Thesis (Ph. D.)--University of Hong Kong, 1968. / Typewritten.

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Thesis (MTech. degree in Pharmaceutical Sciences.)--Tshwane University of Technology, 2010. / Aims to determine the biochemical and histological parameter of bone formed heterotopically in the rodent bioassay osteoinduction model, of enzymatically and chemically treated xenogeneic insoluble collagenous bone matrix (ICBM) loaded with porcine BMP complex, purified according to a proprietary high yield purification procedure.

Cellulose is an attractive raw material that has lately become more interesting thanks to its degradability and renewability and the environmental awareness of our society. With the intention to find new material properties and applications, studies on cellulose derivatization have increased. Dialdehyde cellulose (DAC) is a derivative that is produced by selective cleavage of the C2-C3 bond in an anhydroglucose unit in the cellulose chain, utilizing sodium periodate (NaIO4) that works as a strong oxidant. At a fixed temperature, the reaction time as well as the amount of added periodate affect the resulting aldehyde content. DAC has shown to have promising properties, and by disintegrating the dialdehyde fibers into fibrils, thin films with extraordinary oxygen barrier at high humidity can be achieved. Normally, barrier properties of polysccharide films deteriorate at higher humidity due to their hygroscopic character. This DAC barrier could therefore be a potential environmentally-friendly replacement for aluminum which is utilized in many food packages today. The aim of this study was to investigate the possibilities to produce dialdehyde cellulose at an industrial level, where the regeneration of consumed periodate plays a significant role to obtain a feasible process. A screening of the periodate oxidation of cellulose containing seven experiments was conducted by employing the program MODDE for experimental design. The reaction time was varied between 2-8 hours and the ratio NaIO4 to fiber in was between 1-2 (w/w) for small-scale experiments (1 g fiber), which resulted in an aldehyde content between 14-80 %. An oxidation degree around 30 % was set as a goal, and the optimal point at a fixed temperature of 50°C was assessed to be a ratio of 1.5 and a reaction time of 2.5 h, including 30 min of cooling. Furthermore, the MODDE evaluation suggested that the time and quantity of added periodate equally effected the reaction. An up-scaling of the system with 22.5 g of NaIO4 and 15 g of cellulose fibers and a total reaction time of 3h, resulted in 39 % oxidation degree and a yield of 92 %. For the regeneration of periodate, Oxone® was tested, but too low yields were obtained. More studies are needed in order to understand and optimize this process. Better results where gained when utilizing a 10 % hypochlorite solution (NaOCl) that was refluxed with the filtrate from the periodate oxidation of cellulose. A spectrophotometric method was developed to be able to quantify the amount of periodate and thereby the amount of residual iodate (IO3-), i.e. the byproduct to oxidize back to IO4-. An optimization study was performed with eleven experiments with the time varying between 1-4 hours and the molar ratio of NaOCl to IO3- between 1-4. However, it was found that the residual periodate also consumed the hypochlorite, so the real molar ratio of NaOCl to IO3- and IO4- was only 0.38-1.52. The highest ratio of 1.52 with a reaction time of 4 h generated the highest regeneration of 81 %. From the MODDE evaluation it was suggested that the reaction time does not have as significant effect upon the process as the amount of added NaOCl has. By optimizing this reaction further, it should be possible to reach even more satisfying results. However, it was proved that the precipitated product was sodium paraperiodate, Na3H2IO6, and this regenerated product was successfully used to oxidize cellulose fibers to DAC. Surprisingly, the oxidation degree became much higher, 43 %, despite that the same condition was employed as before, but the reason for this can be the lower pH that was utilized. Even though there still are questions to be answered, this study has contributed to knowledge that could be utilized to take the oxidation process closer to industrialization. / Cellulosa är en attraktiv råvara som blivit alltmer intressant tack vare dess nedbrytbarhet och förnybarhet samt samhällets miljömedvetenhet. Med avsikt att hitta nya materialegenskaper och applikationer har studier på derivatiseringen av cellulosa ökat. Dialdehydcellulosa (DAC) är ett derivat som framställs genom selektiv klyvning av C2-C3-bindningen i en vattenfri glukosenhet i cellulosakedjan där natriumperjodat (NaIO4) fungerar som ett starkt oxidationsmedel. Vid en konstant temperatur påverkar reaktionstiden liksom mängden tillsatt perjodat det resulterande aldehydinnehållet. DAC har visat sig ha lovande egenskaper och genom att lösa upp dialdehydfibrerna till fibriller kan tunna filmer med en utomordentlig syrebarriär vid hög fuktighet erhållas. Normalt sett blir den fina barriären gjord av polysackaridfilmer försämrad vid högre luftfuktighet på grund av den hygroskopiska karaktären. Denna DAC barriär kan därför vara en potentiell och miljövänlig ersättare till det aluminium som används i många livsmedelsförpackningar idag. Syftet med denna studie var att undersöka möjligheterna att kunna producera dialdehydcellulosa på en industriell nivå, där regenerering av förbrukad perjodat spelar en viktig roll för att erhålla en genomförbar process. En screening av perjodatoxidering av cellulosa innehållande sju experiment utfördes genom att använda programmet MODDE för experimentell design. Reaktionstiden varierade mellan 2-8 timmar och förhållandet NaIO4 till fibrer i gram mellan 1-2 för småskaliga experiment (1 g fiber), vilket resulterade i en aldehydhalt mellan 14-80 %. En oxidationsgrad omkring 30 % sattes som ett mål och den optimala punkten vid en konstant temperatur av 50° C bedömdes vara ett förhållande på 1,5 och en reaktionstid om 2,5 timmar inklusive 30 min avsvalning. Vidare föreslog MODDE-utvärderingen att tiden och mängden tillsatt perjodat påverkade reaktionen likvärdigt. En uppskalning av systemet med 22,5 g NaIO4 och 15 g cellulosafibrer och en total reaktionstid om 3 timmar resulterade i en oxidationsgrad på 39 % och ett utbyte på 92 %. För att återgenerera perjodat testades Oxone® men alltför låga utbyten erhölls. Fler studier behövs för att förstå och optimera denna process. Bättre resultat erhölls när en 10 % hypokloritlösning (NaOCl) användes, vilken återloppskokades med filtratet från perjodatoxideringen av cellulosa. En spektrofotometrisk metod utvecklades för att kunna kvantifiera mängden perjodat och därmed mängden kvarvarande jodat (IO3-), dvs. biprodukten att oxidera tillbaka till IO4-. En optimeringsstudie utfördes med elva experiment där tiden varierade mellan 1-4 timmar och det molära förhållandet av NaOCl till IO3- mellan 1-4. Efter detta visade det sig att den kvarvarande perjodaten också konsumerade hypoklorit, så det verkliga molförhållandet mellan NaOCl till IO3- och IO4- var endast 0,38-1,52. Det högsta förhållandet 1,52 med en reaktionstid om 4 timmar genererade den högsta återgenereringen på 81 %. Från MODDE-utvärderingen föreslogs att reaktionstiden inte har lika stor inverkan på processen som mängden tillsatt NaOCl har. Genom att optimera denna reaktion ytterligare bör det vara möjligt att nå än mer tillfredsställande resultat. Hur som helst bevisades det att den utfällda produkten var natriumparaperjodat, Na3H2IO6 och denna regenererade produkt användes framgångsrikt för att oxidera cellulosafibrer till DAC. Överraskande nog blev oxidationsgraden mycket högre, 43 %, trots applicering av samma betingelser som tidigare, men orsaken till detta kan vara att ett lägre pH användes. Även om det fortfarande finns frågor kvar att besvara så har denna studie bidragit till kunskap som kan användas för att ta denna oxidationsprocess närmre industrialisering.

