Co-encapsulation of enzymes and antibodies for chemical deactivation of pathogens on paper

Le papier bioactif est obtenu par la modification de substrat du papier avec des biomolécules et des réactifs. Ce type de papier est utilisé dans le développement de nouveaux biocapteurs qui sont portables, jetables et économiques visant à capturer, détecter et dans certains cas, désactiver les agents pathogènes. Généralement les papiers bioactifs sont fabriqués par l’incorporation de biomolécules telles que les enzymes et les anticorps sur la surface du papier. L’immobilisation de ces biomolécules sur les surfaces solides est largement utilisée pour différentes applications de diagnostic comme dans immunocapteurs et immunoessais mais en raison de la nature sensible des enzymes, leur intégration au papier à grande échelle a rencontré plusieurs difficultés surtout dans les conditions industrielles. Pendant ce temps, les microcapsules sont une plate-forme intéressante pour l’immobilisation des enzymes et aussi assez efficace pour permettre à la fonctionnalisation du papier à grande échelle car le papier peut être facilement recouvert avec une couche de telles microcapsules. Dans cette étude, nous avons développé une plate-forme générique utilisant des microcapsules à base d’alginate qui peuvent être appliquées aux procédés usuels de production de papier bioactif et antibactérien avec la capacité de capturer des pathogènes à sa surface et de les désactiver grâce à la production d’un réactif anti-pathogène. La conception de cette plate-forme antibactérienne est basée sur la production constante de peroxyde d’hydrogène en tant qu’agent antibactérien à l’intérieur des microcapsules d’alginate. Cette production de peroxyde d’hydrogène est obtenue par oxydation du glucose catalysée par la glucose oxydase encapsulée à l’intérieur des billes d’alginate. Les différentes étapes de cette étude comprennent le piégeage de la glucose oxydase à l’intérieur des microcapsules d’alginate, l’activation et le renforcement de la surface des microcapsules par ajout d’une couche supplémentaire de chitosan, la vérification de la possibilité d’immobilisation des anticorps (immunoglobulines G humaine comme une modèle d’anticorps) sur la surface des microcapsules et enfin, l’évaluation des propriétés antibactériennes de cette plate-forme vis-à-vis l’Escherichia coli K-12 (E. coli K-12) en tant qu’un représentant des agents pathogènes. Après avoir effectué chaque étape, certaines mesures et observations ont été faites en utilisant diverses méthodes et techniques analytiques telles que la méthode de Bradford pour dosage des protéines, l’électroanalyse d’oxygène, la microscopie optique et confocale à balayage laser (CLSM), la spectrométrie de masse avec désorption laser assistée par matrice- temps de vol (MALDI-TOF-MS), etc. Les essais appropriés ont été effectués pour valider la réussite de modification des microcapsules et pour confirmer à ce fait que la glucose oxydase est toujours active après chaque étape de modification. L’activité enzymatique spécifique de la glucose oxydase après l’encapsulation a été évaluée à 120±30 U/g. Aussi, des efforts ont été faits pour immobiliser la glucose oxydase sur des nanoparticules d’or avec deux tailles différentes de diamètre (10,9 nm et 50 nm) afin d’améliorer l’activité enzymatique et augmenter l’efficacité d’encapsulation. Les résultats obtenus lors de cette étude démontrent les modifications réussies sur les microcapsules d’alginate et aussi une réponse favorable de cette plate-forme antibactérienne concernant la désactivation de E. coli K-12. La concentration efficace de l’activité enzymatique afin de désactivation de cet agent pathogénique modèle a été déterminée à 1.3×10-2 U/ml pour une concentration de 6.7×108 cellules/ml de bactéries. D’autres études sont nécessaires pour évaluer l’efficacité de l’anticorps immobilisé dans la désactivation des agents pathogènes et également intégrer la plate-forme sur le papier et valider l’efficacité du système une fois qu’il est déposé sur papier.

