Chemical and Biomolecular Engineering - Theses
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ItemFundamental study of physical and biochemical alterations to casein micelles during milk evaporation and ultrafiltration( 2013)Casein represents 80% of the protein in milk, which is predominantly present in the form of hydrated colloidal assemblies known as casein micelles. It is one of the most important components in milk system that has significant influence on the properties of dairy products. It is also the main component of several highly value-added dairy products (such as milk protein concentrate (MPC) and milk protein isolate (MPI)). The objective of this work was to investigate the physico-chemical alterations of skim milk (specifically casein and casein micelles) during processing (evaporation and ultrafiltration) and to understand the processes at a fundamental level in order to determine the effect of the processing parameters on the properties of casein micelles and milk products to ultimately improve the efficiency of dairy processing. Evaporation in the dairy industry is used for concentrating products such as milk and whey while it is also used as a preliminary step to drying. Milk products intended for milk powder are normally concentrated to a final concentration of 40 – 50 % total solids before going to the spray dryer. To reduce heat impact on the heat sensitive components in milk system, evaporation takes place under vacuum at relatively low temperature. In this study, skim milk was concentrated by vacuum evaporation to concentration 12 – 45 % total solids content. The hydration, composition and size of the casein micelle were investigated. The results show that during evaporation, both inter and intra micelle water were removed from the milk system and preferentially the serum water. The alterations were rapidly reversible but not completely. Ultrafiltration is a process in which semi-permeable membranes are used to separate components in a fluid on the basis of size. It is widely used in the dairy industry for recovering, fractionating and concentrating proteins in milk process streams. In this study, skim milk was concentrated by ultrafiltration up to four folds at different processing temperatures. The changes of milk and caseins were discussed and different processing conditions were compared. Casein micelles and colloidal calcium phosphate are affected contemporaneously by the system temperature. A comprehensive physico-chemical investigation of the dynamic responses of casein micelles to changes in temperature was performed in the range 10 °C – 40 °C in real time. The temperature effects on casein micelles were consistent with the results of the ultrafiltration processing at different temperature. Lactose is an important energy source in milk system, and it also regulates the water content of milk during secretion. In evaporation and UF concentration, micellar water behaved differently: the micelle hydration decreased during evaporation, whilst increased during UF concentration. Lactose is highly responsible for this difference, and the lactose effects on casein micelles were studied in this work. This study investigates the temperature dependent dynamics of casein micelles, and physico-chemical behaviours under different lactose concentrations, evaporation or ultrafiltration conditions. The results show that casein micelles and colloidal calcium phosphate (CCP) are dynamic entities which are significantly affected by processing. The results have important implications for improving milk processing in dairy industry.
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ItemInhibitors of amyloid fibril formation( 2013)Despite significant recent advances in medical technology, there is still no commercially available treatment for the amyloid diseases that were first observed by Nicolaus Fontanus in 1639. These amyloids are fibrillar aggregates of misfolded proteins that form plaques in various organs and are the hallmarks of a number of incurable diseases such as Alzheimer’s disease and Parkinson’s disease among others. Alzheimer’s disease is the most well-known amyloid disease and was first described by Alois Alzheimer in 1906. It is widely believed that the amyloids or their precursors are responsible for the tissue damage that eventually leads to these diseases, though there is debate in the literature regarding the poor relationship between amount of fibrils and disease progression. Nonetheless, there is a general consensus that the fibrils are related to the progression of these amyloid diseases. Several strategies to prevent or cure amyloid diseases include reducing the amount of amyloid beta (Aβ) produced and the removal of amyloid plaques. Inhibitors that prevent the formation of amyloid fibrils can prevent amyloid diseases from occurring. Hence, this thesis is concerned with the design and testing of amyloid inhibitors as possible therapeutics for these diseases. In order to achieve this objective, the key universal physical properties of amyloid fibrils involved in their self-assembly have been used to design a generic class of fibril inhibitors. A design of an amphiphilic polymer with a hydrophobic backbone and hydrophilic side chains was proposed as a generic amyloid inhibitor and several compounds with this design were obtained. 