In some diseases it is preferable that the drugs used in their treatment are released in the colon. The colon is also suitable for systemic delivery of a variety of drugs. A variety of systems have been developed for the purpose of achieving colonic targeting. These approaches are either drug-specific (prodrugs) or formulation specific (coated or matrix preparations) and depends on the pH, transit time and pressure or bacteria in the colon. Different polymers, like chitosan, have been evaluated for their susceptibility to degradation by these bacterial enzymes. Chitosan is considered a good candidate for bacterial degradation and is widely available at low cost and has favourable biological properties. To investigate the influence of formulation factors on the properties of chitosan minitablets, it was necessary to ensure that the chitosan had satisfactory powder flow characteristics to ensure uniform compression in the tablet press and to prevent unacceptable variation in the tablet properties such as weight, thickness, disintegration and strength. Moisture content of the powder, particle size and the inclusion of glidants had an effect on the flowability and it could be improved from a composite flow index value of 32.7 to a value of 58.8. The compressibility of chitosan is very poor and different factors that might influence it, was investigated. Compression forces of between 15 and 20 bar resulted in tablets with acceptable physical characteristics. An increase in moisture content, using the powder fraction > 212 ym as well as a decrease in powder weight resulted in tablets with a higher tensile strength. Lower compression forces resulted in tablets that are extremely porous. This suggests that the chitosan can only be compressed at high compression forces which are difficult to obtain using a standard tablet press. The standard tablet press was therefore modified to fill more powder in the die and generate higher compression forces. Minitablets were compressed and the dissolution of isoniazide from these tablets was investigated. Varying the punch depth or the compaction of the powder did not result in the desired slower release of the drug as a result. The porosity of the tablets compressed at all the punch depth settings and compaction percentages was probably too high to have an effect on the wettablity of the tablets and as a result on the dissolution of the isoniazide from the tablets. The inclusion of excipients such as citric acid (an organic acid which would lower the pH in the tablet, allowing the chitosan to form a gel) and pectin (which would form an insoluble complex with the chitosan) into the formulation delayed the dissolution of the isoniazide from the minitablets. Coating of the minitablets with an enteric coating (Eudragit S ®) initially delayed the dissolution of the isoniazide and would protect the tablets from the harsh environment of the stomach so that the tablets will reach the colon and release the drug. / Thesis (Ph.D. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007

Effects of short-term overtemperature on Rene 80 DS were studied using Gleeble thermo-mechanical simulation apparatus. Volume fraction of gamma prime to gamma matrix was quantified and used to assess the effects of time, temperature and stress. Volume fraction was found to decrease with increasing temperature and time. Dissolution was found to occur through both solid and liquid state dissolution. Application of tensile stress was found to influence dissolution behaviour of gamma prime. / May 2017

Submitted in fulfillment of the requirements for the degree of Doctor of Technology: Chemistry, Durban University of Technology, Durban, South Africa, 2015. / This thesis forms part of the Council for Scientific and Industrial Research, Forestry and Forest Products Research Centre (CSIR-FFP) biorefinery project which aims at developing and implementing novel industrial processes production of cellulose textile fibres. The focus of this study is to investigate the dissolution of South African Eucalyptus raw (unbleached) and final (bleached) dissolving pulp and saw dust wood in an ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [Emim][OAc] and the co-solvents [dimethylsulfoxide (DMSO)] or [dimethylformamide (DMF)] mixtures, to obtain regenerated cellulose by the further addition of water and acetone. The IL/co-solvent mixtures were able to dissolve the raw and final pulp samples at 120 ˚C for 6 hours whereas the sawdust wood dissolved in 10 hours. The IL/DMF mixture gave higher cellulose recoveries of 41.88 % for the raw pulp, 49.89 % for the final pulp sample and 32.50 % for sawdust wood while the IL/DMSO mixture gave a recovery of 15.25 % for the raw pulp sample, 36.25 % for the final pulp sample and 17.83 % for the sawdust wood sample. The regenerated cellulose materials were characterized by Fourier Transformer Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Thermo gravimetric Analysis (TGA) and Powder X-Ray Diffraction (pXRD), and compared with a standard microcrystalline of cellulose. It was observed that the FTIR and NMR spectra of the regenerated cellulose and MCC were similar which then indicates that no chemical reaction occurred during the dissolution and regeneration process of cellulose. SEM and X-ray diffraction (XRD) patterns of the results showed that after dissolution the cellulose I (native form), the crystalline structure was completely converted into cellulose II (amorphous) structure, and this was due to the removal of lignin and decrease in cellulose crystallinity. TGA results showed that the regenerated cellulose samples have higher char yields compared to the MCC which is due to the IL remaining in the regenerated cellulose. It was also observed that the addition of the co-solvents decreased the viscosity of the IL mixture, facilitating dissolution of the cellulose that led to additional swelling and reduction of the recalcitrant nature of the cellulose crystalline structure and intermolecular interactions. This led to increased accessibility and dissolution of the cellulose. The findings in this study have the potential to bring ILs closer to applications for biomass technology in particular for an economically viable dissolution method for biomass because ILs have a benefit of being easily separated from the anti-solvent, which provides a simple solution for IL recycle ability and re-use. The novel aspect of this study is: . This is the first study in the South African context to examine the influence of the lignin on the dissolution and regeneration of Eucalyptus sawdust wood and dissolving pulp. / D

The separation of oxidation-reduction reactions into individual half-cells with a resulting "mixed potential" is well known as a dissolution mechanism for metals; however, the mechanism by which non-conducting crystals lose ions to the solution has been studied only slightly.

