Philosophiae Doctor - PhD / The fluoride release and chemical adherence to tooth structure remain the most desirable features of glass ionomer restorative cements (GICs). Although the physical properties for multi-surface restorations are well-defined, even with the introduction of newer GICs not all demands have been met. Yet, increased use of GICs will only be possible if clinicians change their perceptions of the low survival rate of GICs. The lower clinical success rate of GICs is partly due to the marginal integrity and wear over time, which has often been recorded in the literature as restoration failure. The current, well-established restorative options for the primary dentition are Resin Modified Glass Ionomers (RMGICs) and Compomer resins. There is a paradigm shift towards materials that are more biologically favourable. Areas of research for dental materials include antibacterial properties in conjunction with ion release to maintain healthy restored teeth. If a GIC can provide adequate physical properties with the inclusion of the aforementioned features, GICs might become a more viable permanent restorative solution.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis submitted in partial fulfilment for the degree of Master of Science (polymer science) at Stellenbosch University / ENGLISH ABSTRACT: The goal of this study was to synthesize hybrid hydrogels via a chemical crosslinking mechanism through use of chain end functional poly(N-vinyl pyrrolidone)(PVP) with various topologies. The crosslinking chemistries should be benign in nature i.e. at physiological pH ranges and at 37 °C. The degradation products should be biologically tolerable and renal clearance should be possible (< 30 000 g/mol PVP0. PVP of various topologies, controlled molar mass and quantitative chain end functionality was obtained via Reversible Addition Fragmentation chain Transfer (RAFT) mediated polymerization (PDI = 1.1- 1.4). The synthesized polymers were chain end functionalized to introduce thiol or aldehyde moieties. Thiol chain ends were obtained through post polymerization modification of xanthate functional PVP with either aminolysis or reduction. The aldehyde moiety was obtained by post polymerization modification of xanthate end functional PVP with sequential hydrolysis and thermolysis. Thiol functional four arm star PVP was reacted with acrylate difunctional poly(ethylene glycol) (DIAC PEG) crosslinker under standard Michael addition conditions. In order to obtain thioether crosslinked hydrogels from tetra functional star PVP molecules it was found that a minimum thiol functionalization of 30% and a molar ratio of acrylate:thiol of 1:1.1 is required. The Schiff base reaction was used to synthesize imine or secondary amine (after reduction) crosslinks with the lysine residues on either lysozyme or bovine serum albumin (BSA) or the primary amines of bis-(2-amino ethyl)amine). Hydrogels were obtained from aldehyde functionalized PVP molecules with a fraction of functional aldehyde chain ends of 0.88 for difunctional molecules and 0.50 for tetra functional star PVP molecules with lysozyme or BSA crosslinkers. The reaction rate was favoured by lowered pH (<6.0) and an optimum molar ratio of amine : aldehyde of 1:0.8. Hydrogels were analyzed by equilibrium swelling calculations to determine the molar mass between crosslinks and the estimated pore size. In both crosslinking systems the properties of the formed hydrogels were seen to be affected by molar ratio used and by the topology of the crosslinking agent. PVP BSA and PVP PEG hydrogels were tested for 24 h and 48 h cell viability by using H9C2 myoblast cells. A concentration range of 0.25 x 10(2) to 0.01 g/mL was studied. Cell mortality was tested by Trypan blue staining and results were verified with MTT assay. A very low cell death precentage (<37%)was observed. Cells even appeared to experience a stimulatory effect after 48 h of exposure at low concentrations of PVP PEG hydrogel treatments. The properties of the formed hydrogel could be tuned by the molar mass ratios of PVP and