Subdiaphragmatic vagus nerve stimulation (VNS) is being explored as a device-based option for obesity, but translation is limited by the lack of standardized implantation workflows and cuff electrodes that remain stable at the cuff–nerve interface in a moist in vivo environment. Here, we aimed to establish a bench-to–in vivo feasibility platform that integrates a microfabrication-compatible perfluoroalkoxy alkane (PFA) film cuff with a reproducible rabbit surgical procedure and sham-controlled evaluation. The cuff electrode was fabricated using MEMS-based processes and characterized on the bench (impedance/charge metrics), then implanted on the subdiaphragmatic vagus nerve in diet-induced obese rabbits assigned to sham or intermittent VNS at graded current levels (total n = 8; n = 2/group). Body weight was tracked as an exploratory outcome under variable delivered exposure. During the stimulation window, weight trajectories showed heterogeneous, non-monotonic patterns across current levels, with partial rebound after stimulation cessation. Gross inspection and hematoxylin and eosin (H&E) histology indicated preserved fascicular organization with a thin peri-neural fibrotic capsule, assessed qualitatively in this pilot cohort. Overall, these results support feasibility of reproducible subdiaphragmatic implantation and cuff–nerve interface operation and motivate powered studies with exposure-matched delivery logging and expanded metabolic and longitudinal endpoints.

Reliable chip integration remains a major challenge in implantable devices, where continuous fluid exposure, mechanical deformation, and severe space constraints must be addressed simultaneously. Existing chip packaging approaches often create structural dead space and require complex encapsulation, which can increase vulnerability to fluid ingress and long-term reliability degradation under implantation-relevant conditions. This study presents a chip integration strategy based on structural embedding using cyclic olefin copolymer (COC). Integrated circuit chips were embedded into a thermoplastic polymer substrate through an inverse truncated pyramid (ITP) geometry, enabling direct electrical integration without additional interconnection space. The integrated structure was subjected to a broad set of evaluations under implantation-relevant conditions, including in vitro biocompatibility assessment, electrical connectivity measurement, mechanical and thermal reliability testing, long-term insulation evaluation, and functional validation. The proposed approach achieved an electrical connectivity yield of up to 87% after PEDOT:PSS reinforcement. Finite element analysis showed that the ITP geometry redistributed mechanically induced stress away from the chip in terface and facilitated spatial dissipation of chip-generated heat. Long-term soak testing confirmed stable electrical insulation for 380 days, corresponding to aprojectedoperational lifetime of approximately 14.5 years under physiological conditions. Embedded functional devices also retained stable electrical performance after integration. These results demonstrate that the proposed structural embedding strategy enables monolithic, space efficient, and mechanically robust chip integration under implantation-relevant conditions. Taken together, the findings suggest that the proposed approach may offer a promising basis for further development toward compact and reliable implantable devices with integrated electronics.

Cuffless blood pressure (BP) monitoring using wearable devices enables frequent measurement in everyday settings, yet its real-world reliability remains difficult to assess because of calibration dependency and the absence of paired reference BP measurements in uncontrolled settings. This study aimed to characterize measurement stability in watch-based BP monitoring using calibration difference as a reference-free analytical index and to examine how calibration stability varies according to user characteristics and measurement frequency. Calibration difference was defined as the absolute difference between the average cuffless systolic BP (SBP) values measured during the 1-week periods before and after calibration. We analyzed large-scale real-world data from 3 nationwide campaigns conducted between 2021 and 2023, comprising 1714 participants and 5728 calibration-difference instances obtained from Samsung Galaxy Watch measurements. Observed calibration-difference distributions were compared with theoretically derived reference ranges based on day-to-day SBP variability reported across multiple independent cohorts. Statistical analyses and machine learning–based interpretation were used to examine nonlinear and interaction effects associated with age, average SBP, hypertension status, and measurement frequency. Among 5728 calibration-difference instances, the mean calibration difference was 5.95 (SD 4.73) mm Hg. Under the primary analytical assumption of 3 measurements per averaging period, calibration differences in the overall population and in younger or lower-SBP groups were broadly comparable to the theoretically derived reference ranges, whereas older individuals and those with higher average SBP consistently exhibited larger deviations. Age, average SBP, and the minimum number of measurements were independently associated with calibration difference in multivariable regression (all P<.01). Machine learning–based interpretation showed that the contributions of age and average SBP increased more prominently beyond approximately 55 years and 125 mm Hg, respectively. Elevated calibration differences were also observed among younger individuals with hypertension and older individuals without hypertension. Increasing measurement frequency reduced calibration difference according to a significant exponential decay model in the overall population (P<.01), with diminishing returns beyond 3 measurements, whereas older and higher-SBP subgroups continued to benefit from additional measurements. Calibration stability varied substantially across user groups, suggesting that uniform usage protocols may not be sufficient for watch-based BP monitoring in real-world settings. In settings where paired reference BP measurements are unavailable, calibration difference may serve as a scalable analytical index for examining measurement stability, rather than as a substitute for regulatory accuracy assessment. These findings provide a practical framework for evaluating real-world stability and optimizing measurement strategies for cuffless BP monitoring systems.