Non-Viral Gene Therapy to Cells of the bovine Intervertebral Disc

Background. Low back pain is an increasing global health problem, which is associated with intervertebral disc (IVD) damage and degeneration. Major changes occur in the nucleus pulposus (NP), with the degradation of the extracellular matrix (ECM).1 Further studies showed that growth factors from transforming growth factor β (TGFβ) and bone morphogenic proteins (BMP) family may induce chondrogenic differentiation of mesenchymal stem cells (MSC).2 Focusing on non-viral gene therapies and their possible translation into the clinics, we investigated if GDF6 (syn. BMP13 or CDMP2) can induce regeneration of degraded NP. We hypothesized that IVD transfected with plasmid over-expressing GDF6 also up-regulates other NP- and chondrogenic cell markers and enhances ECM deposition. Methods. Bovine nucleus pulposus (bNPC) and annulus fibrosus cells (bAFC) were harvested from bovine coccygeal IVD. Primary cells were then electroporized with plasmid GDF6 (Origene, vector RG211366) by optimizing parameters using the Neon Transfection system (Life Technologies, Basel). After transfection, cells were cultured in 2D monolayer or 3D alginate beads for 7, 14 or 21 days. Transfection efficiency of pGDF6 was analyzed by immunohistochemistry and fluorescent microscopy. Cell phenotype was quantified by real-time RT-PCR. To test a non-viral gene therapy applied directly to 3D whole organ culture, coccygeal bovine IVDs were harvested as previously described. Bovine IVDs were transfected by injection of plasmid GDF6 into the center. Electroporation was performed with ECM830 Square Wave Electroporation System (Harvard Apparatus, MA) using 2-needle array electrode or tweezertrodes. 72 h after tranfection discs were fixed and cryosectioned and analyzed by immunofluorescence against GDF6. Results. RT-PCR and immunohistochemistry confirmed up-regulation of GFP and GDF6 in the primary bNPC/bAFC culture. The GFP-tagged GDF6 protein, however, was not visible, possibly due to failure of dimer formation as a result of fusion structure. Organ IVD culture transfection revealed GDF6 positive staining in the center of the disc using 2-needle array electrode. Results from tweezertrodes did not show any GDF6 positive cells. Conclusion. Non-viral transfection is an appealing approach for gene therapy as it fulfills the translational safety aspects of transiency and lacks the toxic effects of viral transduction. We identified novel parameters to successfully transfect primary bovine IVD cells. For transfection of whole IVD explants electroporation parameters need to be further optimized. Acknowledgements. This project was funded by the Lindenhof Foundation (Funds “Research & Teaching”) Project no. 13-02-F. The imaging part of this study was performed with the facility of the Microscopy Imaging Center (MIC), University of Bern. References. Roughly PJ (2004): Spine (Phila), 29:2691-2699 Clarke LE, McConell JC, Sherratt MJ, Derby B, Richardson SM, Hoyland JA (2014), Arthritis Research & Therapy, 16:R67

A synthetic biology-based device prevents liver injury in mice

BACKGROUND & AIMS The liver performs a panoply of complex activities coordinating metabolic, immunologic and detoxification processes. Despite the liver's robustness and unique self-regeneration capacity, viral infection, autoimmune disorders, fatty liver disease, alcohol abuse and drug-induced hepatotoxicity contribute to the increasing prevalence of liver failure. Liver injuries impair the clearance of bile acids from the hepatic portal vein which leads to their spill over into the peripheral circulation where they activate the G-protein-coupled bile acid receptor TGR5 to initiate a variety of hepatoprotective processes. METHODS By functionally linking activation of ectopically expressed TGR5 to an artificial promoter controlling transcription of the hepatocyte growth factor (HGF), we created a closed-loop synthetic signalling network that coordinated liver injury-associated serum bile acid levels to expression of HGF in a self-sufficient, reversible and dose-dependent manner. RESULTS After implantation of genetically engineered human cells inside auto-vascularizing, immunoprotective and clinically validated alginate-poly-(L-lysine)-alginate beads into mice, the liver-protection device detected pathologic serum bile acid levels and produced therapeutic HGF levels that protected the animals from acute drug-induced liver failure. CONCLUSIONS Genetically engineered cells containing theranostic gene circuits that dynamically interface with host metabolism may provide novel opportunities for preventive, acute and chronic healthcare. LAY SUMMARY Liver diseases leading to organ failure may go unnoticed as they do not trigger any symptoms or significant discomfort. We have designed a synthetic gene circuit that senses excessive bile acid levels associated with liver injuries and automatically produces a therapeutic protein in response. When integrated into mammalian cells and implanted into mice, the circuit detects the onset of liver injuries and coordinates the production of a protein pharmaceutical which prevents liver damage.