crosslinker. The functionality of the crosslinker directly affects the molar mass between crosslinks and thus indirectly the degradation profile. It was concluded that PVP molecules with various topologies, well-defined molar masses and chain end functionality could be obtained via RAFT mediated polymerization. Obtained polymers were successfully modified and crosslinked to obtain hydrogels with stoichiometrically tuneable properties i.e. initial swelling ratio, degradation time, molar mass between crosslinks. The hydrogels had very positive cell viability results that would definitely justify further research into these materials as “tissue-mimetic” materials. / AFRIKAANSE OPSOMMING: Die doel van die studie is om poli(N-viniel pirollidoon) (PVP) gebaseerde hibried hidrogelle te sintetiseer deur middel van kovalente kruisbindings met toepaslike kruisverbinder molekules. Die chemiese reaksies betrokke in die vorming van hierdie kovalente kruisbindings moet gematig van aard wees, by fisiologiese pH en by 37 °C plaasvind. Die degradasieprodukte van die hibried-hidrogel moet biologies verdraagsaam en ook uitskeibaar deur die endokrinologiese sisteem wees. PVP van verskillende topologieë, beheerde molêre massa en kwantitatiewe kettingendfunksionaliteit is berei deur ‘n omkeerbare addisie-fragmentasiekettingoordrag (OAFO)-beheerde polimerisasieproses (PDI = 1.1-1.4). Xantaat-kettingend-PVP is aangepas na thiol of aldehied kettingendfunksies. Thiolendfunksies is verkry deur middel van ‘n aminolisasie-reaksie. Xantaat kettingend-PVP is stapsgewys gemodifiseer deur hidroliese en verhittingstappe om die aldehied ketting-endfunksionaliteit te bekom. Thiol ketting-endfunksionele vier-armige ster-PVP is kovalent gebind aan difunksionele poly(etileen glikol) deur middel van die Michael-addisiereaksie. PVP PEG hidrogelle het slegs gevorm met vier-armige ster-PVP molekules wat oor ‘n minimum van 30 % thiol-funksionaliteit beskik het en ‘n optimale molêre massa verhouding van 1:1.1 vir ankrilaat to thiol. Die Schiff-basisreaksie is gebruik om hidrogel te sintetiseer wat met imiene of amiene (na redusering) kovalente bindings gekruisbind is. In hierdie sisteme het hidrogel slegs gevorm as die aldehied-PVP molekules oor ‘n fraksie funksionele kettingend-waarde van 0.88 vir dialdehied-PVP molekules en 0.5 vir vier armige ster-PVP molekules beskik het. Die reaksie snelheid van die Schiff-basis kovalente bindings is bevoordeel deur die pH te verlaag (≤ 6.0) en ‘n gunstige molêre massa verhouding van 1:0.8 vir die nukleofiel teen oor die akseptor molekule is waargeneem. Ewewigswel berekeninge is gebruik om die molêre massa tussen kruisbindings en die gemiddelde benaderde porieë binne die drie-dimensionele interne struktuur van die hydrogel te bepaal. Die seltoksisiteit van PVP-BSA en PVP-PEG hidrogelle is oor 24 h en 48 h in die teenwoordigheid van H9c2 mioblast-selle getoets. Die hydrogel behandelings is uitgevoer in ‘n konsentrasie reeks van 0.25 x 10(2) tot 0.01 g/mL. Selmortaliteit is getoets deur ‘n Trypan-blou verkleuringstudie. Hierdie resultate is ondersteun deur MTT sel-lewensvatbaarheidstoetse. ‘n Lae selmortaliteit (≤ 37 %) is waargeneem en, opspraakwekkend, het van die selle na 48 h verhoogde vitaliteit getoon in die teenwoordigheid van lae konsentrasies PVP-PEG hidrogelle. Dit is bevind dat hidrogel eienskappe deur stoichiometriese molêre massa verhoudings asook die keuse in die topologie van kruisverbinder beïnvloed word. Hierdie eienskappe het ‘n direkte effek op die degradasieprofiel van die gevormde hidrogel. Samevattend dus is PVP molekules met ‘n variasie van topologieë, spesifieke molêre massas en kettingfunksionalitete deur middel van OAFO-gemedieerde polimerisasies gesintetiseer. Xantaatkettingendfunksionele PVP-molekules kon suksesvol omgeskakel word na die kettingendfunksionaliteit van ons keuse om ‘n hibriedhidrogel met stoichiometries-manupileerbare eienskappe te sintetiseer. Die positiewe sel-lewensvatbaarbheidstudie resultate staaf verdere ondersoeke in hierdie PVPgebaseerde hibried hidrogelmateriaal as ‘n weefsel nabootsingsmateriaal.

