title: A study on the use of indigenous New Zealand plant fibres for producing biomorphic hydroxyapatite fibres and chars used in reinforcing biomedical hydroxyapatite sourced from cattle bone

authors: Siddiqui, Humair Ahmed

abstract: This research describes studies on the use of animal derived hydroxyapatite (HAp) with natural plant fibres. The study was divided into two sections, a major section and a minor section. The major section describes animal derived hydroxyapatite (HAp)-char composites containing low weight percent additions of two different types of plant chars (0.1, 0.5, 1, 1.5 and 2 wt%) derived from harakeke and cabbage tree leaf fibres. 

The work on hydroxyapatite (HAp)-char composites was conducted in three parts, where the initial two parts dealt with the development of precursors for the composite i.e., HAp and char while the third part detailed the composite made from these precursors. The other section of the thesis deals with development of biomorphic biomaterials-based fibres via treatments involving animal derived hydroxyapatite (HAp) and natural plant fibres. Initially waste bovine bone was processed to produce hydroxyapatite via re-precipitation. In this process, the bovine bone was initially converted into crystalline HAp, which was then further processed through acid digestion and alkali neutralisation at varying reaction temperatures, to produce re-precipitated HAp. Further to this, the as-precipitated HAp powders were subsequently subjected to a high temperature calcination process to develop its morphology. Various characterisation methods confirmed the development of pure HAp via re-precipitation and based on their morphological development and crystallinity, HAp that was re-precipitated at 80°C and calcined at 800°C (H₈₀₋₈₀₀), was subsequently chosen as the optimal matrix to be used in the composites. The second part of this study dealt with the development of the reinforcing material for the composites i.e., the char. Harakeke plant leaf fibres and cabbage tree leaf fibres were used to obtain char via pyrolysis followed by acid washing and a “piranha solution” treatment. The harakeke fibrous char was found to have developed carbon nanoscrolls attached to the surface of the char fibres. In contrast, cabbage tree leaf char did not show any form of nano carbon structure with some of the cabbage tree leaf char fibres found to be hollow. Composites were made using re-precipitated hydroxyapatite (H₈₀₋₈₀₀) and natural fibre char. The control samples (made up of H₈₀₋₈₀₀) displayed porous structure (61% porosity and 36% apparent porosity) having compressive strength, diametral tensile strength, Vickers hardness, brittleness index and indentation fracture toughness values of ca. 26 ± 0.8 MPa, 5 ± 0.1MPa, 190 ± 30 HV, 4 ± 0.2 and 0.5 ± 0.1 Mpa.m1/2 respectively. Both types of composites showed an increase in mechanical properties up to certain maximum values of incorporated char before dropping to values either equal to or less than the control sample. The 0.5 wt% harakeke leaf fibre char increased the values of (relative to the control sample) hardness by approx. 118%, diametral tensile strength by 158%, and indentation fracture toughness by 334%. In contrast, 0.5 wt% cabbage tree leaf fibre char addition increased the values of (as compared to the control sample) of compressive strength and hardness by approx. 40% each, diametral tensile strength by 66%, and indentation fracture toughness by 148.5 %. 

The minor section of this thesis reports the successful development of calcium deficient biomorphic HAp fibres using a simple aqueous soaking technique. A harakeke fibre biotemplate was soaked in a bovine digest solution (biogenic source of Ca²⁺ and PO₄³⁻ ions), dried and calcined to obtain HAp fibres. Extensive characterisation was carried out at all stages of the biomorphic fibres.

text: A study on the use of indigenous New Zealand plant fibres for producing biomorphic hydroxyapatite fibres and chars used in reinforcing biomedical hydroxyapatite sourced from cattle bone This research describes studies on the use of animal derived hydroxyapatite (HAp) with natural plant fibres. The study was divided into two sections, a major section and a minor section. The major section describes animal derived hydroxyapatite (HAp)-char composites containing low weight percent additions of two different types of plant chars (0.1, 0.5, 1, 1.5 and 2 wt%) derived from harakeke and cabbage tree leaf fibres. 