Retinal prostheses have been developed to restore vision in patients with photoreceptor degeneration, with neural interfaces playing a crucial role in effective stimulation. Conventional planar electrodes, commonly used in subretinal prostheses, exhibit limitations such as restricted cell-electrode contact and uncontrolled current dispersion, which reduce stimulation efficiency. To address these issues, we developed a novel plateau-structured electrode designed to enhance contact with retinal cells and improve localized stimulation. The electrodes were fabricated using a post-forming process with cyclic olefin copolymer (COC) thermoforming and lamination, ensuring structural stability and reliable encapsulation. Impedance spectroscopy confirmed the electrical performance of the electrodes, with an average impedance of approximately 100 Ω at 1 kHz, demonstrating their suitability for neural stimulation. Future studies will focus on cell adhesion experiments with NIH3T3 fibroblasts to assess biocompatibility and computational modeling using COMSOL Multiphysics® to simulate electric field distribution and optimize stimulation efficiency. The proposed plateau-structured electrode presents a promising approach to overcoming the limitations of conventional planar electrodes in subretinal prostheses. The findings contribute to the advancement of bioelectronic interfaces, with potential applications extending beyond retinal prostheses to neural stimulation devices requiring precise and stable cell-electrode interactions. Furthermore, the structural and fabrication methodologies developed in this study may be applicable to a wide range of biomedical devices where improved electrode stability and selectivity are critical.

In this work, a fabrication process for implantable electrodes using a Cyclic Olefin Copolymer (COC) substrate and a SU-8 passivation layer was presented. COC and SU-8 were shown to be suitable for implantable neural electrodes due to their biocompatibility, chemical resistance, and thermal stability. The electrodes were successfully patterned on the COC film, and the SU-8 passivation layer was coated while maintaining site-opened via photolithography. The photocrosslinking lamination of the substrate and passivation layer was used to produce electrodes with fine line widths of 20um without applying heat.

A retinal prosthesis is a device that can provide artificial vision to people who have lost their sight from certain retinal disorder. Because the device needs to be inserted into the body, high flexibility and reliability is required. Recently, devices using thermoplastic polymers such as LCP and COC as substrates have been studied. Being a highly functional integrated device, retinal prosthesis poses many design challenges. Among them, the stimulation chip embedding can be a particularly important task. Although it is common to use a wire bonding method for chip embedding, there are several limitations that are difficult to apply to implantable device. In this investigation, a novel approach is developed for high spaceefficient electrical connections and perform reliable encapsulation of integrated circuits to replace wire bonding. Since designing and manufacturing the stimulator chip used in retinal prosthesis requires non-negligible cost, a silicon die with the identical shape was selected as a substitute for testing purposes.

Polycarbonate is a polymer that has been widely used including medical application due to its useful properties. It has high temperature resistance, biocompatibility, transparency and low water absorption rate, which are needful characteristics for packaging material of implantable neural prosthetic devices. In this study, we investigated fabrication of neural electrode with polycarbonate film using standard photolithography process and heated hydraulic press for thermal lamination. First, oxygen plasma surface treatment was performed to increase the adhesion between metal and polycarbonate film. Then thin layer of titanium and gold layer were deposited. Metal layer is patterned through standard photolithography techniques. After completing the metal patterning, thermal lamination was performed with site opened polycarbonate film.