Properties of granular analogue model materials: A community wide survey

We report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories. We determined physical characteristics such as bulk density, grain size distribution, and grain shape, and performed ring shear tests to determine friction angles and cohesion, and uniaxial compression tests to evaluate the compaction behaviour. Mean grain size of the materials varied between c. 100 and 400 μm. Analysis of grain shape factors shows that the four different classes of granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands and 3 size fractions of glass beads) can be broadly divided into two groups consisting of 12 angular and 14 rounded materials. Grain shape has an influence on friction angles, with most angular materials having higher internal friction angles (between c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the lowest internal friction angles (between c. 25° and 30°). We interpret this as an effect of intergranular sliding versus rolling. Most angular materials have also higher basal friction angles (tested for a specific foil) than more rounded materials, suggesting that angular grains scratch and wear the foil. Most materials have an internal cohesion in the order of 20–100 Pa except for well-rounded glass beads, which show a trend towards a quasi-cohesionless (C < 20 Pa) Coulomb-type material. The uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains. We interpret this to be related to the initial packing density after sifting, which is higher for rounded grains than for angular grains. Ring-shear test data show that angular grains undergo a longer strain-hardening phase than more rounded materials. This might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains.

Co-encapsulation of enzymes and antibodies for chemical deactivation of pathogens on paper

Le papier bioactif est obtenu par la modification de substrat du papier avec des biomolécules et des réactifs. Ce type de papier est utilisé dans le développement de nouveaux biocapteurs qui sont portables, jetables et économiques visant à capturer, détecter et dans certains cas, désactiver les agents pathogènes. Généralement les papiers bioactifs sont fabriqués par l’incorporation de biomolécules telles que les enzymes et les anticorps sur la surface du papier. L’immobilisation de ces biomolécules sur les surfaces solides est largement utilisée pour différentes applications de diagnostic comme dans immunocapteurs et immunoessais mais en raison de la nature sensible des enzymes, leur intégration au papier à grande échelle a rencontré plusieurs difficultés surtout dans les conditions industrielles. Pendant ce temps, les microcapsules sont une plate-forme intéressante pour l’immobilisation des enzymes et aussi assez efficace pour permettre à la fonctionnalisation du papier à grande échelle car le papier peut être facilement recouvert avec une couche de telles microcapsules. Dans cette étude, nous avons développé une plate-forme générique utilisant des microcapsules à base d’alginate qui peuvent être appliquées aux procédés usuels de production de papier bioactif et antibactérien avec la capacité de capturer des pathogènes à sa surface et de les désactiver grâce à la production d’un réactif anti-pathogène. La conception de cette plate-forme antibactérienne est basée sur la production constante de peroxyde d’hydrogène en tant qu’agent antibactérien à l’intérieur des microcapsules d’alginate. Cette production de peroxyde d’hydrogène est obtenue par oxydation du glucose catalysée par la glucose oxydase encapsulée à l’intérieur des billes d’alginate. Les différentes étapes de cette étude comprennent le piégeage de la glucose oxydase à l’intérieur des microcapsules d’alginate, l’activation et le renforcement de la surface des microcapsules par ajout d’une couche supplémentaire de chitosan, la vérification de la possibilité d’immobilisation des anticorps (immunoglobulines G humaine comme une modèle d’anticorps) sur la surface des microcapsules et enfin, l’évaluation des propriétés antibactériennes de cette plate-forme vis-à-vis l’Escherichia coli K-12 (E. coli K-12) en tant qu’un représentant des agents pathogènes. Après avoir effectué chaque étape, certaines mesures et observations ont été faites en utilisant diverses méthodes et techniques analytiques telles que la méthode de Bradford pour dosage des protéines, l’électroanalyse d’oxygène, la microscopie optique et confocale à balayage laser (CLSM), la spectrométrie de masse avec désorption laser assistée par matrice- temps de vol (MALDI-TOF-MS), etc. Les essais appropriés ont été effectués pour valider la réussite de modification des microcapsules et pour confirmer à ce fait que la glucose oxydase est toujours active après chaque étape de modification. L’activité enzymatique spécifique de la glucose oxydase après l’encapsulation a été évaluée à 120±30 U/g. Aussi, des efforts ont été faits pour immobiliser la glucose oxydase sur des nanoparticules d’or avec deux tailles différentes de diamètre (10,9 nm et 50 nm) afin d’améliorer l’activité enzymatique et augmenter l’efficacité d’encapsulation. Les résultats obtenus lors de cette étude démontrent les modifications réussies sur les microcapsules d’alginate et aussi une réponse favorable de cette plate-forme antibactérienne concernant la désactivation de E. coli K-12. La concentration efficace de l’activité enzymatique afin de désactivation de cet agent pathogénique modèle a été déterminée à 1.3×10-2 U/ml pour une concentration de 6.7×108 cellules/ml de bactéries. D’autres études sont nécessaires pour évaluer l’efficacité de l’anticorps immobilisé dans la désactivation des agents pathogènes et également intégrer la plate-forme sur le papier et valider l’efficacité du système une fois qu’il est déposé sur papier.