The work on hydroxyapatite (HAp)-char composites was conducted in three parts, where the initial two parts dealt with the development of precursors for the composite i.e., HAp and char while the third part detailed the composite made from these precursors. The other section of the thesis deals with development of biomorphic biomaterials-based fibres via treatments involving animal derived hydroxyapatite (HAp) and natural plant fibres. Initially waste bovine bone was processed to produce hydroxyapatite via re-precipitation. In this process, the bovine bone was initially converted into crystalline HAp, which was then further processed through acid digestion and alkali neutralisation at varying reaction temperatures, to produce re-precipitated HAp. Further to this, the as-precipitated HAp powders were subsequently subjected to a high temperature calcination process to develop its morphology. Various characterisation methods confirmed the development of pure HAp via re-precipitation and based on their morphological development and crystallinity, HAp that was re-precipitated at 80°C and calcined at 800°C (H₈₀₋₈₀₀), was subsequently chosen as the optimal matrix to be used in the composites. The second part of this study dealt with the development of the reinforcing material for the composites i.e., the char. Harakeke plant leaf fibres and cabbage tree leaf fibres were used to obtain char via pyrolysis followed by acid washing and a “piranha solution” treatment. The harakeke fibrous char was found to have developed carbon nanoscrolls attached to the surface of the char fibres. In contrast, cabbage tree leaf char did not show any form of nano carbon structure with some of the cabbage tree leaf char fibres found to be hollow. Composites were made using re-precipitated hydroxyapatite (H₈₀₋₈₀₀) and natural fibre char. The control samples (made up of H₈₀₋₈₀₀) displayed porous structure (61% porosity and 36% apparent porosity) having compressive strength, diametral tensile strength, Vickers hardness, brittleness index and indentation fracture toughness values of ca. 26 ± 0.8 MPa, 5 ± 0.1MPa, 190 ± 30 HV, 4 ± 0.2 and 0.5 ± 0.1 Mpa.m1/2 respectively. Both types of composites showed an increase in mechanical properties up to certain maximum values of incorporated char before dropping to values either equal to or less than the control sample. The 0.5 wt% harakeke leaf fibre char increased the values of (relative to the control sample) hardness by approx. 118%, diametral tensile strength by 158%, and indentation fracture toughness by 334%. In contrast, 0.5 wt% cabbage tree leaf fibre char addition increased the values of (as compared to the control sample) of compressive strength and hardness by approx. 40% each, diametral tensile strength by 66%, and indentation fracture toughness by 148.5 %. 

The minor section of this thesis reports the successful development of calcium deficient biomorphic HAp fibres using a simple aqueous soaking technique. A harakeke fibre biotemplate was soaked in a bovine digest solution (biogenic source of Ca²⁺ and PO₄³⁻ ions), dried and calcined to obtain HAp fibres. Extensive characterisation was carried out at all stages of the biomorphic fibres.

year: 2022

title: Augmenting NIR spectra in deep regression to improve calibration

authors: Wohlers, Mark W.

subjects: computer science

abstract: Deep learning, particularly with convolutional neural networks, shows promise in modelling near-infrared spectroscopy (NIRS), but the lack of robust generalisation across instruments often affects performance in practice. Here, we investigate a method to increase the robustness of this approach. The proposed method involves using a simple data augmentation technique during the training process. The performance of convolutional neural network regression is compared to partial least squares regression (PLSR) using kiwifruit data collected from multiple handheld devices over three seasons and mango data collected from a single device over four seasons. The results suggest that data augmentation for NIR spectra can prevent overfitting. In particular, augmenting the training data to mimic spectra collected over multiple devices results in a neural network model with improved performance over PLSR.

text: Augmenting NIR spectra in deep regression to improve calibration Deep learning, particularly with convolutional neural networks, shows promise in modelling near-infrared spectroscopy (NIRS), but the lack of robust generalisation across instruments often affects performance in practice. Here, we investigate a method to increase the robustness of this approach. The proposed method involves using a simple data augmentation technique during the training process. The performance of convolutional neural network regression is compared to partial least squares regression (PLSR) using kiwifruit data collected from multiple handheld devices over three seasons and mango data collected from a single device over four seasons. The results suggest that data augmentation for NIR spectra can prevent overfitting. In particular, augmenting the training data to mimic spectra collected over multiple devices results in a neural network model with improved performance over PLSR.

year: 2023

title: “We wanted to see if you were the real deal”: Teaching as a cultural practice in a challenging environment

authors: Lemon, Katrina Suezanne

abstract: Teaching can be viewed as a cultural practice in which teaching is embedded in the culture of the teacher and informed by the culture of the students (Bell, 2011). In this paper, a narrative is presented detailing an authentic example of teaching in New Zealand in which culture is prioritised. It describes the challenges faced by a young female teacher as she worked in a low decile secondary school with male students, the majority of whom were involved in the Mongrel Mob[1] gang. Her approach and responses were centred in her belief in culturally responsive teaching. The deliberate actions of the teacher led to a turning point for the students, allowing their mana to remain intact as she acknowledged their identity, language and culture. This teacher’s experience provides an example of how a teacher can enable learners in diverse classrooms to succeed in their learning.

text: “We wanted to see if you were the real deal”: Teaching as a cultural practice in a challenging environment Teaching can be viewed as a cultural practice in which teaching is embedded in the culture of the teacher and informed by the culture of the students (Bell, 2011). In this paper, a narrative is presented detailing an authentic example of teaching in New Zealand in which culture is prioritised. It describes the challenges faced by a young female teacher as she worked in a low decile secondary school with male students, the majority of whom were involved in the Mongrel Mob[1] gang. Her approach and responses were centred in her belief in culturally responsive teaching. The deliberate actions of the teacher led to a turning point for the students, allowing their mana to remain intact as she acknowledged their identity, language and culture. This teacher’s experience provides an example of how a teacher can enable learners in diverse classrooms to succeed in their learning.

year: 2017