Intraocular pressure (IOP) is a crucial physiological indicator for the diagnosis and treatment of glaucoma. The current infrequent IOP measurement during an office visit is insufficient to characterize the symptoms. Here, an LC resonator strain sensor in a contact lens, composed of a stretchable inductance coil using liquid metal and a chip capacitor, was developed for real-time IOP monitoring. The lens sensor was operated on the basis of ‘mechanical-electrical’ principle. The rising IOP will increase the curvature radius of the cornea and stretch the inductance coils through the cornea and tear film, leading to a decrease in resonant frequency. The theoretical model of the whole process has been established and explored. The sensor has been scientifically designed and fabricated to be ultra-soft, comfortable, safe without leakage and has a stable signal. The sensor was calibrated on two silicone rubber model eyeballs, respectively, showing linear and stable responses. An experiment on porcine eyes in vitro was conducted. The sensor can track IOP changes and shows much higher sensitivity than the current mainstream lens sensors, which is even an order of magnitude higher than the existing inductive sensor. The high-sensitivity and ultra-flexible liquid-metal-based lens sensor is a promising approach for 24 h continuous IOP monitoring in clinics.
In this paper, we present the development of microfluidic contact lenses, which is based on the advantages of wearable microfluidics and can have great potential in the ophthalmology healthcare field. The development consists of two parts; the manufacturing process and the usability tests of the devices. In the manufacturing process, we firstly extended silane coupling and surface modification to irreversibly bond plastic membranes with microchannel-molded silicone rubber, to form the plastic-PDMS plane assemblies, and then molded the plane into a contact lens by thermoforming. We systematically investigated the effects of thermoforming factors, heating temperatures and the terrace die’s sphere radius on channels by using the factorial experiment design. In addition, various tests were conducted to verify the usability of the devices. Through blockage and leakage tests, the devices were proved to be feasible, with no channel-blockages and could stand high pressures. Through a wearing test, the contact lenses were confirmed to be harmless on the living body. Furthermore, by performing the manipulating test, the device was proved to be liquid-controllable. These works provide a foundation for the applications of microfluidic contact lenses in ophthalmology.
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