title: Production of Bacterial Cellulose Using Low-cost Media

authors: Adnan, Azila Binti

abstract: Bacterial cellulose (BC) is a polymer of glucose monomers, which has unique properties including high crystallinity and high strength.  It has the potential to be used in biomedical applications such as making artificial blood vessels, wound dressings, and in the paper making industry. Unlike cellulose from plant sources, it is not contaminated with non-cellulose compounds, making it a candidate for medical use.  The aim of this thesis was to optimize BC production using the Gram negative bacterium Gluconacetobacter xylinus DSM 46604, including identifying cheaper ingredients for the culture media.  Initial trials were done on solid media and in shake flasks.  Trials were then scaled and done in 3-L and 5-L conventional bioreactors.  Three different processing strategies were used in the bioreactors: batch, fed-batch and continuous.
The morphology of the BC depended on the growth conditions.  Thin sheets were formed in stationary cultures and pellicles were formed in agitated cultures.  The scanning electron microscope micrographs showed that BC produced under static culture tends to be more densely packed than when produced in agitated shake flasks. 
Exploratory trials on agar slants and in agitated shake flasks using glucose, sucrose, and lactose showed that G. xylinus DSM 46604 grew well on glucose and produced BC.  However, there was minimal growth on the other two carbohydrates.  Further trials with initial glucose concentrations between 40 and 100 g/L were done in shake flasks.  Glucose concentration did not affect the BC morphology.  The maximum BC concentration of 1.13 g/L was produced using 50 g/L glucose.  The BC concentration using 100 g/L glucose was only 0.96 g/L.
Shake flask studies with 2 to 9 g/L yeast extract (YE) as a nitrogen source in the media showed the maximum BC concentration of 5.2 g/L was obtained using 5 g/L YE with 50 g/L of glucose.  Increasing the YE to 7 or 9 g/L produced only 4.82 and 4.06 g BC/L respectively. The effect of two cheaper nitrogen sources, fish hydrolysate and fish powder prepared from waste fish, were investigated.  The highest BC concentration of 0.24 g/L was obtained using 20 g/L fish hydrolysate rather than 5 g/L YE.  The BC yield of 0.04 g BC /g carbon substrate used were obtained using 5 g/L YE, 20 g/L fish hydrolysate, or 15 or 20 g/L fish powder.  
The effectiveness of four combinations of banana peel (as a cheaper carbon source) and glucose were investigated in shake flasks trials.  The highest BC concentration of 0.43 g/L was obtained using 10 g/L banana peel extract with 40 g/L glucose.  This was similar to the BC concentration produced with 50 g/L glucose (control).  Trials using the same combination of banana peel and glucose in a 3-L bioreactor produced 1 g/L BC compared with 2.2 g/L for 50 g/L glucose (control).
Shake flask fermentations using 10 to 50 g/L glycerol as the carbon source showed that the highest BC concentration of 1.43 g/L was produced with an initial glycerol of 20 g/L.  Trials done in a 3-L bioreactor produced 2.87 g/L of BC, representing a yield of 0.15 g/g carbon substrate used. 
The effect of aeration and agitation on BC production was studied in 3- and 5-L bioreactors.  The optimal agitation was 200 rpm at constant air flow rate of 0.3 volume air per volume culture broth per minute (vvm).  This produced 4.0 g/L BC and a yield of 0.06 g/g glucose.  The optimal aeration rate at 150 rpm was 1.0 vvm and produced 4.4 g/L BC.  
Various fermentation strategies were then investigated.  The control was batch fermentation on 50 g/L glucose in a 3- or 5-L fermenter.  All runs were done at 30OC, 200 rpm and 1 vvm aeration.  The BC yield when G. xylinus DSM 46604 was grown on 50 g/L glucose using a fill-and-draw fed-batch strategy was 0.05 g/g glucose or glycerol used, which was similar to the control.  The BC yield increased to 0.11 g/g when using a pulse-feed fed-batch strategy but the BC yield in continuous fed-batch was only 0.03 g/g.  It increased under continuous fermentation conditions and the highest yield (0.13 g/g) was achieved at a dilution rate of 0.1 h⁻¹.  If dilution rate was increased further, yields began to decrease.  
Trials were done by replacing 50 g/L glucose with 20 g/L glycerol.  Again, BC yields were higher under continuous conditions than batch fermentation.  The BC yield on 20 g/L using a fill-and-draw fed-batch strategy was 0.2 g/g BC compared with 0.15 g/g for the control.  This increased to 0.39 g/g for a pulse-feed fed-batch strategy.  The BC yield for continuous fed-batch at a dilution rate of 0.1 h⁻¹ was 0.3 g/g.  The highest BC yield under continuous conditions was 0.33 g/g when dilution rate was 0.1 h⁻¹.
These studies showed that cheaper ingredients such as fish powder or hydrolysate and banana peel extract could partially replace conventional nitrogen and carbon sources such as YE and glucose without affecting BC yield.  The BC production was enhanced using fed-batch and continuous processing strategies.  Higher BC yields than reported by much of the literature could be obtaining ujsing a combination of low-cost media ingredients and the best reactor conditions.