3 model amyloid forming proteins: bovine insulin (BI), hen egg white lysozyme (HEWL) and Aβ were used to study the effect of these compounds on amyloid fibril formation. Suitable amyloid-forming conditions for these proteins were identified and fibril formation was monitored using Thioflavin T (ThT) fluorescence and other techniques. A naturally occurring compound that fits the proposed inhibitor design was identified and found to be effective at inhibiting amyloid fibril formation in all 3 protein systems. Unusually large fibrils were formed when incubating BI and HEWL with this natural compound and this has potential nanotechnological applications as nanowire templates. To further test the proposed structure, synthetic polymers based on the proposed structure with different chemical groups were produced and one of them, FA-diacid (“FA” was a designation used by the polymer science group of the University of Melbourne for divinylcyclopentane polymers), showed promising inhibitory capabilities. The FA-diacid was improved with the addition of larger hydrophilic side chains to produce the more effective inhibitors named PNGA and PNGE. Finally, glycoproteins based on the structure of AGP were produced and tested using the 3 proteins and were found to have some inhibitory ability. However, they were not as effective as PNGA or PNGE. The results show that compounds with the proposed inhibitor structure can be effective as a generic amyloid inhibitor, but further modification of the current compounds is needed to improve the effectiveness of these compounds as drugs. Further development on this class of chemicals can lead to the production of a new class of generic amyloid inhibitor that can be used to prevent and halt the progression of presently incurable amyloid diseases such as Alzheimer’s disease.
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ItemNovel polymeric architectures through controlled/living polymerization, click chemistry and supramolecular interactions( 2013)The properties and functions of polymeric materials are not only dictated by their composition but also their structural arrangement (i.e., architecture or topology). Exploration of polymers with novel molecular architectures has become a practical strategy for developing advanced soft nanomaterials essential to emerging nanotechnologies. Utilizing a combination of modern synthetic chemistries including controlled/living polymerization, click chemistry and supramolecular interactions, this body of research resulted in the development of facile, versatile and highly efficient synthetic pathways for the preparation of a fascinating array of unprecedented macro(supra)molecular architectures. A scaffold approach that provides access to a library of highly functionalized core cross-linked star (CCS) polymers was developed. Novel functional star macromolecular architectures including fluorescent, saccharide and amphiphilic polyester-based CCS polymers were synthesized by grafting a polyalkyne CCS polymer scaffold with the corresponding azido functional compounds through click chemistry. Factors affecting the grafting efficiency (i.e., click efficiency) of the azido compounds onto the CCS scaffolds were identified. This study not only introduces a versatile and efficient synthetic route towards highly functionalized CCS polymers, but also provides a valuable reference source for the high density functionalization of complex 3-D nanostructures. The near-quantitative synthesis of polyester-based CCS polymers was demonstrated through organic catalyst-mediated ring opening polymerization. Using this innovative approach, novel benzyl and alkyne end-functional polyester-based CCS polymers were conveniently synthesized in high yields (90 - 96%) at ambient temperatures. Side-reactions that are responsible for trace amounts of low molecular weight impurities in the resulting polymers were identified. The established high-yielding system, which involves no toxic metal catalysts or additives and operates under mild reaction conditions with fast reaction rates, represents a powerful synthetic tool for building new functional star macromolecular architectures. In addition to CCS polymers, other functional supra(macro)molecular polymers were also explored. Poly(pseudo)rotaxanes with star and bottlebrush supramolecular structures were constructed via self-assembly of the corresponding guest macromolecules with α-cyclodextrin (CD) through inclusion complexation. The α-CD inclusion complexation was found to be a useful functionalization strategy for the polyester-based (i.e., poly(ε-caprolactone)) guest macromolecules through non-covalent interactions. Such modification not only alters the inherent chemical and physical properties of the guest polymeric materials but also, surprisingly, affects their molecular size and conformation. Lastly, the synthesis of a novel stereospecific cyclic polymer was demonstrated through the application of metal-catalysed living radical polymerization and ‘click’ chemistry. With an appropriate ring size, the resultant cyclic polymers are capable of forming an unprecedented ‘polypseudorotaxane-type’ supramolecular structure with the complementary linear stereoregular polymers via stereocomplex helix formation. The ‘polypseudorotaxane-type’ stereocomplex exhibits remarkably different physical properties compared to the conventional triple-helix supramolecules derived from the stereocomplexation of linear stereoregular polymer pairs. These results demonstrate that it is possible to manipulate the microstructures and properties of the supramolecular polymers by changing the shape (or topology) of the assembling components. The polymeric architectures presented in this thesis possess well-defined hierarchical arrangements of building blocks and functionalities, which imparts them with intriguing characteristics. They may therefore constitute advanced soft nanomaterials with great potential to applications in life sciences and materials technologies. It is anticipated that the established synthetic protocols will aid in the research and development of the next-generation of polymeric materials.
