Novel Irradiated Axial Rotational Flap Model in the Rodent

Abstract Objectives: To design an easily reproducible rodent rotational skin flap and to evaluate the effects of radiation on flap viability. Methods: Ten rats received 40 Gy irradiation to the abdominal wall. Following a recovery period of one month, a 3 X 8 cm fasciocutaneous flap based axially on the inferior epigastric vessel, was raised and rotated 60 degrees into a contralateral deficit. Five non-irradiated rats underwent the identical procedure as a control. Animals were sacrificed seven days postoperatively, areas of flap necrosis were documented, and histological specimens were taken to compare flap viability and vessel density. Results: 60% of the rats in the irradiated group had necrosis of the distal flap ranging from 1 to 6 cm from the distal edge, whereas none of the animals (0%) in the control group exhibited necrosis (p\u3c0.001). Histology revealed collagen and vascular changes in the irradiated skin. Vascular density analysis revealed a significant difference between radiated and non-radiated flaps; p = 0.004, 0.029 and 0.014 in the distal, middle and proximal segments of the flap respectively. Conclusion: This novel rat axial rotational flap model demonstrates increases flap necrosis and a decrease in vascular density due to the effects of radiation. Using a linear electron accelerator a dose of 40 gy can be delivered to the skin without resulting in devastating gastrointestinal side effects

Modeling for active needle steering in Percutaneous surgery

Precise needle insertion is very important for a number of percutaneous interventions. Yet it is very difficult to achieve in practice. Errors caused by the target movement and needle deflection have been observed for a long time. Yet to date, there are few effective physical-based needle steering systems existing for correcting the needle deflection when it occurs. In addition, many procedures are currently not amenable to needles because of obstacles, such as bone or sensitive tissues, which lie between feasible entry points and potential targets. Thus, there is a clear motivation for needle steering in order to provide accurate and dexterous targeting. This work aims to build a needle-tissue interaction model that can be used for designing a needle steering system. A spring-beam-damper model is adopted in this work, which takes into consideration both the elastic, viscoelastic tissue reactions and the needle flexibility, as well as their interaction effects. Unconstrained modal analysis method, which is computationally efficient, is adopted to analyze the system dynamics. Considering the tissue inhomogeneity and computational efficiency, depth-varying mean parameters are proposed in this thesis to calculate the spring and damper effects. Local polynomial approximations in finite depth segments are used to approximate the unknown depth-varying mean parameters. Based on these approaches, an online parameter estimator has been designed using modified least square method with forgetting factor. Extensive experiments have been carried out in various types of phantoms to validate the needle steering model with the online parameter estimator. Results have shown that the model can track the needle tip trajectory with RMSE (Root Mean Square Errors) less than 1mm after convergence even in the presence of large noises, which come from the reduced mode model, poor initial estimation and sensor noises etc. The convergence rate will be greatly improved if the needle gets supported.DOCTOR OF PHILOSOPHY (MAE

6‑<i>O</i>‑Sulfated Chitosan Promoting the Neural Differentiation of Mouse Embryonic Stem Cells

Embryonic stem cells (ESCs) can be induced to differentiate into nerve cells, endowing them with potential applications in the treatment of neurological diseases and neural repair. In this work, we report for the first time that sulfated chitosan can promote the neural differentiation of ESCs. As a type of sulfated glycosaminoglycan analog, sulfated chitosan with well-defined sulfation sites and a controlled degree of sulfation (DS) were prepared through simple procedures and the influence of sulfated glycosaminoglycan on neural differentiation of ESCs was investigated. Compared with other sulfation sites, 6-<i>O</i>-sulfated chitosan showed the most optimal effects. By monitoring the expression level of neural differentiation markers using immunofluorescence staining and PCR, it was found that neural differentiation was better enhanced by increasing the DS of 6-<i>O</i>-sulfated chitosan. However, increasing the DS by introducing another sulfation site in addition to the 6-<i>O</i> site to chitosan did not promote neural differentiation as much as 6-<i>O</i>-sulfated chitosan, indicating that compared with DS, the sulfation site is more important. Additionally, the optimal concentration and incubation time of 6-<i>O</i>-sulfated chitosan were investigated. Together, our results indicate that the sulfate site and the molecular structure in a sulfated polysaccharide are very important for inducing the differentiation of ESCs. Our findings may help to highlight the role of sulfated polysaccharide in inducing the neural differentiation of ESCs