We first met Prof. Hong Kyun Kim and Prof. Dai Woo Kim, who are ophthalmologists, at a symposium for research exchange. At that time, our research group was interested in wearable electronics for healthcare, and we have studied smart contact lenses in particular. Prof. Hong Kyun Kim and Prof. Dai Woo Kim, who are ophthalmologists at Kyungpook National University Hospital, have been very interested in the research on the early diagnosis of ocular diseases and their therapy. We shared with them the idea that smart contact lenses are very essential and promising because they are available for the early diagnosis of ocular diseases and healthcare. When we met at the symposium, we were convinced that our collaboration would enable us to solve the limitations of each major field and produce novel, interdisciplinary research results. As a result, we succeeded in developing a smart contact lens that can diagnose one of the typical ocular diseases, i.e., glaucoma, and this research was published in Nature Biomedical Engineering.
Glaucoma is a disease that results in blindness because the high intraocular pressure presses continuously on the optic nerve and damages it. Unfortunately, there is no current clinical technology that can repair optic nerves that have been damaged, so the early diagnosis and treatment of glaucoma is very important to prevent its progression. Thus, we fabricated a smart contact lens that can monitor the intraocular pressure by using a strain sensor. In addition, we integrated wireless technology, i.e., near field communication (NFC), with the sensor of the contact lens. The reason for the integration of wireless technology is that this technology is required to enable the real-time monitoring of intraocular pressure without causing users discomfort and difficulty when they measure their intraocular pressure using a smart contact lens. Therefore, we developed a stretchable and transparent antenna capable of NFC communication, thereby achieving wireless communication between the smart contact lens and a smartphone. This system allows people who do not have specialized knowledge in medicine to measure the intraocular pressure. The human study might be the most important part of the smart contact lens we developed. Therefore, from the beginning, our plan included a human study in collaboration with ophthalmology professors to demonstrate the usability, stability, and safety of the smart contact lenses. Through the human study, we obtained quantitative experimental data, including the clinical grading scale and the visual analogue scale score, that are difficult to collect in animal experiments or in-vitro experiments. We believe these experimental data will provide the basis for the practical use of smart contact lenses.
The most challenging part of this research was the development of the strain sensor to measure the intraocular pressure. Very little strain is caused by the change in the intraocular pressure, so, even though the strain sensor had high sensitivity, it was very difficult to measure the change in the intraocular pressure. To overcome this problem, we used a rigid-soft hybrid substrate and a highly-doped Si nanomembrane-based strain sensor that had serpentine geometry. In the previous papers, a rigid-soft hybrid substrate was used to protect the materials and electronics against mechanical stress by locating the electronics on the rigid area (1,2). However, we exploited the mechanical properties of the rigid-soft hybrid substrate inversely. To explain, when the soft contact lens is deformed by a change in intraocular pressure, the rigid region has a negligible change, and the deformation is concentrated on the soft region. We used this effect of concentrating the strain. By fabricating the strain sensor on the soft region where the mechanical deformations are concentrated, the Si strain sensor was able to measure the change in intraocular pressure. It was possible to overcome the challenging part by thinking differently from previously reported papers and fabricating the device following the opposite concept. We will never forget how we felt when this creative idea was successful.
We could characterize the smart contact lenses medically and clinically based on our collaboration with ophthalmologists. Therefore, it was possible to obtain data on the accuracy and reproducibility of the sensors by directly comparing the smart contact lens with a tonometer, which is a clinical instrument that is used to measure intraocular pressure. The smart contact lens that was developed had remarkable accuracy and reliability when compared with conventional clinical instruments. Also, the use of the conventional instruments is limited because they require expert training and high skills. However, the smart contact lenses have an advantage in that they do not require expert training and high skills because they measure the intraocular pressure through the sensor on the lens and transfer the measured data wirelessly to the user’s smartphone. We think the smart contact lenses developed in this research have significant potential to replace the clinical instruments that have been used conventionally for the monitoring of intraocular pressure. In addition, this research is very meaningful because it has been applied in medical studies involving people whereas the previous literature was based on animal experiments. Overall, based on this research, it has been demonstrated that smart contact lenses that have been viewed to date as science fiction could become a reality.
- Park, J. et al. Soft, smart contact lenses with integrations of wireless circuits, glucose sensors, and displays. Sci. Adv. 4, eaap9841 (2018).
- Ji, S. et al. Photo-patternable and Transparent Films Using Cellulose Nanofibers for Stretchable, Origami Electronics. NPG Asia Mater. 8, e299 (2016).