text: Production of Bacterial Cellulose Using Low-cost Media Bacterial cellulose (BC) is a polymer of glucose monomers, which has unique properties including high crystallinity and high strength.  It has the potential to be used in biomedical applications such as making artificial blood vessels, wound dressings, and in the paper making industry. Unlike cellulose from plant sources, it is not contaminated with non-cellulose compounds, making it a candidate for medical use.  The aim of this thesis was to optimize BC production using the Gram negative bacterium Gluconacetobacter xylinus DSM 46604, including identifying cheaper ingredients for the culture media.  Initial trials were done on solid media and in shake flasks.  Trials were then scaled and done in 3-L and 5-L conventional bioreactors.  Three different processing strategies were used in the bioreactors: batch, fed-batch and continuous.
The morphology of the BC depended on the growth conditions.  Thin sheets were formed in stationary cultures and pellicles were formed in agitated cultures.  The scanning electron microscope micrographs showed that BC produced under static culture tends to be more densely packed than when produced in agitated shake flasks. 
Exploratory trials on agar slants and in agitated shake flasks using glucose, sucrose, and lactose showed that G. xylinus DSM 46604 grew well on glucose and produced BC.  However, there was minimal growth on the other two carbohydrates.  Further trials with initial glucose concentrations between 40 and 100 g/L were done in shake flasks.  Glucose concentration did not affect the BC morphology.  The maximum BC concentration of 1.13 g/L was produced using 50 g/L glucose.  The BC concentration using 100 g/L glucose was only 0.96 g/L.
Shake flask studies with 2 to 9 g/L yeast extract (YE) as a nitrogen source in the media showed the maximum BC concentration of 5.2 g/L was obtained using 5 g/L YE with 50 g/L of glucose.  Increasing the YE to 7 or 9 g/L produced only 4.82 and 4.06 g BC/L respectively. The effect of two cheaper nitrogen sources, fish hydrolysate and fish powder prepared from waste fish, were investigated.  The highest BC concentration of 0.24 g/L was obtained using 20 g/L fish hydrolysate rather than 5 g/L YE.  The BC yield of 0.04 g BC /g carbon substrate used were obtained using 5 g/L YE, 20 g/L fish hydrolysate, or 15 or 20 g/L fish powder.  
The effectiveness of four combinations of banana peel (as a cheaper carbon source) and glucose were investigated in shake flasks trials.  The highest BC concentration of 0.43 g/L was obtained using 10 g/L banana peel extract with 40 g/L glucose.  This was similar to the BC concentration produced with 50 g/L glucose (control).  Trials using the same combination of banana peel and glucose in a 3-L bioreactor produced 1 g/L BC compared with 2.2 g/L for 50 g/L glucose (control).
Shake flask fermentations using 10 to 50 g/L glycerol as the carbon source showed that the highest BC concentration of 1.43 g/L was produced with an initial glycerol of 20 g/L.  Trials done in a 3-L bioreactor produced 2.87 g/L of BC, representing a yield of 0.15 g/g carbon substrate used. 
The effect of aeration and agitation on BC production was studied in 3- and 5-L bioreactors.  The optimal agitation was 200 rpm at constant air flow rate of 0.3 volume air per volume culture broth per minute (vvm).  This produced 4.0 g/L BC and a yield of 0.06 g/g glucose.  The optimal aeration rate at 150 rpm was 1.0 vvm and produced 4.4 g/L BC.  
Various fermentation strategies were then investigated.  The control was batch fermentation on 50 g/L glucose in a 3- or 5-L fermenter.  All runs were done at 30OC, 200 rpm and 1 vvm aeration.  The BC yield when G. xylinus DSM 46604 was grown on 50 g/L glucose using a fill-and-draw fed-batch strategy was 0.05 g/g glucose or glycerol used, which was similar to the control.  The BC yield increased to 0.11 g/g when using a pulse-feed fed-batch strategy but the BC yield in continuous fed-batch was only 0.03 g/g.  It increased under continuous fermentation conditions and the highest yield (0.13 g/g) was achieved at a dilution rate of 0.1 h⁻¹.  If dilution rate was increased further, yields began to decrease.  
Trials were done by replacing 50 g/L glucose with 20 g/L glycerol.  Again, BC yields were higher under continuous conditions than batch fermentation.  The BC yield on 20 g/L using a fill-and-draw fed-batch strategy was 0.2 g/g BC compared with 0.15 g/g for the control.  This increased to 0.39 g/g for a pulse-feed fed-batch strategy.  The BC yield for continuous fed-batch at a dilution rate of 0.1 h⁻¹ was 0.3 g/g.  The highest BC yield under continuous conditions was 0.33 g/g when dilution rate was 0.1 h⁻¹.
These studies showed that cheaper ingredients such as fish powder or hydrolysate and banana peel extract could partially replace conventional nitrogen and carbon sources such as YE and glucose without affecting BC yield.  The BC production was enhanced using fed-batch and continuous processing strategies.  Higher BC yields than reported by much of the literature could be obtaining ujsing a combination of low-cost media ingredients and the best reactor conditions.

