Youngjae Chun

CFD and machine-learning optimization of a post-junction obstruction guides the production of PLGA microparticles with sub-5 µm mean diameters and their thermoresponsive attachment to a balloon catheter.

This paper will introduce a radio frequency system to track the location of a stent designed to work inside a human artery. The stent is designed as a hemostasis aid tool for emergency situations where common surgical equipment, such as fluoroscopy systems, is not available, such as on the battlefield. In the application of interest, the stent must be guided to the correct location to achieve effective hemostasis and prevent complications. The locating approach uses the radiation pattern from the transmitter as the reference. When the transmitting frequency changes over a certain range, the measurement amplitude from a receiver depends on its relative location with respect to the transmitter. However, when the input frequency is unequal to the resonance frequency, the radiation pattern varies in an unpredictable way. To solve this problem, a deep learning model was trained to recognize variations in the radiation pattern and predict the receiver’s location as one of the classes in the reference grid. The deep learning model also reduces the impact of noise and disturbing signals, which effectively improves the system’s robustness.

This paper will introduce a location tracking system targeted on a stent when it is deployed into the human artery to achieve hemostasis. This system is proposed to be applied in emergent conditions such as treating injured soldiers on the battlefield where common surgical devices such as fluoroscopy systems are not available. The locating algorithm is based on both magnetic measurements and inertial measurements. The magnetic locating approach detects the sensor’s location in a coordinate system centered with the reference magnet source. The inertial locating approach integrates the linear acceleration and angular velocity measured by the sensor to obtain the angular and linear displacement during a time period. Measurements from all sensors are deeply fused to remove disturbances and noise that degrade the locating accuracy. The focus of this research is to identify all potential error-increasing factors and then provide solutions to correct them to enhance the location measurement reliability. Validation experiments for each improvement approach and the overall locating performance will be introduced.

Introduction: As part of an evidence-based reassessment of ventriculoamniotic shunting for fetal aqueductal stenosis, we developed an animal model for the induction of hydrocephalus, placement of a ventriculoamniotic shunt, and end of study analysis in fetal sheep. Methods: We made multiple revisions to both the animal model and the shunt over time. Regarding the animal model, we found that induction of hydrocephalus at 85 days gestation, shunt placement at 100 days gestation, and study end at 135 days gestation generated the most reproducible results. Conclusion: The purpose of this manuscript was to document step-by-step instructions for hydrocephalus induction, shunt placement, and end of study analysis so that those who wish to develop a fetal hydrocephalus model, repeat our experience with ventriculoamniotic shunting, or test other interventions may benefit from our experience. Moreover, standardization of methodology will allow for meaningful comparisons between investigators.

This paper will introduce a simple locating system to track a stent when it is deployed into a human artery. The stent is proposed to achieve hemostasis for bleeding soldiers on the battlefield, where common surgical imaging equipment such as fluoroscopy systems are not available. In the application of interest, the stent must be guided to the right location to avoid serious complications. The most important features are its relative accuracy and the ease by which it may be quickly set up and used in a trauma situation. The locating approach in this paper utilizes a magnet outside the human body as the reference and a magnetometer that will be deployed inside the artery with the stent. The sensor can detect its location in a coordinate system centered with the reference magnet. In practice, the main challenge is that the locating accuracy will be deteriorated by external magnetic interference, rotation of the sensor, and random noise. These causes of error are addressed in the paper to improve the locating accuracy and repeatability under various conditions. Finally, the system’s locating performance will be validated in benchtop experiments, where the effects of the disturbance-eliminating procedures will be addressed.

According to rough estimates, one in every 125 newborns born in the United States has a congenital cardiac abnormality that must be repaired. With the recent development of new biomaterials and innovative treatment methods, percutaneous cardiac valve replacement has been considered as an alternative to surgical procedures. While percutaneous heart valve replacement is a relatively new procedure with a few commercially available devices, the devices are not sufficiently low-profile, and do not grow with the child. To address this issue, a novel low-profile growing percutaneous pediatric heart valve frame made of two types of unique metallic biomaterials (supere lastic nitinol and biodegradable iron) has been developed through this study. The developed pediatric heart valve frame has an innovative mechanism that will expand its diameter by disconnecting biodegradable metals, enabling the growth of the device with the surrounding tissue in the cardiac space. The thermally treated iron wires show stable and gradual degradation characteristics, showing approximately 7.66% for both wires treated under 350 and 450 °C. Polymer-coated wires show a degradation range of 4.96 to 5.55% depending on the type of coating. Degradation test results show the predicted 9–23 months of degradation depending on the type of surface treatment (e.g., thermal treatment, polymer coating), which is a suitable range when compared with the theoretical arterial vessel remodeling process period in the human vascular system. Radial forces calculated by finite element analysis and measured by mechanical testing matched well, showing 5–6 N with a 20% diameter reduction considering the deployed valve frame in the heart. Biocompatibility study results demonstrated superior cell viability in thermally treated iron wires after 3 days of cell culture and showed rarely found platelets on the surface after 3-h blood exposure tests. Prototype devices were successfully fabricated using optimized advanced joining processes for dissimilar metallic materials such as nitinol and iron. This study represents the first demonstration of self-expanding and biodegradable percutaneous heart valve frames for pediatric patients that grow with a child.

Fetal aqueductal stenosis (AS) is one of the most common causes of congenital hydrocephalus, which increases intracranial pressure due to partial or complete obstruction of cerebrospinal fluid (CSF) flow within the ventricular system. Approximately 2–4 infants per 10,000 births develop AS, which leads to progressive hydrocephalus, which enlarges the head often necessitating delivery by cesarean section. Most babies born with AS are severely neurologically impaired and experience a lifetime of disability. Therefore, a new device technology for venticuloamniotic shunting is urgently needed and has been studied to ameliorate or prevent fetal hydrocephalus development, which can provide a significant impact on patients and their family’s quality of life and on the decrease of the healthcare dollars spent for the treatment. This study has successfully validated the design of shunt devices and demonstrated the mechanical performance and valve functions. A functional prototype shunt has been fabricated and subsequently used in multiple in vitro tests to demonstrate the performance of this newly developed ventriculoamniotic shunt. The shunt contains a main silicone-nitinol composite tube, a superelastic 90° angled dual dumbbell anchor, and an ePTFE valve encased by a stainless-steel cage. The anchor will change its diameter from 1.15 mm (collapsed state) to 2.75 mm (deployed state) showing up to 1.4-fold diameter change in human body temperature. Flow rates in shunts were quantified to demonstrate the valve function in low flow rates mimicking the fetal hydrocephalus condition showing “no backflow” for the valved shunt while there is up to 15 mL/h flow through the shunt with pressure difference of 20 Pa. In vivo ovine study results show the initial successful device delivery and flow drainage with sheep model.