Cannabinoids (CBs) are compounds that activate the CB1 and CB2 receptors. CB receptors mediate many different physiological functions, and cannabinoids have been reported to decrease tumor cell viability, proliferation, migration, as well as to modulate metastasis. In this thesis, the effects of cannabinoids on human colorectal carcinoma Caco-2 cells (Paper I) and mouse P19 embryonal carcinoma (EC) cells (Paper III) were studied.  In both cell lines, the compounds examined produced a concentration- and time-dependent decrease in cell viability. In Caco-2-cells, HU 210 and the pyrimidine antagonist 5-fluorouracil produced synergistic effects upon cell viability. The mechanisms behind the cytocidal effects of cannabinoids appear to be mediated by other than solely the CB receptor, and a common mechanism in Caco-2 and P19 EC cells was oxidative stress. However, in P19 EC cells the CB receptors contribute to the cytocidal effects possibly via ceramide production. In paper II, the association between CB1 receptor immunoreactivity (CB1IR) and different histopathological variables and disease-specific survival of colorectal cancer (CRC) was investigated. In microsatellite stable (MSS) cases there was a significant positive association of the tumor grade with the CB1IR intensity. A high CB1IR is indicative of a poorer prognosis in MSS with stage II CRC patients. Paper IV focused on the cytotoxic effects of cannabinoids during neuronal differentiation. HU 210 affected the cell viability, neurite formation and produced a decreased intracellular AChE activity. The effects of cannabinoids on embryonic development and survival were examined in Paper V, by repeated injection of cannabinoids in fertilized chicken eggs. After 10 days of incubation, HU 210 and cannabidiol (without CB receptor affinity), decreased the viability of chick embryos, in a manner that could be blocked by α-tocopherol (antioxidant) and attenuated by AM251 (CB1 receptor antagonist). In conclusion, based on these studies, the cannabinoid system may provide a new target for the development of drugs to treat cancer such as CRC. However, the CBs also produce seemingly unspecific cytotoxic effects, and may have negative effects on the neuronal differentiation process. This may be responsible for, at least some of, the embryotoxic effects found in ovo, but also for the cognitive and neurotoxic effects of cannabinoids in the developing and adult nervous system.

Fruits and vegetables are known to play an important role in human health due to the range of phytochemicals they contain. Twenty-one peach genotypes and 45 plum genotypes with different flesh and skin color were analyzed for their antioxidant content and antioxidant activity. Anthocyanin content, phenolic content and antioxidant activity were higher in red-flesh than in light-colored flesh peaches. Carotenoid content was higher in yellow-flesh peaches. Among the peaches, the antioxidant activity was well correlated with phenolic content. The anthocyanin content among the plums increased with the red color intensity. Red-flesh plums generally had higher phenolic content than the other plums. Antioxidant activity was higher in red-flesh genotypes; however, it was strongly correlated only with the phenolic content in light-colored flesh plums. Extracts from selected genotypes of peaches and plums and their fractions were evaluated against two breast cancer cell lines (MDA-MB-435 and MCF-7) and one non-cancerous breast line (MCF-10A). The cells were cultured in the presence of peach and plum extracts and their fractions at various concentrations (0-500 µg/ml) and the cell viability and antiproliferation activity was evaluated by MTT assay and Coulter Counter. There was a dose-dependent reduction on cell viability of estrogen-negative MDA-MB-435 breast cancer cells. Only weak activity against MCF-7 was observed at high extract concentrations. There was no activity against MCF-10A after 24 h treatment. Fraction I, which consists of mainly phenolic acids such as chlorogenic acid and a caffeic acid derivative, reduces MDA-MB-435 breast cancer cell viability with the lowest IC50. The second most effective fraction was Fraction II which contained anthocyanins. Fraction III (flavonols) and Fraction IV (polymerized compounds) had no effect on the cell lines. Phenolic acids present in fraction I induced apoptosis in MDA-MB-435 estrogen receptor-negative cell line. Fraction I did not induced apoptosis in MCF-10A, a noncancerous cell line even at higher concentrations than the ones tested in MDA-MB- 435. Apoptosis induced by Fraction I was caspase 3 and PARP independent. After treatment with 50 µg of chlorogenic acid equivalent/ml there was an activation of p- ERK.

