Biocompatible properties of surgical mesh using an animal model

To study the biocompatibility of surgical meshes for use in pelvic reconstructive surgery using an animal model. Eight different types of mesh: Atrium, Dexon, Gynemesh, IVS tape, Prolene, SPARC tape, TVT tape and Vypro II, were implanted into the abdominal walls of rats for 3 months' duration. Explanted meshes were assessed, using light microscopy, for parameters of rejection and incorporation. Type 1 (Atrium, Gynemesh, Prolene, SPARC and TVT) and type 3 (Vypro II, Dexon and IVS) meshes demonstrated different biocompatible properties. Inflammatory cellular response and fibrosis at the interface of mesh and host tissue was most marked with Vypro II and IVS. All type 1 meshes displayed similar cellular responses despite markedly different mesh architecture. The inflammatory response and fibrous reaction in the non-absorbable type 3 meshes tested (IVS and Vypro II) was more marked than the type 1 meshes. The increased inflammatory and fibrotic response may be because of the multifilamentous polypropylene components of these meshes. Material and filament composition of mesh is the main factor in determining cellular response.

Mechanical disruption of seagrass in the digestive tract of the dugong

The cheek teeth in dugongs are considered to be largely non-functional whereas the oral horny pads are important both in mechanical disruption of the diet and in conveying seagrass through the mouth. Particle size distributions of digesta from 41 dead stranded dugongs were examined to investigate the relationship between degree of food breakdown, gut region and functional surface area of the mouthparts. The in vitro ease of fracture of major dietary seagrass species were compared. The rate of food breakdown through the gut appears to be more closely linked to fibre level of the diet than to size or age of the dugong and its mouthparts. Low fibre seagrass, for example Halophila ovalis, breaks down at a faster rate than high fibre seagrass, for example Zostera capricorni both in dugong guts and in vitro. Several structural characteristics of seagrass, including level and arrangement of fibre, and water content, make it particularly amenable to mechanical breakdown. The soft mouthparts of the dugong are highly modified so that the entire oral cavity functions to crush low fibre seagrasses. Thus, the dugong has developed an efficient method of food ingestion and mastication that is suited to processing large quantities of soft seagrass during short dive times. The potential cost to the dugong in having lost its hard dental surfaces is that it has become restricted to a low fibre diet.

Mechanisms influencing levitation and the scaling laws in nanopores: Oscillator model theory

We provide here a detailed theoretical explanation of the floating molecule or levitation effect, for molecules diffusing through nanopores, using the oscillator model theory (Phys. Rev. Lett. 2003, 91, 126102) recently developed in this laboratory. It is shown that on reduction of pore size the effect occurs due to decrease in frequency of wall collision of diffusing particles at a critical pore size. This effect is, however, absent at high temperatures where the ratio of kinetic energy to the solid-fluid interaction strength is sufficiently large. It is shown that the transport diffusivities scale with this ratio. Scaling of transport diffusivities with respect to mass is also observed, even in the presence of interactions.

Nano-emulsion production by sonication and microfluidization - A comparison

The efficiency of sonication and microfluidization to produce nano-emulsions were evaluated in this study. The purpose was to produce an oil-in-water nano-emulsion of d-limonene to apply it in the next step for nano-particle encapsulation. In the entrapment and retention of volatiles or for the microencapsulation efficiency, emulsion size is one of the critical factors. In this study, a bench-top sonicator and an air-driven microfluidizer were used to prepare the emulsions. Results show that, while both methods were capable of producing nano-emulsions of the size range of 150-700 nm, the microfluidizer produced emulsions with narrower size distributions and sonication was more convenient in terms of operation and cleaning. In general, the size of the emulsions decreased with increasing sonication time, or the microfluidization pressure and duration. However, for both sonication and microfluidization, optimal conditions were necessary for emulsification beyond which the emulsion sizes would either increase or have little change with further processing.

