Doctor of Philosophy

dissertationIn microsurgical operating room environments, it is often necessary to cut and reattach vessels multiple times during surgery. The current method of vascular anastomosis is hand suturing. This technique is time consuming, difficult, and requires complex instruments. To solve this problem, researchers have explored alternative ways to improve this technique. Typical examples are staples, clips, cuffing rings, adhesives, and laser welding. The potential of these techniques has been hindered due to the lack of biocompatibility, complex procedures for use, and general inefficiency. As a result, few of these devices have been commercialized. One promising alternative is a ring-pin coupling device. This device has been shown to be useful for venous anastomosis, but lacks the versatility necessary for arterial applications. One purpose of this study was to optimize a vascular coupling design that could be used for arteries and veins of various sizes. To achieve this, finite element analysis was used to simulate the vessel-device interaction during anastomosis. Parametric simulations were performed to optimize the number of pins, the wing pivot point, and the pin offset of the design. The interaction of the coupler with various blood vessel sizes was also evaluated. The optimal vascular coupling device has four rotatable wings and one translatable spike in each wing. Prototypes were manufactured using polytetrafluoroethylene (PTFE) and high-density polyethylene (HDPE). A set of installation tools was designed to facilitate the anastomosis process. Proof-of-concept testing with the vascular coupler using plastic tubes and porcine cadaver vessels showed that the coupler could be efficiently attached to blood vessels, did not leak after the anastomosis was performed, had sufficient joint strength, and had little impact on flow in the vessel. A simplified finite element model assisted in the evaluation of the tearing likelihood of human vessels during installation of the coupler. The entire anastomosis process can be completed in three minutes when using the vascular coupler to join porcine cadaver vessels. A metal-free vascular coupling system that can be used for both arteries and veins was designed, fabricated, and tested. A set of corresponding instruments were developed to facilitate the anastomosis process. Evaluation of the anastomosis by Scanning Electron Microscopy (SEM) and Magnetic Resonance Imaging (MRI) demonstrated that the installation process does not cause damage to the vessel intima and the vascular coupling system is not exposed to the vessel lumen. Mechanical testing results showed that vessels reconnected with the vascular coupling system could withstand 12.7±2.2 N tensile force and have superior leak profiles compared to hand sutured vessels. The anastomotic process was successfully demonstrated on both arteries and veins in cadaver and live pigs

A data-driven method to reduce excessive contact pressure of hand orthosis using a soft sensor skin

Discomfort under customised hand orthosis has been commonly reported in clinics due to excessive contact pressures, leading to low patient adherence and decreased effectiveness of orthosis. However, the current orthosis adjustment by clinicians to reduce pressures based upon subjective feedback from patients is inefficient and prone to variability. Therefore, a quantitative method to guide orthosis adjustment was proposed here by developing a data-driven method. Firstly, Verbal Protocol Analysis was employed to convert the implicit process of orthosis customisation into working models of clinicians. Relevant data to inform a new solution development to reduce excessive contact pressure were extracted from the working models in terms of time consumption and iterations of tasks. Secondly, a new soft sensor skin with strategically placed sensing units to measure static contact pressures under hand orthoses was developed. Finite element simulations were conducted to reveal the required contact pressure range (0.02 – 0.078 MPa) and the distribution of relatively high pressures in 12 key areas. A new fabrication method was proposed to produce the sensor skin, which was then characterised and tested on the subject. The results show that the sensor unit has a pressure range from 0.01 MPa to 0.1 MPa with the maximum repeatability error of 6.4% at 0.014 MPa, and the maximum measurement error of 8.26% at 0.023 MPa. Thirdly, a new method was proposed to predict contact pressures associated with the moderate level of discomfort at critical spots under hand orthoses. 40 patients were recruited to collect contact pressures under two types of orthoses using the sensor skin, and their discomfort perceptions were measured with a categorical scale. Based on these data, artificial neural networks for five identified critical spots on the hand were built to predict pressure thresholds that clinicians can use to adjust orthoses, thus reducing excessive contact pressures. The neural networks show satisfactory prediction accuracy with R2 values over 0.89 of regression between network outputs and measurements. Collectively, this thesis proposed a novel method for clinicians to adjust orthoses quantitatively and reduce the need for subjective assessment for patients. It provided a platform to further investigate the pressure for patients with other conditions.Open Acces