title: Assessment of Plasma Deposition Parameters for DED Additive Manufacturing of AA2319

authors: Rodríguez-González, Paula

abstract: Arc-directed energy deposition using wire as feedstock is establishing itself as a 3D printing method capable of obtaining additively manufactured large structures. Contrasting results are reported in the literature about the effect of the deposition parameters on the quality of the deposited tracks, as it is highly dependent on the relationship and intercorrelations between the individual input parameters, which are generally deposition-technique-dependent. This study comprehensively analysed the effect of several deposition parameters and clarified their interactions in plasma metal deposition of Al alloys. It was found that, although no straightforward correlation between the individual input parameters investigated and the measured output deposition track’s quality aspects existed, the input current had the greatest effect, followed by the wire feed speed and its interaction with the input current. Moreover, the greatest effect of changing the shielding gas atmosphere, including the gas mixture, flow rate and plasma flow, was on the penetration depth, and fine-tuning the frequency/balance ratio and the preheating of the deposition substrates reduced the amount of porosity. This study demonstrates that well-deposited multi-layer walls made out of Al alloys can successfully be achieved via plasma metal deposition.

text: Assessment of Plasma Deposition Parameters for DED Additive Manufacturing of AA2319 Arc-directed energy deposition using wire as feedstock is establishing itself as a 3D printing method capable of obtaining additively manufactured large structures. Contrasting results are reported in the literature about the effect of the deposition parameters on the quality of the deposited tracks, as it is highly dependent on the relationship and intercorrelations between the individual input parameters, which are generally deposition-technique-dependent. This study comprehensively analysed the effect of several deposition parameters and clarified their interactions in plasma metal deposition of Al alloys. It was found that, although no straightforward correlation between the individual input parameters investigated and the measured output deposition track’s quality aspects existed, the input current had the greatest effect, followed by the wire feed speed and its interaction with the input current. Moreover, the greatest effect of changing the shielding gas atmosphere, including the gas mixture, flow rate and plasma flow, was on the penetration depth, and fine-tuning the frequency/balance ratio and the preheating of the deposition substrates reduced the amount of porosity. This study demonstrates that well-deposited multi-layer walls made out of Al alloys can successfully be achieved via plasma metal deposition.

year: 2023

title: Chracterisation of Mighty during Skeletal Muscle Regeneration

authors: Dyer, Kelly Anne

subjects: skeletal muscle

abstract: Satellite cells are a distinct lineage of myogenic precursors that are responsible for the growth of muscle during post-natal life and for its repair after damage. During muscle growth and regeneration satellite cells are activated in response to growth signals from the environment, which induces the expression of one or both of the two MRFs, Myf-5 or MyoD. Activated satellite cells migrate to the site of injury and proliferate before these transcription factors go on to activate transcription of myogenic genes. The myoblasts can then adopt one of two fates. Some myoblasts initiate terminal differentiation and are able to either fuse into existing myofibres to repair them, or fuse with other myoblasts to form new fibres. Other myoblasts do not differentiate but instead return to quiescence and adopt a satellite cell position on repaired or newly formed fibres.

Mighty, a downstream target of myostatin that was discovered by the Functional Muscle Genomics Laboratory has recently been shown to induce cell hypertrophy in cell culture through enhanced differentiation and fusion of myoblasts. Myostatin-null mice have hypertrophic muscles and an improved muscle regeneration phenotype. These mice have also been shown to have higher basal levels of Mighty in skeletal muscle than wild-type mice. In this thesis the expression profile of Mighty during skeletal muscle regeneration was characterised in relation to MyoD. 

During regeneration Mighty gene expression was induced at day five post-injury in both wild-type and myostatin-null mice. In the myostatin-null mice Mighty gene expression remained elevated at day seven post injury in contrast to the levels in the wild-type, which had decreased at this time point. By day-14 and day-28 post-injury Mighty levels were decreased. The up-regulation of Mighty occurs at the time of peak myotube formation in regenerating skeletal muscle, consistent with a role for Mighty in enhancing differentiation and fusion of myoblasts. The extended up-regulation of Mighty in the myostatin-null muscle may be responsible for the enhanced regeneration phenotype of these mice.

Analysis of the myotube and reserve cell populations, which are an in vitro model of satellite cells, from both C2C12 cells and Mighty over-expressing clones (Clone 7 and Clone 11) showed that Mighty expression down-regulates two satellite cell markers, CD34 and Sca-1. Both these molecules have been recently shown to be involved in myoblast fusion and reserve cell specification, although their exact role in these processes is not yet known. Expression of Sca-1 is associated with a slowly proliferating non-dividing state while CD34 is associated with the population of reserve cells that do not fuse when notch signalling is inhibited. The results of this thesis indicate that Mighty over-expression may cause the enhanced fusion phenotype by regulating these two molecules.

