An artificially-intelligent cornea with tactile sensation enables sensory expansion and interaction

The cornea is the transparent, highly innervated anterior structure of the eye that focuses light and protects internal ocular tissues. Its dense innervation confers extreme tactile sensitivity, eliciting the involuntary corneal reflex (eyelid closure) upon mechanical or light stimulation. Corneal diseases can cause blindness; more than 10 million people suffer bilateral corneal blindness. Corneal transplantation remains the primary therapy, but donor scarcity limits availability to approximately 1 in 70 patients, with an estimated 12.7 million awaiting transplantation. Artificial corneal substitutes (e.g., Boston Kpro, Aurolab Kpro, MICOF, osteo-odonto-keratoprosthesis) can restore optical clarity and refraction in severe corneal opacification. However, current devices reproduce only partial functions (protection and refraction) and do not reconstruct tactile sensation or the corneal reflex. Developing a smarter artificial cornea that integrates tactile sensation and further offers sensory expansion and interactive capabilities—while maintaining the high transparency and low haze of a natural cornea via invisible built-in electronics—is therefore of significant importance for vision restoration and neuroprosthetics.

Several artificial corneal prostheses have been developed and clinically applied. The Boston Kpro (PMMA-based collar-button design) is the most widely implanted worldwide; Aurolab Kpro shares its design as a more affordable alternative. MICOF Kpro uses a threaded PMMA optic supported by a titanium frame with relatively mild surgical invasiveness. The osteo-odonto-keratoprosthesis uses an autologous tooth-derived lamina as a frame for a PMMA optical cylinder. These devices have acceptable outcomes in visual restoration, safety, practicality, and cost, yet none reconstruct corneal tactile sensation or the protective corneal reflex. Concurrently, smart contact lenses and transparent wearable ocular electronics demonstrate the feasibility of integrating sensors and electronics into transparent substrates, motivating the pursuit of invisible, high-transparency neuromorphic components for ocular neuroprosthetics. The unmet need is for an artificial cornea that merges optical performance with neuromorphic sensing and reflex-like actuation.

System architecture: An artificial corneal reflex arc was constructed by integrating (i) sensor-oscillation circuits (mechanical vibration sensor and a separate light sensor variant) that convert external stimuli into spike trains, (ii) zinc tin oxide (ZTO) ion-gel-gated synaptic transistors as neuromorphic processing elements to transfer and integrate information, and (iii) electrochromic actuators (PEDOT:PSS on ITO/PET with LiClO4 gel electrolyte) to modulate transmitted light, mimicking eyelid contraction. An amplifier circuit conditioned synapse outputs to drive the actuator. ZTO artificial synapse fabrication: Digitally aligned ZTO fiber channels were printed via electrohydrodynamic nanowire printing. Printing ink comprised Zn(NO3)2·6H2O, SnCl2·2H2O, and PVP (Mw≈1,300,000) dissolved in DMF (stirred at 50 °C for 12 h). Printing parameters: ≈1 kV applied to metallic nozzle, nozzle–collector distance 3.5 mm, injection rate 50 nL/min; substrates: Si/SiO2. Printed fibers were annealed at 500 °C for 2 h. Gold source/drain electrodes (≈80 nm) were thermally deposited through a shadow mask. The ion gel gate dielectric (presynaptic input) used PVDF-HFP:[EMIM-TFSI]:acetone at 1:4:7 by weight, dried at 70 °C for 30 min and transferred onto the ZTO channel. Typical devices employed ≈19 fibers, yielding ≈288 Au/ZTO junctions. Flexible devices were also fabricated on PI substrates. Electrochromic actuator: A sandwich ITO/PET–PEDOT:PSS–LiClO4 gel–ITO/PET structure was used. Coloration is driven by reversible Li+ insertion/extraction in PEDOT:PSS under applied voltage. Optical transmittance, response time, refractive index (n), and extinction coefficient (k) were characterized under different voltages and durations. Characterization and analysis: ZTO fibers with Zn:Sn molar ratios of 7:3, 1:1, and 3:7 were fabricated and characterized by SEM (morphology; pitch 100–200 μm; diameter ~650 nm), AFM (height ~200 nm), HRTEM/SAED (crystallinity; lattice spacings 0.332 and 0.263 nm), XRD (rutile-like for 3:7; wurtzite-like for 7:3; amorphous for 1:1), and XPS (O 1s deconvolution indicating oxygen vacancies). Optical properties (visible transmittance and haze) were measured for stripe and grid patterns (pitches 100 and 200 μm). Electrical synaptic behavior was evaluated via aEPSC responses to presynaptic spikes: PPF, spike-number/duration/voltage/frequency dependent plasticity (SNDP, SDDP, SVDP, SFDP), and retention (STP vs LTP). Field-effect mobility was extracted. First-principles calculations (DFT with VASP; AIMD for amorphous structure) were performed to optimize structures, and compute band structures and DOS for the three compositions. System-level demonstrations:

