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Anchorage management is a key factor for successful orthodontic treatments, as it is essential to maximize desired tooth movements and mitigate unwanted forces. Skeletal anchorage, mainly miniscrew implants (MSIs) fixed to the bone, is widely used in daily orthodontic practice to achieve effective orthodontic tooth movement. Nevertheless, the clinical use of MSIs is associated with relatively low success rate, due to lack of osseointegration between implant surface and surrounding bone tissue. Therefore, this thesis aims to improve the osseointegration of MSIs by surface modification. In chapter 2, we comprehensively reviewed clinically applied surface modifications of MSIs, that is sandblasting, large-grit, acid etching (SLA), anodic oxidation (OA) and ultraviolet photofunctionalization (UVP). These techniques have positively influence in vitro and in vivo. However, the biological improvement in clinical studies is not so significant. Considering the limitation of current studies, finding an alternative to modify MSIs for bone tissue regeneration is proposed. In chapter 3, the biomimetic calcium phosphate (BioCaP) coating was successfully applied on medical grade smooth stainless steel (SSL) surface, with the immersing period in a biomimetic modified Tyrode (BMT) solution for 48 hours, followed by the same period in a supersaturated calcium phosphate solution (CPS). This optimum coating condition was selected because of the improved roughness and wettability of SSL surface after coating. Moreover, the cell seeding efficiency, cell spreading area and cell proliferation of human osteoblast-like cell MG63 were increased on the BioCaP coated SSL surface in vitro. To further explore the drug-carrier capability, and increase the osteogenic capability of the BioCaP coating, in chapter 4, BMP2 was incorporated into the BioCaP coating on smooth SSL surface, and compared with uncoated porous Ti, smooth SSL, and smooth SSL with the BioCaP coating. It showed that the BMP2 incorporated BioCaP coating was hydrophilic, with curly crystal-like morphology. In vitro studies showed that the cell seeding efficiency, cell proliferation, and osteogenic differentiation on this surface were significantly higher than that of SSL surface. In chapter 5, we aimed to evaluate the osteoconductivity of the BioCaP coating in vivo. The time-course osteointegration process of Ti mini-pin implants furnished with the BioCaP coating in a model of metaphyseal tibial was investigated, and bovine serum albumin (BSA) was involved as a model protein. A significant increase in BIC% occurred as early as at week 1 in the crystalline BioCaP coating group, compared with that at week 2 in no coating group and amorphous seeding layer group. These findings demonstrate that the BioCaP coating enhances the osteoconductivity of Ti mini-pin implants in vivo. Therefore, such surface modification has the potential in increasing the success rate of MSIs in orthodontic clinics. In chapter 6, anticancer drug-incorporated BioCaP coating on calcium phosphate particles have been proposed. Modified curcumin (mcur) was selected in this study because it can promote osteogenesis and selectively kill osteosarcoma cells.This mcur@BioCaP suppressed osteosarcoma cell and fibroblasts, and promoted osteogenesis. This mcur@BioCaP with osteogenic differentiation capability and enhanced anti-osteosarcoma effects can be a promising strategy for osteosarcoma post-surgical treatment. Based on the research described in this thesis, it can be concluded that the currently available surface modifications on miniscrew implants do not provide significant clinical improvement. Our research findings demonstrate that the BioCaP coating can be successfully applied on metallic surfaces and improves their biocompatibility and osteoconductivity. Moreover, the incorporation of BMP2 into this coating can be a promising proposal to facilitate early osseointegration. Taken together, the BioCaP coating can be a promising technique to increase the success rate of miniscrew implants in orthodontic applications.

Anchorage management is a key factor for successful orthodontic treatments, as it is essential to maximize desired tooth movements and mitigate unwanted forces. Skeletal anchorage, mainly miniscrew implants (MSIs) fixed to the bone, is widely used in daily orthodontic practice to achieve effective orthodontic tooth movement. Nevertheless, the clinical use of MSIs is associated with relatively low success rate, due to lack of osseointegration between implant surface and surrounding bone tissue. Therefore, this thesis aims to improve the osseointegration of MSIs by surface modification. In chapter 2, we comprehensively reviewed clinically applied surface modifications of MSIs, that is sandblasting, large-grit, acid etching (SLA), anodic oxidation (OA) and ultraviolet photofunctionalization (UVP). These techniques have positively influence in vitro and in vivo. However, the biological improvement in clinical studies is not so significant. Considering the limitation of current studies, finding an alternative to modify MSIs for bone tissue regeneration is proposed. In chapter 3, the biomimetic calcium phosphate (BioCaP) coating was successfully applied on medical grade smooth stainless steel (SSL) surface, with the immersing period in a biomimetic modified Tyrode (BMT) solution for 48 hours, followed by the same period in a supersaturated calcium phosphate solution (CPS). This optimum coating condition was selected because of the improved roughness and wettability of SSL surface after coating. Moreover, the cell seeding efficiency, cell spreading area and cell proliferation of human osteoblast-like cell MG63 were increased on the BioCaP coated SSL surface in vitro. To further explore the drug-carrier capability, and increase the osteogenic capability of the BioCaP coating, in chapter 4, BMP2 was incorporated into the BioCaP coating on smooth SSL surface, and compared with uncoated porous Ti, smooth SSL, and smooth SSL with the BioCaP coating. It showed that the BMP2 incorporated BioCaP coating was hydrophilic, with curly crystal-like morphology. In vitro studies showed that the cell seeding efficiency, cell proliferation, and osteogenic differentiation on this surface were significantly higher than that of SSL surface. In chapter 5, we aimed to evaluate the osteoconductivity of the BioCaP coating in vivo. The time-course osteointegration process of Ti mini-pin implants furnished with the BioCaP coating in a model of metaphyseal tibial was investigated, and bovine serum albumin (BSA) was involved as a model protein. A significant increase in BIC% occurred as early as at week 1 in the crystalline BioCaP coating group, compared with that at week 2 in no coating group and amorphous seeding layer group. These findings demonstrate that the BioCaP coating enhances the osteoconductivity of Ti mini-pin implants in vivo. Therefore, such surface modification has the potential in increasing the success rate of MSIs in orthodontic clinics. In chapter 6, anticancer drug-incorporated BioCaP coating on calcium phosphate particles have been proposed. Modified curcumin (mcur) was selected in this study because it can promote osteogenesis and selectively kill osteosarcoma cells.This mcur@BioCaP suppressed osteosarcoma cell and fibroblasts, and promoted osteogenesis. This mcur@BioCaP with osteogenic differentiation capability and enhanced anti-osteosarcoma effects can be a promising strategy for osteosarcoma post-surgical treatment. Based on the research described in this thesis, it can be concluded that the currently available surface modifications on miniscrew implants do not provide significant clinical improvement. Our research findings demonstrate that the BioCaP coating can be successfully applied on metallic surfaces and improves their biocompatibility and osteoconductivity. Moreover, the incorporation of BMP2 into this coating can be a promising proposal to facilitate early osseointegration. Taken together, the BioCaP coating can be a promising technique to increase the success rate of miniscrew implants in orthodontic applications.

