The vast majority of pharmaceutical drug products are developed, manufactured, and delivered in the solid-state where the active pharmaceutical ingredient (API) is crystalline. With the potential to exist as polymorphs, salts, hydrates, solvates, and cocrystals, each with their own unique associated physicochemical properties, crystals and their forms directly influence bioavailability and manufacturability of the final drug product. Understanding and controlling the crystalline form of the API throughout the drug development process is absolutely critical. Interfacial properties, such as surface energy, define the interactions between two materials in contact. For crystal growth, surface energy between crystal surfaces and liquid environments not only determines the growth kinetics and morphology, but also plays a substantial role in controlling the development of the internal structure. Surface energy also influences the macroscopic particle interactions and mechanical behaviors that govern particle flow, blending, compression, and compaction. While conventional methods for surface energy measurements, such as contact angle and inverse gas chromatography, are increasingly employed, their limitations have necessitated the exploration of alternative tools. For that reason, the first goal of this research was to serve as an analytical method development report for atomic force microscopy and determine its viability as an alternative approach to standard methods of analysis. The second goal of this research was to assess whether the physical and the mathematical models developed on the reference surfaces such as mica or graphite could be extended to organic crystal surfaces. This dissertation, while dependent upon the requisite number of mathematical assumptions, tightly controlled experiments, and environmental conditions, will nonetheless help to bridge the division between lab-bench theory and successful industrial implementation. In current practice, much of pharmaceutical formulation development relies on trial and error and/or duplication of historical methods. With a firm fundamental understanding of surface energetics, pharmaceutical scientists will be armed with the knowledge required to more effectively estimate, predict, and control the physical behaviors of their final drug products.

A versatile AFM local oxidation lithography was developed for fabricating clean protein patterns ranging from nanometer to sub-millimeter scale on octadecyltrichlorosilane (OTS) layer of Si (100) wafer. This protein patterning method can generate bio-active protein pattern with a clean background without the need of the anti-fouling the surface or repetitive rinsing. As a model system, lysozyme protein patterns were investigated through their binding reactions with antibodies and aptamers by AFM. Polyclonal anti-lysozyme antibodies and anti-lysozyme aptamer are found to preferentially bind to the lysozyme molecules on the edge of a protein pattern before their binding to the interior ones. It was also demonstrated that the topography of the immobilized protein pattern affects the antibody binding direction. We found that the anti-lysozyme antibodies binding to the edge lysozyme molecules on the half-buried pattern started from the top but the binding on the extruded pattern started from the side because of their different spatial accessibility. In addition, after incubating lysozyme pattern with anti-lysozyme aptamer in buffer solution for enough long time, some fractal-shaped aptamer fibers with 1-6nm high and up to tens of micrometers long were formed by the self-assembling of aptamer molecules on the surface. The aptamer fibers anchor specifically on the edge of protein patterns, which originates from the biospecific recognition between the aptamer and its target protein. Once these edge-bound fibers have formed, they can serve as scaffolds for further assembly processes. We used these aptamer fibers as templates to fabricate palladium and streptavidin nanowires, which anchored on the pattern edges and never cross over or collapse over each other. The aptamer fiber scaffold potentially can lead to an effective means to fabricate and interface nanowires to existing surface patterns.

No description available.

