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Comparison and development of particle coating devices [Primerjava in razvoj naprav za oblaganje delcev]
Abstract
Particle coating technology is a process that is being used in pharmaceutical industry for many decades. Particles are coated with the purpose of taste masking of unpalatable substances, protection from light, moisture and oxygen from the atmosphere surrounding the particles, aesthetic reasons, better acceptance by users and modified release. In this article the coating process is presented in term of process equipment. Various process equipment can be used for particle coating, which is in general divided to coating drums and fluid bed devices. The first part comprehends some of the most important improvements in drum coating technology. Additionaly the fluid bed technology is described together with certain device subtypes that have enabled more efficient coating deposition and production of high quality and uniformly coated particles.
... In the pharmaceutical industry it is used to coat tablets or pellets with drug substances or functional films that, e.g. control the release of the drug substance [3][4][5][6]. The process typically takes place in a fluid bed, as illustrated in Fig. 1, in which particles are kept near minimum fluidization by a fluidization air flow that is supplied through a distributor plate at the bottom of the fluid bed. ...
Particle cycle and residence time distributions in different regions, particularly in the spray zone, play an important role in fluid bed coating. In this study, a DEM-CFD (discrete element method, computational fluid dynamics) model is employed to determine particle cycle and residence time distributions in a laboratory-scale Wurster fluid bed coater. The calculations show good agreement with data obtained using the positron emission particle tracking (PEPT) technique. The DEM-CFD simulations of different size particles show that large particles spend a longer time in the spray zone and in the Wurster tube than small particles. In addition, large particles are found on average to move closer to the spray nozzle than small particles, which implies that the large particles could shield small particles from the spray droplets. Both of these effects suggest that large particles receive a greater amount of coating solution per unit area per cycle than small particles. However, the simulations in combination with the PEPT experiments show that this is partly compensated for by a longer cycle time for large particles. Large particles thus receive more coating per unit area per pass through the spray zone, but also travel through the spray zone less frequently than small particles.
Microencapsulation is a process in which tiny droplets or solid particles are surrounded with a continuous layer of appropriate material in order to protect the encapsulated core or modify its properties. In recent years rapid development of microencapsulation technology can be observed also in the field of pharmaceutical technology. Microencapsulation enables protection of incorporated drug, controlled drug release, transformation of the aggregate state of material, and enhanced water dispersibility of hydrophobic drugs. Due to high diversity of methods, this paper proposes a classification and description of the main microencapsulation technologies. When deciding for microencapsulation technique one should consider that available methods can not be used universally, therefore the goal and the characteristics of encapsulate should be considered carefully. Afterwards suitable matrix material and process conditions can be selected in relation to the desired size and morphology of microcapsules as well as encapsulation efficiency and drug release mechanism.
As there is strong interest in coating increasingly smaller particles or pellets for use in compacted dosage forms, there is a need for better small particle coating systems. This study explored the use of swirling airflow to enhance the performance of the bottom spray coating system. Firstly, pellet coating in the non-swirling airflow of conventional Wurster coating was compared with that of swirling airflow in precision coating under standardized conditions. Secondly, precision coating was studied in greater details at different airflow rates (60-100m(3)/h) and partition gaps (6-22mm). Precision coating was found to have higher Reynolds numbers (Re) than Wurster coating, indicating higher turbulence. It produced coated pellets of better properties than Wurster coating, having less agglomeration and gross surface defects, more uniform coats, increased flow and tapped density, and slower drug release. Higher surface roughness did not affect the yield. In precision coating, increasing airflow rates decreased the degree of agglomeration but had minimal effect on pellet quality attributes (colour intensity, colour uniformity and surface roughness) and yields. Increasing partition gaps increased the degree of agglomeration proportionally, but this effect was small. However, greater changes in yield, surface roughness, colour intensity and colour uniformity were detected. This study showed that precision coating, while having a higher drying ability, was able to maintain the same yield and produce coated pellets with superior quality compared to Wurster coating. In precision coating, airflow rate had greater influence on the drying of pellets while partition gap had greater influence on pellet quality attributes.