P. Van der Meeren

Accurate particle size distribution determination by nanoparticle tracking analysis based on 2-D Brownian dynamics simulation

A physical model is presented to simulate the average step length distribution during nanoparticle tracking analysis experiments as a function of the particle size distribution and the distribution of the number of steps within the tracks. Considering only tracks of at least five steps, numerical simulation could be replaced by a normal distribution approximation. Based on this model, simulation of a step length distribution allows obtaining a much more reliable estimation of the particle size distribution, thereby reducing the artificial broadening of the distribution, as is typically observed by direct conversion of step length to particle size data. As this fitting procedure also allowed including data from particles that were followed for a relatively low number of steps, the measurement time could be reduced for particles that are known to be monodisperse. Whereas the inversion is less sensitive towards the particle size distribution width, still similar values were obtained for both the average diameter and standard deviation of a polystyrene latex sample irrespective of the track length, provided that the latter included at least five steps.

Optimization of the column loadability for the preparative HPLC Separation of soybean phospholipids

A simple and rapid preparative-scale separation method was investigated in order to obtain pure soybean phospholipids. Because of technical and economical reasons, two coarse, irregular silica gels were selected. Comparing both stationary phases, a ternary mixture of hexane, 2-propanol and water yielded a different elution order of the phospholipids at analytical sample loads, in spite of the chemical similarity of these packing materials. During scaleup, it became obvious that the retention characteritics were largely influenced by the sample load, thus making the 15–35 μm RSiL inappropriate for preparative-scale separations of phospholipids. Moreover, the column loadability could be increased by controlling the flow rate. Hence, a solvent program was elaborated which enabled a column loadability of up to 2% by weight of the stationary phase. Using analytical high performance liquid chromatography, it was shown that the method proposed yielded over 90% pure phospholipids at a recovery of nearly 80%.

A successful strategy for the production of cationic magnetoliposomes

Summary The present work describes a strategy and the mechanistic background for synthesizing magnetoliposomes (MLs) in which the bi-layered coating is partly composed of positively charged lipids. In a first step, neutral MLs are prepared from zwitterionic phosphatidylcholine vesicles and magnetite nanocores stabilized with an anionic surfactant, and then incubated with cationic vesicles formed from phosphatidylcholine and dioleoyltrimethylammoniumpropane. During this latter step, spontaneous intermembrane lipid transfer occurs. After reaching an equilibrium state, the desired cationic MLs are captured from the mixture in a high-gradient magnetophoresis setup.

Protection of polyunsaturated oils against ruminal biohydrogenation and oxidation during storage using a polyphenol oxidase containing extract from red clover

Polyunsaturated fatty acid (PUFA) are to a large extent subject to biohydrogenation in a ruminal environment, which results to the healthy value of these PUFA being lost upon dietary addition to ruminants. PUFA are also prone to lipid oxidation upon storage. Therefore, it was tested whether emulsions could be protected against in vitro ruminal biohydrogenation and oxidation during storage by using protein extracts rich in polyphenol oxidase, an enzyme responsible for browning of plant tissues. PUFA rich emulsions were made with a protein extract from red clover (Trifolium pratense L.) before adding a synthetic diphenol (4-methylcatechol) to induce protection. Results after in vitro incubation confirmed the hypothesis and indicated the potential to prevent PUFA in linseed or fish oil from ruminal biohydrogenation and oxidation during storage through addition of 4-methylcatechol to the emulsions. Protection depended on the amount of oil present and protein concentrations in the emulsions. Protection efficiency increased with increasing the amounts of diphenol present in the emulsion per unit interfacial surface area. It is suggested that protection is caused by an effective encapsulation by cross-linking of the protein layer at the emulsion interface. For the first time, a method is described to protect PUFA using an enzyme abundantly available in nature, polyphenol oxidase, in combination with 4-methylcatechol.

The Importance of the Cosolvent Propylene Glycol on the Antimicrobial Preservative Efficacy of a Pharmaceutical Formulation by DOE-Ruggedness Testing

The aim of this study was to statistically evaluate the influence of the concentration of the co-solvent propylene glycol on the preservative efficacy of a complex pharmaceutical suspension-emulsion formulation containing methyl- and propylparaben. Preservative Efficacy Tests (PETs) were performed using the validated pharmacopoeial methodology with five test organisms over 1 month on lab-scale test formulations. These were independently prepared according to a Box-Behnken experimental design with a triplicate central point at 0.22% m/m methylparaben, 0.22% m/m propylparaben, and 2.75% m/m propylene glycol, and with an additional corner point of the Box-Behnken cube. We evaluated the preservative efficacies against the criteria of the United States Pharmacopeia (USP) and European Pharmacopoeias (PhEur) for formulations for oral use, as well as by the statistical comparison of the slopes obtained by linear regression of log (CFU/g) vs. time. With an initial bacterial challenge of 106 CFU/g for each of the three bacterial strains, no survivals were detected after 7 days. For the two fungal strains, box plots and analysis of variance showed significant, concentration-dependent, main effects: the three variables significantly influenced the kill-rate of C. albicans, while A. niger was predominantly influenced by the cosolvent propylene glycol, and only to a minor extent by methylparaben and not at all by propylparaben. These findings were confirmed by taking the pharmacopoeial criteria as the evaluation basis, where the dominant influence of propylene glycol concentration is apparent. It was concluded that the cosolvent propylene glycol is at least of equal preservative importance than both parabens.