During steady-state walking both active foot placement and ankle moment control contribute to mediolateral gait stability. Ankle moment control complements foot placement by correcting foot placement error through center-of-pressure shifts during single stance. This complementary relationship may be exploited to train foot placement control . Ankle moment constraints may promote a gait pattern with a higher degree of foot placement control. Since task constraints can interact with the effects of ankle moment constraints, the mechanisms through which training effects could manifest may differ depending on using a split- or a single-belt treadmill. When older adults trained for multiple sessions, their foot placement precision improved. As they also improved their gait stability, I speculate that the complementary relationship between foot placement and ankle moment control can be exploited to train mediolateral steady-state gait stability.

Deltas formed and change by erosion and sedimentation of sand and mud driven by river flow, ebb and flood. Deltas often have channel networks where the upstream river channel splits in several places, known as bifurcations, into two downstream channels. At bifurcations, river flow and the tides distribute sediment over the channel network and determine the development of the entire delta landscape. In most situations in river bifurcations, one of the two downstream branches fills in and is abandoned. For bifurcations with a large influence of the tides, the distribution of flow and sediment is complex and less well understood than in river-dominated bifurcation. This thesis improves our understanding of the morphodynamics of tide-influenced bifurcations. A novel one-dimensional (1D) numerical model was developed to simulate morphodynamics in tide-influenced river networks. The results of the 1D model are validated by a well-established two-dimensional model. The outcomes show that: (1) with tides, channels are less likely to fill in and be abandoned than in river-dominated bifurcation system, and (2) in channel networks with multiple-bifurcations, the final morphological equilibrium strongly depends on the initial conditions, meaning that the delta development is a complex result of the river- and coastal processes and the history of the system.

Background: Steady-state gait characteristics appear promising as predictors of falls in stroke survivors. However, assessing how stroke survivors respond to actual gait perturbations may result in better fall predictions. We hypothesize that stroke survivors who fall have a diminished ability to adequately adjust gait characteristics after gait is perturbed. This study explored whether gait characteristics of perturbed gait differ between fallers and non fallers. Method: Chronic stroke survivors were recruited by clinical therapy practices. Prospective falls were monitored over a six months follow up period. We used the Gait Real-time Analysis Interactive Lab (GRAIL, Motekforce Link B.V., Amsterdam) to assess gait. First we assessed gait characteristics during steady-state gait and second we examined gait responses after six types of gait perturbations. We assessed base of support gait characteristics and margins of stability in the forward and medio-lateral direction. Findings: Thirty eight stroke survivors complete our gait protocol. Fifteen stroke survivors experienced falls. All six gait perturbations resulted in a significant gait deviation. Forward stability was reduced in the fall group during the second step after a ipsilateral perturbation. Interpretation: Although stability was different between groups during a ipsilateral perturbation, it was caused by a secondary strategy to keep up with the belt speed, therefore, contrary to our hypothesis fallers group of stroke survivors have a preserved ability to cope with external gait perturbations as compared to non fallers. Yet, our sample size was limited and thereby, perhaps minor group differences were not revealed in the present study.

Background: Steady-state gait characteristics appear promising as predictors of falls in stroke survivors. However, assessing how stroke survivors respond to actual gait perturbations may result in better fall predictions. We hypothesize that stroke survivors who fall have a diminished ability to adequately adjust gait characteristics after gait is perturbed. This study explored whether gait characteristics of perturbed gait differ between fallers and non fallers. Method: Chronic stroke survivors were recruited by clinical therapy practices. Prospective falls were monitored over a six months follow up period. We used the Gait Real-time Analysis Interactive Lab (GRAIL, Motekforce Link B.V., Amsterdam) to assess gait. First we assessed gait characteristics during steady-state gait and second we examined gait responses after six types of gait perturbations. We assessed base of support gait characteristics and margins of stability in the forward and medio-lateral direction. Findings: Thirty eight stroke survivors complete our gait protocol. Fifteen stroke survivors experienced falls. All six gait perturbations resulted in a significant gait deviation. Forward stability was reduced in the fall group during the second step after a ipsilateral perturbation. Interpretation: Although stability was different between groups during a ipsilateral perturbation, it was caused by a secondary strategy to keep up with the belt speed, therefore, contrary to our hypothesis fallers group of stroke survivors have a preserved ability to cope with external gait perturbations as compared to non fallers. Yet, our sample size was limited and thereby, perhaps minor group differences were not revealed in the present study.

