Human body fluids and secretions contain molecules known as biomarkers which contain a large amount of information on the health of the body and the presence of diseases. Among secretions, tears are considered the best source of biomarkers, with concentrations similar to those found in the blood. Tears are also sterile, readily available, and less susceptible to the damaging effects of temperature change, evaporation, and the rate of secretion.
A collaborative team, which also includes a group of the Terasaki Institute for Biomedical Innovation, has developed a manufacturing method to address all challenges in making diagnostic and therapeutic hydrogel contact lenses for biomarker detection (here you can find the complete study).
The importance of biomarkers
Useful and measurable biomarkers found in tears include sodium ions, useful indicators of dry eye syndrome (afflicts 25% of Italians), and the glucose molecules, an early diagnostic tool for diabetes. Additionally, tear pH measurement can be used to check cell viability, drug efficacy, and signs of disease.
For this, the ability to effectively collect tears and measure their pH and biomarker levels in real time is very important. The approach explored by the Terasaki Institute team is based on the idea of biosensors to obtain diagnostic and therapeutic contact lenses. Such contact lenses would include tiny channels on their surface to guide the flow of tears into tiny reservoirs for collection and monitoring. Smart lens with formidable capabilities, to put it briefly.
Diagnostic and therapeutic contact lenses: hydrogel hypothesis
Flexible and transparent materials, known as hydrogels, are currently also used commercially to make contact lenses. They are easy to work with and affordable. However, to date, they have not been shown to be ideal materials with which to model channels and tanks, as they are sensitive to the necessary manufacturing techniques.
In previous studies, hydrogels have had less luck. They have been vulnerable to deformations caused by solvents or by the temperature and vacuum conditions that are required by some manufacturing methods. Other methods have produced hydrogel channels with rough surfaces or non-uniform sizes.
The team began by optimizing the hydrogel's components to achieve elastic characteristics that would allow them to engineer it into various shapes with a smooth surface profile. They later modeled microchannels in the hydrogel with the use of a 3D printed shape. The final step in the manufacturing process was to collect the hydrogel channels by bonding an additional layer of hydrogel to the surface of the microchannel.
Once completed, the prototype was extensively tested in conveying and collecting fluids. The extent of (artificial) tears in the canals was measured at different hydration levels. Note also that when the hydrogel was slightly dehydrated, the flow of liquid in the channels stopped, but when additional rhythmic pressure was applied, the flow resumed. This was an important demonstration supporting the hypothesis that blinking would also provide the necessary pressure and additional hydration to promote tear flow into the contact lens and, therefore, into the eye.
In addition to the successful fabrication of hydrogel microchannels for commercial diagnostic and therapeutic contact lenses, we also found that blink pressure can facilitate tear exchange in the lens through these microchannels. This is an exciting discovery. And it paves the way for preventing dry eye disease, a condition commonly found in contact lens wearers. We aim to develop a proprietary contact lens that actively treats this condition by improving tear flow in the eye.
Shiming Zhang, Ph.D., research team of the Terasaki Institute
Possible applications of new diagnostic and therapeutic contact lenses
"Production of the successful prototype described here and efforts to refine its capabilities mark significant progress in contact lens biosensing." To say it is Ali Khademhosseini, Ph.D., director and CEO of the Terasaki Institute. "This innovative work fits well with our institute's mission to create solutions that restore or improve people's health."