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ItemMolecular structure effects on polymeric honeycomb film formation( 2013)Polymeric films with uniform porous patterns and narrow pore size distributions are of great interests for variety of applications. Among currently available porous patterned films, honeycomb films have attracted significant attention due to their rapid and facile fabrication technique, termed as the Breath Figure technique. Following its first report in 1911, the Breath Figure technique has been intensively utilised to produce hexagonal patterned porous films from polymers with various molecular structures and architectures over the past 20 years. More recently the major focus of honeycomb film formation has been directed at their possible practical applications. However, to a lesser extent, fundamental research into the nature and mechanism of honeycomb film formation has declined. This thesis aims to establish a deeper fundamental understanding of the Breath Figure process thus establishing a simple and robust approach for honeycomb formation via the exploration of critical molecular structure effects on the polymeric honeycomb film formation, including (a) a systematic study on polymer composition influence on the formation of honeycomb structures; (b) the development of highly reproducible honeycomb films on non-planar surfaces; (c) the development of efficient blending system for honeycomb film formation; and (d) a new hypothesis outlining the key factors influencing honeycomb film formation. A range of star shaped fluorinated polymers were designed and synthesised with various degrees of fluorination. The glass transition temperatures (Tg) of star polymers and the hydrophobicity of the resultant honeycomb patterned films were found to be directly related to the degree of fluorination. The pore diameter distribution and uniformity of honeycomb films were also influenced by the varying polymer molecular structures. To further investigate the fluorine effect on honeycomb film formation, a fluorinated block copolymer macroinitiator was synthesised and used to prepare both core cross-linked star (CCS) polymers and micelles, whereby the outer shell and core, respectively, were comprised of fluorinated segments. The hydrophobicity of their honeycomb films was observed to be impacted significantly by the location of the fluorine segments in each molecular structure. A limitation in the application of honeycomb films is there propensity for poor reproducibility on non-planar surfaces, often with the formation of major cracks. Previously high Tg polymers were observed to be unable to form regular porous films devoid of cracking on non-planar surfaces. As new candidates for this application, a series of fluorinated star polymers with varying Tg’s and Young’s modulus (E) were prepared and characterised. Changes in fluorination were shown to directly influence their E. It was discovered that their non-cracking honeycomb film formation on nonplanar surfaces was highly dependent on the Young’s modulus (E) of these polymers rather than their Tg. The molecular effects on honeycomb film formation were thoroughly studied based on a single polymer system. Herein, a blending system composed of two linear polymers was then introduced to investigate the molecular structure effects on honeycomb film formation. Accordingly, a series of fluorinated linear gradient polymers were synthesised and blended with linear poly(methyl methacrylate) (PMMA) and polystyrene (PS). Notably, the blending of as little as 1 %wt. of a fluorinated additive enabled linear PMMA and PS to form honeycomb films which would otherwise not form. Importantly this study was the basis for the development of a new hypothesis which explains the key factors for honeycomb film formation. PMMA based CCS polymers were previously considered as the good candidates for honeycomb film formation. However, their star shaped molecular architecture does not guarantee the formation of regular porous patterned films. By blending PMMA CCS polymers with fluorinated additives developed in this work, both planar and non-planar honeycomb film formation from PMMA CCS polymers was remarkably improved. The reasons for improved film formation were explained by the newly developed hypothesis. In this thesis, the molecular structure effects on honeycomb film formation was well investigated via a systematic study on systems using fluorinated polymers alone, or as additives in blended systems. The new hypothesis which was developed to explain the influences of polymer properties on honeycomb film formation will have a profound influence on the development of advanced porous polymeric materials in the future.
