The mechanics of disc degeneration from an engineering and computational modelling viewpoint

The anatomy and microstructure of the spine and in particular the intervertebral disc are intimately linked to how they operate in vivo and how they distribute loads to the adjacent musculature and bony anatomy. The degeneration of the intervertebral discs may be characterised by a loss of hydration, loss of disc height, a granular texture and the presence of annular lesions. As such, degeneration of the intervertebral discs compromises the mechanical integrity of their components and results in adaption and modification in the mechanical means by which loads are distributed between adjacent spinal motion segments.

Theoretical investigation of thermal tweezers for parallel manipulation of atoms and nanoparticles on surfaces

A major focus of research in nanotechnology is the development of novel, high throughput techniques for fabrication of arbitrarily shaped surface nanostructures of sub 100 nm to atomic scale. A related pursuit is the development of simple and efficient means for parallel manipulation and redistribution of adsorbed atoms, molecules and nanoparticles on surfaces – adparticle manipulation. These techniques will be used for the manufacture of nanoscale surface supported functional devices in nanotechnologies such as quantum computing, molecular electronics and lab-on-achip, as well as for modifying surfaces to obtain novel optical, electronic, chemical, or mechanical properties. A favourable approach to formation of surface nanostructures is self-assembly. In self-assembly, nanostructures are grown by aggregation of individual adparticles that diffuse by thermally activated processes on the surface. The passive nature of this process means it is generally not suited to formation of arbitrarily shaped structures. The self-assembly of nanostructures at arbitrary positions has been demonstrated, though these have typically required a pre-patterning treatment of the surface using sophisticated techniques such as electron beam lithography. On the other hand, a parallel adparticle manipulation technique would be suited for directing the selfassembly process to occur at arbitrary positions, without the need for pre-patterning the surface. There is at present a lack of techniques for parallel manipulation and redistribution of adparticles to arbitrary positions on the surface. This is an issue that needs to be addressed since these techniques can play an important role in nanotechnology. In this thesis, we propose such a technique – thermal tweezers. In thermal tweezers, adparticles are redistributed by localised heating of the surface. This locally enhances surface diffusion of adparticles so that they rapidly diffuse away from the heated regions. Using this technique, the redistribution of adparticles to form a desired pattern is achieved by heating the surface at specific regions. In this project, we have focussed on the holographic implementation of this approach, where the surface is heated by holographic patterns of interfering pulsed laser beams. This implementation is suitable for the formation of arbitrarily shaped structures; the only condition is that the shape can be produced by holographic means. In the simplest case, the laser pulses are linearly polarised and intersect to form an interference pattern that is a modulation of intensity along a single direction. Strong optical absorption at the intensity maxima of the interference pattern results in approximately a sinusoidal variation of the surface temperature along one direction. The main aim of this research project is to investigate the feasibility of the holographic implementation of thermal tweezers as an adparticle manipulation technique. Firstly, we investigate theoretically the surface diffusion of adparticles in the presence of sinusoidal modulation of the surface temperature. Very strong redistribution of adparticles is predicted when there is strong interaction between the adparticle and the surface, and the amplitude of the temperature modulation is ~100 K. We have proposed a thin metallic film deposited on a glass substrate heated by interfering laser beams (optical wavelengths) as a means of generating very large amplitude of surface temperature modulation. Indeed, we predict theoretically by numerical solution of the thermal conduction equation that amplitude of the temperature modulation on the metallic film can be much greater than 100 K when heated by nanosecond pulses with an energy ~1 mJ. The formation of surface nanostructures of less than 100 nm in width is predicted at optical wavelengths in this implementation of thermal tweezers. Furthermore, we propose a simple extension to this technique where spatial phase shift of the temperature modulation effectively doubles or triples the resolution. At the same time, increased resolution is predicted by reducing the wavelength of the laser pulses. In addition, we present two distinctly different, computationally efficient numerical approaches for theoretical investigation of surface diffusion of interacting adparticles – the Monte Carlo Interaction Method (MCIM) and the random potential well method (RPWM). Using each of these approaches we have investigated thermal tweezers for redistribution of both strongly and weakly interacting adparticles. We have predicted that strong interactions between adparticles can increase the effectiveness of thermal tweezers, by demonstrating practically complete adparticle redistribution into the low temperature regions of the surface. This is promising from the point of view of thermal tweezers applied to directed self-assembly of nanostructures. Finally, we present a new and more efficient numerical approach to theoretical investigation of thermal tweezers of non-interacting adparticles. In this approach, the local diffusion coefficient is determined from solution of the Fokker-Planck equation. The diffusion equation is then solved numerically using the finite volume method (FVM) to directly obtain the probability density of adparticle position. We compare predictions of this approach to those of the Ermak algorithm solution of the Langevin equation, and relatively good agreement is shown at intermediate and high friction. In the low friction regime, we predict and investigate the phenomenon of ‘optimal’ friction and describe its occurrence due to very long jumps of adparticles as they diffuse from the hot regions of the surface. Future research directions, both theoretical and experimental are also discussed.

