No description available.

A scalable method for the synthesis of polyethylene terephthalamide microcapsules grafted with polyacrylic acid to enable pH responsiveness has been developed. Microcapsules were produced by interfacial polymerisation of an oil-in-water emulsion in a 2 L batch reactor and subsequently circulated through an external loop reactor for UV irradiative surface grafting. Ungrafted microcapsule samples yielded 1.0 - 1.2 g desiccated capsules per experiment. Initial production trials were subject to severe agglomeration, observed during dialysis of the microcapsules with 30 % (v/v) ethanol solution. Lowering of the terephthaloyl dichloride monomer concentration, to 0.2 mol L⁻¹ in the chloroform / cyclohexane (3 : 1) organic solution, alleviated this unwanted agglomeration. Laser diffraction particle size analysis revealed microcapsules were produced with a 51 µm average diameter. A purpose built external loop irradiation reactor was used to facilitate graft polymerisation of acrylic acid on the microcapsules, using 254 nm UV light at 19 mW cm⁻². Characterisation of the external loop flow regime showed a mild deviation from ideal plug flow, with a vessel dispersion number of 0.014 and a Reynolds number of 1310. Confirmation of monomer polymerisation was ascertained by back titration and Fourier transform infrared spectroscopy. No distinction between homopolymer and grafted polyacrylic acid could be made by these characterisation methods. A Taguchi analysis on variables influencing grafting revealed high temperature to contribute most significantly to graft yield, followed by a long irradiation period. The development of a packed column pulse response method for testing pH response showed a high repeatability. However, release profile testing of a microcapsule slurry with an observed graft yield of 1.13 mmol g⁻¹ did not provide a definitive pH-based release of mPEG 5000 or PEGylated TAMRA dye. Determination of acrylic acid polymerisation kinetics following UV irradiation of the microcapsules is required for future optimisation of a functional graft yield.

Stroke is a leading cause of disability in the world, for which there currently is no effective treatment. One potential method for treating stroke is to stimulate the endogenous neural stem/progenitor cells (NSPCs) in the subventricular zone (SVZ) of adult brain to replace the tissue lost during stroke. Two growth factors that have shown promise in eliciting functional repair in rodent models of stroke are epidermal growth factor (EGF) and erythropoietin (EPO). However, there is a significant challenge in delivering protein drugs in a minimally invasive yet effective manner. In this thesis, a minimally invasive polymer-based system is developed to control the sequential release of EGF followed by EPO. This system comprises of a hyaluronan-methylcellulose (HAMC) hydrogel and two types of polymeric particles, and is applied epicortically to deliver EGF and EPO to stroke-injured mouse brains in a minimally invasive manner. In this thesis, the following are demonstrated: 1) The ability of therapeutics delivered locally to reach the target site after delivery is crucial for the success of local delivery strategies. PEG-modification leads to enhanced penetration distance of EGF. 2) When delivered epicortically to the stroke-injured mouse brain using HAMC, PEG-EGF penetrates further into the brain compared to unmodified EGF. Both EGF and PEG-EGF stimulated NSPC proliferation in the SVZ, but the extent of stimulation is greater when PEG-EGF is delivered compared to unmodified EGF. 3) The transport of EPO is similar in the uninjured and the stroke-injured brain following epicortical delivery from HAMC. EPO delivered epicortically from HAMC is able to reach the SVZ and can enhance neurogenesis in the stroke-injured brain. 4) A composite delivery system is engineered where PEG-EGF and EPO are individually encapsulated in different polymeric particles, and the particles are embedded in the HAMC hydrogel matrix. Stroke-injured animals that receive composite-mediated growth factor treatments ultimately achieve repair comparable to that achieved using a conventional catheter/osmotic minipump infusion system, without causing tissue damage associated with insertion of the infusion system into the brain.