• Mechanical corneal reflex arc: vibration sensor–oscillator → ZTO-3:7 AS → amplifier → paired electrochromic actuators to emulate bilateral, ipsilateral, and contralateral reflex outcomes by selective pathway disconnections.
• Light-perception integration: replaced vibration sensor with a light sensor–oscillator; measured spike frequency vs illuminance (22–583 lx) and corresponding synaptic/actuator responses to demonstrate adaptive transmittance. A robot platform was equipped for proof-of-concept. Applications of synapses: STP devices (ZTO-7:3, ZTO-1:1) generated Morse code; LTP device (ZTO-3:7) simulated Pavlovian associative learning using paired stimuli.

• Fabrication and properties of ZTO fibers: Digitally aligned, long, continuous ZTO fibers (diameter ~650 nm; height ~200 nm; pitch 100–200 μm) achieved superior transparency and low haze when patterned sparsely: transmittance up to 99.89% and haze as low as 0.36% at 550 nm (stripe, 200 μm), outperforming other transparent conductors (e.g., AgNW, CuNW, ITO, AZO, FTO, PEDOT:PSS, CNT, graphene) in combined metrics. The complete synaptic device on glass showed ~78.91% transmittance at 550 nm.
• Tunable crystal structure and chemistry: Composition-dependent phases were observed: ZTO-7:3 (wurtzite-like), ZTO-1:1 (amorphous), ZTO-3:7 (rutile-like). Oxygen vacancy-related O 1s XPS components increased with higher Sn: Ob area ratios ~18% (7:3), ~30% (1:1), ~43% (3:7).
• Electrical synaptic behavior and mobility: All devices exhibited anticlockwise hysteresis indicating ion-modulated carrier density. aEPSC peak increased and decay slowed as Zn:Sn decreased (more Sn), attributed to more ion-trapping oxygen vacancies and shallow donors. Extracted electron mobilities: 8.9 cm²/V·s (7:3), 6.3 cm²/V·s (1:1), 12.8 cm²/V·s (3:7).
• Plasticity control (STP vs LTP): • PPF: Maximum PPF index at Δt=50 ms: 133.0% (7:3), 127.7% (1:1), 132.5% (3:7); PPF decreased with increasing Δt. • SNDP: ΔaEPSC increased monotonically with spike number; at ns=50, ZTO-3:7 exhibited LTP with ~1 min retention, while 7:3 and 1:1 showed STP. • SFDP: aEPSC and gain increased with frequency (0.5→10 Hz), demonstrating high-pass filtering; gain highest for ZTO-3:7. • SDDP/SVDP: Longer duration and higher amplitude spikes increased aEPSC; ZTO-3:7 retained responses (LTP), whereas 7:3 and 1:1 relaxed quickly (STP).
• DFT/AIMD insights: Band gaps (DFT) increased with more Sn (3:7 largest); DOS at Fermi level rose as Zn:Sn decreased, consistent with increased conductivity and aEPSC. Experimental optical bandgaps (3.62, 3.54, 3.66 eV for 7:3, 1:1, 3:7) showed similar trends though larger than DFT values.
• Electrochromic actuator performance: Progressive darkening with 0–3 V; 90% transmittance change time ~4.3 s at 3 V; estimated ~9% change within 150 ms, partially matching eyelid-closure duration (100–150 ms). Refractive index and extinction coefficient changes indicated refractive capability.
• Artificial corneal reflex demonstrations: Complete mechanical reflex arc produced bilateral reflex when intact; no reflex upon afferent/central disconnection; ipsilateral/contralateral reflex upon selective efferent path disconnection—mimicking neurological examination outcomes.
• Sensory expansion and interaction: Light sensor–oscillator produced spike frequency scaling from 0.5 Hz at 22 lx to 10 Hz at 583 lx. Increased illuminance raised synaptic output and reduced actuator transmittance, achieving adaptive light regulation. A robot equipped with the device demonstrated visible adaptive darkening under bright light.
• Additional demonstrations: • Encrypted communication: STP devices (ZTO-1:1 threshold 7.5 μA; ZTO-7:3 threshold 1.5 μA) encoded Morse code letters (e.g., “NKU”, “YES”). • Associative learning: LTP device (ZTO-3:7) simulated Pavlovian learning; post-training, “bell” (1 V, 50 ms) alone crossed a 14.5 μA threshold to indicate salivation.
• Flexibility: ZTO-3:7 synapse on PI maintained synaptic characteristics with <7% variation after 2000 bending cycles, supporting wearable integration.