Nitrification is currently the most common means of ammonia removal from wastewaters in temperate climates. In conventional suspended growth systems operating in northern climate regions, nitrification completely ceases at temperatures below 8°C. This is a considerable concern in passive treatment systems where wastewater temperatures can reach as low as 1°C for extended periods in the winter months. There is evidence biofilm technologies have the ability to nitrify at low temperatures, however, the literature is missing an understanding of low temperature nitrification and the subsequent impacts during seasonal changes. Additionally, there is an urgent need to gain a fundamental knowledge of the interplay between nitrifying performance optimization, biofilm morphology and the microbiome. This research aims to fill these needs using nitrifying moving bed biofilm reactors (MBBRs) at the lab and pilot scale. This research concluded the most important factor determining MBBR carrier selection is a combination of surface area and pore space size. Although high surface area to volume carriers are attractive, the propensity to clog at high loading rates significantly decreases the removal rates. The viability of the biomass and ammonia oxidizing bacterial communities were not significantly changed, indicating the ammonia removal rates were reduced due to loss of surface area in the clogged carriers. Operation at 1°C demonstrated significant rates of nitrification can be attained and stable for extended periods of operation. This study developed the first kinetic curve at 1°C with a maximum removal rate of 0.35 gN/m2·d. The performance of the post carbon removal nitrifying MBBR systems were shown to be enhanced at 1°C by an increase in the viable embedded biomass as well as thicker biofilm. This effectively increased the number of viable cells present during low temperature operation, which partially compensated for the significant decrease in rate of ammonia removal per nitrifying cell. At all studied loading rates at 1°C, the ammonia oxidizing bacteria were primarily in the family Nitrosomonadaceae (greater than 95 percent abundance of AOB population) and the nitrite oxidizing bacteria were primarily the genus Nitrospira (greater than 99 percent abundance of NOB population). Operation at 20°C demonstrated high rates of removal in high loaded condition and robustness in extreme low loaded conditions. In both high loaded and extreme low loaded conditions the viability of the nitrifying biomass was sustained, with the family Nitrosomonadaceae as the primary ammonia oxidizing bacteria and the genus Nitrospira as the primary nitrite oxidizing bacteria. In extreme low loaded conditions and as well during start-up phases there are high prevalence of bacteria not directly related to the nitrification process. Their presence however indicates a dynamic process with changes in microbial composition within the biofilm matrix in response to varying conditions. Change in microbial composition likely helps stabilize and maintain the biofilm matrix enhancing process robustness in the temperate climates. The new knowledge gained in this research optimizes the operation of nitrifying MBBR systems and elucidates the impacts of operational conditions on the biofilm and microbial community of nitrifying MBBR systems to further our understanding of nitrifying attached growth treatment technologies. The results of this study are anticipated to be used to design the first MBBR treatment system for year round ammonia removal in passive treatment systems located in northern climate regions.

Recently, magnetic nanoparticles are finding an increased use in biomedical applications and research. Nanobeads are widely used for cell separation, biosensing and cancer therapy, among others. Due to their properties, nanowires (NWs) are gaining ground for similar applications and, as with all biomaterials, their cytotoxicity is an important factor to be considered before conducting biological studies with them. In this work, the cytotoxic effects of nickel NWs (Ni NWs) were investigated in terms of cell viability and damage to the cellular membrane. Ni NWs with an average diameter of 30-34 nm were prepared by electrodeposition in nanoporous alumina templates. The templates were obtained by a two-step anodization process with oxalic acid on an aluminum substrate. Characterization of NWs was done using X-Ray diffraction (XRD) and energy dispersive X-Ray analysis (EDAX), whereas their morphology was observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cell viability studies were carried out on human colorectal carcinoma cells HCT 116 by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) cell proliferation colorimetric assay, whereas the lactate dehydrogenase (LDH) homogenous membrane fluorimetric assay was used to measure the degree of cell membrane rupture. The density of cell seeding was calculated to obtain a specific cell number and confluency before treatment with NWs. Optical readings of the cell-reduced MTT products were measured at 570 nm, whereas fluorescent LDH membrane leakage was recorded with an excitation wavelength of 525 nm and an emission wavelength of 580 - 640 nm. The effects of NW length, cell exposure time, as well as NW:cell ratio, were evaluated through both cytotoxic assays. The results show that cell viability due to Ni NWs is affected depending on both exposure time and NW number. On the other hand, membrane rupture and leakage was only significant at later exposure times. Both cytotoxic assessment assays showed an earlier cytotoxic effect in case of shorter NWs, with longer ones having a more marked toxicity, albeit with a delay in time. These findings demonstrate that different levels of biocompatibility can be obtained with specific doses and properties of Ni NWs and can serve as guideline for future experiments.