The ability to bypass most cellular barriers to gain access to intracellular compartments has great potential in cell biology. The possibilities range from efficient delivery of macromolecules such as plasmids to small proteins and oligonucleotides that are sensitive to degradation. In biomedicine, easy access means enhanced cellular imaging and delivery of many therapeutics currently hampered by poor stability and cellular uptake. Carbon Nanotubes (CNTs) are attractive in these applications due to their efficient cellular uptake. While mode of entry of CNTs into cells is debatable, possibly their natural shape allows for their selective penetration across biological barriers in a non-destructive way, making them versatile as membrane permeating particles. The present study explores the diverse functionalities of CNTs including: 1) Efficient delivery of DNA into HeLa cells using vertically aligned MWNT arrays, 2) The use of Single Walled Carbon Nanotubes (SWNTs) as nano detoxifiers and 3) the design of SWNTs for efficient cellular uptake. Generally, vertically aligned nanoneedles have been used to influence the behavior and differentiation of various cell types. In the first work described in chapter 2, periodic high-density array MWNT nanoneedles is shown to support cell growth and penetrate into HeLa cells, making it ideal for use in cellular imaging and the efficient delivery of plasmid DNA into cells. Most importantly, we show that transfection with the MWNT substrate exhibited more uniformity in comparison to the commercially available lipofection procedure. Lipofection involves the formation of a complex of DNA and cationic lipids that interact with the cell via electrostatic interactions, leading to internalization, DNA escape into the cytosol, and the eventual transport into the nucleus. Functionalized CNTS have demonstrated great biocompatibility and potential for drug delivery in vitro. In the work described in chapter 3, we synthesized acid-oxidized and non-covalently PEGlyated SWNTs, which were reported previously for drug delivery purposes, and explored their potential for detoxification in the bloodstream. We investigated the binding of SWNTs to a pore-forming toxin pyolysin. The SWNTs were found to prevent toxin-induced pore formation in the cell membrane of human red blood cells. Quantitative hemolysis assay and scanning electron microscopy were used to evaluate the inhibition of hemolytic activity of pyolysin. Unlike HeLa cells, human red blood cells did not internalize oxidized SWNTs according to Raman spectroscopy data. Molecular modeling and circular dichroism measurements were used to predict the 3D structure of pyolysin (domain 4) and its interaction with SWNTs. The Tryptophan-rich hydrophobic motif in the membrane-binding domain of pyolysin, a common construct in a large family of cholesterol-dependent cytolysins (CDCs), showed high affinity for SWNTs. In the final two chapters, chapters 4 and 5, we focused on shorter CNTs (<70 nm) that have less length variations. This enabled the determination of several length related characteristics such as cellular uptake and distribution of SWNTs within between cells. Here, cellular uptake of two water-soluble SWNTs, Short SWNTs (S_SWNTs) and Ultra-Short SWNTs (US_SWNTs), was evaluated against various mammalian cells. Cellular entry of S_SWNTs (chapter 4), similar in dimensions to those reported in the literature, is shown to be affected by their hydrophilic corona and exhibit time-dependent nuclear accumulation. In contrast, US_SWNTs show no dependence of cellular entry on their hydrophilic exterior (chapter 5). Furthermore, intracellular localization and excretion of the US_SWNTs is observed to be cell type-dependent. Results presented in this work show the potential of CNTs as nano detoxifiers. We also use CNTs as vertically aligned nanoneedles and as colloids to efficiently traverse the plasma membrane. While CNTs as nanoneedles show the potential as an efficient means of transfecting mammalian cells, the use of S_SWNTs and US_SWNTs highlight some key observations including the physical and chemical properties (size, surface functionality) and cell type influence on cellular uptake and intracellular trafficking. These findings contribute to the interpretation of SWNT-cell interactions by providing a correlation between CNT length and cellular uptake and also cell type on trafficking of internalized SWNTs. With the realization of the enhanced permeability and retention effects, tumor vascular leakiness resulting from increased angiogenesis and vasoactive factors enhancing permeability at the diseased site, nanoparticles that have long circulation time have higher chance of accumulating at the diseased sites.

No description available.

No description available.

