Jeesu Kim

Continuous knee flexion monitoring is important for rehabilitation and gait analysis, but optical motion capture is generally confined to laboratories, and wearable electrical sensors may be affected by drift, misalignment, or electromagnetic interference. This study presents a brace-integrated system based on a fiber Bragg grating (FBG) embedded in a functionally segmented, multi-hardness silicone strain transfer substrate. The substrate was placed in a dedicated brace recess, avoiding a separate rigid transduction mechanism. A portable interrogation unit enabled wireless transmission and real-time brace-derived angle estimation during sit-to-stand and walking tasks. Calibration against brace hinge angles from 0° to 90° showed a nonlinear Bragg wavelength–angle relationship, modeled using a fourth-order polynomial whose order was selected using a separately acquired validation set that was also used for performance assessment. Validation based on 10 angle-wise mean estimates yielded R² = 0.9992, RMSE = 0.90°, and MAE = 0.68°, with Bland–Altman 95% limits of agreement of −1.46° to +2.05°. The 0° stability record had a wavelength standard deviation of 1.41 pm and a linear trend of −0.193 pm/min, and Allan deviation analysis gave a wavelength noise floor of 0.089 pm at an averaging time of 24 s. Noise-equivalent angular variation ranged from 0.08° to 0.52°. During a sustained 30° hold, the estimated angle drifted at −0.089°/min, but comparison of the 0° and 30° records in wavelength units showed that the undeformed condition reproduced approximately 59% of that drift, although the non-simultaneous comparison does not establish a common-mode thermal contribution. An uncompensated temperature change of 1 K corresponds to between 0.31° and 1.98° of apparent angle change. Proof-of-concept measurements in two participants, both of whom are authors, produced brace-derived profiles qualitatively consistent with expected task kinematics but revealed a cumulative zero-offset shift of 3.2° across two sit-to-stand cycles. Because no simultaneous anatomical reference was acquired, the dynamic results establish feasibility and waveform plausibility rather than measurement accuracy. The results support the engineering feasibility of this brace-integrated optical architecture, while identifying temperature compensation and cyclic loading characterization as prerequisites for anatomical and clinical validation.

Simultaneous pulse-wave sensing at the carotid and radial arteries is challenging because the two sites require different mechanical coupling conditions and manually held carotid probes are susceptible to contact pressure and motion disturbances. This study presents a reference-assisted fiber Bragg grating (FBG) system comprising a wristband-type radial unit and a stamp-type carotid unit containing mechanically decoupled measurement and reference FBGs. Reference FBG regression (RFR) was used to suppress components shared by the carotid channels. In a 41.8 s recording from one male participant in his twenties, the reference and carotid measurement channels were essentially uncorrelated within the pulse-wave band (r = −0.05). After signal mean removal, RFR reduced power below 1 Hz by 74.3% without attenuating the pulse-band power (+11.4%), increasing the relative-power signal quality index from 0.174 to 0.458. Pulse transit time (PTT) was estimated by foot-centered windowed correlation. Analysis of 54 cardiac cycles yielded a representative PTT of 0.055 s. With an effective path length of 0.48 m, the corresponding pulse-wave velocity (PWV) was 8.7 m/s, with a within-record bootstrap 95% interval of 7.7–9.9 m/s. Estimates from eight non-overlapping 5 s segments were 9.1 ± 1.8 m/s. RFR produced lower segment-to-segment PTT variability than the baseline processing methods (coefficient of variation, 20.3% versus 34.6–46.7%). These results demonstrate the technical feasibility of reference-assisted FBG sensing for simultaneous carotid–radial pulse-wave acquisition and preliminary PWV estimation. Further validation requires higher-rate acquisition, repeated measurements, a larger cohort, and comparison with a reference PWV device.