Structure of saccharose-based carbon and transport of confined fluids: hybrid reverse Monte Carlo reconstruction and simulation studies

We present results of the reconstruction of a saccharose-based activated carbon (CS1000a) using hybrid reverse Monte Carlo (HRMC) simulation, recently proposed by Opletal et al. [1]. Interaction between carbon atoms in the simulation is modeled by an environment dependent interaction potential (EDIP) [2,3]. The reconstructed structure shows predominance of sp(2) over sp bonding, while a significant proportion of sp(3) hybrid bonding is also observed. We also calculated a ring distribution and geometrical pore size distribution of the model developed. The latter is compared with that obtained from argon adsorption at 87 K using our recently proposed characterization procedure [4], the finite wall thickness (FWT) model. Further, we determine self-diffusivities of argon and nitrogen in the constructed carbon as functions of loading. It is found that while there is a maximum in the diffusivity with respect to loading, as previously observed by Pikunic et al. [5], diffusivities in the present work are 10 times larger than those obtained in the prior work, consistent with the larger pore size as well as higher porosity of the activated saccharose carbon studied here.

Systematic selection of solvents for the fabrication of 3D combined macro- and microporous polymeric scaffolds for soft tissue engineering

In this study, we investigate the fabrication of 3D porous poly(lactic-co-glycolic acid) (PLGA) scaffolds using the thermally-induced phase separation technique. The current study focuses on the selection of alternative solvents for this process using a number of criteria, including predicted solubility. toxicity, removability and processability. Solvents were removed via either vacuum freeze-drying or leaching, depending on their physical properties. The residual solvent was tested using gas chromatography-mass spectrometry. A large range of porous, highly interconnected scaffold architectures with tunable pore size and alignment was obtained, including combined macro- and microporous structures and an entirely novel 'porous-fibre' structure. The morphological features of the most promising poly(lactic-co-glycolic acid) scaffolds were analysed via scanning electron microscopy and X-ray micro-computed tomography in both two and three dimensions. The Young's moduli of the scaffolds under conditions of temperature, pH and ionic strength similar to those found in the body were tested and were found to be highly dependent on the architectures.

Correct procedures for the calculation of heats of adsorption for heterogeneous adsorbents from molecular simulation

Several procedures for calculating the heat of adsorption from Monte Carlo simulations for a heterogeneous adsorbent are presented. Simulations have been performed to generate isotherms for nitrogen at 77 K and methane at 273.15 K in graphitic slit pores of various widths. The procedures were then applied to calculate the heat of adsorption of an activated carbon with an arbitrary pore size distribution. The consistency of the different procedures shows them to be correct in calculating interaction energy contributions to the heat of adsorption. The currently favored procedure for this type of calculation, from the literature, is shown to be incorrect and in serious error when calculating the heat of adsorption of activated carbon.

Particle number emissions and source signatures of an industrial facility

The work presented was conducted within the scope of a larger study investigating impacts of the Stuart Oil Shale project, a facility operating to the north of the industrial city of Gladstone, Australia. The aims of the investigations were threefold: (a) the identification of the plant signatures in terms of particle size distributions in the submicrometer range (13-830 nm) through stack measurements, (b) exploring the applicability of these signatures in tracing the source contributions at locations of interest, at a distance from the plant, and (c) assessing the contribution of the plant to the total particle number concentration at locations of interest. The stack measurements conducted for three different conditions of plant operation showed that the particle size distributions were bimodal with average modal count median diameters (CMDs) of 24 (SD 4) and 52 (SD 9) nm. The average of all the particle size distributions recorded within the plant sector at a site located 4.5 km from the plant, over the sampling period when the plant was operating, also showed a bimodal distribution. The modal CMDs in this case were 27 and 50 nm, similar to those at the stack. This bimodal size distribution is distinct from the size distribution of the most common ambient anthropogenic emission source, which is vehicle emissions, and can be considered as a signature of this source. The average contribution of the plant (for plant sector winds) was estimated to be (10.0 +/- 3.8) x 10(2) particles cm(-3) and constituted approximately a 50% increase over the local particle ambient concentration for plant sector winds. This increase in particle number concentration compared to the local background concentration, while high compared to the clean environment concentration, is not significant when compared to concentrations generally encountered in the urban environment of Brisbane.