O ibuprofeno é um anti-inflamatório não-esteroidal (AINE) que possui propriedades analgésicas e anti-térmicas e é empregado na terapêutica em casos dores discretas e moderadas, artrite reumatóide, osteoartrite e dismenorréia primária, nas concentrações de 200, 300, 400 e 600 mg. Entretanto, a formulação contendo 200 mg não está disponível no mercado farmacêutico brasileiro. No presente trabalho, foi desenvolvida uma formulação de comprimidos de ibuprofeno 200 mg que apresentou, além de outras características físico-químicas adequadas, um ótimo perfil de dissolução. Foram testadas oito formulações, obtidas a partir de um projeto fatorial fracionado, avaliando-se diversos excipientes. Além disto, as formulações foram submetidas à temperatura ambiente, 37 ºC e 50 ºC, e analisadas à 30 e 60 dias, com o objetivo de avaliar as transformações físicas que podem ocorrer durante o armazenamento das mesmas. Os resultados das análises físico-químicas foram tratados estatisticamente, utilizando-se o programa STATGRAFCS, através de uma análise exploratória e de um estudo de efeitos. Concluiu-se, então, que a melhor formulação foi a seguinte: IBUPROFENO - 200; AMIDO - 47; LACTOSE - 72; CELULOSE MICROCRISTALINA - 23; ESTEARATO DE MAGNESIO - 8. / Ibuprofen is a non steroidal antiinflamatory drug (NSAD), that has analgesic and antipyretic properties. It is used in terapeutic cases of mild to moderant pain, rheumatoid arthritis, osteoarthritis, and primary dysmenorrhea, in the 200, 300, 400, and 600 mg of concentration. In the Brazilian pharmaceutical market the formulation of 200 mg doesn\'t exist. In this study, a formulation of ibuprofen was developed for 200 mg tablets, that has suitable physical-chemical properties and an excellent dissolution profile. The eight formulations tested were obtained from factorial designs, evaluating several excipients. These formulations also had been submitted at room temperature, 37 ºC, and 50 ºC and were analised at 30 and 60 days, with the objective to evaluate the physical transformatiom that could have occurred during that time. The results were tested statistically by the STATGRAFCS program, using the exploratory analysis and the effects study. The final results showed that the best formulation was: IBUPROFEN - 200; STARCH - 47; LACTOSE - 72; MICROCRYSTALLINE CELLULOSE - 23; MAGNESIUM STEARATE - 8.

Controlled hydrogel dissolution allows for: 1) atraumatic material removal after it served its function, 2) site-specific delivery of encapsulated therapeutics (e.g., proteins, small molecules), and 3) a tailored administration of an agent with high efficiency. Dissolution of covalently crosslinked hydrogels has been accomplished by incorporating cleavable moieties that undergo ester hydrolysis or enzymatic degradation. Recently, thiol-disulfide exchange, retro Michal-type reactions, retro Diels-Alder reactions, and thiol-thioester exchange chemistries have gained attention, as they provide a responsive synthetic handle for engineering hydrogel dissolution rates. We synthesized, characterized and tested in vivo two on-demand dissolvable dendritic thioester hydrogel dressings for second-degree burn care and hemorrhage control. The hydrogels are composed of lysine-based dendrons and PEG-based crosslinkers, which were prepared in high yields. In context of hemorrhage, there is an unmet clinical need for an on-demand dissolvable sealant for non-compressible hemorrhage or areas of body not amenable to treatment with a torniquet. In a model of in vivo hemorrhage control of intra-abdominal wounds, our hydrogel reduced blood loss by 33% in severe hepatic hemorrhage and by 22% in aortic injury, as compared to untreated controls. There is an unmet clinical need for a second-degree burn dressing that can be removed atraumatically and serve as a barrier to bacterial infection. When our hydrogel was used as a dressing, local and systemic bacterial proliferation after wound contamination was significantly lower than in the untreated group. The total bacterial burden of the burn wound in the positive controls was significantly higher than in the hydrogel group and the negative controls (1.39x10E8 ± 8.30x10E7 CFU/g v. 4.04x10E3 ± 3.99x10E3 CFU/g v. 6.88x10E2 ± 6.38x10E2 respectively; P = 0.009). Also, the total systemic bacterial burden in the positive controls was significantly higher than the hydrogel group and the negative controls (9x10E2 ± 7.76x10E7 CFU/g v. 5x10E1 ± 0 CFU/g v. 5x10E1 ± 0 CFU/g, respectively; P = 0.031). A unique feature of both hydrogel systems is their capability to be dissolved on-demand via thiol-thioester exchange reaction with a biocompatible solution following its initial application – thus the wound area can be re-exposed to allow for definitive surgical care.

