On October 31th, the paper entitled "Tunable Hydrogel Electronics for Diagnosis of Peripheral Neuropathy" was published online in Advanced Materials. Ganguang Yang is the first author of this paper. Prof. Hao Wu and Dr. Yutian Liu from the Union Hospital are the co-corresponding authors of this paper.
As one of the most common neurological diseases, peripheral neuropathy has attracted tremendous attention in the past decade. Due to many causes of this disease including diabetes, traumatism, alcoholism, etc., the number of patients diagnosed with peripheral neuropathy has surpassed 7 000,000 worldwide with constantly increasing trends. When suffering from peripheral neuropathy, patients tend to have motor or sensory impairments that greatly affect their daily life. Additionally, long treatment and rehabilitation processes will create great economic burdens for patients. Since timely intervention can delay the development of the disease, there is an urgent need to implement effective early diagnoses. At present, analyzing the amplitude, conduction velocity, and latency of electromyography signals is generally regarded as an efficacious method to evaluate the degree of nerve injury. During the process, electromyography signals are originated from action potentials of neurons which are mainly induced by metal rigid stimulation electrodes applying pulse voltages and conducted through the nerve, eventually collected by commercial gel electrodes. When the nerve is damaged, the values of amplitude and conduction velocity are prone to fall below the threshold and the latency usually surpasses the threshold values. Due to the diversity of injured nerves, signal amplitudes ranging from microvolts to millivolts and different detection locations, commercial electrodes with high modulus and poor stretchability have trouble in establishing conformal contact with skin, dramatically degrading stimulation and recording performances. Meanwhile, rigid stimulation electrodes without adhesion are inclined to require a manual auxiliary press for fixation on the skin, which increases the motion artifacts and labor intensity for medical staff. Furthermore, patients' skins exhibit different sensitivity due to their diversity including hairy/hairless skin, children’s fragile skin, and the elderly’s slack skin, which requires customized adhesion for electrodes. Nevertheless, commercial gel electrodes usually demonstrate unadjustable adhesion, probably causing discomfort to patients during the detachments. Therefore, existing electrodes still exhibit limitations in enabling superior stimulation and recording properties while ensuring gentle removal in the diagnosis of peripheral neuropathy.
To address these issues, the authors present a polyaspartic acid-modified dopamine/ethyl-based ionic liquid hydrogel (PDEH) with rapidly adjustable adhesion, strengthened stretchability, and conductivity to optimize the device/skin interfaces. By further embedding a silver-liquid metal (SLM) layer, we fabricate the PDEH-SLM devices to fulfill the accurate diagnosis of peripheral neuropathy and benign detachments. When initiated with a one-step electric field treatment to induce the breaking and recombination of catechol-borate groups and electrostatic bonds, the hydrogel achieves high speed and wide ranges of adhesion regulation (pigskin substrate: 20 s, 112 folds; Pt substrate: ~0.1 s, 26 folds), outperforming existing tunable-adhesion hydrogels. Meanwhile, the diffusion of Zn ions from a Zn anode leads to the formation of metal coordination bonds, further improving the stretchability of hydrogels to 1760%. To overcome the dehydration and low conductivity of hydrogels, ionic liquids are introduced into hydrogel networks, conducive to achieving higher charge capability, lower interfacial impedance, and long-lasting measurements.
Hydrogel on-skin patches for the diagnosis of peripheral neuropathy
The authors further verify the feasibility of hydrogel devices for accurate diagnoses of peripheral neuropathy in sensory, motor, and mixed nerves. For various body parts, such as fingers, the elderly’s loose skin, hairy skin, and children’s fragile skin, we regulate the adhesion of PDEH-SLM devices to establish intimate device/skin interfaces or ensure benign removal. Noticeably, hydrogel patches achieve precise diagnoses of nerve injuries in these clinical cases while providing extra advantages of more effective stimulation/recording performances. These patches offer a promising alternative for the diagnosis and rehabilitation of neuropathy in future.
Diagnosis of neuropathy on mixed nerves
The above research work was supported by the National Natural Science Foundation of China (No. 2022YFB4700201, U2013213, 92048302, 52188102, and 82201548) and the STAR Project by the School of Mechanical Science and Engineering of Huazhong University of Science and Technology.
Original link： https://doi.org/10.1002/adma.202308831