Jeongdae Ha’s research while affiliated with Daegu Gyeongbuk Institute of Science and Technology and other places

System-level wearable electronics require to be flexible to ensure conformal contact with the skin, but they also need to integrate rigid and bulky functional components to achieve system-level functionality. As one of integration methods, folding integration offers simplified processing and enhanced functionality through rigid-soft region separation, but so far, it has mainly been applied to modality of electrical sensing and stimulation. This paper introduces a vialess heterogeneous skin patch with multi modalities that separates the soft region and strain-robust region through folded structure. Our system includes electrical and optical modalities for hemodynamic and cardiovascular monitoring, and a force-electrically driven micropump for drug delivery. Each modality is demonstrated through on-demand drug delivery, flexible waveguide-based PPG monitoring, and ECG and body movement monitoring. Wireless data transmission and real-time measurement validate the feedback operation for multi-modalities. This engineered closed-loop platform offers the possibility for broad applications, including cardiovascular monitoring and chronic disease management.

Structures such as 3D buckling have been widely used to impart stretchability to devices. However, these structures have limitations when applied to piezoelectric devices due to the uneven distribution of internal strain during deformation. When strains with opposite directions simultaneously affect piezoelectric materials, the electric output can decrease due to cancellation. Here, we report an electrode design tailored to the direction of strain and a circuit configuration that prevents electric output cancellation. These designs not only provide stretchability to piezoelectric nanogenerators (PENGs) but also effectively minimize electric output loss, achieving stretchable PENGs with minimal energy loss. These improvements were demonstrated using an inorganic piezoelectric material (PZT thin film) with a high piezoelectric coefficient, achieving a substantial maximum output power of 8.34 mW/cm³. Theoretical modeling of the coupling between mechanical and electrical properties demonstrates the dynamics of energy harvesting, emphasizing the electrode design. In vitro and in vivo experiments validate the device’s effectiveness in biomechanical energy harvesting. These results represent a significant advancement in stretchable PENGs, offering robust and efficient solutions for wearable electronics and biomedical devices.

By monitoring brain neural signals, neural recorders allow for the study of neurological mechanisms underlying specific behavioural and cognitive states. However, the large brain volumes of non-human primates and their extensive range of uncontrolled movements and inherent wildness make it difficult to carry out covert and long-term recording and analysis of deep-brain neural signals. Here we report the development and performance of a stealthy neural recorder for the study of naturalistic behaviours in non-human primates. The neural recorder includes a fully implantable wireless and battery-free module for the recording of local field potentials and accelerometry data in real time, a flexible 32-electrode neural probe with a resorbable insertion shuttle, and a repeater coil-based wireless-power-transfer system operating at the body scale. We used the device to record neurobehavioural data for over 1 month in a freely moving monkey and leveraged the recorded data to train an artificial intelligence model for the classification of the animals’ eating behaviours.

The use of water-based chemistry in photolithography during semiconductor fabrication is desirable due to its cost-effectiveness and minimal environmental impact, especially considering the large scale of semiconductor production. Despite these benefits, limited research has reported successful demonstrations of water-based photopatterning, particularly for intrinsically water-soluble materials such as Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) due to significant challenges in achieving selective dissolution during the developing process. In this paper, we propose a method for the direct patterning of PEDOT:PSS in water by introducing an amphiphilic Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO, P123) block copolymer to the PEDOT:PSS film. The addition of the block copolymer enhances the stretchability of the composite film and reduces the hydrophilicity of the film surface, allowing for water absorption only after UV exposure through a photoinitiated reaction with benzophenone. We apply this technique to fabricate tactile and wearable biosensors, both of which benefit from the mechanical stretchability and transparency of PEDOT:PSS. Our method represents a promising solution for water-based photopatterning of hydrophilic materials, with potential for wider applications in semiconductor fabrication.

Surface electromyography (sEMG) sensors play a critical role in diagnosing muscle conditions and enabling prosthetic device control, especially for lower extremity robotic legs. However, challenges arise when utilizing such sensors on residual limbs within a silicon liner worn by amputees, where dynamic pressure, narrow space, and perspiration can negatively affect sensor performance. Existing commercial sEMG sensors and newly developed sensors are unsuitable due to size and thickness, or susceptible to damage in this environment. In this paper, our sEMG sensors are tailored for amputees wearing sockets, prioritizing breathability, durability, and reliable recording performance. By employing porous PDMS and Silbione substrates, our design achieves exceptional permeability and adhesive properties. The serpentine electrode pattern and design are optimized to improve stretchability, durability, and effective contact area, resulting in a higher signal-to-noise ratio (SNR) than conventional electrodes. Notably, our proposed sensors wirelessly enable to control of a robotic leg for amputees, demonstrating its practical feasibility and expecting to drive forward neuro-prosthetic control in the clinical research field near future.

Precise monitoring of neurotransmitters, such as dopamine (DA), is critical for understanding brain function and treating neurological disorders since dysregulation of DA implicates in a range of disorders, including Parkinson's disease (PD), schizophrenia, and addiction. This study proposes a multi‐deformable double‐sided (MDD) DA‐sensing probe with the three‐electrode system in all‐in‐one form for reliable real‐time monitoring of DA dynamics by integrating working, reference, and counter electrodes on a single probe. The proposed probe achieves high DA sensitivity and selectivity in virtue of enzyme immobilization on the 3D nanostructures grown on working electrode. Also, the serpentine design is employed for the electrodes to withstand in various deformations by achieving high stretchability and manage the stress induced on the probe. Experimental and computational analysis demonstrates an effective reduction in induced‐stress on the electrodes. The MDD DA‐sensing probe is implanted into the brain with success to enable real‐time, in vivo monitoring of DA levels in rodents. Furthermore, DA dynamic changes are monitored before and after treatment with L‐DOPA in hemi‐PD mice. This extremely deformable implantable probe has the potential for use in the study and treatment of neurodegenerative diseases, providing reliable monitoring of DA dynamics with minimal damage to brain tissue.

Treatment trends for Parkinson’s disease are revolutionizing from conventional pharmaceutical treatment depending on the patient’s symptoms to closed-loop electroceutical treatment in order to minimize the crucial pharmacokinetic drawbacks. Over the decades, closed-loop neuromodulations have been achieved by electroceutical devices based on continuous electrical stimulation and sensing of electrophysiological biomarkers. However, critical drawbacks have been observed with vulnerable to artefacts from the nearby stimulation electrode and frequent adjustment of stimulation parameters. On the contrary, direct monitoring of neurochemicals allows high spatial resolution, signal specificity and interference-free detection compared to closed-loop DBS. Here, we propose an artificial homeostasis system with electrochemical sensing and pharmaceutical stimulation for impaired brain function. In order to implement the artificial homeostasis system by mimicking the brain system, we have reported an implantable multi-deformable double-sided DA-sensing probe with an all-in-one structure by integrating three-electrode system and drug refillable microfluidic probe with controllable injection for synchronized diagnosis and treatment. The experimental and computational analysis clearly indicate that the proposed probes could serve as potential tools for building artificial homeostasis by the bio-responsive closed-loop system with an electropharmaceutical approach.