year: 2015

title: Synthesis, microstructure and mechanical properties of bulk ultrafine grained Ti-47Al-2Cr (at%) alloy

authors: Nadakuduru, Vijay Navaratna

subjects: ultrafine grained

abstract: Hot isostatic pressing (HIP) and powder compact forging of Ti/Al/Cr composite powders of composition Ti-47Al-2Cr (at%) have been carried out to synthesize bulk ultrafine grained Ti-47Al-2Cr alloy. The Ti/Al/Cr composite powders were produced using high energy mechanical milling of elemental Ti, Al, Cr powders in a retsch planetary mill. The microstructure and mechanical properties of the bulk consolidated alloy produced using different processing techniques has been investigated. The mechanical properties of the alloy were studied in tension and compression both at room and elevated temperatures especially to know the formability of the material.

The bulk alloy samples produced by HIP for 2 hours at 1000 degrees C had porosity of approximately ~ 5%, indicating that the HIP time was not sufficient to close the pores. The microstructure mainly consisted of TiAl as the major phase and Ti(Al) and Ti3Al as minors, the unreacted Ti(Al) phase in the microstructure was mainly due to the initial powder condition, in which a small fraction of powder particles were rich in Ti. Tensile testing of the alloy samples was carried out at different temperatures. At room temperature the alloy was fairly brittle, without any plastic deformation, and had a fracture strength of ~ 100 MPa. At elevated temperatures the samples became ductile, as reflected by considerable amounts of tensile elongations at 800 degrees C and above. The maximum amount of elongation was found to be between 70 - 80% at 900 degrees C. The tensile yield strength at 800 degrees C was in the range of 84-90 MPa and decreased to 55-58 MPa with the testing temperature of the samples to 900 degrees C. In compression the alloy showed plastic yielding and yield strength of ~ 1.4 GPa at room temperature. Compression testing at 900 degrees C revealed that compressive deformations equivalent to a height reduction of 50% could be easily achieved without cracking. 

