Khoury, F. | Search bioRxiv

bioRxiv2026

Adaptive Charge Modulation Enables Focal, Selective Spinal Cord Stimulation

Clinical neuromodulation primarily employs near-field low frequency electrical stimulation to activate neurons in the immediate vicinity of the electrode. We introduce Adaptive Charge Modulation (ACM), a spatiotemporal, charge-balanced stimulation strategy that focuses activation at deep tissue sites distant from the stimulating contacts. We apply ACM to stimulate deep regions of the spinal cord, distant from dorsal root entry zones which are preferentially activated during low frequency stimulation (LFS). ACM applies multipolar, biphasic rectangular pulses to exceed activation thresholds in deeper neuronal populations, with reduced surface activation, potentially due to high-frequency suppression of neural activity. In epidural spinal cord stimulation in rats, ACM achieved single-muscle selectivity among fourteen monitored muscles with minimal co-activation of other muscles. Using simultaneous, high spatiotemporal resolution, 2,112-channel brain-spine recordings, we characterized the response latencies and pathways consistent with focal recruitment at depth. We observed chronic stability of the electrode and ACM in freely behaving animals over 68 days post-implantation. By enabling focal activation with epidural surface electrodes, ACM may expand the reach and precision of neuromodulation and neural interfaces.

bioengineering↗

bioRxiv2025

Rapid-Response, High-Gain Inkjet-Printed Organic Electrochemical Transistors with Geometry-Optimized Design for Neural Recording and Biosensing

Organic Electrochemical Transistors (OECTs) are witnessing rapid growth in biomedical applications and are increasingly becoming an integral part of bio-electronic interfaces. High-performing OECTs are typically fabricated using multistep photolithography and conventional spin-coating and lift-off processes, and while printing techniques have emerged as promising alternatives, they still face challenges in achieving comparable resolutions, reproducibility and performance metrics. Several groups have demonstrated printed OECTs using PEDOT:PSS as the channel material, highlighting the promise of additive manufacturing for scalable bioelectronics. In this work, we build upon these advances and develop an optimized inkjet-printed OECT platform that achieves transconductance values up to 15 mS and sub-millisecond response times as low as 0.31 ms. Our approach systematically optimizes OECT geometrical parameters--channel width, length, and thickness--through precise patterning and oxygen plasma surface modification to overcome longstanding limitations in inkjet printing resolution and reproducibility. The resulting devices exhibit outstanding electrical stability, high amplification, and fast dynamic response. Using a configuration optimized for biosensing, we demonstrate the detection of the heart failure biomarker NT-proBNP within a clinically relevant range of 10-400 pg/mL, with a sensitivity of 0.038% {Delta}IDS/pg/mL. In a separate configuration on a flexible substrate tailored for in vivo biopotential recording, we showcase the devices capabilities by effectively capturing epileptic seizure progression in a rat model with high signal fidelity. This work demonstrates how careful process and geometry optimization can close the performance gap between printed and conventionally fabricated OECTs, enabling scalable, reproducible, and substrate-flexible bioelectronic platforms.

bioengineering↗