In conclusion the data in this thesis supports a role for Mighty in the myotube formation phase of regeneration and may be able to enhance regeneration by recruiting more myoblasts to terminal differentiation by altering CD34 and    Sca-1 expression.

text: Chracterisation of Mighty during Skeletal Muscle Regeneration Satellite cells are a distinct lineage of myogenic precursors that are responsible for the growth of muscle during post-natal life and for its repair after damage. During muscle growth and regeneration satellite cells are activated in response to growth signals from the environment, which induces the expression of one or both of the two MRFs, Myf-5 or MyoD. Activated satellite cells migrate to the site of injury and proliferate before these transcription factors go on to activate transcription of myogenic genes. The myoblasts can then adopt one of two fates. Some myoblasts initiate terminal differentiation and are able to either fuse into existing myofibres to repair them, or fuse with other myoblasts to form new fibres. Other myoblasts do not differentiate but instead return to quiescence and adopt a satellite cell position on repaired or newly formed fibres.

Mighty, a downstream target of myostatin that was discovered by the Functional Muscle Genomics Laboratory has recently been shown to induce cell hypertrophy in cell culture through enhanced differentiation and fusion of myoblasts. Myostatin-null mice have hypertrophic muscles and an improved muscle regeneration phenotype. These mice have also been shown to have higher basal levels of Mighty in skeletal muscle than wild-type mice. In this thesis the expression profile of Mighty during skeletal muscle regeneration was characterised in relation to MyoD. 

During regeneration Mighty gene expression was induced at day five post-injury in both wild-type and myostatin-null mice. In the myostatin-null mice Mighty gene expression remained elevated at day seven post injury in contrast to the levels in the wild-type, which had decreased at this time point. By day-14 and day-28 post-injury Mighty levels were decreased. The up-regulation of Mighty occurs at the time of peak myotube formation in regenerating skeletal muscle, consistent with a role for Mighty in enhancing differentiation and fusion of myoblasts. The extended up-regulation of Mighty in the myostatin-null muscle may be responsible for the enhanced regeneration phenotype of these mice.

Analysis of the myotube and reserve cell populations, which are an in vitro model of satellite cells, from both C2C12 cells and Mighty over-expressing clones (Clone 7 and Clone 11) showed that Mighty expression down-regulates two satellite cell markers, CD34 and Sca-1. Both these molecules have been recently shown to be involved in myoblast fusion and reserve cell specification, although their exact role in these processes is not yet known. Expression of Sca-1 is associated with a slowly proliferating non-dividing state while CD34 is associated with the population of reserve cells that do not fuse when notch signalling is inhibited. The results of this thesis indicate that Mighty over-expression may cause the enhanced fusion phenotype by regulating these two molecules.

In conclusion the data in this thesis supports a role for Mighty in the myotube formation phase of regeneration and may be able to enhance regeneration by recruiting more myoblasts to terminal differentiation by altering CD34 and    Sca-1 expression.

year: 2006

title: Sustainability and Indigeneity

authors: Daya-Winterbottom, Trevor

abstract: In the lead up to the Rio Conference on Environment and Development 1992, New Zealand enshrined the concept of the sustainable management of natural and physical resources in statute law by enacting the Resource Management Act 1991. Implementing the concept of sustainable management in domestic law gave rise to a tension between anthropocentric and ecological approaches for implementing the statute that were not resolved by the Courts until 2014. However, the adoption of an ecological approach to implementing the statute did not assuage the desire for statutory reform unlocked by the previous debate. Most recently, the reform trajectory has resulted in Parliamentary scrutiny of an exposure draft Bill that replaces the concept of sustainable management with a new concept of the welfare and wellbeing of the environment rooted firmly in indigenous perspectives on earth governance, guardianship, and intergenerational equity. My paper will critically interrogate the implications of adopting the concept of the welfare and wellbeing of the environment for the future of sustainability, and what implications this approach could have for environmental law generally in the Anthropocene both comparatively and internationally.

text: Sustainability and Indigeneity In the lead up to the Rio Conference on Environment and Development 1992, New Zealand enshrined the concept of the sustainable management of natural and physical resources in statute law by enacting the Resource Management Act 1991. Implementing the concept of sustainable management in domestic law gave rise to a tension between anthropocentric and ecological approaches for implementing the statute that were not resolved by the Courts until 2014. However, the adoption of an ecological approach to implementing the statute did not assuage the desire for statutory reform unlocked by the previous debate. Most recently, the reform trajectory has resulted in Parliamentary scrutiny of an exposure draft Bill that replaces the concept of sustainable management with a new concept of the welfare and wellbeing of the environment rooted firmly in indigenous perspectives on earth governance, guardianship, and intergenerational equity. My paper will critically interrogate the implications of adopting the concept of the welfare and wellbeing of the environment for the future of sustainability, and what implications this approach could have for environmental law generally in the Anthropocene both comparatively and internationally.

year: 2022