 Direct powder compact forging using canned powder compacts of the Ti/Al/Cr composite powder was successfully used to produce bulk consolidated Ti-47Al-2Cr alloy samples. It has been observed that the density of the bulk consolidated alloy sample after forging varied from the centre to the periphery. XRD analysis showed that the forged samples, consisted of TiAl (as major phase) along with Ti(Al) and Ti3.3Al phases. Mechanical testing of the samples showed that the samples exhibited brittle type of fracture both in tension and compression at room temperature and the fracture strength of the samples was in the range of 115 - 130 MPa in tension and 1.38-1.4 GPa in compression without any yielding. When being tested at 900 degrees C, the samples became very ductile showing yield strength in the range of 70-90 MPa and elongation to fracture between 80-165% in tension, and a yield strength of ~ 65 MPa and 50% deformation in compression was easily achievable.

 Nearly fully dense Ti-47-2Cr alloy samples with density of ~98% were produced by using HIP at 1000 degrees C for a duration of 3 hours. TEM observations revealed equiaxed grains with grain sizes in the range of 200-500 nm. The tensile testing of the alloy samples at different temperatures revealed that the brittle to ductile transition temperature of the alloy was in the range of 700 and 750 degrees C, similar to that reported from literatures. The alloy showed significantly higher strengths both at room and at elevated temperatures, due to the low level of porosity in the sample. Elongation of  95 - 117% at 750 degrees C  and 70-100% at 800 degrees C was observed.

The ultrafine grained Ti-47Al-2Cr alloy produced using a combination of mechanical milling and HIP/powder compact forging has demonstrated good formability at elevated temperatures leaving a large space for secondary processing to improve the quality of the material.

text: Synthesis, microstructure and mechanical properties of bulk ultrafine grained Ti-47Al-2Cr (at%) alloy Hot isostatic pressing (HIP) and powder compact forging of Ti/Al/Cr composite powders of composition Ti-47Al-2Cr (at%) have been carried out to synthesize bulk ultrafine grained Ti-47Al-2Cr alloy. The Ti/Al/Cr composite powders were produced using high energy mechanical milling of elemental Ti, Al, Cr powders in a retsch planetary mill. The microstructure and mechanical properties of the bulk consolidated alloy produced using different processing techniques has been investigated. The mechanical properties of the alloy were studied in tension and compression both at room and elevated temperatures especially to know the formability of the material.

The bulk alloy samples produced by HIP for 2 hours at 1000 degrees C had porosity of approximately ~ 5%, indicating that the HIP time was not sufficient to close the pores. The microstructure mainly consisted of TiAl as the major phase and Ti(Al) and Ti3Al as minors, the unreacted Ti(Al) phase in the microstructure was mainly due to the initial powder condition, in which a small fraction of powder particles were rich in Ti. Tensile testing of the alloy samples was carried out at different temperatures. At room temperature the alloy was fairly brittle, without any plastic deformation, and had a fracture strength of ~ 100 MPa. At elevated temperatures the samples became ductile, as reflected by considerable amounts of tensile elongations at 800 degrees C and above. The maximum amount of elongation was found to be between 70 - 80% at 900 degrees C. The tensile yield strength at 800 degrees C was in the range of 84-90 MPa and decreased to 55-58 MPa with the testing temperature of the samples to 900 degrees C. In compression the alloy showed plastic yielding and yield strength of ~ 1.4 GPa at room temperature. Compression testing at 900 degrees C revealed that compressive deformations equivalent to a height reduction of 50% could be easily achieved without cracking. 

