The Power Challenge in Smart Contact Lenses

Smart contact lenses promise to transform healthcare, augmented reality, and everyday information access by placing microelectronics directly on the eye. Yet the dream of a fully functional, all-day wearable lens has been held back by one fundamental hurdle: power. The eye is an unforgiving environment for electronics — any device must be ultra-thin, flexible, biocompatible, and safe. Traditional button-cell batteries are far too bulky, rigid, and potentially hazardous. Even the smallest coin cell would make a lens unwearable and risk chemical leakage. As a result, researchers and engineers have had to rethink power from the ground up, designing miniature energy storage and harvesting systems that can deliver milliwatts of power in a form factor thinner than a human hair.

The energy requirements of a smart contact lens vary depending on its features. A lens that simply measures glucose or intraocular pressure once per minute might need only a few microwatts, while a lens with an augmented reality display or continuous wireless data streaming could require hundreds of microwatts or more. Balancing these demands with safety, comfort, and longevity is the central engineering challenge. Recent breakthroughs in battery chemistry, wireless power transfer, and energy harvesting are now turning the once-futuristic concept into a practical reality.

Miniaturized Battery Breakthroughs

Battery technology for smart contact lenses has moved far beyond simple adaptations of existing coin cells. Researchers are developing custom batteries that are not only small but also flexible, transparent in some cases, and safe for prolonged contact with the eye. These batteries often rely on new materials and architectures that allow them to conform to the curvature of the cornea without impeding vision or causing discomfort.

Solid-State Batteries

Solid-state batteries are widely considered the most promising candidate for next-generation smart contact lenses. Unlike conventional lithium-ion batteries that use liquid or gel electrolytes, solid-state batteries employ a solid electrolyte. This eliminates the risk of leakage, a critical safety requirement for any device worn on the eye. Solid electrolytes also allow for thinner, more flexible cells because they can be deposited as thin films using techniques such as sputtering or atomic layer deposition.

Recent research published in Nature Communications demonstrated a solid-state lithium battery with an energy density of over 500 Wh/L, thin enough to be incorporated into the edge of a contact lens without affecting vision. Companies like Samsung and Google-owned Verily Life Sciences have filed patents for solid-state battery designs that integrate directly into the lens periphery, using the annular region around the pupil. The solid-state approach also offers improved cycle life and faster charging compared to liquid-electrolyte cells, making it ideal for daily-rechargeable smart lenses.

Thin-Film Lithium Batteries

Thin-film lithium batteries are another key innovation. These batteries are fabricated by depositing layers of cathode, electrolyte, and anode onto a flexible substrate, resulting in cells that are only a few tens of micrometers thick. Companies like Cymbet and Imprint Energy have developed flexible, rechargeable thin-film batteries that can be shaped to fit the curvature of the eye. Power density remains modest compared to larger batteries, but for low-power sensors and wireless communication, these thin-film cells can provide enough energy for several hours of continuous use. Advances in electrode materials, such as lithium cobalt oxide and lithium nickel manganese cobalt oxide, continue to improve capacity and reduce charging times.

Supercapacitors for Burst Power

Some smart lens designs combine a small battery with a supercapacitor. Supercapacitors store energy electrostatically rather than chemically, allowing them to deliver very high currents in short bursts — ideal for powering a wireless data transmission or a display update. They also charge almost instantly and can last for hundreds of thousands of cycles. Recent work at the University of California, Los Angeles, developed a transparent, flexible supercapacitor using graphene and carbon nanotubes that could be integrated into the lens material itself. While supercapacitors alone cannot provide long-term energy storage, they complement a battery by handling peak loads and extending overall system life.

Wireless Charging Technologies

Even the best miniature battery will eventually need recharging. For smart contact lenses, wired charging is obviously impractical. Wireless power transfer (WPT) offers a seamless way to replenish energy without removing the lens, using inductive or resonant coupling through a charging case or a head-mounted device.

Inductive Coupling

Inductive coupling is the most mature wireless charging technology for biomedical implants. A transmitter coil in a charging case or a pair of glasses generates an alternating magnetic field that induces a current in a receiver coil embedded in the lens. The receiver coil must be small and thin, typically made of copper wire wound around the lens periphery or printed as a metallic spiral on the lens edge. Power transfer efficiency decreases rapidly with distance, so the charging case must bring the coils close together (within a few millimeters). Early prototypes from companies like Mojo Vision and researchers at the University of Michigan have achieved power levels of several milliwatts across a distance of 2–3 mm, sufficient to charge a small battery in a few hours.

