Multifunctional hydrogel electronics for closed-loop antiepileptic treatment

Abstract

Closed-loop strategies offer advanced therapeutic potential through intelligent disease management. Here, we develop a hydrogel-based, single-component, organic electronic device for closed-loop neurotherapy. Fabricated out of conductive hydrogels, the device consists of a flexible array of microneedle electrodes, each of which can be individually addressed to perform electrical recording and control chemical release with sophisticated spatiotemporal control, thus pioneering a smart antiseizure therapeutic system by combining electrical and pharmacological interventions. The recorded neural signal acts as the trigger for a voltage-driven drug release in detected pathological conditions predicted by real-time electrophysiology analysis. When implanted into epileptic animals, the device enables autonomous antiseizure management, where the dosing of antiepileptic drug is controlled in a time-sensitive, region-selective, and dose-adaptive manner, allowing the inhibition of seizure outbursts through the delivery of just-necessary drug dosages. The side effects are minimized with dosages three orders of magnitude lower than the usage in approaches simulating existing clinical treatments.

Fig. 1.. Schematic diagram of a closed-loop bioelectronic system for adaptive antiepileptic treatment.

The hydroElex device with an array of drug-loaded and hydrogel-based microneedle electrodes was applied for multiplexed electrophysiology recording and controlled drug release. The recorded neural spiking signal acts as closed-loop feedback to trigger a voltage-driven drug release in detected pathological conditions, where seizure occurrence is predicted by real-time electrophysiology analysis. The closed-loop bioelectronic system includes a hydroElex device that works as a biosignal sensor and responsive interface for drug intervention, signal acquisition system, data storage, and data processing package (blue). Red molecules represent antiepilepsy drugs for the treatment. Green and yellow cells represent neurons in cortical tissues.

Fig. 2.. Synthesis and characterization of the DMA/PEDOTS-IPN conductive hydrogel.

(A) Workflow of synthesis procedures of the DMA/PEDOTS-IPN hydrogel. (B) Photogram and scanning electron microscopy (SEM) images of the hydrogels. The SEM images (ii, iii, and iv) show the microscale structure of the boxed region at different scales. Scale bar, 1 cm (i); 100 μm (ii); 15 μm (iii); 5 μm (iv). (C) FTIR spectra showing the chemical components of the hydrogels. (D) Measurement of the swelling volume change of the hydrogels (n = 3). (E) Characterization of long-term degradation of the hydrogels by measuring the weight loss over a 25 day period (n = 3). (F) Characterization of the conductivity of the hydrogels with different formulations of DMAPS content (n = 5). (G) Tensile test of the hydrogels. (H) Comparison of Young’s modulus among neural tissues, the DMA/PEDOTS-IPN hydrogel-based electrodes, and some commonly used electrodes for recording neural signals. The conductive materials and the nerve tissues are shaded in blue or yellow, respectively. The error bars indicate the SD. *P < 0.05. N.S., not significant, by Student’s t test.

Fig. 3.. Fabrication of the implantable hydroElex device.

(A) Schematic of a four-step fabrication process to fabricate the hydroElex device. (B) SEM images showing the side view of the casted hydrogel electrodes and the quantification of the height and the tip sharpness of the microneedle morphology (n = 6). Scale bar, 200 μm. The error bars indicate the standard deviation. (C) An overview photograph of a flexible hydroElex device. Scale bar, 0.5 cm. For the enlarged view, scale bar, 2 mm. (D) A close-up photograph of a hydroElex device with individually addressable hydrogel electrodes. Scale bar, 1 mm. (E) Top-view SEM image of the hydrogel electrodes coated with an SU-8 insulation layer. Scale bar, 500 μm. (F) SEM image showing an enlarged view of a single hydrogel electrode with (left) or without (right) insulation coating. Scale bar, 150 μm. (G) Test of mechanical strength the hydrogel electrodes with or without drug loading (GABA). (H) Exploded view of the hydroElex device integrated with a microfluidic refill component, consisting of a SU-8 insulation layer, a conductive hydrogel-based electrode array, an Cr/Au circuit layer, a soft PET substrate, and a PDMS-based soft microfluidic layer as drug supplementary channels to refill each electrode in a programmable format. (I) The photograph of a hydroElex with microfluidic channels. The hematoxylin dye (red) flows into the microfluidic channels to visualize the refilling of the selected electrodes (blue). Scale bar, 1 mm. (J) Deformation of a hydroElex device under large mechanical stress. Scale bar, 2 mm. (K) Photograph of a mouse implanted with a hydroElex device. Scale bar, 1 cm.

