Electrospinning is a novel technique to fabricate non-woven fibers with sizes ranging from nano to micrometers. Polymers have been electrospun into nanofibers that can be developed into desirable materials with excellent biocompatibility and biodegradability for biomedical applications in wound healing and tissue regeneration. These nanofiber materials can be further functionalized to be loaded with bioactive molecules, including antibacterial agents, functional proteins that promote tissue reconstruction while protect host tissues from contamination. This study focuses on the development of multifunctional nanofibers that are incorporated with antibacterial drug(s) and immobilized with bioactive proteins. These nanofibers are potentially useful for wound care and tissue engineering scaffolding to provide both infection control and promotion of wound healing or tissue regenerations.

Electrospinning is a novel technique to fabricate non-woven fibers with sizes ranging from nano to micrometers. Polymers have been electrospun into nanofibers that can be developed into desirable materials with excellent biocompatibility and biodegradability for biomedical applications in wound healing and tissue regeneration. These nanofiber materials can be further functionalized to be loaded with bioactive molecules, including antibacterial agents, functional proteins that promote tissue reconstruction while protect host tissues from contamination. This study focuses on the development of multifunctional nanofibers that are incorporated with antibacterial drug(s) and immobilized with bioactive proteins. These nanofibers are potentially useful for wound care and tissue engineering scaffolding to provide both infection control and promotion of wound healing or tissue regenerations.

This thesis is concerned with studies towards the total synthesis of a class of natural products - the oxazolomycins. Attention was focused on the left-hand side triene fragment and right-hand side lactam heterocyclic system. This thesis describes the synthesis of a racemic terminal phenyl analogue of oxazolomycin A and C, possessing the left-hand side triene geometry as required. A novel truncated pyridine analogue is also described. The molecules represent a racemic total synthesis of analogues of phthoxazolin A and inthomycins B and C. The synthesis is based upon a crucial Stille cross-coupling reaction between stannane and diene iodide fragments. The stannane fragment was synthesised using literature precedented methods and the vinyl halide prepared using a highly stereoselective Wittig, Takai homologation or Stork reaction leading to a variety of ratios of mixtures of Z, E and E, E diene halides. These investigations led to the availability of 1:1, 3:1 and 1:3 mixtures of Z, Z, E : Z, E, E left hand side triene fragments possessing the required stereochemistries for oxazolomycin A and C. Utilising existing methodology developed in the Moloney group, investigations were carried out towards construction of β-keto esters possessing terminal hydroxyl functions, suitable for diastereoselective aldol ring closure. Following extensive protecting group manipulation and N-acylation coupling optimisation, a TIPS protected β-keto acid, existing as predominantly the keto tautomer, was successfully coupled to an oxazolidine heterocycle. This N-acylated oxazolidine upon Dieckmann cyclisation would present an advanced intermediate of opposite configuration (Lserine is used here as a cheaper starting material for the construction of the oxazolidine instead of D-serine) to the oxazolomycin right-hand side.

This research investigates the use of conducting polymer coatings on platinum (Pt) electrodes for use in neuroprostheses. Conducting polymers aim to provide an environment conducive to neurite outgrowth and attachment at the electrode sites, producing intimate contact between neural cells and stimulating electrodes. Conducting polymers were electropolymerised onto model Pt electrodes. Conventional polymers polypyrrole (PPy) and poly-3,4-ethylenedioxythiphene (PEDOT) doped with polystyrenesulfonate (PSS) and para-toluenesulfonate (pTS)were investigated. Improvement of material properties was assessed through the layering of polymers with multi-walled carbon nanotubes (MWNTs). The ability to incorporate cell attachment bioactivity into polymers was examined through the doping of PEDOT with anionic laminin peptides DCDPGYIGSR and DEDEDYFQRYLI. Finally, nerve growth factor (NGF), was entrapped in PEDOT during polymerisation and tested for neurite outgrowth bioactivity against the PC12 cell line. Each polymer modification was assessed for electrical performance over multiple reduction-oxidation cycles, conductivity and impedance spectroscopy, mechanical adherence and hardness, and biological response. Scanning electron microscopy was used to visualise film topography and x-ray photon spectroscopy was employed to examine chemical constitution of the polymers. For application of electrode coatings to neural prostheses, optimal bioactive conducting polymer PEDOT/pTS/NGF was deposited on electrode arrays intended for implantation. PC12s were used to assess the bioactivity of NGF functionalised PEDOT when electrode size was micronised. Flexibility of the design was tested by tailoring PEDOT bioactivity for the cloned retinal ganglion cell, RGC-5, differentiated via staurasporine. It was established that PEDOT films had superior electrical and cell growth characteristics, but only PPy was able to benefit from incorporation of MWNTs. Bioactive polymers were produced through inclusion of both laminin peptides and NGF, but the optimum film constitution was found to be PEDOT doped with pTS with NGF entrapped during electrodeposition. Application of this polymer to an implant device was confirmed through positive neurite outgrowth on vision prosthesis electrode arrays. The design was shown to be flexible when tailored for RGC-5s, with differentiation occurring on both PEDOT/pTS and PEDOT/DEDEDYFQRYLI. Conducting polymers demonstrate the potential to improve electrode-cell interactions. Future work will focus on the effect of electrical stimulation and design of bioactive polymers with improved cell attachment properties.

