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Batch fluid-bed processing equipment: A design overview; Part I
... Particle motion may be in a spouted bed, a vibro-bed, external recirculating beds or a Würster coater. For a comprehensive review of the operating principles, along with the advantages and disadvantages of the different coating equipment arrangements, the reader is referred to the works of [12][13][14]. ...
... The physical approach optimises the process conditions so that the forces causing agglomerate break-up dominate and overwhelm the forces tending to hold particles together [7]. This is evident in the many variations of fluidised bed equipment used in coating applications (e.g., [12][13][14]). The fluid beds used for coating were first used for agglomeration and drying and therefore encourage particle-particle interaction, which can be a problem for coating. ...
Air-suspension particle coating has been slow to develop in the food industry. This is not surprising considering the economic constraints for low cost ingredients and low cost processing. Therefore, a need exists to adapt the process and formulation knowledge developed in the high-value pharmaceutical and health care industries to higher volume, low-cost production in the food industry. This paper reviews the current state of the art of air suspension coating as applied to the food industry. Of the few current applications, most have been developed by statistical experimentation which belies an understanding at the interface between food science and process engineering. This review concludes that a phenomenological approach is necessary in order to advance knowledge and accelerate product development. Such an approach will yield results independent of both the substrate powder and the coating device, which can be applied widely to select suitable coating materials and methods of application. A following paper will then elucidate key micro-level phenomena and discuss their implications.
... Accurate adjustment of the inlet airflow rate was vital for successful granulation processes, especially when granulated with high process air humidity. The airflow was created by turbine fan suction located upstream from the product processing area, a common configuration (Olsen, 1989 ). Flow rate (g/s) was measured from the inlet air duct and fan speed (Hz, 1/s) from the turbine. ...
... Compensating techniques should be evaluated to further support the design space: higher temperature of the inlet air, higher flow rate of the inlet air (if possible) and slower or pulse spraying of the granulating liquid (Schaefer and Wørts, 1978a; Schaafsma et al., 1999; Morris et al., 2000 ). The best option would, however, be sophistication of the process air: a humidifier and a dehumidifier together control the dew point of the process air (Olsen, 1989; Greenhalgh and Westrup, 1997). If dehumidification is not possible, pulses of dry air may prevent over-wetting and bed collapse. ...
The physical measurements of a fluid bed granulator can be exploited in construction of an operating window, a design space, for process performance. The purpose of this study was to determine the influence of inlet air humidity changes on temperature in different parts of a granulator system, on fluidisation behaviour and on the particle size of the final granules. A humidifying setup was constructed on a bench-scale fluid bed granulator that enabled elevated humidity levels and sharp humidity changes of the inlet air. Ibuprofen granules were produced at the various inlet air humidity levels classified as low, intermediate and high. A novel fluidisation parameter was developed. The more improperly the particles were fluidising the smaller was the relationship of airflow rate and fan speed. Four different failure modes were identified and classified, based on the fluidisation parameter: over-fluidisation, risk of improper fluidisation, improper fluidisation and collapsed bed. It was possible to construct process trajectories for smooth fluidisation, which the optimal granulation process should follow.
... However, synthesizing the metal coated sphere involved a complicated procedure, and achieving the controlled thickness of the metal deposition on structures is crucial for designing the devices. In addition, numerous chemical and physical film coating methods have been recently developed, such as melt, superficial fluid, compression, self-assembly procedures, and fluidized bed spray drying methods [13][14][15][16]. The thin film can be deposited by physical vapour deposition (PVD) using solid-state reaction [17] and in-situ polymerization processes [18,19]. ...
In this work, a novel method for coating the polymeric substrate with an aqueous metallic powder (Aluminum) solution was developed. In the modified fluidized bed, assisted bottom spray coater was used to achieve the
strong interfacial coating of the aluminum on the fluidized spherical expanded polystyrene (EPS) substrate and polyvinyl alcohol (PVA) as a binder. The coated aluminum metal exhibits a layered thickness of 340 ± 50 µm.