Fig. 4.. Functional characterization of the hydroElex device.

(A) Cyclic voltammogram of a hydroElex device in PBS. (B) Quantification of the CSC of increasing CV cycles (n = 3). (C) Impedance of a hydroElex device at different frequencies (n = 3). The inset shows the impedance measured at 1000 Hz after a long-term incubation in PBS (n = 3). (D) Representative recordings of square waveform using the hydroElex device (middle) and its comparison to a tungsten electrode (right). (E) Diagram of the ex vivo experiment for characterizing the voltage-driven drug release from a hydroElex device. The molecules were released into a block of agarose, which was collected and analyzed using spectroscopy. (F) Cyclic GABA release from a hydrogel electrode at a fixed voltage stimulation (200 mV for 3 min). The examined parameters include release amount per cycle (orange), cumulative release percentage (red), and remaining percentage (blue) (n = 3). (G and H) Triggered release of GABA and VPA from a single electrode as a function of various triggered voltages (G) and durations (H) (n = 3). The chemical was loaded at 1 mg/ml. The error bars indicate the SD.

Fig. 5.. Combined function of electrophysiological recording and triggered pharmaceutical intervention in a hydroElex implant.

(A) Illustration of the implantation of hydroElex device and 4-ap injection site on a mouse brain. (B) Representative LFP recordings (gray) and associated power spectrum before (top) and after (bottom) seizure induction by 4-ap injection. (C) Representative LFP recordings from three adjacent electrodes with increasing distance from the seizure induction site (Ch1, 2 mm; Ch2, 3 mm; Ch3, 4 mm). Red arrowheads indicate the appearance of induced abnormal high-frequency spiking activity. (D) Statistical analysis of seizure-like events (SLEs) in three different channels before (Ctrl) and after 4-ap injection (SLE, n = 6). (E) Timeline of in vivo drug intervention for antiseizure management by hydroElex when fully developed epileptic activity were detected by the same device (hydroElex clearance). (F) LFP recording and the associated power spectrum showing the antiseizure efficacy. (G) Quantification of the SLEs in the epileptic animals at different stages (“SLE,” “Healthy state,” and “hydroElex clearance”; n = 6). (H) Analysis of the amplitude and duration of abnormal β oscillation (13 to 30 Hz) at different stages. The error bars denote the SD. n = 6. *P < 0.05 by Student’s t test.

Fig. 6.. The closed-loop strategy for seizure control.

(A) Schematic diagram for hydroElex-assisted closed-loop seizure management based on a real-time multisite LFP recording and adaptive drug delivery on epileptic rodents. (B) Representative raw data showing the whole process of a closed-loop adaptive anti-seizure management. Continuous real-time surveillance of neurophysiology was performed using a hydroElex implant. Abnormal surge (>3.5%, indicated by red arrowheads) of β oscillation in the power spectrum was extracted as the feedback feature to trigger adaptive dosing of VPA. The animal’s recovery was also monitored by neurophysiological recording after a series pharmaceutical intervention (five VPA administrations), which were autonomously engaged and stopped. (C) Adaptive dosing control by varying voltage stimulation (200 mV, 3 to 6 min) based on the change of β oscillation amplitude to trigger drug release from an individual electrode of the hydroElex device. (D and E) Comparison of different administration strategies for antiseizure management using antiepileptic drug, VPA. The efficacy is evaluated by the frequency of SLE [(D) n = 6] and abnormal β oscillation [(E) n = 5]. The error bars denote the SD. *P < 0.05 by Student’s t test.

Fig. 7.. Long-term in vivo biocompatibility of the hydroElex.

(A) Photogram of a hydroElex device after being used in a mouse brain. Scale bar, 500 μm. (B) Fluorescence microscopic images of a coronal cortical slice with a hydroElex electrode insertion track [Iba1, red; glial fibrillary acidic protein (GFAP), green; NeuN, blue]. Scale bar, 100 μm. (C) Fluorescent microscopic images of the cortical regions surrounding a hydrogel electrode 4 weeks after a hydroElex device implantation. Scale bar, 50 μm. (D) Staining for inflammatory biomarker, CD68, in coronal tissues isolated from a brain implanted with a hydroElex for 4 weeks. Scale bar, 50 μm. (E to H) Statistical analysis of different cell component changes related to the device in vivo biocompatibility, including microglia (E), astrocytes (F), neuron (G), and CD68⁺ cells (H). For (E) to (H), n = 5. Error bars denote the SD. N.S. by Student’s t test.