Prolonged therapy required to effectively treat mycobacterial infection frequently results in severe dose-limiting side-effects and drug resistance due to patient non-compliance with protracted dosage regimens. Biodegradable poly-a-hydroxy acid microspheres and microcapsules containing rifampicin (RIF) and isoniazid (INH) respectively have been prepared with the intention of providing high sustained site-specific concentrations to overcome some of the shortcomings of existing oral treatments. Due to the high dose, hydrophilicity and instability of both drugs, formulation strategies to attain high drug loading and methodologies to characterize in vitro drug release during ongoing decomposition were required. Stability indicating HPLC assays to quantify drug release have been developed, validated and applied to monitor drug release based on cumulative quantification of drug and degradates. A mathematical correction for serial decompositions associated with RIF was made based on the terminal pseudo equilibrium observed during stability studies. An isocratic HPLC assay was prospectively developed for the quantification of both drugs and their major metabolites in biological samples. Further preformulation studies confirmed the absence of significant polymorphs for both drugs when recrystallized from solvents later used in formulation development. Furthermore, thermal analysis revealed only modest interaction between the drugs and Resomer®. The high and moderate water solubilities of INH (145 mgmL-1) and RIF (1 mgmL-1) determined the selection of spray-drying (SD) and emulsion solvent evaporation (ESE) for RIF, whereas preparation of INH microcapsules relied solely on the former technique. Examination of the effects of varying RIF: polymer ratio, phase volumes and continuum presaturation with selected poly(L-lactide) and poly(D, L-lactide-co-glycolide) (PDLGA) Resomer® identified optimum conditions to maximize drug loading during a comparison of aqueous ESE with spray-drying with a range of nine further amorphous Resomer® polymers. Although yields were generally higher with ESE (85-90 %), SD (45- 75 %) was considered a superior preparation technique on the basis of the rapid production of microspheres of high and predictable drug loading (100 % of that attempted), with monodisperse granulometry and superior morphology. Release profiles were typically asymptotic characterized by a rapid `burst' of release followed by a slow release of residual entrapped RIF, irrespective of the preparative technique or polymer used. Poor yields (7.2 %) when SD low molecular weight (MW) PDLGA (8 kD) were greatly enhanced (74.8 %) by reduction in drying temperature and substitution of chloroform: dichloromethane (CFM: DCM) (1: 1) cosolvent with DCM. These conditions were adopted as the optimum parameters for further studies of blends of low (2 kD, R104) and moderate (11 kD, R202H) MW poly(D, L-lactide) (PDLLA); materials which demonstrated excellent sprayability and dramatically modulated the release of drug when combined compared to their use alone. Drug release showed a remarkable dependence on blend, dramatic acceleration being observed between 44 and 48 %w/w R104. Release over this range showed a marked dependence on medium temperature and led to the proposal of an autohydration mechanism linked to the hydrophilicity and glass transition (T9) of the blend which accounted for the sigmoidal profiles observed. First order dependence of release allowed calculation of Arrhenius derived activation energies of drug release in glassy anhydrous and rubbery plastic matrices of 630 and 320 J mol-1. Hydration and thermal studies supported the postulated diffusion mechanism, whereas granulometric and morphological examinations demonstrated that erosion did not contribute significantly. The criticality of matrix composition was further highlighted when interchange with nominally identical polymer, R202H, shifted the critical composition to 30 %w/w R104. Moreover, this observation contested the batch-to-batch reproducibility of commercial polymer. Substitution of DCM with halothane (HAL) and acetone (ACT) had a profound influence on the properties of compositionally identical ('R104: R202'H, 30: 70) microspheres, particularly release kinetics. This was attributed to the more rapid drying kinetics with the poor solvent, ACT, and the generation of a porous matrix. Consequently, drug was largely released during the 'burst' phase. Superior solvents, HAL and DCM resulted in enhanced matrix coherence at the expense of considerable residual solvent burdens (6 - 12.5 %), which allowed extensive matrix relaxation as solvent was lost with first order kinetics. This ageing process was followed by the development of an endotherm associated with the Tg as the matrix stabilized with a resultant increase in the induction period and a general retardation of drug release. Extension of the concept of blending R104 as release 'initiator' to a range of MW PDLGA of 50: 50 and 75: 25 comonomer ratio as release 'modulator' was of limited success generating release profiles reminiscent of each polymer when used alone. The magnitude of the 'burst' correlated to the precipitation kinetics of the predominant complementary PDLGA polymer as determined by cloud-point titration. Due to the more hydrophilic nature of the copolymers, at the critical concentration uncontrolled hydration resulted in a single rapid release phase. Spray-dried biodegradable INH microcapsules were prepared by a two stage process whereby SD cores of drug or in combination with biodegradable albumin or casein were subsequently coated with PDLGA by SD. The highly crystalline, aggregated and irregular morphology of SD drug resulted in poor coating efficiency and a rapid release of encapsulated drug. Protein microspheres of superior sphericity allowed more effective coating and hence slower INH release. It is concluded that SD has excellent industrial potential for the preparation of biodegradable poly-a-hydroxy acid microspheres for high dose drugs to be delivered directly to their site of action, e. g., intra-pulmonary. Indeed, the granulometry of these particles and, in particular, the hydrophilic character of blends of PDLLA described have considerable potential for the sustained delivery of drugs in the low volumes of fluid that prevails in the lung. These formulations might offset some of the limitations of current oral antimycobacterial therapy.