The effect of fluidization airflow rate, spray rate, atomization air pressure, and inlet air temperature on the aluminum coating on the EPS spheres was investigated for the first time. The substantial integrity, interfacial bonding and surface morphology of aluminum coating were confirmed through XRD, FTIR, shaking test and SEM
analysis. In addition, a remarkably high dielectric constant of 12,000 compared to the dielectric constant of the pristine EPS sphere of 60 at low frequency was observed.
... The high-velocity zone is located bellow the draft tube where a jet of gas is employed to convey the particles upward through the draft tube until a certain height where the particles fall into the low velocity zone. 86,93,[106][107][108][109] The Wurster coating process is the most preferred method for the application of controlled release coating of the small particulates, particularly in pharmaceutical industries. It is reported that the Wurster process provides the most uniform and smoothest final product among different forms of fluidized bed coaters. ...
In this article, the coating of the particles is studied in different coating processes using various coating solutions. The solutions are mainly composed of solvent, polymer, plasticizer, colorant/opacifier and antitack agent. There are a number of polymeric solutions for the coating of the particles as explained in detail in this article. Different approaches have been used for the coating of the particles which can mainly be classified as melt coating, supercritical fluid coating, compression coating, and spray drying coating. Spray drying coating is considered as the most proper method for the coating of the multiparticulates (i.e., encapsulation) conducted in pan coaters and fluidized bed coaters. It is concluded that the fluidized bed coating method is the most promising and widely used technique for the coating of the particles in pharmaceutical, food, and agricultural industries. Accordingly, the coating of the particles in fluidized bed coating systems (i.e., top-spray fluidized bed, tangential-spray fluidized bed, and bottom-spray fluidized bed) is deeply described with the emphasis of the bottom-spray fluidized bed coating (Wurster) technique. This article concludes that the fluid bed coating technology has brilliant feature for the coating of the particles. It elucidates the advantages and limitations of each fluidized bed coating processes depending on the different application. The Wurster coating is the superior technique among the other coating methods in order to obtain uniform and high quality coating for the particulates. Finally, the coating mechanism in fluidized bed coaters is elaborated more deeply. The coating life cycle is divided into different stages including: (1) particle movement, (2) atomization, (3) wetting the particle surfaces, and (4) drying and film formation.
... STREA-1 has been widely used in the pharmaceutical industry to perform fluid-bed drying, granulation and coating of solid low-molecularweight drug powders (Olsen, 1989a,b). This coater came with two spraying designs, topspray and bottom-spray. ...
The feasibility of spray-coating fine lactose powders with recombinant human deoxyribonuclease (rhDNase) using a bench-top fluid-bed processor (STREA-1) was studied. The effect of operating parameters, system design and protein formulation on coating performance was evaluated and compared with a laboratory-scale, Würster processor (GPCG-1), as reported previously (Maa and Hsu, 1996a). Protein denaturation occurred during spray-coating in both processors, though to a lesser degree in STREA-1 than in GPCG-1. The cause of protein denaturation during coating was determined to be thermally induced and most likely occurred during drying. The combined effect of shear and heat on protein aggregation during atomization was found to be insignificant. GPCG-1 outperformed STREA-1 in terms of particle agglomeration and product yield. Particle agglomeration in the latter could be reduced by increasing the atomizing pressure and decreasing the liquid feed rate. Overall, this report demonstrates that it is feasible to use the bench-top fluid-bed processor for protein spray-coating, but the application on fine carriers ( < 100 μm) is limited.
... For particle coating, batch-type fluid-bed processors have long been used in the pharmaceutical industry for preparing solid dosage forms of non-protein-related drugs [78,79]. Due to recent advances in the development of fluid-bed coating systems such as the Würster spray coater, it allows powders as small in size as 50 µm to be coated and has further expanded the application of powder coating in the pharmaceutical industry [80,81,82]. ...
