keum and his team tested how reliable these values are in diabetic rabbits. They got the contact lenses on the eye when they were anesthetized and then received an insulin injection. “The eye glucose sensor first showed an increase in glucose values up to 30.5 milligrams per liter and then a decrease to only 16.7 milligrams per liter when the insulin effect started,” the researchers report. “These values were in good agreement with the blood sugar values.” Repeated tests also showed that the biosensor still worked reliably even with contact lenses up to 63 days old.
Anti-diabetic retinal agent released
“But in addition to this, our contact lens has the unique function of releasing active ingredients,” emphasize Keum and his team. The drug container developed for this purpose consists of several ultra-thin compartments in a silicon dioxide thin film in which titanium and gold electrodes are integrated. A wafer-thin gold membrane covers the reservoirs. If the lens registers too high a sugar value, either the integrated chip or an external, wirelessly connected control device can trigger the metered release of the active ingredient from the compartments. This is activated by a weak current, which is fed into the container via the electrodes and dissolves the gold ceiling of the compartments. In initial tests, the lid was released within 40 seconds, the researchers report. In order to test how their contact lens works in practice, the diabetic rabbits again had to be used. They were given contact lenses that contained the plant ingredient genistein. It is considered a promising remedy for diabetic retinal damage.
The tests showed that after the active ingredient container of the contact lens was activated by a wireless signal, it released the genistein as hoped. Using fluorescence analysis of the retina, Keum and his team were able to demonstrate that the active ingredient had penetrated through the cornea of the rabbit eyes to the retina. Further analyzes showed that the agent had a therapeutic effect on the rabbit retina. “We have successfully demonstrated the feasibility of smart contact lenses for non-invasive and continuous diabetes diagnosis and diabetic therapy for retinopathy,” say the researchers. Heat release measurements also showed that these contact lenses are harmless to the eye and are compatible. “These smart contact lenses could therefore open up new avenues for health monitoring and therapy,” Keum and his colleagues state. Since a similar contact lens for glaucoma monitoring has already been approved by the US drug agency FDA, they also see good chances for their diabetes lens.
Source: Do Hee Keum (Pohang University of Science and Technology, South Korea) et al., Science Advances, doi: 10.1126 / sciadv.aba3252