Soft, smart contact lenses with integrations of wireless circuits, glucose sensors, and displays

Abstract

Recent advances in wearable electronics combined with wireless communications are essential to the realization of medical applications through health monitoring technologies. For example, a smart contact lens, which is capable of monitoring the physiological information of the eye and tear fluid, could provide real-time, noninvasive medical diagnostics. However, previous reports concerning the smart contact lens have indicated that opaque and brittle components have been used to enable the operation of the electronic device, and this could block the user's vision and potentially damage the eye. In addition, the use of expensive and bulky equipment to measure signals from the contact lens sensors could interfere with the user's external activities. Thus, we report an unconventional approach for the fabrication of a soft, smart contact lens in which glucose sensors, wireless power transfer circuits, and display pixels to visualize sensing signals in real time are fully integrated using transparent and stretchable nanostructures. The integration of this display into the smart lens eliminates the need for additional, bulky measurement equipment. This soft, smart contact lens can be transparent, providing a clear view by matching the refractive indices of its locally patterned areas. The resulting soft, smart contact lens provides real-time, wireless operation, and there are in vivo tests to monitor the glucose concentration in tears (suitable for determining the fasting glucose level in the tears of diabetic patients) and, simultaneously, to provide sensing results through the contact lens display.

Fig. 1. Stretchable, transparent smart contact lens system.

(A) Schematic illustration of the soft, smart contact lens. The soft, smart contact lens is composed of a hybrid substrate, functional devices (rectifier, LED, and glucose sensor), and a transparent, stretchable conductor (for antenna and interconnects). (B) Circuit diagram of the smart contact lens system. (C) Operation of this soft, smart contact lens. Electric power is wirelessly transmitted to the lens through the antenna. This power activates the LED pixel and the glucose sensor. After detecting the glucose level in tear fluid above the threshold, this pixel turns off.

Fig. 2. Properties of a stretchable and transparent hybrid substrate.

(A) Schematic image of the hybrid substrate where the reinforced islands are embedded in the elastic substrate. (B) SEM images before (top) and during (bottom) 30% stretching. The arrow indicates the direction of stretching direction. Scale bars, 500 μm. (C) Effective strains on each part along the stretching direction indicated in (B). (D) AFM image of the hybrid substrate. Black and blue arrows indicate the elastic region and the reinforced island, respectively. Scale bar, 5 μm. (E) Photograph of the hybrid substrates molded into contact lens shape. Scale bar, 1 cm. (F) Optical transmittance (black) and haze (red) spectra of the hybrid substrate. (G) Schematic diagram of the photographing method to identify the optical clarity of hybrid substrates. (H) Photographs taken by camera where the OP-LENS–based hybrid substrate (left) and the SU8-LENS–based hybrid substrate (right) are located on the camera lens.

Fig. 3. Wireless display circuit on the hybrid substrate.

(A) Schematic image of the wireless display circuit. The rectifier and LED are in the reinforced regions. The transparent, stretchable AgNF-based antenna and interconnects are in an elastic region. (B) Relative change in transmitted voltage by antenna as a function of applied strain. (C) Characteristics of Si diode on the hybrid substrate by applying 0 and 30% in tensile strain. (D) Rectified properties of the fabricated rectifier. (E) Photograph of wireless display on the hybrid substrate. Scale bar, 1 cm. (F) Photographs (left, off-state; right, on-state) of operating wireless display with lens shape located on the artificial eye. Scale bars, 1 cm.

Fig. 4. Characterization of the glucose sensor.

(A) Difference in response between glucose concentrations of 0.1 and 0.9 mM for the sensor with GOD functionalization (black) and GOD-CAT functionalization (red). (B) Real-time continuous monitoring according to the glucose concentrations (inset, calibration curves of the glucose sensor). (C) Electrical response for the sensors with different solutions (red, buffered solution; blue, solution of artificial tear). Each data point indicates the average for 10 samples, and error bars represent the SD. (D) Relative changes in the resistance of glucose sensor as a function of tensile strain (red, sensor on the hybrid substrate; black, sensor on the elastomeric film with no use of the hybrid substrate).

Fig. 5. Soft, smart contact lens for detecting glucose.

(A) Schematic image of the soft, smart contact lens. The rectifier, the LED, and the glucose sensor are located on the reinforced regions. The transparent, stretchable AgNF-based antenna and interconnects are located on an elastic region. (B) Photograph of the fabricated soft, smart contact lens. Scale bar, 1 cm. (C) Photograph of the smart contact lens on an eye of a mannequin. Scale bar, 1 cm. (D) Photographs of the in vivo test on a live rabbit using the soft, smart contact lens. Left: Turn-on state of the LED in the soft, smart contact lens mounted on the rabbit’s eye. Middle: Injection of tear fluids with the glucose concentration of 0.9 mM. Right: Turn-off state of the LED after detecting the increased glucose concentration. Scale bars, 1 cm. (E) Heat tests while a live rabbit is wearing the operating soft, smart contact lens. Scale bars, 1 cm.