Monitoring dendritic cells in clinical practice using a new whole blood single-platform TruCOUNT assay

Dendritic cells (DC) from distinct DC subsets are essential contributors to normal human immune responses. Despite this, reliable assays that enable DC to be counted precisely have been slow to evolve. We have now developed a new single-platform flow cytometric assay based on TruCOUN(TM) beads and the whole blood Lyse/No-Wash protocol that allows precise counting of the CD14(-) blood DC subsets: CD11c(+)CD16(-) DC, CD11c(+)CD16(+) DC, CD123(hi) DC, CD1c(+) DC and BDCA-3(+) DC. This assay requires 50 mul of whole blood; does not rely on a hematology blood analyser for the absolute DC counts; allows DC counting in EDTA samples 24 It after collection; and is suitable for cord blood and peripheral blood. The data is highly reproducible with intra-assay and inter-assay coefficients of variation less than 3% and 11%, respectively. This assay does not produce the DC-T lymphocyte conjugates that result in DC counting abnormalities in conventional gradient-density separation procedures. Using the TruCOUNT assay, we established that absolute blood DC counts reduce with age in healthy individuals. In preliminary studies, we found a significantly lower absolute blood CD11c(+)CD16(+) DC count in stage III/IV versus stage I/II breast carcinoma patients and a lower absolute blood CD123(hi) DC count in multiple myeloma patients, compared to age-matched controls. These data indicate that scientific progress in DC counting technology will lead to the global standardization of DC counting and allow clinically meaningful data to be obtained. (C) 2003 Elsevier B.V. All rights reserved.

