Relation between surface roughness of free films and process parameters in spray coating.

A novel spraying apparatus was developed to obtain reproducible free sprayed films. Aqueous solutions of PolyVinyl Alcohol PVA 4-98, HydroxyPropyl MethylCellulose HPMC 603 and HPMC 615 were used as reference coating materials. The apparatus is composed by a spraying system, a closed chamber containing a rotating Teflon cylinder, a pressured air supply system, a spray solution supply system, and a computerized control system. The spraying air pressure, the cylinder rotation speed, and the cylinder-spray nozzle distance were tailored in such a manner that the roughness of the obtained free films was similar to that from reference coated particles. Optimum spraying process conditions were found for all three coating materials using design of experiments. The morphology of the sprayed films obtained using the optimum conditions is evaluated by means of scanning electron microscopy (SEM), and atomic force microscopy (AFM), and then compared with those from corresponding cast films and coating layers on particles. A match was found between the morphology of sprayed films and that from the corresponding coating layer on the particle surface. The spray apparatus produced reproducible sprayed films with tuneable roughness and/or smoothness depending on the set of processing parameters.

Characterization of physical and viscoelastic properties of polymer films for coating applications under different temperature of drying and storage.

The increasing tendency to enhance consumer products with added functionality is leading to ever more complex products. Nowadays more and more particulate products are coated to give the product specific functionalities. An appropriate approach is needed to be able to satisfy customer's requirements. In this work, three reference well-known coating agents, namely two grades of hydroxypropyl methylcellulose (HPMC) and one polyvinyl alcohol (PVA) were selected and investigated. Aqueous solutions of such polymers were obtained and viscosity and shear stress were measured function of shear rate, temperature and polymer concentration. The viscosities of the solutions appear to be mainly shear rate independent, they clearly show Newtonian behaviour. Drying and storage conditions influence on morphology and structure of the cast films were evaluated using scanning electron microscope (SEM). Dynamic mechanical thermal analysis (DMTA) experiments were carried out on HPMC and PVA cast films to assess the viscoelastic properties over wide temperature-frequency range. The time-temperature superposition principle was used to determine the shift factor, aT, and to compose a master curve. Magnitudes and profiles of storage modulus, E', loss modulus, E'', and tan delta master curves are discussed with relation to drying and storage conditions. No impact of drying temperature on the polymer properties was observed whereas the effect of storage temperature resulted to be relevant in terms of shifts in glass transition temperature and, only partially, changes in the magnitudes of E' and E''.

Detection of odorous compounds in breath.

Previous studies have demonstrated that hydrogen sulfide and methyl mercaptan play a major role in oral malodor. In the present study, we tested the hypothesis that other compounds found in mouth air can also contribute to halitosis. Mouth air of 40 healthy volunteers and 40 persons with halitosis was analyzed and compared by gas chromatography-mass spectrometry, two sulfur monitors, and organoleptically. Nearly 700 different compounds were detected. Hydrogen sulfide, methyl mercaptan, dimethyl sulfide, di- and trisulfide were increased in persons with breath odor. These compounds were all significantly correlated with the organoleptic score. We concluded that hydrogen sulfide, methyl mercaptan and, to a much lesser extent, dimethyl sulfide, di- and trisulfide can contribute to oral malodor. The role of other compounds, such as amines and organic acids, seems insignificant.

Strategy for selection of methods for separation of bioparticles from particle mixtures.

The desired product of bioprocesses is often produced in particulate form, either as an inclusion body (IB) or as a crystal. Particle harvesting is then a crucial and attractive form of product recovery. Because the liquid phase often contains other bioparticles, such as cell debris, whole cells, particulate biocatalysts or particulate by-products, the recovery of product particles is a complex process. In most cases, the particulate product is purified using selective solubilization or extraction. However, if selective particle recovery is possible, the already high purity of the particles makes this downstream process more favorable. This work gives an overview of typical bioparticle mixtures that are encountered in industrial biotechnology and the various driving forces that may be used for particle-particle separation, such as the centrifugal force, the magnetic force, the electric force, and forces related to interfaces. By coupling these driving forces to the resisting forces, the limitations of using these driving forces with respect to particle size are calculated. It shows that centrifugation is not a general solution for particle-particle separation in biotechnology because the particle sizes of product and contaminating particles are often very small, thus, causing their settling velocities to be too low for efficient separation by centrifugation. Examples of such separation problems are the recovery of IBs or virus-like particles (VLPs) from (microbial) cell debris. In these cases, separation processes that use electrical forces or fluid-fluid interfaces show to have a large potential for particle-particle separation. These methods are not yet commonly applied for large-scale particle-particle separation in biotechnology and more research is required on the separation techniques and on particle characterization to facilitate successful application of these methods in industry.

Quantification of solid cell material by detection of membrane-associated proteins and peptidoglycan.

Quantification of solid cell material (cell debris) is necessary for the optimisation of the efficiency of bioseparations. Cell debris can be quantified by detection of a component present in the cell wall that can act as a marker for cell debris. Membrane-associated proteins have previously been used as a marker for cell debris. This marker was quantified by SDS-PAGE with densiometry. In this paper cell debris quantification methods are presented that are faster and more accurate, i.e. membrane-associated protein quantification with the Protein 50 Labchip of Agilent Technologies, or that make use of peptidoglycan as marker for cell debris, i.e. a spectrophotometric muramic acid assay.