Colloid–membrane interaction effects on flux decline during cross-flow ultrafiltration of colloidal silica on semi-ceramic membranes

In order to investigate colloid–colloid, as well as colloid–membrane interaction effects on the flux decline occurring during membrane processes, filtration tests were performed at different electrolyte concentrations, as well as at different pH values. The surface properties of the colloidal silica particles were determined by electrophoretic light scattering, whereas the surface charge characteristics of the ultrafiltration membranes were derived from streaming potential measurements. From the flux versus transmembrane pressure curves, it was derived that both high and low salt concentrations were preferable to optimise the permeate flux provided that both particles and membrane had similar charge characteristics. At low salt concentration, this behaviour was due to colloid–colloid as well as colloid–membrane repulsive interactions, which largely reduced concentration polarisation. At high salt concentrations, flocculation of the colloidal dispersions gave raise to large, porous flocs. As a consequence of the latter effect, the concentration–polarisation layer became highly permeable. On the other hand, a severe flux decline was observed at pH conditions where the colloidal particles and the ultrafiltration membrane were oppositely charged, giving rise to attractive electrostatic interactions. The results indicate that the performance of ultrafiltration membranes is strongly affected by its interaction with the colloidal particles in the feed. Optimum conditions are obtained if repulsive interactions prevail, which may be accomplished by proper conditioning of the feed.

Partial resolution of molecular species during liquid chromatography of soybean phospholipids and effect on quantitation by light-scattering

SummaryUsing both synthetic phospholipids and soybean phosphatidylcholine (PC), it is shown that the retention of phospholipids during normal-phase chromatography is not only determined by the polar headgroup, but also by the fatty acid composition. Although fatty acid methyl ester determinations reveal that this effect only causes an enrichment of some fatty acids in subsequent fractions of the same phospholipid class, still a large influence on the peak shape is observed. As a further consequence, the evaporative light scattering detector output is greatly affected, so that accurate quantitation of phospholipid classes requires the availability of standards of the same origin.

Comparison of emulsifying properties of milk fat globule membrane materials isolated from different dairy by-products

Emulsifying properties of milk fat globule membrane (MFGM) materials isolated from reconstituted buttermilk (BM; i.e., BM-MFGM) and BM whey (i.e., whey-MFGM), individually or in mixtures with BM powder (BMP) were compared with those of a commercial dairy ingredient (Lacprodan PL-20; Arla Foods Ingredients Group P/S, Viby, Denmark), a material rich in milk polar lipids and proteins. The particle size distribution, viscosity, interfacial protein, and polar lipids load of oil-in-water emulsions prepared using soybean oil were examined. Pronounced droplet aggregation was observed with emulsions stabilized with whey-MFGM or with a mixture of whey-MFGM and BMP. No aggregation was observed for emulsions stabilized with BM-MFGM, Lacprodan PL-20, or a mixture of BM-MFGM and BMP. The surface protein load and polar lipids load were lowest in emulsions with BM-MFGM. The highest protein load and polar lipids load were observed for emulsions made with a mixture of whey-MFGM and BMP. The differences in composition of MFGM materials, such as in whey proteins, caseins, MFGM-specific proteins, polar lipids, minerals, and especially their possible interactions determine their emulsifying properties.

A methodological approach for direct quantification of the activated sludge floc size distribution by using different techniques

The activated sludge floc size distribution (FSD) is investigated by using different measurement techniques in order to gain insight in FSD assessment as well as to detect the strengths and limitations of each technique. A second objective was to determine the experimental conditions that allow a representative and accurate measurement of activated sludge floc size distributions. Laser diffraction, Time Of Transition (TOT) and Dynamic Image Analysis (DIA) devices were connected in series. The sample dilution liquid, the dilution factor and hydraulic flow conditions avoiding flocculation proved to be important. All methods had certain advantages and limitations. The MastersizerS has a broader dynamic size range and provides accurate results at high concentrations. However, it suffers from an imprecise evaluation of small size flocs and is susceptible to particle shape effects. TOT suffers less from size overestimation for non-spherical particles. However, care should be taken with the settings of the transparency check. Being primarily a counting technique, DIA suffers from a limited size detection range but is an excellent technique for process visualization. All evaluated techniques turned out to be reliable methods to quantify the floc size distribution. Selection of a certain method depends on the purpose of the measurement.

Design and Development of Magnetoliposome-Based Theranostics

Magnetoliposomes (MLs) consist of nanometre-sized magnetite cores, enwrapped by a bilayer of phospholipid molecules. In the past we showed that these nanocolloids can be exploited as powerful biocompatible magnetic resonance imaging (MRI) contrast agents. In the present work, we report on the partitioning of the amphiphilic drug, (R/S)-propranolol, within the lipidic envelope of MLs, built up of the zwitterionic dimyristoylphosphatidylcholine. Furthermore, it is also shown that MLs are easily internalized by 3T3 fibroblasts, used in this study as a representative cell model, without damaging cell viability. Overall, the results deliver the proof-of-concept that drug-loaded MLs have great potential as unique intracellular theranostics, i.e., as a nanoscale delivery system with combinatory therapeutic-diagnostic imaging modalities.