Publication Search Results

Now showing 1 - 4 of 4
  • (2022) Cao, Jun
    This thesis focuses on the development and applications of magnetic resonance electrical properties tomography (MREPT), which is an emerging imaging modality to noninvasively obtain the electrical properties of tissues, such as conductivity and permittivity. Chapter 2 describes the general information about human research ethics, MRI scanner, MR sequence and the method of phase-based MREPT implemented in this thesis. Chapter 3 examines the repeatability of phase-based MREPT in the brain conductivity measurement using balanced fast field echo (bFFE) and turbo spin echo (TSE) sequences, and investigate the effects of compressed SENSE, whole-head B_1 shimming and video watching during scan on the measurement precision. Chapter 4 investigates the conductivity signal in response to short-duration visual stimulus, compares the signal and functional activation pathway with that of BOLD, and tests the consistency of functional conductivity imaging (funCI) with visual stimulation across participants. Chapter 5 extends the use of functional conductivity imaging to somatosensory stimulation and trigeminal nerve stimulation to evaluate the consistency of functional conductivity activation across different types of stimuli. In addition, visual adaptation experiment is performed to test if the repetition suppression effect can be observed using funCI. Chapter 6 explores if resting state conductivity networks can be reliably constructed using resting state funCI, evaluates the consistency of persistent homology architectures, and compares the links between nodes in the whole brain. Chapter 7 investigates the feasibility of prostate conductivity imaging using MREPT, and distinctive features in the conductivity distribution between healthy participants and participants with suspected abnormalities.

  • (2022) Qiao, Laicong
    There has been a rapid-growing market and academic enthusiasm for small wearable molecular diagnostic platforms driven by the growing demand for continuous monitoring of human health. Wearable devices need to be portable, stretchable, and ideally re-configurable to be able to work for different analytes. Such flexible physiological monitoring devices which are non-invasive or minimally-invasive represent the next frontier of biomedical diagnostics. They may make it possible to predict and prevent diseases or facilitate treatment by diagnosing diseases at the initial stages. However, there are many problems that restrict further applications of these devices. Firstly, there are a limited number of bio-materials which are highly flexible, biocompatible and have anti-fouling properties; such biomaterials are needed as substrates for wearable devices. Secondly, traditional biosensors used in wearable devices focus on the detection of physical signals (such as heartbeat) and small chemical molecules, e.g. Na+, K+. These are not sufficient to provide in depth health information which requires sensing of large molecules such as proteins, ideally in real time, which is currently challenging. This provides a motivation to develop highly sensitive wearable biosensors for the detection of large molecules in sweat. This thesis centres on the development of a bio-material based wearable device for continuous detection of crucial analytes in human sweat. To achieve this target, our first aim was to design a highly bio-compatible flexible material as a substrate for wearable devices. A tough and anti-fouling three-network hydrogel has been prepared by integrating a zwitterionic polymer network into a robust double-network hydrogel. Secondly, to fill the gap between technological development of continuous and non-invasive detection of different analytes in human sweat, a patterned sweat-based biosensor was created for the detection of key biomolecules. This sensor was produced by placing specific aptamers or enzymes on flexible working electrodes. In addition, nanotechnology methods have been applied to refine the bio-sensing interface to further increase the sensitivity of our sensors. Finally, a sample collection chip has been combined with our high sensitivity sensors to fabricate a wearable device for sweat bio-sensing purposes. Future research may involve integration of a commercially available wireless signal readout module with this wearable biosensing device. The outcomes of this work may provide new insights for the development of wearable devices for continuous measurement of a spectrum of analytes in sweat, as an important step towards point-of-care diagnostics

  • (2023) Lang, Yandong
    The magnitude of the diffusivity that characterizes lateral mixing in the ocean is about 106 -108 times larger than that of vertical mixing. The lateral direction is along the direction of the neutral tangent plane (same as the direction of the locally referenced potential density surface). However, due to the helical nature of the neutral trajectories (the normal vector of the neutral tangent plane is not curl-free), well-defined neutral surfaces do not exist. Well-defined but only approximately neutral surfaces have traditionally been chosen based on either (i) constructing a three-dimensional density variable whose iso-surface (the surface with a constant density value of the density variable) describes the lateral direction, or (ii) creating a two-dimensional approximately neutral surfaces (ANS), which are normally more neutral than the iso-surfaces of the three-dimensional density variable A three-dimensional neutral density variable is here derived called rSCV, which is an improvement on the neutral density rn of Jackett and McDougall (1997). Compared with rn, rSCV is independent of pressure and thus is insensitive to the ubiquitous vertical heaving motions of waves and eddies, and has similar neutrality as rn. The material derivatives (the rate of change of the density variables) of rSCV and rn have also been derived using numerical methods. The material derivative of rSCV is shown to be close to that of rn. Oceanographers have traditionally estimated the quality of an ANS by focusing on the fictitious vertical diffusion caused by lateral diffusion being applied in the wrong direction. This thesis shows that the spurious advection through an ANS is another important consideration that limits the accuracy and usefulness of an ANS. Because of this concern, a two-dimensional approximately neutral surface is constructed called the Wu.s-surface, which minimizes the spurious dia-surface advection through the surface. The spurious dia-surface advection through the Wu.s-surface is more than a hundred times smaller than that on the most neutral ANS to date, however, the fictitious diapycnal diffusion on it is larger. Therefore, the Wu.s+s2-surface is created to control both the spurious dia-surface advection and the fictitious diapycnal diffusion on the surface. It is shown that minimizing the fictitious diffusion and the spurious dia-surface advection is important for using such surfaces in inverse studies. Hence the Wu.s+s2-surface is the best choice of surface for such studies.

  • (2024) Jalandhra, Gagan
    Osteochondral tissue comprises of complex chemical, cellular and physical gradients which pose an immense challenge for repair via traditional tissue engineering approaches. Granular hydrogels have emerged as an exciting new opportunity for control of micro- and macro- scale properties for fabrication of complex tissue environments. This thesis explores the utility of gelMA-microgel based granular scaffolds for tissue engineering, with a focus on the osteochondral interface. First, scaffolds were optimised for MSC chondrogenesis by manipulating interstitial filler volume. Higher volumes were found to promote cell sphericity, proliferation, and aggregation, which led to enhanced chondrogenic matrix deposition. Second, incorporation of bioactive Laponite® -RD and -XLG nanosilicates is explored for MSC osteogenesis. Nanosilicate inclusion significantly enhanced MSC osteogenesis but was not found to be osteo-inductive. Third, embedded extrusion printing was utilised for deposition of a bone-mimetic ink in optimised MSC-laden microgel suspensions. Photo-crosslinkable gelMA microgels allowed tuning of ink properties, thus improving robustness. Over 21 days, MSCs exhibited gradient-like chondrogenic ECM deposition away from the bone and mineralisation close to it. Lastly, vascular structures were fabricated using a casting approach for straight channels and direct writing with a sacrificial ink for complex geometries. Design of a novel PDMS-based reactor allowed channel fabrication and long-term perfusion of constructs within the same setup. Taken together, this thesis demonstrates the modularity and versatility of gelMA microgel based granular suspensions and lays the foundation for their use in the fabrication of complex tissue models replete with vasculature.