The Wurster process is a coating technique that is well suited to uniformly coat or encapsulate individual particulate materials. This technology is characterized by the location of a spray nozzle at the bottom of a fluidized bed of solid particles. The particles are suspended in the fluidizing air stream that is designed to induce a cyclic flow of the particles past the spray nozzle. The nozzle sprays an atomized flow of coating solution, suspension, or other coating vehicle. 

The atomized coating material collides with the particles as they are carried away from the nozzle. The temperature of the fluidizing air is set to appropriately evaporate solution or suspension solvent or solidify the coating material shortly after colliding with the particles.

All coating solids are left on the particles as a part of the developing film or coating. This process is continued until each particle is coated uniformly to the desired film thickness.

The Wurster process is an industry recognized coating technique for precision application of film coat to particulate materials such as powders, crystals, or granules. The technology can be used to encapsulate solid materials with diameters ranging from near 50µm to several centimeters.   The process has a greater drying capacity than other coating systems due to a relatively high fluidizing air velocity. Since the particles actually separate as they are carried away from the nozzle, it is possible to coat small particles without agglomeration. Coating possibilities are relatively unlimited including the ability to place a hydrophilic coat on a hydrophobic core, or a water-based coat on a water-soluble core.  Coating properties can be optimized with coat formulation parameters, processing conditions, and layering.

Applications of the Wurster Process

Pharmaceutical: The coating of pharmaceuticals helps ensure stability and prolong the shelf life of reactive ingredients.  Capsules may be coated for improved capsule barrier properties.  Coating is a most effective way of masking the taste or odor of a particular drug, making products more palatable. Time release and controlled release properties can be readily achieved through Wurster processing with proper coating formulas and the use of enteric coatings.

Foods: In the food industry the Wurster Process has been used to encapsulate vitamins, minerals, and functional food ingredients. Food ingredients can be coated to mask an undesirable flavor or improve stability and shelf life. Thin or partial coatings are very effective in reducing the caking of certain materials.

Nutraceutical:  Nutritional ingredients may require a coating to optimize stability of an ingredient or product.  Ingredient release properties can be optimized for intended health benefits.

Animal Feeds: Nutrients, medicine and other additives may be taste masked to improve acceptance by the animals. Medicaments may be stabilized by protective coatings. Coatings may also be used to delay release after ingestion.

Chemical:  Coatings of chemicals can provide controlled or delayed release properties, change absorption or surface properties, or isolate active chemical in a mixture.  The Wurster process has the capacity to utilize a wide variety of coating materials; thus, permitting great flexibility in product design.

Agricultural: Seeds have been coated for easier handling and to increase their size to permit machine planting.  Coating may contain pesticides and/or nutrients to improve germination and yields.  Rodenticides are coated to provide taste masking and controlled release properties.

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