An investigation into the factors affecting the metered atomisation of superheated liquids has been carried out. The investigation was aimed primarily at developing an understanding of the factors which affect the performance of. respiratory drug delivery systems (Suspension Pressurised Metered Dose Inhalers). Initial investigations used a semi-empirical sizing technique, representing the human airways, to identify the major variables (formulation and geometric) which affect the performance of the MDI system. Computer models were developed to describe both continuous and metered discharge from a superheated-liquid aerosol generator. These models were based on the concept of thermal and dynamic equilibrium, but they were improved and extended, to describe metered discharge, by including empirical corrections obtained from continuous discharge experiments. Experimental investigations using 'instrumented inhalers' were used to confirm the validity of the computer model. The experimental investigations encompassed the use of conventional CFC's and the new non-chlorinated propellants 134A and 227. The computer models and droplet correlation function developed during these investigations represent powerful tools for use in the design of both current and future HFC/HFA powered metered dose inhaler delivery systems.

No description available.

The use of polysaccharides as building blocks in the development of drugs and contrast agents delivery systems is rapidly growing. This can be attributed to the outstanding virtues of polysaccharides such as biocompatibility, biodegradability, upgradability, multiple reacting groups and low cost. The focus of this thesis was to develop and characterize novel starch based hydrogels and nanoparticles for delivery of drugs and imaging agents. To this end, two different systems were developed. The first system includes polymer and nanoparticles prepared by graft polymerization of polymethacrylic acid and polysorbate 80 onto starch. This starch based platform nanotechnology was developed using the design principles based on the pathophysiology of breast cancer, with applications in both medical imaging and breast cancer chemotherapy. The nanoparticles exhibited a high degree of doxorubicin loading as well as sustained pH dependent release of the drug. The drug loaded nanoparticles were significantly more effective against multidrug resistant human breast cancer cells compared to free doxorubicin. Systemic administration of the starch based nanoparticles co-loaded with doxorubicin and a near infrared fluorescent probe allowed for non-invasive real time monitoring of the nanoparticles biodistribution, tumor accumulation, and clearance. Systemic administration of the clinically relevant doses of the drug loaded particles to a mouse model of breast cancer significantly enhanced therapeutic efficacy while minimizing side effects compared to free doxorubicin. A novel, starch based magnetic resonance imaging (MRI) contrast agent with good in vitro and in vivo tolerability was formulated which exhibited superior signal enhancement in tumor and vasculature. The second system is a co-polymeric hydrogel of starch and xanthan gum with adjustable swelling and permeation properties. The hydrogels exhibited excellent film forming capability, and appeared to be particularly useful in controlled delivery applications of larger molecular size compounds. The starch based hydrogels, polymers and nanoparticles developed in this work have shown great potentials for controlled drug delivery and biomedical imaging applications.