Modelling the growth of prion protein aggregates in the brain in variant Creutzfeldt-Jakob disease

Deposition of insoluble prion protein (PrP) in the brain in the form of protein aggregates or deposits is characteristic of the ‘transmissible spongiform encephalopathies’ (TSEs). Understanding the growth and development of these PrP aggregates is important both in attempting to the elucidate of the pathogenesis of prion disease and in the development of treatments designed to prevent or inhibit the spread of prion pathology within the brain. Aggregation and disaggregation of proteins and the diffusion of substances into the developing aggregates (surface diffusion) are important factors in the development of protein aggregates. Mathematical models suggest that if aggregation/disaggregation or surface diffusion is the predominant factor, the size frequency distribution of the resulting protein aggregates in the brain should be described by either a power-law or a log-normal model respectively. This study tested this hypothesis for two different types of PrP deposit, viz., the diffuse and florid-type PrP deposits in patients with variant Creutzfeldt-Jakob disease (vCJD). The size distributions of the florid and diffuse plaques were fitted by a power-law function in 100% and 42% of brain areas studied respectively. By contrast, the size distributions of both types of plaque deviated significantly from a log-normal model in all brain areas. Hence, protein aggregation and disaggregation may be the predominant factor in the development of the florid plaques. A more complex combination of factors appears to be involved in the pathogenesis of the diffuse plaques. These results may be useful in the design of treatments to inhibit the development of protein aggregates in vCJD.

Liquid-liquid extraction in a pilot scale rotating disc contactor

A study of the hydrodynamics and mass transfer characteristics of a liquid-liquid extraction process in a 450 mm diameter, 4.30 m high Rotating Disc Contactor (R.D.C.) has been undertaken. The literature relating to this type of extractor and the relevant phenomena, such as droplet break-up and coalescence, drop mass transfer and axial mixing has been revjewed. Experiments were performed using the system C1airsol-350-acetone-water and the effects of drop size, drop size-distribution and dispersed phase hold-up on the performance of the R.D.C. established. The results obtained for the two-phase system C1airso1-water have been compared with published correlations: since most of these correlations are based on data obtained from laboratory scale R.D.C.'s, a wide divergence was found. The hydrodynamics data from this study have therefore been correlated to predict the drop size and the dispersed phase hold-up and agreement has been obtained with the experimental data to within +8% for the drop size and +9% for the dispersed phase hold-up. The correlations obtained were modified to include terms involving column dimensions and the data have been correlated with the results obtained from this study together with published data; agreement was generally within +17% for drop size and within +14% for the dispersed phase hold-up. The experimental drop size distributions obtained were in excellent agreement with the upper limit log-normal distributions which should therefore be used in preference to other distribution functions. In the calculation of the overall experimental mass transfer coefficient the mean driving force was determined from the concentration profile along the column using Simpson's Rule and a novel method was developed to calculate the overall theoretical mass transfer coefficient Kca1, involving the drop size distribution diagram to determine the volume percentage of stagnant, circulating and oscillating drops in the sample population. Individual mass transfer coefficients were determined for the corresponding droplet state using different single drop mass transfer models. Kca1 was then calculated as the fractional sum of these individual coefficients and their proportions in the drop sample population. Very good agreement was found between the experimental and theoretical overall mass transfer coefficients. Drop sizes under mass transfer conditions were strongly dependant upon the direction of mass transfer. Drop Sizes in the absence of mass transfer were generally larger than those with solute transfer from the continuous to the dispersed phase, but smaller than those with solute transfer in the opposite direction at corresponding phase flowrates and rotor speed. Under similar operating conditions hold-up was also affected by mass transfer; it was higher when solute transfered from the continuous to the dispersed phase and lower when direction was reversed compared with non-mass transfer operation.