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ItemReactive absorption of carbon dioxide into promoted potassium carbonate solvents( 2013)The increase in the carbon dioxide (CO2) emissions to our atmosphere is the major contributor to global climate change. A number of methods for reducing greenhouse gases have been proposed including carbon capture and sequestration (CCS). To date, reactive absorption of CO2 into amine solvents is undoubtedly the most widely used technology for CO2 capture. Much research has been devoted to developing alternatives to amine solvents. One of the many potential solvent candidates is potassium carbonate (K2CO3). Although potassium carbonate is associated with lower cost, less toxicity and is less prone to degradation effects when compared to the current industrial benchmark solvent, monoethanolamine (MEA), it has a low rate of reaction resulting in poor mass transfer performance. Developing a non-toxic and affordable promoter will facilitate the use of potassium carbonate solvent systems for CO2 capture. Using a well-characterized wetted wall column (WWC), the reaction kinetics of CO2 into unpromoted and borate-promoted potassium carbonate (K2CO3) solutions have been studied. Results presented here show that, at 80 °C, the addition of small amounts of boric acid (0.2 M, 0.6 M and 1.5 M) accelerates the overall absorption process of CO2 in carbonate solvents by 3 %, 10 % and 29 % respectively. The Arrhenius expression for the reactions CO2 + OH¯ and CO2 + B(OH)4¯ are kOH [M-1 s-1] = 2.53×1011exp(-4311/T [K]) and kborate [M-1 s-1] = 5.5×1011exp(-6927/T [K]); and the activation energies are 35.8 kJ mol 1 and 57.6 kJ mol 1 respectively. The reaction kinetics of CO2 absorption into a potassium carbonate solution promoted with monoethanolamine (MEA) have also been evaluated under conditions resembling those found at industrial CO2 capture plants. Results presented here show that at 63 °C the addition of MEA in small quantities, 1.1 M (5 wt%) and 2.2 M (10 wt%), accelerates the overall rate of absorption of CO2 in a 30 wt% potassium carbonate solvent by a factor of 16 and 45 respectively. The Arrhenius expression for the reaction between CO2 and MEA is kMEA [M-1 s-1] = 4.24×109exp(-3825/T [K]) where the activation energy is 31.8 kJ mol-1. Experimental results have been incorporated into an existing Aspen PlusTM model using the E-NRTL thermodynamic package. The resulting model replicates pilot plant data and simulates industrial capture processes employing K2CO3 and MEA as the capture agent. In addition, the absorption kinetics of carbon dioxide (CO2) into amino acid promoted potassium carbonate solutions has been studied. Experiments were conducted at concentrations up to 2.0 M and temperatures from 40 – 82 °C. Results presented here show that the addition of 1.0 M glycine, sarcosine and proline accelerates the overall rate of absorption of CO2 into a 30 wt% K2CO3 solvent by a factor of 22, 45 and 14 respectively at 60 °C. The Arrhenius expressions for the reaction between CO2 and aforementioned amino acids are k2-Gly [M-1 s-1] = 1.22×1012exp(-5434/T [K]), k2-Sar [M-1 s-1] = 6.24×1010exp(-1699/T [K]) and k2-Pro [M-1 s-1] = 1.02×1011exp(-2168/T [K]) where the activation energies are 45.2 kJ mol-1, 14.1 kJ mol-1 and 18.0 kJ mol-1 respectively. The reaction order with respect to glycine is found to be 1, while the reaction order with respect to sarcosine and proline is observed to be in the range of 1.3 – 1.6 and 1.2 – 1.3 respectively. The effect of adding small amounts of commercial carbonic anhydrase enzyme, namely Novozymes NS81239, on the absorption of CO2 into a 30 wt% potassium carbonate has been investigated. Results demonstrated that at 40 °C, the addition of this enzyme (300 mg L-1, 600 mg L-1 and 1300 mg L-1) enhances the pseudo-first-order rate constant and thus, the overall absorption process of CO2 into potassium carbonate solvents by 14 %, 20 % and 34 %. However, a further increase in the concentration to 6600 mg L-1 appears to be ineffective as it presents no greater catalytic effect than that from 1300 mg L-1 [NCA]. It is also found that at a constant enzyme concentration, the overall absorption of CO2 into carbonate solvents increases with temperature ranging from 40 °C to 60 °C. Above this range, an increase in temperature proves to be counter-productive. Results from this study have implications for the operation of carbonate based solvent systems for carbon capture processes, and more specifically will allow more accurate design of absorber units.