The perpetuation of the reigning dominants in climax woodland, and the maintenance of species diversity, are discussed by reference to published work: the importance of the regeneration gap is outlined, and seed production and seedling mortality are investigated as being key factors in the establishment of young trees. Beech masting has been studied by an eight-season record of seed production by individual trees in many places, developing a unique series of objective records for England. There appears to be a basic biennial masting pattern, with a requirement for suitable climatic conditions and the proximity of other beech trees for effective cross-pollination. The effects of defoliation upon the growth of young oaks has been investigated by a controlled experiment on 196 saplings in a plot in Wolverhampton. This has contributed data on a larger population for a longer period than has previously been published. The responses of the trees to light defoliation were not marked but, as the level of defoliation increased, greater numbers of growth zones, more leaves and smaller leaves became apparent, together with impaired relative growth rates and abnormal wood structure. Ramets of cloned oak have been established in a unique outdoor plot. Their synchronous phenology permitted further analysis of defoliation responses, including field measurements of photosynthetic rates. Tree shelter tubes were shown to promote earlier second flushes and to lessen fluctuations in temperature and maintain high humidity. Observations have been made in woodlands, especially in the West Midlands where surveys have established that natural regeneration is taking place, at least in the gaps created by fallen trees. The possibility of encouraging natural regeneration of trees and ground flora on land set aside from agriculture is considered. A synthesis is made of the topics investigated, discussing the origin of the intermittent nature of the phenomena of growth spurts and masting.

published_or_final_version / Dentistry / Master / Master of Orthodontics

No description available.

When routine repair mechanisms fail to regenerate severe burn wounds, mesenchymal stem cell therapy is considered. However, engrafted mesenchymal stem cells are prone to become myofibroblasts when exposed to high mechanical tension and pro-fibrotic cytokines in the wound microenvironment. Myofibroblast activity increases wound stiffness and activates healthy precursor cells into destructive phenotype, resulting in pathological remodelling and hypertrophic scarring. Using soft silicone substrates with near-physiological stiffness, I tested the hypothesis that myofibroblast characteristics acquired by mesenchymal stem cells in cell culture are preserved by microRNA modifications typical for fibrosis and demonstrated that priming mesenchymal stem cells on soft substrates protect them from subsequent activation and that the mechanically propagated myofibroblast memory is mediated by miR-21. This study aims to demonstrate that suppressing myofibroblast activation will maximize and prolong the beneficial regenerative effects of mesenchymal stem cells while terminating harmful and excessive tissue remodelling characteristic for fibrosis upon engraftment.

When routine repair mechanisms fail to regenerate severe burn wounds, mesenchymal stem cell therapy is considered. However, engrafted mesenchymal stem cells are prone to become myofibroblasts when exposed to high mechanical tension and pro-fibrotic cytokines in the wound microenvironment. Myofibroblast activity increases wound stiffness and activates healthy precursor cells into destructive phenotype, resulting in pathological remodelling and hypertrophic scarring. Using soft silicone substrates with near-physiological stiffness, I tested the hypothesis that myofibroblast characteristics acquired by mesenchymal stem cells in cell culture are preserved by microRNA modifications typical for fibrosis and demonstrated that priming mesenchymal stem cells on soft substrates protect them from subsequent activation and that the mechanically propagated myofibroblast memory is mediated by miR-21. This study aims to demonstrate that suppressing myofibroblast activation will maximize and prolong the beneficial regenerative effects of mesenchymal stem cells while terminating harmful and excessive tissue remodelling characteristic for fibrosis upon engraftment.