Kayla Viegas | Macquarie University (original) (raw)
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Papers by Kayla Viegas
There is an increasing requirement, in a variety of fields, for the ability to make microscopic m... more There is an increasing requirement, in a variety of fields, for the ability to make microscopic movements or to position items with high degree of accuracy. In this paper, a parallel mechanism with prismatic actuators which encompasses three degrees of freedom and can produce motion on a microscopic level is proposed and developed. In order to produce such motion, the mechanism is composed of compliant joints and links and flexure hinges, so it may also be referred to as a compliant mechanism. First, the detailed design of motion systems for the machine structure is introduced, followed by the mathematical analysis based on kinematics model of the presented mechanism. Finally, a comprehensive Finite Element Method analysis is carried out for the device optimization.
Artery Research
The lasting legacy of Donald McDonald has been in the establishment of physiological and biophysi... more The lasting legacy of Donald McDonald has been in the establishment of physiological and biophysical principles of the relation of blood pressure and flow in arteries. This relation is determined by physical properties of arteries, among which wall stiffness is a dominant parameter. Increased arterial stiffness leads to an increase in pulse pressure due to alterations in the capacitive properties of large arteries and the increase in pulse wave velocity, which leads to early return of reflected waves. While the haemodynamic and biophysical effects of arterial stiffness have been studied extensively and are well established, the underlying mechanisms responsible for the alteration of the structural properties of the arterial wall are not as well understood. Some potential mechanisms will be addressed in relation to the interaction of the cellular and acellular components and their effect on the structural integrity of the arterial wall. The modification of the smooth muscle cell to influence medial calcification and the endothelium-dependent nitric oxide pathways affecting the extracellular matrix through post-translational modification of proteins form part of positive feedback mechanisms in the regulation of arterial stiffness through cellular and molecular processes. This is further modulated by neurogenic effects on smooth muscle contractility affecting wall stiffness. While the passive effects on the arterial wall due to blood pressure and heart rate cannot be readily modified, uncovering cellular, molecular and neurogenic mechanisms regulating arterial stiffness can offer novel means to interrogate pathways leading to the detrimental effects of degeneration of arterial function and altered relation of pressure and flow.
Biomedical Engineering Online, 2011
Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathog... more Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events. Methods Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD). Results Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa. Conclusions This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.
There is an increasing requirement, in a variety of fields, for the ability to make microscopic m... more There is an increasing requirement, in a variety of fields, for the ability to make microscopic movements or to position items with high degree of accuracy. In this paper, a parallel mechanism with prismatic actuators which encompasses three degrees of freedom and can produce motion on a microscopic level is proposed and developed. In order to produce such motion, the mechanism is composed of compliant joints and links and flexure hinges, so it may also be referred to as a compliant mechanism. First, the detailed design of motion systems for the machine structure is introduced, followed by the mathematical analysis based on kinematics model of the presented mechanism. Finally, a comprehensive Finite Element Method analysis is carried out for the device optimization.
Artery Research
The lasting legacy of Donald McDonald has been in the establishment of physiological and biophysi... more The lasting legacy of Donald McDonald has been in the establishment of physiological and biophysical principles of the relation of blood pressure and flow in arteries. This relation is determined by physical properties of arteries, among which wall stiffness is a dominant parameter. Increased arterial stiffness leads to an increase in pulse pressure due to alterations in the capacitive properties of large arteries and the increase in pulse wave velocity, which leads to early return of reflected waves. While the haemodynamic and biophysical effects of arterial stiffness have been studied extensively and are well established, the underlying mechanisms responsible for the alteration of the structural properties of the arterial wall are not as well understood. Some potential mechanisms will be addressed in relation to the interaction of the cellular and acellular components and their effect on the structural integrity of the arterial wall. The modification of the smooth muscle cell to influence medial calcification and the endothelium-dependent nitric oxide pathways affecting the extracellular matrix through post-translational modification of proteins form part of positive feedback mechanisms in the regulation of arterial stiffness through cellular and molecular processes. This is further modulated by neurogenic effects on smooth muscle contractility affecting wall stiffness. While the passive effects on the arterial wall due to blood pressure and heart rate cannot be readily modified, uncovering cellular, molecular and neurogenic mechanisms regulating arterial stiffness can offer novel means to interrogate pathways leading to the detrimental effects of degeneration of arterial function and altered relation of pressure and flow.
Biomedical Engineering Online, 2011
Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathog... more Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events. Methods Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD). Results Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa. Conclusions This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.