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ItemDurability as a function of microstructure of alkali-activated slag/fly ash binders( 2013)Reducing the global effects of greenhouse gas emissions from Portland cement manufacturing has been one of the main drivers for the development of alternative clinker-free binders, such as alkali-activated binders, as new materials for the concrete and construction industry. The challenge is, however, to investigate if this material can promise durability performance as good as, or even better than, Portland cement based concrete. Thus, this thesis analyzes the response of alkali-activated binders based on slag and fly ash to a range of exposure environments. The knowledge of microstructural development of activated binders using slag and fly ash as precursors is largely limited to relatively immature samples, while it is known that changes in the binder phase can proceed even at an advanced curing age. The dissolution of fly ash blended into an activated slag-rich binder may be slow, and this justifies investigation well beyond the most commonly studied curing age of 28 days. It is vital to understand the evolution of phases over time for various mix proportions of slag and fly ash in order to design for specific strengths or to ensure durability. Therefore, the microstructural changes taking place in alkali-activated slag/fly ash binders up to the age of 180 days are analyzed. The gel structure of an alkali-activated slag or slag-fly ash blend binder differs from that of Portland cement, and therefore there is little information in the open literature regarding the role of water in alkali-activated slag and slag/fly ash blends. As in Portland cement binders, the application of different drying methods to alkali-activated materials promotes changes in the pore structure and modifies the binding phases, leading to different results regarding the permeability of alkali-activated materials, which is critical in determination of the potential long-term durability of concretes made from these binders. Several common permeability testing methods used for analysis of conventional Portland cements are evaluated for their applicability in alkali-activated materials. The durability in chlorides with respect to slag/fly ash proportion is investigated, and a new understanding of chloride binding effects and the role of porosity is derived. The application of standard drying protocols and chloride accelerated and ponding test are also investigated for their suitability in alkali-activated binders. The mechanism of deterioration in sulfate rich environment is determined using both magnesium and sodium sulfate solutions, to understand the effect of sulfate cations on alkali-activated binders. Microstructural changes are analyzed in paste, mortar and concrete samples, indicating different mechanisms and extents of damage in different sulfate solutions. The effect of fly ash inclusion in alkali-activated slag on binding gels evolutions is seen to be significant in determining durability performance of alkali-activated binders, and this is the key outcome highlighted in this thesis.
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ItemThe mechanical characterisation of nanostructured biomaterials( 2013)Hydrogel materials have demonstrated unique potential for biomedical application in areas ranging from macroscopic tissue engineering scaffolds to targeted nanoparticles for in vivo therapeutic delivery. Such propensity for biological application is largely due to the inherently high degree of hydration and low rigidity of hydrogel networks, which, being similar to those of natural tissue, often lead to good biocompatibility. The mechanics and nanostructure of such materials have been reported to have a significant effect on biological processes; from cellular interaction and fenestration clearance, to capillary flow and dynamics during circulation. This thesis examines novel methods forthe characterisation of both nanostructured planar and particulate hydrogel systems, using atomic force microscopy (AFM) force spectroscopy techniques in physiological buffer. The mechanical properties and material parameters for soft nanostructured biomaterials (thiol-modified poly(methacrylic acid) and poly(L-glutamic acid)) in various architectures (planar film, core-shell particle, free-standing capsule, and nanoporous particle) are herein investigated. It was found that a wide variety of soft structures could be characterised mechanically, and the corresponding results interpreted according to established theories and models for compressive deformation. As such, evaluation of the Young’s modulus for the hydrogel systems investigated in this thesis demonstrate the crucial role that system architecture and network density play in the resilience of soft structures to applied force. Compressive forces which occur in the biological domain, such as for cellular internalisation and soft-tissue cell retention, were subsequently linked to conclusions drawn from AFM measurements. Such preliminary investigations showed that both intrinsic and extrinsic properties of nanostructured hydrogels influenced cellular interaction; thereby forming the basis for further mechanobiological studies, allowing for the future rational design of nanostructured hydrogel biomaterial systems for in vivo biomedical applications.