 Direct powder compact forging using canned powder compacts of the Ti/Al/Cr composite powder was successfully used to produce bulk consolidated Ti-47Al-2Cr alloy samples. It has been observed that the density of the bulk consolidated alloy sample after forging varied from the centre to the periphery. XRD analysis showed that the forged samples, consisted of TiAl (as major phase) along with Ti(Al) and Ti3.3Al phases. Mechanical testing of the samples showed that the samples exhibited brittle type of fracture both in tension and compression at room temperature and the fracture strength of the samples was in the range of 115 - 130 MPa in tension and 1.38-1.4 GPa in compression without any yielding. When being tested at 900 degrees C, the samples became very ductile showing yield strength in the range of 70-90 MPa and elongation to fracture between 80-165% in tension, and a yield strength of ~ 65 MPa and 50% deformation in compression was easily achievable.

 Nearly fully dense Ti-47-2Cr alloy samples with density of ~98% were produced by using HIP at 1000 degrees C for a duration of 3 hours. TEM observations revealed equiaxed grains with grain sizes in the range of 200-500 nm. The tensile testing of the alloy samples at different temperatures revealed that the brittle to ductile transition temperature of the alloy was in the range of 700 and 750 degrees C, similar to that reported from literatures. The alloy showed significantly higher strengths both at room and at elevated temperatures, due to the low level of porosity in the sample. Elongation of  95 - 117% at 750 degrees C  and 70-100% at 800 degrees C was observed.

The ultrafine grained Ti-47Al-2Cr alloy produced using a combination of mechanical milling and HIP/powder compact forging has demonstrated good formability at elevated temperatures leaving a large space for secondary processing to improve the quality of the material.

year: 2009

title: Taku Ara, Taku Mahara: Pākehā Family Experiences of Kaupapa Māori and Bilingual Education

authors: Barnes, Alexander Louis

subjects: Kaupapa Maori

abstract: Kaupapa Māori (indigenous Māori-centred philosophies) initiatives have transformed various social, cultural and public projects in the domains of governance and constitutional issues, health, education, the environment, community development and research in Aotearoa – New Zealand. As a Pākehā graduate of te kōhanga reo and kura kaupapa Māori (Māori language immersion pre-school and primary school), this research is concerned with exploring the impact of kaupapa Māori and bilingual educational initiatives on my life and the lives of two other Pākehā families who share similar educational backgrounds. This foundational study utilises qualitative narrative inquiry methods as a means of understanding and analysing the implications for Pākehā as a result of their participation in kaupapa Māori and bilingual education. An intergenerational family approach is used in this research whereby the individual voices and experiences of young adults are heard equally alongside their parents’. Collectively understood, the themes represented in this research offer a unique means of understanding why Päkehä families decided to be involved in Māori immersion settings, and what these experiences mean to them now. One of the principle aims of this study is that it be used as a platform for dialogue amongst Pākehā, non-Māori and Māori about the future direction of bicultural education in Aotearoa – New Zealand.

text: Taku Ara, Taku Mahara: Pākehā Family Experiences of Kaupapa Māori and Bilingual Education Kaupapa Māori (indigenous Māori-centred philosophies) initiatives have transformed various social, cultural and public projects in the domains of governance and constitutional issues, health, education, the environment, community development and research in Aotearoa – New Zealand. As a Pākehā graduate of te kōhanga reo and kura kaupapa Māori (Māori language immersion pre-school and primary school), this research is concerned with exploring the impact of kaupapa Māori and bilingual educational initiatives on my life and the lives of two other Pākehā families who share similar educational backgrounds. This foundational study utilises qualitative narrative inquiry methods as a means of understanding and analysing the implications for Pākehā as a result of their participation in kaupapa Māori and bilingual education. An intergenerational family approach is used in this research whereby the individual voices and experiences of young adults are heard equally alongside their parents’. Collectively understood, the themes represented in this research offer a unique means of understanding why Päkehä families decided to be involved in Māori immersion settings, and what these experiences mean to them now. One of the principle aims of this study is that it be used as a platform for dialogue amongst Pākehā, non-Māori and Māori about the future direction of bicultural education in Aotearoa – New Zealand.

year: 2006