It is well known that protein/peptide-based drug formulations are more stable in the solid state than in the liquid state, thereby offering stability advantages in ambient temperature storage, product shipping/distribution, and long-term shelf life. Novel powder-based drug delivery systems recently emerging for applications in sustained release, inhalation, intradermal delivery, etc, add more value to protein solid dosage forms. Despite great research interests in understanding the drying effects on protein stability and a large collection of publications focusing on this area, systematic accounts of powder formation techniques are lacking. This review is to summarize a number of methods currently available for protein powder preparation. Some are common methods such as lyophilization, spray drying, pulverization, and precipitation, and some methods are more recently developed such as supercritical fluid precipitation, spray-freeze drying, fluidized-bed spray coating and emulsion precipitation. In addition to examining the individual process effect on protein stability that is always the focus of formulation scientists, this review also likes to evaluate each method from a more practical sense in terms of process versatility and scalability. The conclusion is that each method has its own advantages and the use of a method is formulation and application specific. With the understanding of the principles and advantages of these methods, it can benefit our choice on selecting appropriate techniques for preparing a desired protein powder formulation for specific applications.
... Fluid-bed spray coating has long been used in the pharmaceutical industry for oral solid dosage preparations of nonprotein-based drugs (15,16) and is a mature technology for coating macro-particles (200-1000 m) at large-scale production (>> 1 kg). Spray coating using 100-m seed particles became feasible only after Wü rster spray coaters were developed (17)(18)(19). ...
Fluid-bed spray-coating process is widely used to prepare non-protein pharmaceutical solid dosage forms using macro-size seed particles (200-1000 microm) at kilogram batch sizes. In this study we developed a small-scale fluid-bed spray-coating process (20 g) to produce micro-sized vaccine powder formulations (40-60 microm) for epidermal powder immunization (EPI) METHODS: A bench-top spray coater was used to spray two vaccines, diphtheria toxoid (dT) and alum-adsorbed hepatitis-B surface antigen (Alum-HBsAg), onto crystalline lactose particles of 40-60 microm in diameter. Particle properties such as particle size, surface morphology, and degree of particle agglomeration were determined. Protein stability was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The immunogenicity of the vaccine was evaluated in vivo by needle injection and epidermal powder immunization (EPI) of mice or guinea pigs.
Coating feasibility was demonstrated for both vaccine formulations containing different excipients. However, the nature of the vaccine antigen appeared to affect coating feasibility in terms of particle agglomeration considerably. Delivery of spray-coated dT and alum-HBsAg through EPI to mice and guinea pigs, respectively, generated significant antibody responses, at a level comparable to liquid formulation delivered subcutaneously through needle/syringe injection.
The new spray-coating process represents an important technical advance and may provide a useful tool for developing high-valued biopharmaceutical powder formulations for novel applications. The strong in vivo performance of the coated dT and alum-HBsAg powders by EPI further demonstrated that spray-coating is a viable dry powder formulation process and the skin's epidermal layer presents an efficient vaccine delivery route.
Preformulation is often used to describe the physical and chemical characteristics of substances and mixtures used in pharmaceutical products. It is part of the research and development (R&D) unit of the pharmaceutical industry. Both preformulation and formulation are parts of pharmaceutics, and their application in formulation development in the industry is known as the industrial pharmacy . Issues related to scaling‐up dosage forms from the R&D stage to the pilot stage and thereafter to production are numerous and often lead to failure in producing the planned dosage form unless addressed and resolved. Compliance with taking medications is a huge issue in clinical practice. Combination products offer one solution to improving patient compliance. Via transmucosal delivery system, drugs are transported through a transmucosal pathway by placing them in the mouth, nose, or another route.
This article addresses a case study of the development of a fluid bed spray drying process for a protein for agricultural uses.
This chapter discusses the fluidized bed coating and granulation. Fluidized beds, both with and without internals, offer many advantages over conventional granulation and coating equipment such as pans, drums, and mixers. Fluidized beds, by virtue of the air or gas required to fluidize the solids, typically have high rates of heat and mass transfer leading to uniform temperature distribution within the bed and relatively short processing times. Moreover, the shearing forces exerted in such beds help to control the formation of agglomerates, and the movement of fluidizing gas, including bubbles, which causes solids to circulate within the equipment providing a constant flow of bed particles through the spray zone, which is essential for uniform product quality. The main goal of this chapter is to provide a technical basis or framework for analyzing fluidized bed coating and granulation operations.