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ItemIon exchange and temperature: development of mathematical model for the prediction of ion exchange equilibria with respect to temperature for a multi-component system( 2013)Ion exchange is a versatile separation, purification and water treatment technology. The most important applications of ion exchange are found in the food and beverage, pharmaceutical, hydrometallurgical, metals finishing, nuclear, petrochemical, power and environmental waste management industries. Ion exchange has also found use for ion exchange chromatography and the remediation of contaminated soil in Antarctica. Prediction and modeling of ion exchange equilibria are essential for the design and development of efficient ion exchange processes. A broad survey of the published literature has shown that a number of semi-theoretical models have been developed which can successfully predict equilibrium behaviour of four components systems from binary system data. No comprehensive work has been conducted to examine the effects of temperature on cation exchange equilibrium behaviour for multi-component system. This study aims to extend the semi-empirical thermodynamics exchange model originally developed by Mehablia et al. (1994) to incorporate temperature dependence for multi-component ion exchange equilibria with minor modification. In this model the Pitzer electrolyte solution model, incorporating the effects of ion association with respect to temperature, is used to describe the non-idealities of solution phase. The equilibrium constant is calculated at each temperature via the approach of Agersinger and Davidson and correlated with temperature. The Wilson model is used to describe the non-idealities of the exchanger phase. The variations of the Wilson binary interaction parameters with temperature are correlated. The proposed model is used to design the more efficient ion exchange processes by allowing designers to optimize the operating temperature of the process. This model may be used to predict performance at temperatures other than those for which experimental data has been collected.
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ItemUltrasonics as a new platform technology in dairy processing( 2013)It has been shown recently that the use of ultrasound (US) on dairy whey systems can lead to a reduction in the size of whey protein aggregates and a consequent reduction in viscosity. Further, application of ultrasound after heat treatment can lead to a heat stable dairy product. However, a number of unanswered questions remain regarding this approach and this thesis attempts to answer some of these questions. Prior to commercialisation, a comparison with other physical shear and high pressure processes is required to determine the viability of US in the dairy industry. The thesis shows that at identical energy density of 153 J/ml, both sonication at 20 kHz and homogenisation at 80 bar of a 5 wt% whey protein concentrate (WPC80) solution provided similar reductions in whey protein aggregate size and viscosity. Smaller reductions were observed in samples subjected to high shear mixing at the same energy density, which may be the result of excessive foaming. The work shows that free radicals are absent in both the high shear mixing and homogenisation processes, implying that high shear forces is responsible for the observed changes, rather than acoustic collapse events. In addition, heat stability was achieved in all systems, with the best results again obtained for both homogenisation and sonication. Hence, the combination of a heat treatment followed by any suitable high shear process is capable of producing a low viscosity, heat stable product. A further concern was whether ultrasound impacted only the aggregate size or whether there were more subtle changes to the secondary structure of the protein. In this thesis, the changes in aggregation and secondary structure of the individual whey proteins and their mixtures upon sonication and the combination of heat and sonication were studied. No structural changes were observed in any native protein solution upon sonication at 31 J/mL using a 20 kHz sonicator. Prolonged sonication led to minor structural changes in pure β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) solutions, as shown using fourier transform infrared spectroscopy (FTIR) analysis, but these proteins remained predominantly in their native β-sheet and α-helical structure respectively. None of the heated and sonicated protein samples showed any large increases in β-sheet content. Hence, with the conditions performed for heat and US treatments in this thesis, no drastic alteration in the secondary structure of the protein were observed in US of dairy whey solutions. In the dairy industry, membrane ultrafiltration (UF) is used for the concentration of whey to produce whey protein concentrate. A further aim of the thesis was to determine the impact of ultrasound if applied upstream of the UF unit to reduce membrane fouling and increase productivity. In addition, the combination of heat and US pre treatment is investigated as it is a promising approach to produce heat stable powders while alleviating membrane fouling. The use of sonication on 5 to 10 wt% WPC80 solutions had a small but significant effect on membrane fouling – for the 10 wt% solution, the cake growth factor fell from 0.66 to 0.44 × 10 11 m/kg and the steady state flux increased from 16.8 to 17.7 L/m2.h. Similar subtle effects were observed with fresh whey, with the cake growth factor falling from 3.7 to 3.0 × 10 11 m/kg. This may reflect the low solids concentration used in these experiments and the use of more concentrated protein solutions might lead to more positive results. Conversely, a pronounced effect was observed in the heat-treated feeds: with increasing solids concentration, both pore blockage and cake growth grew for all heat-treated feeds but these two parameters remained low for the pre-heated and sonicated feed. Sonication was also found to delay the ‘gelling’ of proteins as indicated by the higher gel concentration obtained in the pre heated and sonicated feed (27 wt%) relative to a solution exposed only to heat (21 wt%). However, 100% flux recoveries upon cleaning were not achievable in heat treated feeds and surface charge measurements indicated that protein deposit remained attached to the membrane surface. This may be due to the inability of the chemical cleaning agents to break down large, denatured protein aggregates formed during heating. microfiltration (MF) of skim milk on its selectivity and productivity was also investigated. In skim milk MF, the best selectivity was obtained at the lowest TMP of 55 kPa. A pre heated and sonicated feed provided the lowest whey protein and highest casein rejections, with values of 85.8 and 97.9 % respectively, and the greatest absolute flux of approximately 10 L/m2.h. However, the selectivity and flux obtained were considerably lower than that generally observed with the use of ceramic membranes.