Thermal tweezers for manipulation of adatoms and nanoparticles on surfaces heated by interfering laser pulses

We conduct the detailed numerical investigation of a nanomanipulation and nanofabrication technique—thermal tweezers with dynamic evolution of surface temperature, caused by absorption of interfering laser pulses in a thin metalfilm or any other absorbing surface. This technique uses random Brownian forces in the presence of strong temperature modulation (surfacethermophoresis) for effective manipulation of particles/adatoms with nanoscale resolution. Substantial redistribution of particles on the surface is shown to occur with the typical size of the obtained pattern elements of ∼100 nm, which is significantly smaller than the wavelength of the incident pulses used (532 nm). It is also demonstrated that thermal tweezers based on surfacethermophoresis of particles/adatoms are much more effective in achieving permanent high maximum-to-minimum concentration ratios than bulk thermophoresis, which is explained by the interaction of diffusing particles with the periodic lattice potential on the surface. Typically required pulse regimes including pulse lengths and energies are also determined. The approach is applicable for reproducing any holographically achievable surfacepatterns, and can thus be used for engineering properties of surfaces including nanopatterning and design of surface metamaterials.

Bioactive mesopore-glass microspheres with controllable protein-delivery properties by biomimetic surface modification

Microsphere systems with the ideal properties for bone regeneration need to be bioactive, and at the same time possess the capacity for controlled protein/drug-delivery; however, the current crop of microsphere system fails to fulfill these properties. The aim of this study was to develop a novel protein-delivery system of bioactive mesoporous glass (MBG) microspheres by a biomimetic method through controlling the density of apatite on the surface of microspheres, for potential bone tissue regeneration. MBG microspheres were prepared by using the method of alginate cross-linking with Ca2+ ions. The cellular bioactivity of MBG microspheres was evaluated by investigating the proliferation and attachment of bone marrow stromal cell (BMSC). The loading efficiency and release kinetics of bovine serum albumin (BSA) on MBG microspheres were investigated after coprecipitating with biomimetic apatite in simulated body fluids (SBF). The results showed that MBG microspheres supported BMSC attachment and the Si containing ionic products from MBG microspheres stimulated BMSCs proliferation. The density of apatite on MBG microspheres increased with the length of soaking time in SBF. BSA-loading efficiency of MBG was significantly enhanced by co-precipitating with apatite. Furthermore, the loading efficiency and release kinetics of BSA could be controlled by controlling the density of apatite formed on MBG microspheres. Our results suggest that MBG microspheres are a promising protein-delivery system as a filling material for bone defect healing and regeneration.