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures. A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures. A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

Dit artikel is met toestemming overgenomen uit Orthopedagogiek Onderzoek en Praktijk, 2015, nr. 2, Garant Uitgevers nv Onderzoek naar leesmotivatie toont aan dat leesplezier en leesvermijding twee afzonderlijke constructen zijn in plaats van twee uiteinden van eenzelfde dimensie. Beide constructen worden van belang geacht bij het leesonderwijs. In deze studie is de stabiliteit van leesplezier en leesvermijding onderzocht. Drie jaar lang zijn drie cohorten leerlingen (groep 4 en 7 basisonderwijs en 2de klas vmbo) met behulp van vragenlijsten bevraagd op hun leesplezier en leesvermijding. Stabiliteit van leesplezier en leesvermijding is op groepsniveau vastgesteld met behulp van een gemengde tussen en binnen subjecten variantieanalyse. Daarnaast is ook gekeken naar de rangordening van leerlingen: dit zegt iets over individuele verandering ten opzichte van de groep. Vergelijking tussen en binnen cohorten over drie jaren geeft aan dat het effect van tijd op leesplezier en leesvermijding voor de cohorten verschilt. De gegevens tonen dat leesplezier stabiel is in de middenbouw van het basisonderwijs maar afneemt in de bovenbouw, een afname die zich voortzet in het vmbo. Leesvermijding daarentegen neemt af in de middenbouw en vervolgens weer toevanaf de bovenbouw van het basisonderwijs, om te stabiliseren in de bovenbouw van het vmbo. Rangordecorrelaties per meetmoment laten zien dat leerlingen ten opzichte van leeftijdsgenoten redelijk stabiel zijn in leesplezier en in leesvermijding, met uitzondering van leesvermijding in cohort 2 (groep 4). De conclusie is dat vanaf de bovenbouw in het basisonderwijs, vmbo-leerlingen een ontwikkeling doormaken die tendeert naar minder leesplezier en meer leesvermijding: een ontwikkeling die een uitdaging betekent voor docenten om leerlingen gemotiveerd aan het lezen te houden.

Dit artikel is met toestemming overgenomen uit Orthopedagogiek Onderzoek en Praktijk, 2015, nr. 2, Garant Uitgevers nv Onderzoek naar leesmotivatie toont aan dat leesplezier en leesvermijding twee afzonderlijke constructen zijn in plaats van twee uiteinden van eenzelfde dimensie. Beide constructen worden van belang geacht bij het leesonderwijs. In deze studie is de stabiliteit van leesplezier en leesvermijding onderzocht. Drie jaar lang zijn drie cohorten leerlingen (groep 4 en 7 basisonderwijs en 2de klas vmbo) met behulp van vragenlijsten bevraagd op hun leesplezier en leesvermijding. Stabiliteit van leesplezier en leesvermijding is op groepsniveau vastgesteld met behulp van een gemengde tussen en binnen subjecten variantieanalyse. Daarnaast is ook gekeken naar de rangordening van leerlingen: dit zegt iets over individuele verandering ten opzichte van de groep. Vergelijking tussen en binnen cohorten over drie jaren geeft aan dat het effect van tijd op leesplezier en leesvermijding voor de cohorten verschilt. De gegevens tonen dat leesplezier stabiel is in de middenbouw van het basisonderwijs maar afneemt in de bovenbouw, een afname die zich voortzet in het vmbo. Leesvermijding daarentegen neemt af in de middenbouw en vervolgens weer toevanaf de bovenbouw van het basisonderwijs, om te stabiliseren in de bovenbouw van het vmbo. Rangordecorrelaties per meetmoment laten zien dat leerlingen ten opzichte van leeftijdsgenoten redelijk stabiel zijn in leesplezier en in leesvermijding, met uitzondering van leesvermijding in cohort 2 (groep 4). De conclusie is dat vanaf de bovenbouw in het basisonderwijs, vmbo-leerlingen een ontwikkeling doormaken die tendeert naar minder leesplezier en meer leesvermijding: een ontwikkeling die een uitdaging betekent voor docenten om leerlingen gemotiveerd aan het lezen te houden.