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ItemNovel biocompatible and biodegradable poly(ethylene glycol)- based scaffolds for soft tissue engineering( 2013)The development of new three-dimensional (3D) biocompatible constructs with improved properties for tissue regeneration is central to advances in the field of tissue engineering. Materials of natural and synthetic origin have been widely investigated for the production of tissue engineering scaffolds via various fabrication methods. Continuing research aims to fabricate scaffolds that possess the important properties of biodegradability, biocompatibility, mechanical integrity, and minimal immunogenicity. Achieving this objective is generally quite difficult since these properties are often dependant on each other and tailoring one property often compromises the other. In this research, we have employed novel synthetic approaches utilising epoxy/amine and acid chloride/alcohol chemistries to prepare poly(ethylene glycol) (PEG)-based scaffolds that are biocompatible and biodegradable, and possess excellent mechanical integrities, making them suitable for various soft-tissue engineering applications. Initially ultrathin Chitosan-PEG hydrogel films (CPHFs) were prepared using epoxy-amine chemistry via diepoxy functionalised PEG, chitosan amines and the co-cross-linker cystamine. The resultant films were very robust and possessed desirable biocompatible and biodegradable properties while supporting the attachment and proliferation of corneal endothelial cells (CECs). To eliminate the issues associated with the use of naturally sourced polymers, we were able to subsequently develop fully synthetic 50 μm thin PEG hydrogel films (PHFs). Acid chloride/alcohol chemistry, together with a facile fabrication method was utilised to produce the PHFs. PHFs were found to possess excellent tensile properties and promoted the in vitro attachment and proliferation of corneal endothelial cells with natural morphologies. In vitro degradation and cytotoxicity studies demonstrated the biodegradable and non-toxic characteristics. In an in vivo ovine model, the hydrogel films adhered naturally onto the interior corneal surface while displaying neither toxicity nor immunogenicity. The PHFs did not hinder the function of the native corneal endothelium, demonstrating their suitability for implantation. To further exploit acid chloride/alcohol chemistry, 3D porous PEG sponges and scaffolds were produced via novel gas foaming, and salt-templating techniques respectively. The rapid exothermic reaction and the HCl gas production results in the formation of highly porous polyester PEG sponges (PPSs), while a salt template was utilised to control pore sizes to produce the hydrogel scaffolds (SPHs). Both PPSs and SPHs possessed excellent mechanical integrities and demonstrated biodegradability and minimal toxicity in vitro. In vivo studies revealed complete infiltration of PPSs and SPHs with vascular tissue within 8 weeks. The porous scaffolds have minimal immunogenicity, and non-toxicity as demonstrated by an in vivo rat model, and can undergo complete degradation to non-toxic products by 16 weeks. The novel PEG hydrogel films and porous scaffolds demonstrate highly desirable physico-chemical properties with excellent biocompatible responses in vivo. Encompassing all the desirable properties of biocompatibility, biodegradability, mechanical integrity and complete tissue integration in vivo, the fabricated scaffolds are excellent candidates for advanced soft-tissue engineering applications.