O ibuprofeno é um anti-inflamatório não-esteroidal (AINE) que possui propriedades analgésicas e anti-térmicas e é empregado na terapêutica em casos dores discretas e moderadas, artrite reumatóide, osteoartrite e dismenorréia primária, nas concentrações de 200, 300, 400 e 600 mg. Entretanto, a formulação contendo 200 mg não está disponível no mercado farmacêutico brasileiro. No presente trabalho, foi desenvolvida uma formulação de comprimidos de ibuprofeno 200 mg que apresentou, além de outras características físico-químicas adequadas, um ótimo perfil de dissolução. Foram testadas oito formulações, obtidas a partir de um projeto fatorial fracionado, avaliando-se diversos excipientes. Além disto, as formulações foram submetidas à temperatura ambiente, 37 ºC e 50 ºC, e analisadas à 30 e 60 dias, com o objetivo de avaliar as transformações físicas que podem ocorrer durante o armazenamento das mesmas. Os resultados das análises físico-químicas foram tratados estatisticamente, utilizando-se o programa STATGRAFCS, através de uma análise exploratória e de um estudo de efeitos. Concluiu-se, então, que a melhor formulação foi a seguinte: IBUPROFENO - 200; AMIDO - 47; LACTOSE - 72; CELULOSE MICROCRISTALINA - 23; ESTEARATO DE MAGNESIO - 8. / Ibuprofen is a non steroidal antiinflamatory drug (NSAD), that has analgesic and antipyretic properties. It is used in terapeutic cases of mild to moderant pain, rheumatoid arthritis, osteoarthritis, and primary dysmenorrhea, in the 200, 300, 400, and 600 mg of concentration. In the Brazilian pharmaceutical market the formulation of 200 mg doesn\'t exist. In this study, a formulation of ibuprofen was developed for 200 mg tablets, that has suitable physical-chemical properties and an excellent dissolution profile. The eight formulations tested were obtained from factorial designs, evaluating several excipients. These formulations also had been submitted at room temperature, 37 ºC, and 50 ºC and were analised at 30 and 60 days, with the objective to evaluate the physical transformatiom that could have occurred during that time. The results were tested statistically by the STATGRAFCS program, using the exploratory analysis and the effects study. The final results showed that the best formulation was: IBUPROFEN - 200; STARCH - 47; LACTOSE - 72; MICROCRYSTALLINE CELLULOSE - 23; MAGNESIUM STEARATE - 8.

Thesis (Ph.D. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007

The microstructures and performance of Ni-based alloys and Ni-WC (nickel-tungsten carbide) composite overlays deposited by plasma transferred arc welding have been studied. The Ni-alloy overlays had similar microstructures consisting of Ni dendrites, with interdendritic Ni-based eutectics, borides and carbides. Low hardness alloy overlays contained a smaller fraction of interdendritic phases relative to the high hardness alloys. The interdendritic regions make a significant contribution to the hardness since they are more than twice as hard as primary dendrites. The Ni-WC composites contained similar phases, however WC dissolution was observed leading to the formation of other carbides. Ni-alloys with low carbon and Cr content exhibited the lowest WC dissolution. The Ni-WC overlays produced using these dilute alloys generally performed better in ASTM G65 wear tests. This was likely due to the reduced dissolution which avoided formation of brittle secondary phases, maintaining a short mean free path between WC particles and allowing increased impact energy absorption. / Materials Engineering

Ph.D. / Environmental Science and Engineering / Chromate-containing precipitates can affect the mobility of toxic Cr(VI) in the subsurface, control its concentration in groundwater, limit its bioavailability, and impede remediation of chromium contaminated sites. This dissertation focuses on two iron-chromate precipitates, KFe [subscript 3](CrO4)[subscript 2](OH)[subscript 6] (the chromate analog of the sulfate mineral jarosite) and KFe(CrO4)[subscript 2].2H2O, that we identified in a soil contaminated by chrome plating solutions. The precipitates were identified using scanning and transmission electron microscopy, as well as powder x-ray diffraction. KFe[subscript 3](CrO4)[subscript 2](OH)[subscript 6] occurs as small (2-5 um) crystals interspersed within the bulk soil. KFe(CrO4)[subscript 2].2H2O forms crusts of larger crystals (10-50 um) in cracks and fractures of the soil. / Due to highly mathematical nature of the abstract, only the first paragraph is shown.