Aeration of food is considered to be a good method to create a texture and mouthfeel of food products that is liked by the consumer. However, traditional foams are not stable for a prolonged time. Microbubbles are air bubbles covered with a shell that slows down disproportionation significantly and arrests coalescence. Protein stabilized microbubbles are seen as a promising new food ingredient for encapsulation, to replace fat, to create new textures, and to improve sensorial properties of foods. In order to explore the possible functionalities of microbubbles in food systems, a good understanding is required regarding the formation of protein stabilized microbubbles as well as their stability in environments and at conditions encountered in food products. The aim of this research was to investigate the key parameters for applications of microbubbles in food systems. In Chapter 1 an introduction to this topic is given. In Chapter 2, the effect of the microbubble preparation parameters on the microbubble characteristics, like the microbubble yield, size and stability, was investigated. The protein Bovine Serum Albumin (BSA) and the method sonication was used to manufacture the microbubbles. The manufactured number and stability of microbubbles was highest when they were prepared at a pH around 5 to 6, just above the isoelectric point, and at an ionic strength of 1.0 M. This can be related to the protein coverage at the air/water interface of air bubbles formed during sonication. At a pH close to the isoelectric point the BSA molecules is in its native configuration. Also the repulsion between the proteins is minimized at these pH values and ionic strength. Both the native configuration and the limited repulsion between the proteins result in an optimal protein coverage during the first part of sonication. Also a high protein concentration contributes to a higher surface coverage. The surface coverage is proportional to the protein concentration up to a concentration of 7.5% after which an increase in protein concentration did not lead to a substantial increase in the number of microbubble . In the second part of sonication the protein layer around the air bubble becomes thicker and stronger by heat induced protein-protein interactions. We found that and at a preheating temperature of 55-60°C, about 5 °C below the BSA denaturation temperature, and a final solution temperature of 60-65°C most microbubbles were obtained, while at higher temperatures mainly protein aggregates and (almost) no microbubbles are formed. This suggests that at temperature of around 60°C to 65°C protein aggregated mostly at the air-water interface creating a multi-layered shell, while at higher temperature, they also aggregated in bulk. These aggregates cannot form microbubbles. We found that optimal preparation parameters strongly depend on the protein batch. We hypothesize that the differences in microbubble formation between the protein batches is due to (small) differences in the protein molecular and denaturation properties that determine the temperature at which the molecules start to interact at the air-water interface. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the driving force for the shrinkage was the Laplace pressure, resulting in an air flux from the bubbles to the solution. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure. In Chapter 3 and Chapter 4, microbubble stability at environments and conditions representative for food products were studies. In Chapter 3 we investigated the stability upon addition of surfactants and acid, When surfactants or acid were added, the microbubbles disappeared in three subsequent steps. The release of air from the microbubble can be well described with the two-parameter Weibull process. This suggests two processes are responsible for the release of air: 1) a shell-weakening process and 2) a random fracture of the weakened shell. After the air has been released from the microbubble the third process is identified in the microbubble disintegration: 3) the shell disintegrated completely into nanometer-sized particles. The probability of fracture was exponentially proportional to the concentration of acid and surfactant, meaning that a lower average breaking time and a higher decay rate were observed at higher surfactant or acid concentrations. For different surfactants, different decay rates were found. The disintegration of the shell into monomeric proteins upon addition of acid or surfactants shows that the interactions in the shell are non-covalent and most probably hydrophobic. After surfactant addition, there was a significant time gap between complete microbubble decay (release of air) and complete shell disintegration, while after acid addition the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay. In Chapter 4 the stability of the microbubbles upon pressure treatment, upon fast cooling after heating and at different storage temperatures was studied. The microbubble stability significantly decreased when microbubbles were pressurized above 1 bar overpressure for 15 seconds or heated above 50°C for 2 minutes. Above those pressures the microbubbles became unstable by buckling. Buckling occurred above a critical pressure. This critical pressure is determined by the shell elastic modulus, the thickness of the shell, and the size of the microbubble. Addition of crosslinkers like glutaraldehyde and tannic acid increased the shell elastic modulus. It was shown that microbubbles were stable against all tested temperatures (up to 120°C) and overpressures (4.7 bar) after they were reinforced by crosslinkers. From the average breaking time at different storage temperatures, we deduced that the activation energy to rupture molecular bonds in the microbubbles shell is 27 kT. In Chapter 5, we investigated the effect of microbubbles on the rheological, tribological sensorial properties of model food systems and we compared this effect to the effect on food systems with emulsion droplets and without an added colloid. We investigated the effect in three model food systems, namely fluids with and without added thickener and a mixed gelatine-agar gel. In a sensory test panellists were asked whether they could discriminate between samples containing microbubbles, emulsion droplets or no added colloid. Emulsions could be sensorially well distinguished from the other two samples, while the microbubble dispersion could not be discriminated from the protein solution. Thus, we concluded that at a volume fraction of 5% of these BSA covered microbubbles were not comparable to oil-in-water emulsions. The good discrimination of emulsion might be ascribed to the fact that emulsion had a lower friction force (measured at shear rates form 10 mm/s to 80 mm/s) than that microbubbles dispersions and protein solutions. Upon mixing emulsions and microbubble dispersions the friction value approximated that of emulsions. This effect was already noticed at only 1.25% (v/v) oil, indicating that microbubbles had not a significant contributions to the friction of these samples. Also microbubble dispersions with and without protein aggregates were compared. The microbubble dispersions with and without thickener containing protein aggregates had a higher viscosity than the those samples without protein aggregates. Protein aggregates in the gelled microbubble sample yielded a higher Young’s modulus and fracture stress. The differences between the gelled samples could be well perceived by the panellists. We attribute this mainly to the fracture properties of the gel. In general we concluded that microbubbles, given their size of ~ 1 mm and volume fraction of 5%, did not contribute to a specific mouthfeel. Finally in Chapter 6, the results presented in the previous chapters are discussed and put in perspective of the general knowledge on microbubbles production, stability, and applications in food. We described the main mechanisms leading to microbubble formation and stability. We showed that the production parameters significantly influence the interactions in the microbubble shell, and the those interactions highly determine the stability of the microbubbles under several conditions. We reported about limitations of sonication as a method to produce microbubbles suitable for food applications and we provided some ways to overcome these limitations. The use of microbubbles in food systems has been explored and we clearly see possible applications for microbubbles in food. We reported about directions for possible further research. In this work we made significant progress in understanding the interactions in the microbubble shell and their relation to microbubble stability. We also advanced in comprehension towards possible applications of microbubbles in food.

