Particle carrier materials

When the reaction product is soluble in water, enzyme regeneration is difficult to achieve, since the enzyme is often lost during isolation of the product. One way to overcome this problem is application of immobilised enzyme systems. The enzyme is either covalently or ionically attached to an insoluble carrier material or is entrapped in a gel. Depending on the size of the particles used, a simple filtration and washing procedure can be used to separate the immobilised enzyme from the dissolved product A well-known example of this technique is the industrial production of 6-APA. 

Adhesive mixtures require large carrier crystals to improve the handhng properties of the powders. Dispersion of the small drng particles over the larger carrier material should assure dose uniformity. However, the small dmg particles shonld be removed from the carrier material dnring inhalation, to render an aerosol clond of respirable particles. If the particles remain on the carrier, month or throat deposition of the drng will occur, which might decrease therapeutic efficacy or cause serious side-effects. 

Other studies have shown how monodispersed silica particles can be used as carrier material for pigments and dyes (68-73). Various reactive dyes, containing a sulfonic acid group, can be attached to the surface or incorporated into the growing silica particles (71). The resulting pigment particles have better color properties due to the con-... 

Encapsulated Flavors. Modified procedures during the past decade have permitted the preparation of encapsulated flavors with flavor levels over twice that of prior available products. Spray drying has been the principal key to this success. First, an oil flavnr is emulsified into an aqueous solution or is dispersed in an edible carrier material, after which the emulsion is pumped through an atomizer into a high-temperature chamber. The water evaporates rapidly, and particles of carrier material are formed around the flavor. However, some of the flavor component reaches the surface of the product. This requires the addition uf antioxidants to suppress oxidative changes in the flavor ingredient. 

To give the particles the required momentum, they should be densely packed and rigid and have a well-defined narrow particle size distribution. Friable and oblique particles are not desirable because the penetration depth will increase if the particle characteristic is more variable (Hickey 2001). Studies have been performed with particles ranging from 20 to 40 J,m in size and 1.1 to 7.9 g/cm3 in density impacting human cadaver skin (Kendall et al. 2000). Velocities of up to 260 m/s were applied to particles of this size range. For many applications, smaller particles of about 1 to 4 j,m diameter may be required for an optimized delivery. To deliver particles of this size into the skin, higher densities and impact velocities are required. For this reason, gold particles are used as a carrier material for the delivery of plasmid DNA vaccines (Kendall et al. 2001). 

Wetability and dispersibility. The carrier material may also have an enhancing effect on the wetability and dispersibility of the drug in the dissolution media. This should retard any agglomeration or aggregation of the particles, which can slow the dissolution process. 

The pyrolyser is a patented rotating cone reactor. Biomass particles ( 1) are fed near the bottom of the pyrolysis reactor (Rl) together with an excess flow of hot heat carrier material such as sand, where it is being pyrolysed at 500 to 600°C. The... 

The fact that a considerable part of the organic substances in tbe atmosphere exists adsorbed onto particles, supports the use of carrier materials in the UV-irradiation experiments. The investigations show that "organic compounds (chlorinated olefins and freons) picked as model substances are very rapidly degraded to CO2 and HCl if they are irradiated with wavelenths above 290 nm adsorbed on surfaces [7,8 ]. 

On account of the numerous chain joints subject to the abrasive action of dust and fine particles of material, the depreciation of bucket carriers is much more rapid when in operation than when idle, so, provided the hours of operation per year number 60 per cent or more of the available annual working hours—usually taken as 2,500— depreciation per year is customarily taken as chargeable only during actual working hours. 

When the fine droplets of emulsion created by atomization come into contact with the hot air within the drying chamber, the moisture evaporates and the carrier material solidifies. Hereby particles of the flavour base are trapped within a dry shell formed by the carrier. 

A reduced reaction rate may result from external diffusional restrictions on the surface of carrier materials. In stirred tanks external diffusion plays a minor role as long as the reaction liquid is stirred sufficiently. Further, partition effects can lead to different solubilities inside and outside the carriers. Partition has to be taken into account when ionic or adsorptive forces of low concentrated solutes interact with carrier materials [81 - 83]. The most crucial effects are observed in porous particles due to internal or porous diffusion as outlined below. 

In packed bed reactors the enzyme-catalyzed reaction is carried out in a column of 100 pl-10 ml volume. The column is filled with tiny particles bearing the immobilized enzyme. The continuously formed reaction product is indicated colorimetrically or electrochemically. Enzyme carrier materials with advantageous flow behavior are porous glass with pores of a defined size, organic polymers, like nylon powder, and inorganic polymers. 

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