Thesis (Ph. D.)--Victoria University (Melbourne, Vic.), 2007. / Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2009. / Includes bibliographical references (p. 106-121).

Vascular calcification is the formation of mineralised tissue within the walls of arteries. The pathology has many similarities to embryonic bone formation and involves the osteogenic differentiation of vascular smooth muscle cells (VSMCs) and matrix mineralisation. Recent studies have demonstrated that the bioactive sphingolipids, ceramide and sphingosine-1-phosphate (S1P), regulate embryonic bone formation. Ceramide can be generated by lysosomal acid sphingomyelinase (L-SMase) and neutral sphingomyelinase (N-SMase), and be converted to sphingosine by acid ceramidase (ACDase) and subsequently to S1P by sphingosine kinases (SK1 & SK2). This study tested the hypothesis that ceramide and S1P also regulate VSMC matrix mineralisation. VSMCs were cultured in the presence of 3 mM β-glycerophosphate (BGP) to induce osteogenic differentiation and matrix mineralisation. During VSMC mineralisation there were decreases in the activities of L-SMase and N-SMase and increases in the levels of C18 and C20 ceramide. S1P levels also increased during mineralisation as did SK1 and SK2 mRNA and SK activity. These results demonstrate that ceramide and S1P have the potential to regulate VSMC mineralisation. The exogenous addition of C2 ceramide decreased the rate of VSMC matrix mineralisation. Consistent with this, when VSMCs were cultured with 3 mM BGP and the joint L-SMase and ACDase inhibitor, desipramine, total ceramide levels increased and no matrix mineralisation was detected. These findings suggest that ceramide is an inhibitor of VSMCs matrix mineralisation. It was also noted in the presence of 3 mM BGP and desipramine that the mineralisation-associated increase in S1P was inhibited. In agreement with this, when exogenous S1P was added to the VSMCs an increase in matrix mineralisation was observed. Thus, S1P acts as a promoter of matrix mineralisation. To determine how S1P was promoting matrix mineralisation the signalling roles of the ezrin, radixin and moesin (ERM) proteins were investigated. The short-term stimulation of VSMCs with S1P led to the phosphorylation of the ERM proteins and over the mineralisation time-course, when S1P levels increased, the levels of ERM phosphorylation also increased. When VSMCs were cultured in the presence of 3 mM BGP and the inhibitor of ezrin phosphorylation, NSC668394, a decrease in matrix mineralisation was observed. No increases in ERM phosphorylation were seen in the presence of desipramine during the mineralisation time-course Therefore, S1P may be increasing matrix mineralisation through promoting the phosphorylation of the ERM proteins. This work has demonstrated that ceramide inhibits and S1P promotes VSMC matrix mineralisation in vitro. Additionally, this work identifies activation of ERM proteins, downstream of S1P, as a novel signalling pathway promoting matrix mineralisation. Characterisation of novel regulators of VSMC matrix mineralisation in vitro gives insight into the complex mechanisms contributing to vascular calcification in vivo and will aid in identification of novel therapeutic targets.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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