This thesis explores relevant fluid dynamic processes for the formation of uniformly sized droplets in microfluidic systems. Growing droplets made from a bulk source have often liquid threads or jets in between to supply liquid to the droplet. Liquid threads and jets are however known to be instable and finding parameters determining their instability/stability will possibly promote a more controlled formation of uniformly sized droplets. Different droplet formation processes in microfluidic devices are explained, such as cross-flow, co-flow and flow focussing. Dimensionless numbers (introduced in chapter 1) represent the ratio of relevant forces or pressures acting on the fluids and/or their interfaces. These forces and pressures originate from their related fluid dynamic parameters, such as viscosity, interfacial tension, mass density and velocity of the fluid within a specific fluidic confinement with a certain length scale. We show that the dimensionless Reynolds, Weber and Capillary numbers can be associated with the stability of liquid threads and/or jets and provide insight in droplet formation processes. The phenomenon of spontaneous droplet formation at low flow rates of an inner fluid confined in a microfluidic channel is studied in chapter 2. A short overview of known processes of spontaneous droplet formation with micro-engineered microfluidic devices is presented. We have studied the process of auto breakup with rectangular and round glass capillaries, the latter provided with micro-corrugations and uniform sized droplets were obtained, but only if the outer fluid is able to enter the capillary during droplet formation. The process of auto breakup is described by a new analytical model described in chapter 3. The model states that the instability of a liquid thread is induced by the decrease of a local liquid thread pressure inside the capillary near the growing droplet. Predicted droplet sizes have been experimentally verified accurately, and also the predicted breakup length inside a micro-corrugated capillary has been verified. The model states that viscous flow stabilises the liquid thread and that auto breakup happens as long as the capillary number is below a critical capillary number of 0.0625. Above 0.0625 droplets grow infinitely large. Auto breakup is however already hampered at Capillary numbers above 0.03, because between 0.03 and 0.0625 no well controlled droplet sizes could be obtained by auto breakup. This is explained by the observed formation of a partially collapsed inner liquid thread that remains open and supplies the growing droplet with inner fluid. In chapter 4 the formation and stability of a liquid thread in free surface flow feeding a large growing droplet is demonstrated and discussed. The shape of the liquid thread is positively tapering (towards the droplet) and can be described accurately by a Navier-Stokes based ordinary differential equation (ODE) assuming steady state, axisymmetry and an averaged fluid velocity over the cross section of the liquid thread. The axial shape of a viscous liquid thread is concave and its radial dimension has initially a cubic dependence with respect to the axial dimension. A driving force to stabilise the liquid thread was identified, which is a pressure gradient Q = Q0/L – Q1. Q0 is the pressure drop over thread length L, and Q1 is interfacial based dissipation of energy of the outer fluid. The maximum length of the liquid thread is predicted to be reached when Q goes towards 0 as the ratio Q0/Q1. Shape and stability of emanating liquid jets, which appear after impact of falling droplets from a deep liquid, is presented in chapter 5. During rise and fall of the jet due to gravity, the jet is additionally decelerated towards the liquid surface by a tensile retraction force from the surface tension force exerted on the jet surface by the liquid bath. The retracting force generates an inertial deceleration pressure inside the jet that is balanced by the local Laplace pressure, herewith defining its local curvature and therefore also the shape of the complete jet. A deceleration based Young-Laplace equation is introduced and the predicted shape is experimentally verified for different fluids. Furthermore, the size of droplets forming on the tip of the jet can also be explained by the found pressure balance between the local Laplace pressure and the inertial deceleration of the jet (including the forming droplet). In general we found that the stability of a liquid thread or jet seems correlated with an applied pressure difference that is distributed between the begin and end of the thread or jet. Studying auto breakup (chapters 2 and 3) of a confined liquid thread it was found that only when the applied pressure is high enough the liquid thread is stable and infinitely large droplets are formed. For the free surface flow liquid thread (chapter 4) it was found that breakup happens when the applied pressure gradient over the length of the thread goes to zero. For the emanating jet (chapter 5) an inertial pressure difference between the base and tip of the jet comes into existence that opposes the squeezing Laplace pressure that wants to break up the liquid jet. Furthermore we found that the last stages of droplet breakup from a liquid thread or jet appeared to follow universal pinch-off, and also that micro-thread formation is observed between droplet and liquid thread or jet.

Unexpected findings of the banned antibiotic chloramphenicol in products of animal origin, feed and straw prompted urgent investigation. Therefore a monitoring study in straw was carried out. The monitoring showed that in 37 sample chloramphenicol was detected. In 7 samples a concentration above 0.3 μg kg-1 was found with the highest result at 6.8 μg kg-1. Next the hypothesis was studied that the chloramphenicol is naturally present in soil, through production by soil bacteria, and subsequently can be transferred to crops. First, the stability of chloramphenicol in soil was studied. The fate of chloramphenicol highly depends on soil type and showed a half-life of approximately one day in non-sterile topsoil. It was found to be more stable in sub-soil and sterile soils. Second, the production of chloramphenicol in soil was studied and it was confirmed that Streptomyces venezuelae can produce chloramphenicol at appreciable amounts in non-sterile soil. Third, a transfer study was carried out using wheat and corn grown on three different soils, that were weekly exposed to aqueous chloramphenicol solutions at different levels. Chloramphenicol was taken up by crops as determined by chiral liquid chromatography coupled to tandem mass spectrometric analysis and the levels in crop were found to be bioavailability related. It was concluded that chloramphenicol residues can occur naturally in crops as a result of the production of chloramphenicol by soil bacteria in their natural environment and subsequent uptake by crops.

Lipid bilayer stability in relation to oxide nanoparticles All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles. Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments. Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere. Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

Unexpected findings of the banned antibiotic chloramphenicol in products of animal origin, feed and straw prompted urgent investigation. Therefore a monitoring study in straw was carried out. The monitoring showed that in 37 sample chloramphenicol was detected. In 7 samples a concentration above 0.3 μg kg-1 was found with the highest result at 6.8 μg kg-1. Next the hypothesis was studied that the chloramphenicol is naturally present in soil, through production by soil bacteria, and subsequently can be transferred to crops. First, the stability of chloramphenicol in soil was studied. The fate of chloramphenicol highly depends on soil type and showed a half-life of approximately one day in non-sterile topsoil. It was found to be more stable in sub-soil and sterile soils. Second, the production of chloramphenicol in soil was studied and it was confirmed that Streptomyces venezuelae can produce chloramphenicol at appreciable amounts in non-sterile soil. Third, a transfer study was carried out using wheat and corn grown on three different soils, that were weekly exposed to aqueous chloramphenicol solutions at different levels. Chloramphenicol was taken up by crops as determined by chiral liquid chromatography coupled to tandem mass spectrometric analysis and the levels in crop were found to be bioavailability related. It was concluded that chloramphenicol residues can occur naturally in crops as a result of the production of chloramphenicol by soil bacteria in their natural environment and subsequent uptake by crops.