Influence of spherical intraocular lens implantation and conventional laser in situ keratomileusis on peripheral ocular aberrations

Aim: To measure the influence of spherical intraocular lens implantation and conventional myopic laser in situ keratomileusis on peripheral ocular aberrations. Setting: Visual & Ophthalmic Optics Laboratory, School of Optometry & Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia. Methods: Peripheral aberrations were measured using a modified commercial Hartmann-Shack aberrometer across 42° x 32° of the central visual field in 6 subjects after spherical intraocular lens (IOL) implantation and in 6 subjects after conventional laser in situ keratomileusis (LASIK) for myopia. The results were compared with those of age matched emmetropic and myopic control groups. Results: The IOL group showed a greater rate of quadratic change of spherical equivalent refraction across the visual field, higher spherical aberration, and greater rates of change of higher-order root-mean-square aberrations and total root-mean-square aberrations across the visual field than its emmetropic control group. However, coma trends were similar for the two groups. The LASIK group had a greater rate of quadratic change of spherical equivalent refraction across the visual field, higher spherical aberration, the opposite trend in coma across the field, and greater higher-order root-mean-square aberrations and total root-mean-square aberrations than its myopic control group. Conclusion: Spherical IOL implantation and conventional myopia LASIK increase ocular peripheral aberrations. They cause considerable increase in spherical aberration across the visual field. LASIK reverses the sign of the rate of change in coma across the field relative to that of the other groups. Keywords: refractive surgery, LASIK, IOL implantation, aberrations, peripheral aberrations

Investigation of inclusions trapped inside Libyan Desert glass by Raman microscopy

Several specimens of Libyan Desert Glass (LDG), an enigmatic natural glass from Egypt, were subjected to investigation by micro-Raman spectroscopy. The spectra of inclusions inside the LDG samples were successfully measured through the layers of glass and the mineral species were identified on this basis. The presence of cristobalite as typical for high-temperature melt products was confirmed, together with co-existing quartz. TiO2 was determined in two polymorphic species, rutile and anatase. Micro-Raman spectroscopy proved also the presence of minerals unusual for high-temperature glasses such as anhydrite and aragonite.

Expression of chondromodulin-1 in the temporomandibular joint condylar cartilage and disc

BACKGROUND: The temporomandibular joint (TMJ) cartilage consists of condylar cartilage and disc and undergoes continuous remodeling throughout post-natal life. To maintain the integrity of the TMJ cartilage, anti-angiogenic factors play an important role during the remodeling process. In this study, we investigated the expression of the anti-angiogenic factor, chondromodulin- 1 (ChM-1), in TMJ cartilage and evaluate its potential role in TMJ remodeling. METHODS: Eight TMJ specimens were collected from six 4-month-old Japanese white rabbits. Safranin-O staining was performed to determine proteoglycan content. ChM-1 expression in TMJ condylar cartilage and disc was determined by immunohistochemistry. Three human perforated disc tissue samples were collected for investigation of ChM-1 and vascular endothelial growth factor (VEGF) distribution in perforated TMJ disc. RESULTS: Safranin-O stained weakly in TMJ compared with tibial articular and epiphyseal cartilage. In TMJ, ChM-1 was expressed in the proliferative and hypertrophic zone of condylar cartilage and chondrocyte-like cells in the disc. No expression of ChM-1 was observed in osteoblasts and subchondral bone. ChM-1 and VEGF were both similarly expressed in perforated disc tissues. CONCLUSIONS: ChM-1 may play a role in the regulation of TMJ remodeling by preventing blood vessel invasion of the cartilage, thereby maintaining condylar cartilage and disc integrity.

Macular function in tilted disc syndrome

Tilted disc syndrome can cause visual field defects due to an optic disc anomaly. Recent electrophysiological findings demonstrate reduced central outer retinal function with ophthalmoscopically normal maculae. We measured macular sensitivity with the microperimeter and performed psychophysical assessment of mesopic rod and cone luminance temporal sensitivity (critical fusion frequency)in a 52-year-old male patient with tilted disc syndrome and ophthalmoscopically normal maculae. We found a marked reduction of sensitivity in the central 20 degrees and reduced rod- and cone-mediated mesopic visual function. Our findings extend previous electrophysiological data that suggest an outer retinal involvement of cone pathways and present a case with rod and cone impairment mediated via the magnocellular pathway in uncomplicated tilted disc syndrome.