Local liquid holdups and hysteresis in a 2-D packed bed using X-ray radiography

An X-ray visualization technique has been used for the quantitative determination of local liquid holdups distribution and liquid holdup hysteresis in a nonwetting two-dimensional (2-D) packed bed. A medical diagnostic X-ray unit has been used to image the local holdups in a 2-D cold model having a random packing of expanded polystyrene beads. An aqueous barium chloride solution was used as a fluid to achieve good contrast on X-ray images. To quantify the local liquid holdup, a simple calibration technique has been developed that can be used for most of the radiological methods such as gamma ray and neutron radiography. The global value of total liquid holdup, obtained by X-ray method, has been compared with two conventional methods: drainage and tracer response. The X-ray technique, after validation, has been used to visualize and quantify, the liquid hysteresis phenomena in a packed bed. The liquid flows in preferred paths or channels that carry droplets/rivulets of increasing size and number as the liquid flow rate is increased. When the flow is reduced, these paths are retained and the higher liquid holdup that persists in these regions leads to the holdup hysteresis effect. Holdup in some regions of the packed bed may be an order of magnitude higher than average at a particular flow rate. (c) 2005 American Institute of Chemical Engineers

Capillary break-up rheometry of low-viscosity elastic fluids

We investigate the dynamics of the capillary thinning and break-up process for low viscosity elastic fluids such as dilute polymer solutions. Standard measurements of the evolution of the midpoint diameter of the necking fluid filament are augmented by high speed digital video images of the break up dynamics. We show that the successful operation of a capillary thinning device is governed by three important time scales (which characterize the relative importance of inertial, viscous and elastic processes), and also by two important length scales (which specify the initial sample size and the total stretch imposed on the sample). By optimizing the ranges of these geometric parameters, we are able to measure characteristic time scales for tensile stress growth as small as 1 millisecond for a number of model dilute and semi-dilute solutions of polyethylene oxide (PEO) in water and glycerol. If the final aspect ratio of the sample is too small, or the total axial stretch is too great, measurements are limited, respectively, by inertial oscillations of the liquid bridge or by the development of the well-known beads-on-a-string morphology which disrupt the formation of a uniform necking filament. By considering the magnitudes of the natural time scales associated with viscous flow, elastic stress growth and inertial oscillations it is possible to construct an operability diagram characterizing successful operation of a capillary break-up extensional rheometer. For Newtonian fluids, viscosities greater than approximately 70 mPas are required; however for dilute solutions of high molecular weight polymer, the minimum Viscosity is substantially lower due to the additional elastic stresses arising from molecular extension. For PEO of molecular weight 2.10(6) g/mol, it is possible to measure relaxation times of order 1 ms in dilute polymer solutions with zero-shear-rate viscosities on the order of 2-10 mPas.

Modelling oxygen diffusion and cell growth in a porous, vascularising scaffold for soft tissue engineering applications

Soft tissue engineering presents significant challenges compared to other tissue engineering disciplines such as bone, cartilage or skin engineering. The very high cell density in most soft tissues, often combined with large implant dimensions, means that the supply of oxygen is a critical factor in the success or failure of a soft tissue scaffold. A model is presented for oxygen diffusion in a 15-60 mm diameter dome-shaped scaffold fed by a blood vessel loop at its base. This model incorporates simple models for vascular growth, cell migration and the effect of cell density on the effective oxygen diffusivity. The model shows that the dynamic, homogeneous cell seeding method often employed in small-scale applications is not applicable in the case of larger scale scaffolds such as these. Instead, we propose the implantation of a small biopsy of tissue close to a blood supply within the scaffold as a technique more likely to be successful. Crown Copyright (c) 2005 Published by Elsevier Ltd. All rights reserved.

Tailoring surface properties to build colloidal diagnostic devices: Controlling interparticle associations

The ability to control the surface properties and subsequent colloidal stability of dispersed particles has widespread applicability in many fields. Sub-micrometer fluorescent silica particles (reporters) can be used to actively encode the combinatorial synthesis of peptide libraries through interparticle association. To achieve these associations, the surface chemistry of the small fluorescent silica reporters is tailored to encourage robust adhesion to large silica microparticles onto which the peptides are synthesized. The interparticle association must withstand a harsh solvent environment multiple synthetic and washing procedures, and biological screening buffers. The encoded support beads were exposed to different solvents used for peptide synthesis, and different solutions used for biological screening including phosphate buffered saline (PBS), 2-[N-morpholino]ethane sulfonic acid (VIES) and a mixture of MES and N-(3-dimethyl-aminopropyl)-N'-ethylcarbodiimide (EDC). The number of reporters remaining adhered to the support bead was quantified after each step. The nature of the associations were explored and tested to optimize the efficiency of these phenomena. Results presented illustrate the influence of the surface functionality and polyelectrolyte modification of the reporters. These parameters were investigated through zeta potential and X-ray photoelectron spectroscopy.