Aeration of food is considered to be a good method to create a texture and mouthfeel of food products that is liked by the consumer. However, traditional foams are not stable for a prolonged time. Microbubbles are air bubbles covered with a shell that slows down disproportionation significantly and arrests coalescence. Protein stabilized microbubbles are seen as a promising new food ingredient for encapsulation, to replace fat, to create new textures, and to improve sensorial properties of foods. In order to explore the possible functionalities of microbubbles in food systems, a good understanding is required regarding the formation of protein stabilized microbubbles as well as their stability in environments and at conditions encountered in food products. The aim of this research was to investigate the key parameters for applications of microbubbles in food systems. In Chapter 1 an introduction to this topic is given. In Chapter 2, the effect of the microbubble preparation parameters on the microbubble characteristics, like the microbubble yield, size and stability, was investigated. The protein Bovine Serum Albumin (BSA) and the method sonication was used to manufacture the microbubbles. The manufactured number and stability of microbubbles was highest when they were prepared at a pH around 5 to 6, just above the isoelectric point, and at an ionic strength of 1.0 M. This can be related to the protein coverage at the air/water interface of air bubbles formed during sonication. At a pH close to the isoelectric point the BSA molecules is in its native configuration. Also the repulsion between the proteins is minimized at these pH values and ionic strength. Both the native configuration and the limited repulsion between the proteins result in an optimal protein coverage during the first part of sonication. Also a high protein concentration contributes to a higher surface coverage. The surface coverage is proportional to the protein concentration up to a concentration of 7.5% after which an increase in protein concentration did not lead to a substantial increase in the number of microbubble . In the second part of sonication the protein layer around the air bubble becomes thicker and stronger by heat induced protein-protein interactions. We found that and at a preheating temperature of 55-60°C, about 5 °C below the BSA denaturation temperature, and a final solution temperature of 60-65°C most microbubbles were obtained, while at higher temperatures mainly protein aggregates and (almost) no microbubbles are formed. This suggests that at temperature of around 60°C to 65°C protein aggregated mostly at the air-water interface creating a multi-layered shell, while at higher temperature, they also aggregated in bulk. These aggregates cannot form microbubbles. We found that optimal preparation parameters strongly depend on the protein batch. We hypothesize that the differences in microbubble formation between the protein batches is due to (small) differences in the protein molecular and denaturation properties that determine the temperature at which the molecules start to interact at the air-water interface. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the driving force for the shrinkage was the Laplace pressure, resulting in an air flux from the bubbles to the solution. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure. In Chapter 3 and Chapter 4, microbubble stability at environments and conditions representative for food products were studies. In Chapter 3 we investigated the stability upon addition of surfactants and acid, When surfactants or acid were added, the microbubbles disappeared in three subsequent steps. The release of air from the microbubble can be well described with the two-parameter Weibull process. This suggests two processes are responsible for the release of air: 1) a shell-weakening process and 2) a random fracture of the weakened shell. After the air has been released from the microbubble the third process is identified in the microbubble disintegration: 3) the shell disintegrated completely into nanometer-sized particles. The probability of fracture was exponentially proportional to the concentration of acid and surfactant, meaning that a lower average breaking time and a higher decay rate were observed at higher surfactant or acid concentrations. For different surfactants, different decay rates were found. The disintegration of the shell into monomeric proteins upon addition of acid or surfactants shows that the interactions in the shell are non-covalent and most probably hydrophobic. After surfactant addition, there was a significant time gap between complete microbubble decay (release of air) and complete shell disintegration, while after acid addition the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay. In Chapter 4 the stability of the microbubbles upon pressure treatment, upon fast cooling after heating and at different storage temperatures was studied. The microbubble stability significantly decreased when microbubbles were pressurized above 1 bar overpressure for 15 seconds or heated above 50°C for 2 minutes. Above those pressures the microbubbles became unstable by buckling. Buckling occurred above a critical pressure. This critical pressure is determined by the shell elastic modulus, the thickness of the shell, and the size of the microbubble. Addition of crosslinkers like glutaraldehyde and tannic acid increased the shell elastic modulus. It was shown that microbubbles were stable against all tested temperatures (up to 120°C) and overpressures (4.7 bar) after they were reinforced by crosslinkers. From the average breaking time at different storage temperatures, we deduced that the activation energy to rupture molecular bonds in the microbubbles shell is 27 kT. In Chapter 5, we investigated the effect of microbubbles on the rheological, tribological sensorial properties of model food systems and we compared this effect to the effect on food systems with emulsion droplets and without an added colloid. We investigated the effect in three model food systems, namely fluids with and without added thickener and a mixed gelatine-agar gel. In a sensory test panellists were asked whether they could discriminate between samples containing microbubbles, emulsion droplets or no added colloid. Emulsions could be sensorially well distinguished from the other two samples, while the microbubble dispersion could not be discriminated from the protein solution. Thus, we concluded that at a volume fraction of 5% of these BSA covered microbubbles were not comparable to oil-in-water emulsions. The good discrimination of emulsion might be ascribed to the fact that emulsion had a lower friction force (measured at shear rates form 10 mm/s to 80 mm/s) than that microbubbles dispersions and protein solutions. Upon mixing emulsions and microbubble dispersions the friction value approximated that of emulsions. This effect was already noticed at only 1.25% (v/v) oil, indicating that microbubbles had not a significant contributions to the friction of these samples. Also microbubble dispersions with and without protein aggregates were compared. The microbubble dispersions with and without thickener containing protein aggregates had a higher viscosity than the those samples without protein aggregates. Protein aggregates in the gelled microbubble sample yielded a higher Young’s modulus and fracture stress. The differences between the gelled samples could be well perceived by the panellists. We attribute this mainly to the fracture properties of the gel. In general we concluded that microbubbles, given their size of ~ 1 mm and volume fraction of 5%, did not contribute to a specific mouthfeel. Finally in Chapter 6, the results presented in the previous chapters are discussed and put in perspective of the general knowledge on microbubbles production, stability, and applications in food. We described the main mechanisms leading to microbubble formation and stability. We showed that the production parameters significantly influence the interactions in the microbubble shell, and the those interactions highly determine the stability of the microbubbles under several conditions. We reported about limitations of sonication as a method to produce microbubbles suitable for food applications and we provided some ways to overcome these limitations. The use of microbubbles in food systems has been explored and we clearly see possible applications for microbubbles in food. We reported about directions for possible further research. In this work we made significant progress in understanding the interactions in the microbubble shell and their relation to microbubble stability. We also advanced in comprehension towards possible applications of microbubbles in food.