Scanning probe microscopy (SPM) nanolithography has been found to be a powerful and low-cost approach for sub-100 nm patterning. In this thesis, the possibility of using a state-of-the-art SPM system to controllably deposit nanoparticles on patterned Si substrates with high positional control has been explored. These nanoparticles have a range of interesting properties and have been characterised by electron microscopy and scanning probe microscopy. The influence of different deposition parameters on the nanoparticle properties was studied. Contact mode atomic force microscopy (AFM)-based local oxidation nanolithography (LON) was used to oxidise sample surfaces. Two different substrates were studied which were native oxide silicon (Si) and molybdenum (Mo). A number of factors that influence the height and width of the oxide features were investigated in order to achieve the optimal oxidation efficiency. The height and width of the oxide structures were found to be strongly dependent on the applied voltage and scan speed. The tunneling AFM (TUNA) technique was used to measure the ultralow currents flowing between the tip and the sample during the oxidation process. It was found that a threshold voltage for our oxidation experiments was -4.0 ± 1.6 V applied to the tip when fabricating geometric patterns as well as 2.9 ± 1.6 V and 2.8 ± 2.2 V applied to the substrate for nanodot fabrication. In addition, comparisons of nanodot-array patterns produced with different AFM tips were studied. The influence of applied voltage, type of AFM tip and substrate, humidity and ramping time has been studied for dot formation providing a comparison between native oxide Si and Mo surfaces. The nanodot sizes were found to be clearly dependent on the applied voltage, type of substrate, relative humidity and ramping time. Dip-pen nanolithography (DPN) was used to study a direct deposition strategy for gold (Au) nanodot fabrication on a native oxide Si substrate. In this process, hydrogen tetrachloroaurate (HAuCl4) molecules were deposited onto the substrate via a molecular diffusion process, in the absence of electrochemical reactions. This approach allowed for the generation of Au dots on the SiO2 substrate without the need for surface modification or additional electrode structures. The dependence of the size of the Au dots on different „scanning coating‟ (SC) times of AFM tips was studied. A thermal annealing process was used to decompose the generated HAuCl4 molecular dots to leave Au (0) metal dots. A stereomicroscope has been used for preliminary observation of different steps of Au deposition treatments. A scanning electron microscope (SEM) was used to characterise the SC AFM tips both before and after the DPN process. SEM energy-dispersive X-ray spectroscopy (EDS) has provided information about the elemental content of deposited particles for different annealing temperatures. Fountain-pen nanolithography (FPN) has also been used to study nanowriting of HAuCl4 salt and a variety of solvents on a native oxide Si surface. In this technique, a nanopipette was mounted within an AFM to deliver appropriate solutions to the silica substrate. We found that an aqueous Au salt solution was the most suitable ink for depositing gold using the FPN technique. In the case of solvents alone, ethanol and toluene were achieved with depositing onto a SiO2 substrate using the FPN technique.

Inorganic based membranes which have a symmetric/asymmetric structure have been produced using an immersion induced phase inversion and sintering method. An organic binder solution (dope) containing yttria-stabilised zirconium (YSZ) particles is spun through a triple orifice spinneret to form a hollow fibre precursor, which is then sintered at elevated temperatures to form a ceramic support. The phase inversion process for the formation of hollow fibre membranes was studied in order to produce the best morphological structure/support for palladium based membranes. The spinning parameters, particle size, non-solvent concentration, internal coagulant as well as the calcination temperature were investigated in order to determine the optimum values. Sintering temperature was also investigated, which would yield a sponge-like structure with an optimized permeability, while retaining a smooth outer surface. The supports produced by phase inversion were characterized in terms of dimension by mercury porosimetry, compressed air permeability, Surface Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The morphology of the produced ceramic support showed either dense or porous characteristics governed by the dynamics of the phase inversion process. The particle size of YSZ was examined in order to decrease the amount of agglomerates in the spinning suspension. Zetasizer tests indicated that at 15 minutes, the ultrasonic bath effectively homogenised the YSZ particles and prohibited soft agglomerates from reforming in the spinning suspension. In this study, an increase in air gap had no noticeable effect on the finger like voids but it had a considerable effect on both the inner diameter (ID) and outer diameter (OD) of the green fibres, while an increase in bore liquid flow rate and extrusion pressure promoted viscous fingering and significant effect on the ID and OD of the fibres, respectively. There was a decrease in porosity and permeability with increasing sintering temperature, addition of water concentration in the spinning suspension and varying Nmethylpyrrolidone (NMP) aqueous solution of the internal coagulant. The amount of YSZ added to the starting suspension influenced the properties of the support structure. Viscous deformation was observed for dope with lower particle loading thus resulted in the formation of cracks and defects during sintering. / >Magister Scientiae - MSc

Visco-elastic behaviour at the nano-level of a commonly used polymer (PET) is characterised using atomic force microscopy (AFM) at a range of temperatures. The modulus, indentation creep and relaxation time of the PET film (thickness = 100 m) is highly sensitive to temperature over an experimental temperature range of 22¿175 ¿C. The analysis showed a 40-fold increase in the amount of indentation creep on raising the temperature from 22 ¿C to 100 ¿C, with the most rapid rise occurring above the glass-to-rubber transition temperature (Tg = 77.1 ¿C). At higher temperatures, close to the crystallisation temperature (Tc = 134.7 ¿C), the indentation creep reduced to levels similar to those at temperatures below Tg. The calculated relaxation time showed a similar temperature dependence, rising from 0.6 s below Tg to 1.2 s between Tg and Tc and falling back to 0.6 s above Tc. Whereas, the recorded modulus of the thick polymer film decreases above Tg, subsequently increasing near Tc. These visco-elastic parameters are obtained via mechanical modelling of the creep curves and are correlated to the thermal phase changes that occur in PET, as revealed by differential scanning calorimetry (DSC).