No description available.

Poly Brominated Diphenyl Ethers (PBDEs) are known flame retardants with highly persistent and lipophilic in nature. The continued usage of PBDE in various products amplifies the human burden of PBDEs. It is therefore, important to study the potential toxicological and/or biological effects of PBDE exposure in human. In this study we investigated the mode of action of PBDE induced toxicity in human liver by exposing human hepatocarcinoma cells in a time (24-72h) and dose (0-100μM) dependent manner. The highest test dose caused an inhibition in cell viability up to 50% after 72h, whereas lower doses (<50μM) showed slight increase in cell viability. Likewise, higher doses caused significant accumulation of intracellular ROS over time. Further, increase in caspase-3 enzyme levels and DNA fragmentation showed that, lower brominated PBDEs induce liver toxicity through accumulation of toxic metabolites and reactive oxygen species over time leading to caspase-mediated apoptotic cell death.

This study is aimed to evaluate the degradation characteristics, cell viability and host tissue responses of PDLLA/PRGD/beta-TCP (PRT) composite nerve scaffold, which was fabricated by poly(D, L-lactic acid) (PDLLA), RGD peptide(Gly-Arg-Gly-Asp-Tyr, GRGDY, abbreviated as RGD) modified poly-{(lactic acid)-co-[(glycolic acid)-alt-(L-lysine)]}(PRGD) and beta-tricalcium phosphate (beta-TCP). The scaffolds' in vitro degradation behaviors were investigated in detail by analysing changes in weight loss, pH and morphology. Then, the 3-(4,5-dimethyl-2-thiazolyl) -2,5-diphenyl-2 -H-tetrazolium bromide (MTT) assay and cell live/dead assay were carried out to assess their cell viability. Moreover, in vivo degradation patterns and host inflammation responses were monitored by subcutaneous implantation of PRT scaffold in rats. Our data showed that, among the tested scaffolds, the PRT scaffold had the best buffering capacity (pH - 6.1-6.3) and fastest degradation rate (12.4%, 8 weeks) during in vitro study, which was contributed by the incorporation of beta-TCP nanoparticles. After in vitro and in vivo degradation, the high porosity structure of PRT could be observed using scanning electron microscopy. Meanwhile, the PRT scaffold could significantly promote cell survival. In the PRT scaffold implantation region, less inflammatory cells (especially for neutrophil and lymphocyte) could be detected. These results indicated that the PRT composite scaffold had a good biodegradable property; it could improve cells survival and reduced the adverse host tissue inflammation responses.

>Magister Scientiae - MSc / Introduction The blood-testis barrier (BTB) is formed by tight junctions between adjacent Sertoli cells. The barrier formed by these tight junction helps to create a specialized environment for spermatogenesis and provide an immunological barrier to protect developing germ cells. Methamphetamine (Meth) is known as neurotoxin however, its effects on the male reproductive system, especially on Sertoli cells and, the BTB are not well established. Therefore, this study aimed to determine the effects of Meth on the TM4 mouse testis Sertoli cell line and on the integrity of the BTB permeability. Materials and Methods This study investigated the effect of selected concentrations of Meth (0.1 μM, 1 μM, 10 μM, 20 μM and 100 μM) on TM4 mouse testis Sertoli cell line for 24 until 96 hours, using two treatments: an “acute” study (24 hrs exposure) and a “chronic” study, where treatment occurred on a daily basis over 96 hrs. The following parameters were investigated: viability, cell proliferation, mitochondrial activity, monolayer permeability.