The influence of nutrient supply and cell density on the growth and survival of intervertebral disc cells in 3D culture

The adult human intervertebral disc (IVD) is normally avascular. Changes to the extracellular matrix in degenerative disc disease may promote vascularisation and subsequently alter cell nutrition and disc homeostasis. This study examines the influence of cell density and the presence of glucose and serum on the proliferation and survival of IVD cells in 3D culture. Bovine nucleus pulposus (NP) cells were seeded at a range of cell densities (1.25 × 10(5)-10(6) cells/mL) and cultured in alginate beads under standard culture conditions (with 3.15 g/L glucose and 10 % serum), or without glucose and/or 20% serum. Cell proliferation, apoptosis and cell senescence were examined after 8 days in culture. Under standard culture conditions, NP cell proliferation and cluster formation was inversely related to cell seeding density, whilst the number of apoptotic cells and enucleated "ghost" cells was positively correlated to cell seeding density. Increasing serum levels from 10% to 20% was associated with increased cluster size and also an increased prevalence of apoptotic cells within clusters. Omitting glucose produced even larger clusters and also more apoptotic and senescent cells. These studies demonstrate that NP cell growth and survival are influenced both by cell density and the availability of serum or nutrients, such as glucose. The observation of clustered, senescent, apoptotic or "ghost" cells in vitro suggests that environmental factors may influence the formation of these phenotypes that have been previously reported in vivo. Hence this study has implications for both our understanding of degenerative disc disease and also cell-based therapy using cells cultured in vitro.

Polymer fractionation by continuous chromatography

A review is given of general chromatographic theory, the factors affecting the performance of chromatographi c columns, and aspects of scale-up of the chromatographic process. The theory of gel permeation chromatography (g. p. c.) is received, and the results of an experimental study to optimize the performance of an analytical g.p.c. system are reported. The design and construction of a novel sequential continuous chromatographic refining unit (SCCR3), for continuous liquid-liquid chromatography applications, is described. Counter-current operation is simulated by sequencing a system of inlet and outlet port functions around a connected series of fixed, 5.1 cm internal diameter x 70 cm long, glass columns. The number of columns may be varied, and, during this research, a series of either twenty or ten columns was used. Operation of the unit for continuous fractionation of a dextran polymer (M. W. - 30,000) by g.p.c. is reported using 200-400 µm diameter porous silica beads (Spherosil XOB07S) as packing, and distilled water for the mobile phase. The effects of feed concentration, feed flow rate, and mobile and stationary phase flow rates have been investigated, by means of both product, and on-column, concentrations and molecular weight distributions. The ability to operate the unit successfully at on-column concentrations as high as 20% w/v dextran has been demonstrated, and removal of both high and low molecular weight ends of a polymer feed distribution, to produce products meeting commercial specifications, has been achieved. Equivalent throughputs have been as high as 2.8 tonnes per annum for ten columns, based on continuous operation for 8000 hours per annum. A concentration dependence of the equilibrium distribution coefficient, KD observed during continuous fractionation studies, is related to evidence in the literature and experimental results obtained on a small-scale batch column. Theoretical treatments of the counter-current chromatographic process are outlined, and a preliminary computer simulation of the SCCR3 unit t is presented.