Solvent extraction of phosphoric acid

This work investigated the purification of phosphoric acid using a suitable organic solvent, followed by re-extraction of the acid from the solvent using water. The work consisted of practical batch and continuous studies and the economics and design of a full scale plant, based on the experimental data. A comprehensive literature survey on the purification of wet process phosphoric acid by organic solvents is presented and the literature describing the design and operation of mixer-settlers has also been reviewed. In batch studies, the equilibrium and distribution curves for the systems water-phosphoric acid-solvent for Benzaldehyde, Cyclohexanol and Methylisobutylketone (MIBK) were determined together with hydrodynamic characteristics for both pure and impure systems. The settling time increased with acid concentration, but power input had no effect. Drop size was found to reduce with acid concentration and power input. For the continuous studies a novel horizontal mixer~settler cascade was designed, constructed and operated using pure and impure acid with MIBK as the solvent. The cascade incorporates three air turbine agitated, cylindrical 900 ml mixers, and three cylindrical 200 ml settlers with air-lift solvent interstage transfer. Mean drop size in the fully baffled mixer was correlated. Drop size distributions were log-normal and size decreased with acid concentration and power input and increased with dispersed phase hold-up. Phase inversion studies showed that the width of the ambivalent region depended upon rotor speed, hold-up and acid concentration. Settler characteristics were investigated by measuring wedge length. Distribution coefficients of impurities and acid were also investigated. The following optimum extraction conditions were found: initial acid concentration 63%, phase ratio of solvent to acid 1:1 (v/v), impeller speed recommended 900 r.p.m. In the washing step the maximum phase ratio of solvent to water was 8:1 (v/v). Work on phosphoric acid concentration involved constructing distillation equipment consisting of a 10& spherical still. A 100 T/d scale detailed process design including capital cost, operating cost and profitability was also completed. A profit model for phosphoric acid extraction was developed and maximised. Recommendations are made for both the application of the results to a practical design and for extensions of the study.

Do β-amyloid (Aβ) deposits in patients with Alzheimer's disease and Down's syndrome grow according to the log-normal model?

The size frequency distributions of diffuse, primitive and classic β- amyloid (Aβ) deposits were studied in single sections of cortical tissue from patients with Alzheimer's disease (AD) and Down's syndrome (DS) and compared with those predicted by the log-normal model. In a sample of brain regions, these size distributions were compared with those obtained by serial reconstruction through the tissue and the data used to adjust the size distributions obtained in single sections. The adjusted size distributions of the diffuse, primitive and classic deposits deviated significantly from a log-normal model in AD and DS, the greatest deviations from the model being observed in AD. More Aβ deposits were observed close to the mean and fewer in the larger size classes than predicted by the model. Hence, the growth of Aβ deposits in AD and DS does not strictly follow the log-normal model, deposits growing to within a more restricted size range than predicted. However, Aβ deposits grow to a larger size in DS compared with AD which may reflect differences in the mechanism of Aβ formation.

Modelling growth of prion protein aggregates in the brain in variant Creutzfeldt-Jakob disease

Deposition of insoluble prion protein (PrP) in the brain in the form of protein aggregates or deposits is characteristic of the ‘transmissible spongiform encephalopathies’ (TSEs). Understanding the growth and development of PrP aggregates is important both in attempting to elucidate the pathogenesis of prion disease and in the development of treatments designed to inhibit the spread of prion pathology within the brain. Aggregation and disaggregation of proteins and the diffusion of substances into the developing aggregates (surface diffusion) are important factors in the development of protein deposits. Mathematical models suggest that if either aggregation/disaggregation or surface diffusion is the predominant factor, then the size frequency distribution of the resulting protein aggregates will be described by either a power-law or a log-normal model respectively. This study tested this hypothesis for two different populations of PrP deposit, viz., the diffuse and florid-type PrP deposits characteristic of patients with variant Creutzfeldt-Jakob disease (vCJD). The size distributions of the florid and diffuse deposits were fitted by a power-law function in 100% and 42% of brain areas studied respectively. By contrast, the size distributions of both types of aggregate deviated significantly from a log-normal model in all areas. Hence, protein aggregation and disaggregation may be the predominant factor in the development of the florid deposits. A more complex combination of factors appears to be involved in the pathogenesis of the diffuse deposits. These results may be useful in the design of treatments to inhibit the development of PrP aggregates in vCJD.