Photoacoustic imaging is a noninvasive imaging modality with considerable potential for theranostic applications, providing high-resolution visualization of molecular and physiological responses to treatment. Among the diverse materials investigated for constructing theranostic nanoplatforms, hyaluronic acid has attracted substantial interest because of its biocompatibility, hydrophilicity, chemical modifiability, and affinity for CD44 receptors, which are frequently overexpressed in various cancer cells. Moreover, appropriately engineered hyaluronic acid-based formulations offer opportunities for localized and transdermal delivery, potentially reducing the need for systemic administration and expanding the applicability of noninvasive phototherapy, particularly for superficial lesions. In this review, we summarize recent advances in hyaluronic acid-based nanoplatforms for photoacoustic imaging-monitored phototherapy, categorized into photothermal therapy, photodynamic therapy, and their combination. We further discuss their material design, targeting and delivery mechanisms, photoacoustic monitoring capabilities, therapeutic performance, and key challenges for clinical translation.

Optical-resolution photoacoustic microscopy has become an important biomedical imaging modality for visualizing optical absorption contrast with micrometer-scale spatial resolution in superficial tissues. Because this modality relies on tightly focused laser illumination, precise optical alignment is essential, and free-space-to-fiber laser coupling is one of the most critical alignment steps. This issue becomes particularly important in transportable optical-resolution photoacoustic microscopy systems, where repetitive manual readjustment is required. Although our previous automated coupling approach based on motorized mirror control reduced the need for manual beam-path alignment, its optimization capability was limited when the focal position relative to the fiber core is not actively controlled. In this study, we propose an upgraded automated fiber-coupling module that integrates beam steering and fiber-side focusing alignment. In addition to the incident beam path control using motorized mirrors, a piezo-driven three-axis stage carries the coupling objective lens to align the focused beam with the fiber core. The coupled light was divided into imaging and monitoring paths, enabling real-time feedback-based optimization. The proposed module was validated by achieving high-quality photoacoustic images of both phantom and biological tissue through automated coupling. By extending automated coupling from mirror-based beam steering alone to combined beam steering and three-axis fiber-core alignment, the proposed coupling module provides a practical solution for improving the robustness, usability, and transportability of optical-resolution photoacoustic microscopy platforms and other fiber-coupled optical imaging systems.

Functional near-infrared spectroscopy (fNIRS) is a portable, non-invasive tool for studying cortical function in children with neurodevelopmental and neurological disorders. Although fNIRS use is increasing, heterogeneous study paradigms and cortical targets have limited cross-condition comparisons and the identification of shared research priorities. This systematic review maps cortical regions and reporting patterns in five key conditions—autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), cerebral palsy (CP), hypoxic–ischemic encephalopathy (HIE), and epilepsy (Ep)—from January 2015 to December 2025. A systematic search across five databases identified 72 relevant studies meeting PRISMA 2020 criteria, revealing both similarities and differences across disorders. The prefrontal cortex (PFC) was studied in all five conditions (5/5: 100%), making it the most consistently investigated cortical region. The parietal and temporal cortices were studied in 4 of 5 conditions (80%). The frontal cortex had the most regions investigated, while the temporal cortex showed the most consistent coverage across conditions (2.25 conditions per region). Beyond regional preferences, condition-specific patterns were aligned with their disorder phenotypes: social brain networks in ASD, prefrontal executive systems in ADHD, sensorimotor changes in CP, cerebrovascular monitoring in HIE, and state-dependent changes in Ep. Across conditions, researchers found altered prefrontal activity, disrupted connectivity, and compensatory brain responses, supporting broader frameworks. Collectively, these findings identify the PFC as a shared target for transdiagnostic fNIRS investigations while highlighting important gaps in regional coverage and methodological consistency. Despite methodological differences, fNIRS shows promise for identifying both shared and unique brain patterns in pediatric neurodevelopmental and neurological disorders. This review provides a framework for prioritizing cortical targets and guiding future standardized fNIRS research in pediatric populations.