Living organisms are made up of a multitude of individual cells that are surrounded by biomolecules and fluids. It is well known that cells are highly regulated by biochemical signals; however it is now becoming clear that cells are also influenced by the mechanical forces and mechanical properties of the local microenvironment. Extracellular forces causing cellular deformation can originate from many sources, such as fluid shear stresses arising from interstitial or blood flow, mechanical stretching during breathing or compression during muscle contraction. Cells are able to sense variations in the mechanical properties (elasticity) of their microenvironment by actively probing their surroundings by utilizing specialized proteins that are involved in sensing and transmitting mechanical information. The actin cytoskeleton and myosin-II motor proteins form a contractile (actomyosin) network inside the cell that is connected to the extracellular microenvironment through focal adhesion and integrin sites. The transmission of internal actomyosin strain to the microenvironment via focal adhesion sites generates mechanical traction forces. Importantly, cells generate traction forces in response to extracellular forces and also to actively probe the elasticity of the microenvironment. Many studies have demonstrated that extracellular forces can lead to rapid cytoskeletal remodeling, focal adhesion regulation, and intracellular signalling which can alter traction force dynamics. As well, cell migration, proliferation and stem cell fate are regulated by the ability of cells to sense the elasticity of their microenvironment through the generation of traction forces. In vitro studies have largely explored the influence of substrate elasticity and extracellular forces in isolation, however, in vivo cells are exposed to both mechanical cues simultaneously and their combined effect remains largely unexplored. Therefore, a series of experiments were performed in which cells were subjected to controlled extracellular forces as on substrates of increasing elasticity. The cellular response was quantified by measuring the resulting traction force magnitude dynamics. Two cell types were shown to increase their traction forces in response to extracellular forces only on substrates of specific elasticities. Therefore, cellular traction forces are regulated by an ability to sense and integrate at least two pieces of mechanical information - elasticity and deformation. Finally, this ability is shown to be dependent on the microtubule network and regulators of myosin-II activity.

No description available.

No description available.

Collagen is one of the major protein constituents in mammals and is present in all tissues and organs with the exceptions of keratin tissues such as hair and nails. Collagen monomers self-aggregate into a number of structures. In order to understand the physical bases for the structural polymorphism observed in collagen, a good starting point is one of the simplest collagen aggregates, segmental long spacing (SLS) collagen. Although SLS collagen formation induced by the presence of adenosine 5’-triphosphate is widely known, effects of other triphosphates, on the other hand, are much less studied. By varying the pH, it is discovered that all the nucleoside 5’-triphophsates, as well as inorganic triphosphate, are able to induce SLS formation over certain pH ranges. Adenosine 5’-diphosphate and para-nitrophenylphosphate cannot induce SLS formation at any pH. Based on the pH ranges at which SLS collagen can be formed, it is concluded the triphosphate functionality, with one negative charge per phosphate group, is primarily responsible for the formation of SLS collagen. Since inorganic triphosphate is able to induce SLS collagen formation, the presence of the nucleoside is optional for the assembly process; however if present, the assembly process prefers the nucleosides carrying acidic protons. Using electron spectroscopic imaging (ESI) technique, it is found phosphorus, present only in nucleotides but not in polypeptides, is localized in certain regions of SLS collagen, forming a unique banding pattern transverse the long axis of the SLS collagen. Nitrogen mapping indicates the localization of phosphorus is not due to accumulation of materials. The phosphorus banding pattern demonstrates an excellent consistency across SLS collagen assembled from both bovine and recombinant human collagen monomers. Results from molecular simulation are consistent with the experimental results. All threephosphate groups seem to be involved in the assembly process to some degree. In the last chapter of the thesis, a reliable protocol to synthesis native type collagen fibers is introduced.