This thesis explores relevant fluid dynamic processes for the formation of uniformly sized droplets in microfluidic systems. Growing droplets made from a bulk source have often liquid threads or jets in between to supply liquid to the droplet. Liquid threads and jets are however known to be instable and finding parameters determining their instability/stability will possibly promote a more controlled formation of uniformly sized droplets. Different droplet formation processes in microfluidic devices are explained, such as cross-flow, co-flow and flow focussing. Dimensionless numbers (introduced in chapter 1) represent the ratio of relevant forces or pressures acting on the fluids and/or their interfaces. These forces and pressures originate from their related fluid dynamic parameters, such as viscosity, interfacial tension, mass density and velocity of the fluid within a specific fluidic confinement with a certain length scale. We show that the dimensionless Reynolds, Weber and Capillary numbers can be associated with the stability of liquid threads and/or jets and provide insight in droplet formation processes. The phenomenon of spontaneous droplet formation at low flow rates of an inner fluid confined in a microfluidic channel is studied in chapter 2. A short overview of known processes of spontaneous droplet formation with micro-engineered microfluidic devices is presented. We have studied the process of auto breakup with rectangular and round glass capillaries, the latter provided with micro-corrugations and uniform sized droplets were obtained, but only if the outer fluid is able to enter the capillary during droplet formation. The process of auto breakup is described by a new analytical model described in chapter 3. The model states that the instability of a liquid thread is induced by the decrease of a local liquid thread pressure inside the capillary near the growing droplet. Predicted droplet sizes have been experimentally verified accurately, and also the predicted breakup length inside a micro-corrugated capillary has been verified. The model states that viscous flow stabilises the liquid thread and that auto breakup happens as long as the capillary number is below a critical capillary number of 0.0625. Above 0.0625 droplets grow infinitely large. Auto breakup is however already hampered at Capillary numbers above 0.03, because between 0.03 and 0.0625 no well controlled droplet sizes could be obtained by auto breakup. This is explained by the observed formation of a partially collapsed inner liquid thread that remains open and supplies the growing droplet with inner fluid. In chapter 4 the formation and stability of a liquid thread in free surface flow feeding a large growing droplet is demonstrated and discussed. The shape of the liquid thread is positively tapering (towards the droplet) and can be described accurately by a Navier-Stokes based ordinary differential equation (ODE) assuming steady state, axisymmetry and an averaged fluid velocity over the cross section of the liquid thread. The axial shape of a viscous liquid thread is concave and its radial dimension has initially a cubic dependence with respect to the axial dimension. A driving force to stabilise the liquid thread was identified, which is a pressure gradient Q = Q0/L – Q1. Q0 is the pressure drop over thread length L, and Q1 is interfacial based dissipation of energy of the outer fluid. The maximum length of the liquid thread is predicted to be reached when Q goes towards 0 as the ratio Q0/Q1. Shape and stability of emanating liquid jets, which appear after impact of falling droplets from a deep liquid, is presented in chapter 5. During rise and fall of the jet due to gravity, the jet is additionally decelerated towards the liquid surface by a tensile retraction force from the surface tension force exerted on the jet surface by the liquid bath. The retracting force generates an inertial deceleration pressure inside the jet that is balanced by the local Laplace pressure, herewith defining its local curvature and therefore also the shape of the complete jet. A deceleration based Young-Laplace equation is introduced and the predicted shape is experimentally verified for different fluids. Furthermore, the size of droplets forming on the tip of the jet can also be explained by the found pressure balance between the local Laplace pressure and the inertial deceleration of the jet (including the forming droplet). In general we found that the stability of a liquid thread or jet seems correlated with an applied pressure difference that is distributed between the begin and end of the thread or jet. Studying auto breakup (chapters 2 and 3) of a confined liquid thread it was found that only when the applied pressure is high enough the liquid thread is stable and infinitely large droplets are formed. For the free surface flow liquid thread (chapter 4) it was found that breakup happens when the applied pressure gradient over the length of the thread goes to zero. For the emanating jet (chapter 5) an inertial pressure difference between the base and tip of the jet comes into existence that opposes the squeezing Laplace pressure that wants to break up the liquid jet. Furthermore we found that the last stages of droplet breakup from a liquid thread or jet appeared to follow universal pinch-off, and also that micro-thread formation is observed between droplet and liquid thread or jet.

