Functional and Tunable Synthetic Hydrogel for Reproductive Tissue Engineering.

Many prepubertal girls and young women suffer from premature ovarian insufficiency induced by chemotherapy given for treatment of cancer and autoimmune diseases. Auto-transplantation of cryopreserved ovarian tissue could restore the lost ovarian endocrine function and fertility. Unfortunately, tissue ischemia, inconsistent graft quality and the risk of re-introducing malignant cells may stand in the way of the clinical translation of this approach. Therefore, isolation and re-implantation of multiple follicles may serve as a safer alternative; individual follicles can be isolated from the stromal environment in the ovarian tissue, and encapsulated in a hydrogel functioning as a supportive matrix for these isolated follicles. In the present study, we engineered an artificial ovarian tissue from the early stage follicles using a synthetic hydrogel, poly(ethylene glycol) vinyl-sulfone (PEG-VS), as a supportive matrix. The chemistry of the multi-arm PEG-VS formed by Michael-type addition allows: [1] modification with integrin binding peptides (such as RGD) for cell adhesion and migration and [2] a precise control over mechanical properties, making it suitable for reproductive tissue engineering applications. In this work, first we characterized the crosslinking kinetics of multi-arm PEG hydrogel. We investigated the role of PEG functionality on bioactive modification and mechanical properties of hydrogels, and the combined effect of mechano-biological properties on behavior of encapsulated cells. While the molar concentration of the reactive functional groups was identical in all the conditions, PEG with a larger number of functional groups on each unit allowed a greater degree of modification as well as a more precise control of mechanical properties, making it more suitable for supporting three-dimensional culture. Next, we modeled premature ovarian failure in mice to analyze the capability of PEG hydrogels to support folliculogenesis, vascularization, steroidogenesis and graft longevity in vivo. PEG hydrogels supported folliculogenesis of enzymatically-isolated follicles, leading to repeating estrous cycles and functioning hypothalamus-pituitary-gonadal axis with physiological levels of follicle-stimulating hormone. Furthermore, we demonstrated re-vascularization of the hydrogel, suggesting its capability of undergoing remodeling process. In summary, this is the first study proving the concept of a fully functional artificial ovarian tissue transplant built on the platform of the synthetic PEG hydrogel.PhDMacromolecular Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133460/1/jiwonk_1.pd

A Study on the development of sustainable water circulation city

Thesis(Master) -- KDI School: Master of Public Management, 2022The global trend of urbanization is increasing impervious urban land areas, resulting in distortion of hydrological water flow in cities. In addition, urbanization and population growth are leading to a sharp increase in water demand, while the climate change is reducing the stability of the water supply, causing water shortages. To restore the soundness of water circulation and to implement sustainable urban water management, it is necessary to accurately identify problems of the urban water circulation system and evaluate its soundness. Urban water problems can also conflict with various stakeholders from various perspectives, such as water supply, urban planning, infrastructure, environment, and urban amenity. The urban water circulation system should be considered holistically, including not only natural water circulation but also artificial water circulation. This study aims to develop a sustainable water circulation city model by considering complex and diverse urban water circulation factors as a whole. To do so, a number of urban water circulation factors and policies are examined through literature review and the case studies of Germany, the United States, and Australia. Various efforts, achievements, and limitations of urban water circulation policies in Korea are also investigated. Following the analysis, the paper proposes a differentiated water circulation city model for Korea, catering to its specific local contexts and conditions. Four issues are given particular attention: institutional issues, project planning issues, governance issues, and evaluation indicator issues. The outcome of this study is expected to contribute to the establishment and revitalization of the water circulation city in Korea.1. Introduction 2. Literature review 3. Research Methods 4. International Case Studies on Urban Water Circulation 5. Analysis of Urban Water Circulation Policies and Projects in Korea 6. Development of Water Circulation City Model 7. ConclusionmasterpublishedJiwon KI

Low-Cost GNSS Simulators with Wireless Clock Synchronization for Indoor Positioning

In regions where global navigation satellite systems (GNSS) signals are unavailable, such as underground areas and tunnels, GNSS simulators can be deployed for transmitting simulated GNSS signals. Then, a GNSS receiver in the simulator coverage outputs the position based on the received GNSS signals (e.g., Global Positioning System (GPS) L1 signals in this study) transmitted by the corresponding simulator. This approach provides periodic position updates to GNSS users while deploying a small number of simulators without modifying the hardware and software of user receivers. However, the simulator clock should be synchronized to the GNSS satellite clock to generate almost identical signals to the live-sky GNSS signals, which is necessary for seamless indoor and outdoor positioning handover. The conventional clock synchronization method based on the wired connection between each simulator and an outdoor GNSS antenna causes practical difficulty and increases the cost of deploying the simulators. This study proposes a wireless clock synchronization method based on a private time server and time delay calibration. Additionally, we derived the constraints for determining the optimal simulator coverage and separation between adjacent simulators. The positioning performance of the proposed GPS simulator-based indoor positioning system was demonstrated in the underground testbed for a driving vehicle with a GPS receiver and a pedestrian with a smartphone. The average position errors were 3.7 m for the vehicle and 9.6 m for the pedestrian during the field tests with successful indoor and outdoor positioning handovers. Since those errors are within the coverage of each deployed simulator, it is confirmed that the proposed system with wireless clock synchronization can effectively provide periodic position updates to users where live-sky GNSS signals are unavailable.Comment: Submitted to IEEE Acces

Correlated parameters in driving behavior models: car-following example and implications for traffic microsimulation

Behavioral parameters in car following and other models of driving behavior are expected to be correlated. An investigation is conducted into the effect of ignoring correlations in three parameters of car-following models on the resulting movement and properties of a simulated heterogeneous vehicle traffic stream. For each model specification, parameters are calibrated for the entire sample of individual drivers with Next Generation Simulation trajectory data. Factor analysis is performed to understand the pattern of relationships between parameters on the basis of calibrated data. Correlation coefficients have been used to show statistically significant correlation between the parameters. Simulation experiments are performed with vehicle parameter sets generated with and without considering such correlation. First, parameter values are sampled from the empirical mass functions, and simulated results show significant difference in output measures when parameter correlation is captured (versus ignored). Next, parameters are sampled under the assumption that they follow the multivariate normal distribution. Results suggest that the use of parametric distribution with known correlation structure may not sufficiently reduce the error due to ignoring correlation if the underlying assumption does not hold for both marginal and joint distributions