The work directly addresses the unmet need for an artificial cornea that restores tactile sensation and reflexive protection while preserving high optical quality. By building an artificial corneal reflex arc with invisible, highly transparent ZTO-based synaptic transistors and electrochromic actuators, the system replicates key native corneal functions (protection, tactile perception, light refraction) and extends capabilities beyond biology by adding light perception and adaptive interaction. Compositionally controlled ZTO crystal phases modulate oxygen-vacancy populations, enabling tunable synaptic plasticity from STP to LTP. This tunability supports neuromorphic functions such as filtering, memory, encryption, and associative learning, and is critical for robust, low-power information processing in ocular neuroprosthetics. The system-level demonstrations of bilateral/ipsi-/contralateral reflex states emulate clinical neurological assessments and highlight diagnostic potential. Integration of a light sensor establishes environmental interaction through adaptive transmittance control, supplying additional ocular protection under variable illuminance. Collectively, these results demonstrate a viable pathway toward transparent, neuromorphic, ocular prosthetics capable of sensory restoration and augmentation.

An artificially-intelligent cornea was developed that emulates native corneal functions—protection, tactile perception, and light refraction—while providing sensory expansion (light perception) and interactive adaptive light regulation. This was achieved through a transparent artificial corneal reflex arc integrating sensor-oscillation circuits, ZTO fiber-based ion-gel-gated synaptic transistors, and PEDOT:PSS electrochromic actuators. Digitally aligned, heavy-metal-free ZTO fibers offered exceptional transparency (up to 99.89%) and low haze (0.36%), and their crystal phase engineering enabled tunable synaptic plasticity (STP↔LTP) powering encrypted communication and associative learning. System demonstrations replicated clinical corneal reflex variants and achieved light-adaptive transmittance, including a robot proof-of-concept. Future work should optimize biocompatibility, long-term stability, miniaturization, and integration to enable clinical translation and transplantation, positioning the technology for neuroprosthetic applications and visual rehabilitation.

The electrochromic actuator’s response time (≈4.3 s for 90% transmittance change at 3 V) is slower than natural eyelid closure; only an estimated ~9% transmittance change occurs within 150 ms, indicating partial replication of blink dynamics. The demonstrations are ex vivo/proof-of-concept without in vivo validation. Biocompatibility, long-term stability, and durability under physiological conditions were not fully assessed. System miniaturization and integration density require improvement for implantable use. The third listed affiliation for some authors is not detailed in the provided text. Further work is needed to optimize materials, packaging, and power for chronic implantation and clinical translation.