Lipid bilayer stability in relation to oxide nanoparticles All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles. Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments. Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere. Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

Dosage forms have been developed over the years for various applications. The dosage form consists of the active drug in combination with pharmaceutical excipients. The pharmaceutical excipients solubilise, suspend, thicken, dilute, emulsify, stabilise, preserve, colour and flavour medicinal agents into efficacious and appealing dosage forms. The dosage form under investigation in this study is of the oral type. The Pheroid® is a unique drug delivery system which consists of an oil-in-water emulsion system. Emulsion based drug systems provide a suitable medium for the delivery of both hydrophobic and hydrophilic drugs which can be incorporated into its oil or water phase for delivery to the site of action. These advantages make them more efficient as dosage form. Emulgels are either emulsion of oil-in-water or water-in-oil type, which is gelled by mixing with gelling agents. Incorporation of emulsion into gel increases its stability and makes it a dual control release system. The presence of the gel phase makes it a non-greasy formulation which favours good patient compliance. A strategy followed to improve the stability of the emulgel system is the packaging of the formula into single dose sachets to protect the product against physical and chemical breakdown during patient usage. All factors such as selection of gelling agent, preservatives and formulation methods influencing the stability and efficacy of Pheroid® emulgel are discussed. In this study, three different emulsifiers were added to the formula and the analysis of visual appearance, pH measurements, rheological studies, light microscopy and confocol laser scanning microscopy (CLSM) will provide an insight to the potential usage of emulgel as drug delivery system. A range of para-hydroxybenzoate esters was tested in the Pheroid® emulgel and the most suitable candidate chosen for further accelerated stability testing. It was thus possible to prepare a single dose emulgel with Carbopol® 934P (0.2% w/v) as an emulsifier, with Nipastat® (0.175% w/v) and PG (10% v/v) as preservatives into a stable dosage form suitable for further product development. PhD (Pharmaceutics), North-West University, Potchefstroom Campus, 2014

Het beschreven onderzoek in dit rapport is onderdeel van het onderzoeksproject ‘gedrag van verdroogde kades’ van het Hoogheemraadschap Delfland. Het onderzoek van Alterra is een bureau- en modelonderzoek en is gericht op scheuren door krimp, die ontstaan in lange perioden met droogte. Onderzocht zijn veenkaden en kleikaden op veen, met een accent op kleikaden omdat deze in Delfland het meeste voorkomen. Bij kleikaden lijkt het grootste risico preferente stroming via de scheuren te zijn. Bomen kunnen door hun diepe beworteling en grote verdamping een extra risico vormen. Langsscheuren in de kruin kunnen met water gevuld worden en dit kan resulteren in een bezwijkmechanisme. Dit is door Deltares nader onderzocht in een parallel rapport.

MSc (Biochemistry), North-West University, Potchefstroom Campus, 2014 Chronic, noncommunicable diseases such as chronic fatigue syndrome (also known as myalgic encephalomyelitis) are rapidly becoming a worldwide epidemic that profoundly affects public health and productivity. Chronic fatigue syndrome (CFS) is characterised by severe and debilitating fatigue and although its etiology is still unknown, recent studies have found considerable evidence that mitochondrial dysfunction and oxidative stress might be responsible for the underlying energy deficit in these patients. Adenine and pyridine nucleotides could be used as potential biomarkers for energy related disorders such as chronic fatigue syndrome because of their various functions in the energy and redox pathways. The first part of this study focussed on developing a liquid chromatography electrosprayionisation tandem mass spectrometry (LC-ESI-MS/MS) method for the quantification of these nucleotides in blood samples. Due to the instability of nucleotides in biological matrices it was also necessary to find a suitable extraction method that would be able to stop enzymatic activity via protein precipitation. Out of the four extraction methods investigated during this study, deproteinisation of whole blood samples with perchloric acid produced the highest nucleotide abundances. Although nucleotide standards were found to be stable in perchloric acid, nucleotide levels in blood samples were not stabilised by addition of perchloric acid. The second part of this study consisted of measuring the nucleotide levels in blood samples of controls and possible CFS patients in order to test the proof of concept of the new LCESI-MS/MS method. Despite changes in the nucleotide levels due to perchloric acid and problems with nucleotide instability, it was still possible to distinguish between the two groups based on the results obtained with the new LC-ESI-MS/MS method. The newly developed LC-ESI-MS/MS method proved to be reliable and adequate for nucleotide quantification in whole blood samples, thus the aim of this study was achieved. Masters

Chronic, noncommunicable diseases such as chronic fatigue syndrome (also known as myalgic encephalomyelitis) are rapidly becoming a worldwide epidemic that profoundly affects public health and productivity. Chronic fatigue syndrome (CFS) is characterised by severe and debilitating fatigue and although its etiology is still unknown, recent studies have found considerable evidence that mitochondrial dysfunction and oxidative stress might be responsible for the underlying energy deficit in these patients. Adenine and pyridine nucleotides could be used as potential biomarkers for energy related disorders such as chronic fatigue syndrome because of their various functions in the energy and redox pathways. The first part of this study focussed on developing a liquid chromatography electrosprayionisation tandem mass spectrometry (LC-ESI-MS/MS) method for the quantification of these nucleotides in blood samples. Due to the instability of nucleotides in biological matrices it was also necessary to find a suitable extraction method that would be able to stop enzymatic activity via protein precipitation. Out of the four extraction methods investigated during this study, deproteinisation of whole blood samples with perchloric acid produced the highest nucleotide abundances. Although nucleotide standards were found to be stable in perchloric acid, nucleotide levels in blood samples were not stabilised by addition of perchloric acid. The second part of this study consisted of measuring the nucleotide levels in blood samples of controls and possible CFS patients in order to test the proof of concept of the new LCESI- MS/MS method. Despite changes in the nucleotide levels due to perchloric acid and problems with nucleotide instability, it was still possible to distinguish between the two groups based on the results obtained with the new LC-ESI-MS/MS method. The newly developed LC-ESI-MS/MS method proved to be reliable and adequate for nucleotide quantification in whole blood samples, thus the aim of this study was achieved. MSc (Biochemistry), North-West University, Potchefstroom Campus, 2014