In the present research, an air-suspension fluidized-bed technique for generation of core and shell microcapsules containing probiotic Lactobacillusparacasei cells was evaluated. The air-suspension process was performed in a Wurster coater system with a bottom-spraying atomizer. In the first stage, a solution containing trehalose, maltodextrin, and probiotic cells was spray-coated onto and absorbed by the inert carrier microcrystalline cellulose to produce nonagglomerating dry coated particles with high probiotic cell viability (10 9 colony-forming units [cfu]/g particles). The effect of inlet air temperature, spray flow rate, solids concentration, cell concentration, and encapsulation formulation on survival was investigated. The inlet air temperature had the most pronounced effect; a 15 degrees C increase in inlet air temperature led to a 250-fold decrease in survival percentage. There was no agglomeration of the coated adsorbed particles at spray flow rates of 1 to 3.5 mL/min. Spray-coating was performed with both laboratory-and pilot-scale Wurster systems. Scaling up the equipment from the lab scale to the pilot scale did not affect cell survival percentage. Low solids concentration (<20%) and low probiotic cell concentration (6%) resulted in a fair survival percentage (35-40). Spraying a solution formulation of trehalose-maltodextrin with dextrose equivalent (DE) 3 at a 1: 1 ratio provided the best protection in terms of cell viability during the spray-coating process as well during storage. Layering with ethylcellulose (ETHOCEL) provided some protection in a low acidic environment (12%); however, the nonuniform coating and cracks detected by scanning electron microscopy (SEM) imaging were the main reasons for the layering's relatively poor protection of the cells against humidity, oxygen, and acid environment.
This study illustrates the application of experimental design and multivariate data analysis in defining design space for granulation and tableting processes. According to the quality by design concepts, critical quality attributes (CQAs) of granules and tablets, as well as critical parameters of granulation and tableting processes, were identified and evaluated. Acetaminophen was used as the model drug, and one of the study aims was to investigate the possibility of the development of immediate- or extended-release acetaminophen tablets. Granulation experiments were performed in the fluid bed processor using polyethylene oxide polymer as a binder in the direct granulation method. Tablets were compressed in the laboratory excenter tablet press. The first set of experiments was organized according to Plackett-Burman design, followed by the full factorial experimental design. Principal component analysis and partial least squares regression were applied as the multivariate analysis techniques. By using these different methods, CQAs and process parameters were identified and quantified. Furthermore, an in-line method was developed to monitor the temperature during the fluidized bed granulation process, to foresee possible defects in granules CQAs. Various control strategies that are based on the process understanding and assure desired quality attributes of the product are proposed. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.
Abstract This paper is a chronological survey of published work in the field of pharmaceutical fluidised-bed granulation. It begins with early experiments in the 1960s and continues to include all relevant published work up to 1990. To aid the reader find published material for further in-depth reading a cross reference to published articles on a subject basis is provided in tabular form.
This article documents a feasibility study on coating fine powders with protein solutions using a Würster spray coater (GPCG-1 from Glatt Air Techniques, Ramsey, NJ). Spray coating was based on a fluid-bed process where fluidized microcarriers were coated inside the Würster column and dried in the fluidization chamber. Recombinant human deoxyribonuclease (rhDNase) was used as the model protein. Lactose powders of two different size ranges, 53-125 and 125-250 microm, were used as the model microcarrier. The amount of protein applied was varied to obtain coatings of varying thickness. The extent of rhDNase loading determined experimentally was found to be consistent with the theoretical value and was also confirmed visually by scanning electron microscopy. The coating showed a strong integrity after being subjected to mechanical force. However, the protein suffered serious aggregation during coating, most likely due to the thermal stress of the process. Aggregation was significantly reduced when rhDNase was formulated with calcium ions, consistent with the observation that Ca(2+) thermally stabilized the protein (as determined by scanning microcalorimetry) in aqueous solution. Thus, our study demonstrates that spray coating, particularly when used in conjunction with rational stabilization strategies, is a feasible alternative to other methods of preparing dried pharmaceutical proteins.
The static bed- and planetary-type microwave dryers currently available to process pharmaceutical materials are not designed to use hot-air fluidization for the purpose of maximizing microwave energy inputs and particle drying. To take advantage of the benefits offered by fluidization, a 1-kg Uni-Gatt laboratory fluid bed processor was modified to support microwave-assisted fluid bed drying of several representative pharmaceutical granulations. The construction, design features, and validation of this new microwave fluid bed processor are presented.
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