Resonant Inductive Coupling

Resonant inductive coupling improves range and efficiency by tuning both transmitter and receiver coils to the same resonant frequency. This method can transfer power over several centimeters, allowing a lens to be charged while a user is wearing a specially designed eyeglass frame or even a sleep mask. A 2023 study in IEEE Transactions on Biomedical Circuits and Systems demonstrated a resonant system operating at 13.56 MHz that delivered 250 µW to a contact lens receiver 5 cm away, with an efficiency of 30%. While still lower than wired charging, such systems enable overnight charging without the need for precise alignment.

RF and NFC Charging

Radio-frequency (RF) energy harvesting using near-field communication (NFC) is also being explored. NFC operates at 13.56 MHz and is already used for wireless payments and data transfer. By integrating a tiny NFC antenna and rectifier into the lens, the device can simultaneously receive power and communicate with an external reader. Although the power levels are low (typically 10–100 µW), they are sufficient for passive sensors that only need to wake up and transmit data periodically. Researchers at the University of Washington have demonstrated NFC-powered contact lenses capable of measuring glucose levels and transmitting results to a smartphone every five minutes.

Energy Harvesting from the Body and Environment

Wireless charging still requires a user to remember to recharge the lens regularly. Energy harvesting techniques aim to extend operational time by scavenging power from the wearer’s own body or from ambient light, making the lens truly autonomous or at least reducing charging frequency.

Piezoelectric Energy from Blinking

Blinking is one of the most natural and frequent human actions — we blink around 15–20 times per minute, or about 28,000 times per day. Each blink produces a small mechanical motion of the eyelid against the lens. Researchers have developed piezoelectric materials that generate voltage when strained. By embedding a thin layer of polyvinylidene fluoride (PVDF) or a lead zirconate titanate (PZT) composite into the lens, the pressure from a blink can be converted into electrical current. A 2021 study in Advanced Energy Materials reported that a PVDF-based energy harvesting lens could generate 3–5 µJ per blink, enough to power a low-power glucose sensor for several seconds. Over a full day, the cumulative energy could recharge a small storage capacitor multiple times, allowing continuous sensor operation.

Thermoelectric Generators from Eye Heat

The human eye maintains a temperature around 32–34°C, while the surrounding air is often cooler. This temperature difference can be exploited using thermoelectric generators (TEGs) that convert heat flow into electricity. Thin-film TEGs made of bismuth telluride or skutterudite materials can be deposited on the outer edge of the lens. A 2020 proof-of-concept from the University of Glasgow demonstrated a flexible TEG that produced 2–4 µW from a 2°C temperature gradient. While these power levels are small, they are continuous, making them ideal for low-power sensors that need always-on monitoring. Recent advances in nanoscale thermoelectrics have improved efficiency, and researchers are now targeting 10 µW from a contact-lens-sized device.

Biofuel Cells Using Tear Glucose

For people with diabetes, glucose is present in tears at levels that correlate with blood glucose. Biofuel cells use enzymes to oxidize glucose and generate electricity. A biofuel cell integrated into a contact lens can both power a glucose sensor and provide real-time readings. The anode contains an enzyme such as glucose oxidase or glucose dehydrogenase that catalyzes glucose oxidation, while the cathode reduces oxygen from the air. The resulting current is proportional to glucose concentration.

A team at the University of California, San Diego, developed a lens with a miniature biofuel cell that produced up to 200 µW per square centimeter of electrode area using natural tear glucose. The energy was sufficient to power a small transponder for short-range wireless communication. One major advantage of biofuel cells is that they don’t require an external charging source — the user’s tears provide both the fuel and the sensing signal.