Intracellular protein determination using droplet-based immunoassays

This paper describes the implementation of a sensitive, on-chip immunoassay for the analysis of intracellular proteins, developed using microdroplet technology. The system offers a number of analytical functionalities, enabling the lysis of low cell numbers, as well as protein detection and quantification, integrated within a single process flow. Cells were introduced into the device in suspension and were electrically lysed in situ. The cell lysate was subsequently encapsulated together with antibody-functionalized beads into stable, water-in-oil droplets, which were stored on-chip. The binding of intracellular proteins to the beads was monitored fluorescently. By analyzing many individual droplets and quantifying the data obtained against standard additions, we measured the level of two intracellular proteins, namely, HRas-mCitrine, expressed within HEK-293 cells, and actin-EGFP, expressed within MCF-7 cells. We determined the concentrations of these proteins over 5 orders of magnitude, from ~50 pM to 1 µM. The results from this semiautomated method were compared to those for determinations made using Western blots, and were found not only to be faster, but required a smaller number of cells. © 2011 American Chemical Society.

Mechanisms of convective drying in thick beds of solids

The literature on heat and mass transfer mechanisms in the convective drying of thick beds of solids has been critically reviewed. Related mathematical models of heat transfer are also considered. Experimental and theoretical studies were made of the temperature distribution within beds, and of drying rates, with various materials undergoing convective drying. The experimental work covered thick beds of hygroscopic and non-hygroscopic materials (glass beads of different diameters, polystyrene pellets, activated alumina and wood powder) at air temperatures of 54°C to 84°C. Tests were carried out in a laboratory drying apparatus comprising a wind tunnel through which the air, of controlled temperature and humidity, was passed over a sample suspended from a balance. Thermocouples were inserted at different depths within the sample bed. The temperature distribution profiles for both hygroscopic and non-hygroscopic beds exhibited a clear difference between the temperatures at the surface and bottom during the constant rate period. An effective method was introduced for predicting the critical moisture content. During the falling rate the profiles showed the existence of a receding evaporation plane; this divided the system into a hotter dry zone in the upper section and a wet zone near the bottom. A graphical procedure was established to predict accurately the position of the receding evaporation front at any time. A new mathematical model, based on the receding evaporation front phenomenon, was proposed to predict temperature distributions throughout a bed during drying. Good agreement was obtained when the model was validated by comparing its predictions with experimental data. The model was also able to predict the duration of each drying stage. In experiments using sample trays of different diameters, the drying rate was found to increase with a decrease in the effective length of the bed surface. During the constant rate period with trays of a small effective length, i.e. less than 0.08 m, an 'inversion' in temperature distribution occurred in the bed; the bottom temperature increased and became greater than that of the surface. Experimental measurements were verified in several ways to ensure this phenomenon was real. Theoretical explanations are given for both the effective length and temperature inversion phenomena.

An Investigation of the destruction of ion exchange resins

Ion exchange resins are used for many purposes in various areas of science and commerce. One example is the use of cation exchange resins in the nuclear industry for the clean up of radioactively contaminated water (for example the removal of 137Cs). However, during removal of radionuclides, the resin itself becomes radioactively contaminated, and must be treated as Intermediate Level Waste. This radioactive contamination of the resin creates a disposal problem. Conventionally, there are two main avenues of disposal for industrial wastes, landfill burial or incineration. However, these are regarded as inappropriate for the disposal of the cation exchange resin involved in this project. Thus, a method involving the use of Fenton's Reagent (Hydrogen Peroxide/soluble Iron catalyst) to destroy the resin by wet oxidation has been developed. This process converts 95% of the solid resin to gaseous CO2, thus greatly reducing the volume of radioactive waste that has to be disposed of. However, hydrogen peroxide is an expensive reagent, and is a major component of the cost of any potential plant for the destruction of ion exchange resin. The aim of my project has been to discover a way of improving the efficiency of the destruction of the resin thus reducing the cost involved in the use of hydrogen peroxide. The work on this problem has been concentrated in two main areas:-1) Use of analytical techniques such as NMR and IR to follow the process of the hydrogen peroxide destruction of both resin beads and model systems such as water soluble calixarenes. 2) Use of various physical and chemical techniques in an attempt to improve the overall efficiency of hydrogen peroxide utilization. Examples of these techniques include UV irradiation, both with and without a photocatalyst, oxygen carrying molecules and various stirring regimes.