Transition metal dichalcogenides (TMDs) have emerged as a versatile class of two-dimensional materials whose strong light-matter interactions and tunable physicochemical properties enable a broad range of biomedical applications. This Review provides a mechanism-driven overview of TMDs as multifunctional platforms for phototherapeutic and optical biosensing technologies, with emphasis on how their atomic structure, electronic configuration, excitonic behavior, and surface chemistry govern optical absorption, energy relaxation, and biointerfacing processes. We first summarize the fundamental optoelectronic characteristics of TMDs that distinguish them from conventional nanomaterials, including strong exciton binding, efficient nonradiative energy dissipation, and layer-dependent symmetry and band structure. Building on these principles, recent advances in TMD-enabled phototherapeutic applications, such as photothermal therapy and photodynamic therapy, are discussed, highlighting how strong near-infrared absorption, high photothermal conversion efficiency, and structural robustness enable precise and durable light-triggered treatments. We then examine emerging optical biosensing modalities based on TMDs, including multiphoton and nonlinear optical imaging, surface-enhanced Raman scattering, and photoacoustic imaging. Across these platforms, exciton-mediated nonlinear responses, defect- and edge-induced charge-transfer pathways, and efficient optothermal transduction allow TMDs to overcome long-standing limitations in sensitivity, photostability, and imaging depth associated with traditional contrast agents. Finally, we discuss current challenges and future opportunities for translating TMD-enabled photonic and optothermal functionalities into scalable, biocompatible, and clinically relevant technologies, positioning TMDs as unifying materials for next-generation theranostic and biosensing platforms.

Fetal alcohol spectrum disorders (FASDs) are caused by prenatal exposure to ethanol (EtOH), leading to developmental brain abnormalities. Cortical organoids derived from human‐induced pluripotent stem cells provide physiologically relevant models to study such neurotoxic effects. However, accurate imaging of nuclear morphology, a key indicator of cytotoxicity and developmental impairment, remains difficult. Traditional fluorescence‐based techniques rely on staining and sectioning, limiting throughput and potentially altering native structures. Herein, we present an ultraviolet photoacoustic microscopy system that targets endogenous nucleic acids at 266 nm excitation, resulting in a lateral resolution of 278 nm, which is sufficient to resolve individual nuclei in situ. The system integrates precise z‐axis scanning for focal‐plane alignment, enabling high‐resolution depth‐resolved imaging of subvolumes within 3D intact live organoids without physical sectioning. Using EtOH‐treated cortical organoids as a model of FASD‐associated neurotoxicity, we observed significant reductions in nuclear area, diameter, and circularity by 46.1%, 20.8%, and 6.0%, respectively, indicating structural damage consistent with apoptosis and impaired neurodevelopment. This method is the first to demonstrate label‐free nuclear imaging in intact live brain organoids, providing a robust and preparation‐free platform for probing disease‐relevant phenotypes, accelerating drug screening, and enabling early toxicity assessments in neurodevelopmental disorder models.

Scanning acoustic microscopy is a useful non-destructive imaging technique for semiconductor inspection, providing acoustic contrast without physical sectioning. However, the selection of an ultrasound transducer for high-quality imaging is not determined by the operating center frequency alone. The focusing condition, represented by the F-number, also plays a critical role in determining the lateral resolution. In this study, the combined effects of the center frequency and F-number on lateral resolution were investigated using wafer-based test samples. Focused ultrasound transducers with different center frequencies were used to image a striped resolution target for quantitative lateral resolution analysis. In addition, a custom-fabricated silicon wafer containing void-mimicking patterns was also imaged for qualitative evaluation. The results show that a higher frequency does not necessarily guarantee better lateral resolution. In fact, a lower-frequency transducer with tighter focusing showed greater image quality compared to a higher-frequency transducer with a larger F-number. These findings indicate that both frequency and F-number should be jointly considered when selecting ultrasound transducers for semiconductor inspection. This wafer-based evaluation provides practical guidance for optimizing imaging conditions in scanning acoustic microscopy, according to target feature size and inspection requirements.