The atomisation of detergent slurries

A study was made to determine the conditions under which the optimum droplet size distribution (ie., narrowest size range with a minimum of fines and over-sized agglomerates), is generated in sprays from centrifugal pressure nozzles. A range of non-Newtonian detergent slurries were tested but the results are of wider application and parallel work was undertaken with water, ionic solutions and chalk slurries. Six centrifugal pressure nozzles were used and the drop-size distributions correlated as a function of fluid properties, pressure, fiowrate, feed temperature, and nozzle characteristics. Measurements were made using a Malvern Particle Size Anayser slung across a specially-designed transparent tower section of approximately 1.2m diameter in order to reduce obscuration caused by the spray and improve existing droplet sizing techniques. The results obtained were based upon the Rosin-Rammler distribution model and the Size Analyser provided a direct print-out of size distribution and the parameters characterising it. A Spraying System nozzle, AAASSTC8-8, produced the optimum spray distribution with the detergent slurry at a temperature of 60°C whilst operating at 1200 psi. With other fluids the Delevan 2.2SJ nozzle produced the optimum spray distribution operating at 1200 psi but with the Spraying Systems nozzles there was no clear-cut optimum set of conditions, ie. the nozzle and pressure varied depending upon the fluid being sprayed. The mechanisms of liquid sheet break-up and droplet dispersion were investigated in specially-constructed, scaled-up, transparent nozzles. A mathematical model of centrifugal pressure nozzle atomisation was developed based upon fundamental operating parameters rather than resorting to empirical correlations. This enabled theoretical predictions to be made over a wide range of operating conditions and nozzle types. The model predictions for volumetric fiowrate, liquid sheet length and air core diameter showed good agreement with the experimentally determined results. However, the model predicted smaller droplet sizes than were produced experimentally due to inaccuracies identified in the initial assumptions.

Cells, surfaces and adhesion

This thesis concerns cell adhesion to polymer surfaces with an experimental emphasis on hydrogels. The thesis begins with a review of the literature and a synthesis of recent evidence to describe the process of cell adhesion in a given situation. The importance of understanding integrin-adhesion protein interactions and adhesion protein-surface interactions is emphasised. The experimental chapters describe three areas of investigation. Firstly, in vitro cell culture techniques are used to explore a variety of surfaces including polyethylene glycol methacrylate (PEGMA) substituted hydrogels, sequence distribution modified hydrogels and worn contact lenses. Cell adhesion to PEGMA substituted gels is found to decrease with increases in polyethylene oxide chain length and correlations are made between sequence distribution and adhesion. Worn contact lenses are investigated for their cell adhesion properties in the presence of antibodies to specific adhesion proteins, demonstrating the presence of vitronectin and fibronectin on the lenses. The second experimental chapter addresses divalent cation regulation of integrin mediated cell adhesion. Several cell types and various cations are used. Zinc, previously not regarded as an important cation in the process, is found to inhibit 3T3 cell adhesion to vitronectin that is promoted by other divalent cations. The final experimental chapter concerns cell adhesion and growth on macroporous hydrogels. A variety of freeze-thaw formed porous gels are investiated and found generally to promote cell growth rate.Interpenetrating networkbased gels (IPN) are made porous by elution of dextrin particles of varying size and loading density. These materials provide the basis for synthetic cartilage. Cartilage cells (chondrocytes) plated onto the surface of the porous IPN materials maintain a rounded shape and hence phenotypic function when a critical pore size and density is achieved. In this way, a prospective implant, made porous at the perpendicular edges contacting natural cartilage can be both mechanically stabilised and encourage the maintenance of normal matrix production at the tissue interface.