Solar Cells and Ambient Light Harvesting

Visible light is abundant in most environments, and photovoltaic cells can be made extremely thin and flexible. Dye-sensitized solar cells (DSSCs) and organic photovoltaics (OPVs) can be fabricated on transparent or semi-transparent substrates, allowing them to be placed around the lens periphery or even over the iris area if designed with a small aperture. A 2022 paper in Nature Energy described a transparent OPV cell integrated into a contact lens that achieved 8.5% power conversion efficiency under indoor lighting (200–500 lux), producing 5–10 µW. This is enough to power a temperature or intraocular pressure sensor continuously. Combining solar cells with a small rechargeable battery or supercapacitor can create a self-sustaining device that only needs occasional top-up.

Integration and Design Considerations

Choosing a power solution is only half the battle; integrating it into a functional smart contact lens requires careful design of every component. The battery or harvester must not obstruct vision, must be biocompatible for at least 24 hours of wear, and must not cause irritation or limit oxygen flow to the cornea. Current lenses typically use a rigid scleral design that rests on the white part of the eye, leaving the central cornea clear. All electronics, including the power source, are placed in the annular region around the pupil.

Another challenge is the interconnection between power components and the rest of the system. Conductive traces must be printed using biocompatible metals like gold or platinum, or using transparent conductive oxides like indium tin oxide (ITO). These traces must be flexible enough to tolerate repeated blinking and lens handling. Researchers are also exploring stretchable electronics, where components are connected by serpentine wires or embedded in a soft polymer matrix. A 2023 innovation from the Korean Institute of Science and Technology used a kirigami-inspired pattern to make a battery and circuit that could stretch up to 50% without losing function.

Power management circuits inside the lens also need to be extremely efficient. A custom chip that regulates voltage, controls charging, and minimizes quiescent current is essential. Companies like Texas Instruments and NXP have developed micro-power management ICs that consume less than 1 µA in standby mode, making them suitable for integration into a lens. The entire power electronics stack must be encapsulated in a parylene or silicone coating to protect the eye from any potential toxins or heat.

Future Directions and Emerging Research

The field of smart contact lens power is moving rapidly. Several promising avenues are being explored to make lenses that never need charging during the day and can operate indefinitely with occasional overnight refills.

Stretchable batteries are one such direction. Instead of using rigid electrodes, researchers are developing batteries with serpentine or wrinkled electrode designs that can stretch and bend with the eye. A team at Stanford recently demonstrated a stretchable lithium-ion battery with an areal capacity of 1.5 mAh/cm² that could be stretched to 150% of its original length without significant performance loss. Such batteries could be placed across the entire lens periphery, maximizing energy storage.

Hybrid systems that combine multiple energy sources are also being designed. For example, a lens could use a piezoelectric harvester from blinking to power a sensor during the day, with a solid-state battery that is wirelessly charged overnight. Or a biofuel cell could supplement a thin-film battery, extending time between recharges. These hybrid approaches offer redundancy and improved energy resilience.

Self-healing electrolytes are another innovation. If a battery develops a microcrack, a self-healing polymer electrolyte can seal it automatically, preventing leakage and short circuits. Researchers at the University of Illinois have developed a polyurethane-based electrolyte that can heal within seconds at body temperature, potentially increasing the safety and lifespan of contact lens batteries.

Finally, wireless power transmission over longer distances is being investigated using ultrasonic or laser-based methods. Ultrasound can travel through tissue and might allow a lens to be charged from a small patch behind the ear or from a smartphone. Laser power beaming, while requiring line-of-sight, could deliver milliwatts of power to a lens from a ceiling-mounted source. Both are early-stage but could eventually eliminate the need for any physical connection or charging case.

Conclusion

Powering a smart contact lens is one of the most challenging engineering problems in wearable devices, but recent innovations are turning obstacles into opportunities. Miniature solid-state batteries and thin-film cells now provide safe, flexible energy storage. Wireless charging via inductive or resonant coupling offers a convenient way to recharge daily. Energy harvesting from blinking, body heat, tears, and ambient light promises to reduce or eliminate the need for external power. Each approach has its strengths, and the most practical lenses will likely use a combination of storage and scavenging tailored to the specific application.

As research continues, we can expect to see commercial smart contact lenses that operate for a full day on a single charge, with seamless overnight charging in a sleek case. These devices will monitor health metrics, display information, and even overlay digital content onto the real world — all without compromising comfort or safety. The innovations in battery life and power supply described here are the unsung heroes making that vision a reality.