(W0930-06-33) Increased Spray Rates for Particulate Coating Using Wurster Pro Technology

Purpose: Bottom spray Wurster coating is a widely used process for applying API or functional coating for sustained and extended release or just barrier coating on to multi-particulates. In many cases, the process can be very long because high spray rates are not able to be achieved without agglomerating the particulates. This is especially true when using coating systems that are tacky. For such systems, talc or other glidants are typically added to the coating solution which helps to reduce the tendency of agglomeration. This allows for slightly faster spray rates. One of the draw backs of such systems is that there are solids suspended in the solution which can cause sedimentation and plugging of spray nozzles. Such suspensions also need to be stirred continuously to avoid any such issues during processing. Wurster Pro was developed as a novel method to remove talc or any such anti-tacking agents from coating solutions and supplied in a powder form without sacrificing its advantages to attain high spray rates. The primary goal of this work was to evaluate if Wurster Pro can provide comparable coating efficiency at relatively higher spray rates than the standard Wurster process.

Methods: The coating trials were conducted using a VFC-Lab 3 FLO-COATER® (Freund-Vector Corporation) with an 8” Wurster insert and a VFC-15M FLO-COATER® (Freund-Vector Corporation) with a 9" Wurster insert. For the Wurster Pro set-up, a precision powder feeder (Coperion, K-Tron), was used to deliver anti-tacking agent, talc, during the process. For both the processes, 3 kg sugar spheres (Suglets® 18/20) were used as a core material. The coating formulation for the standard Wurster process contained 7.5% w/w ethyl cellulose, 0.75% w/w dibutyl sebacate (DBS), 2.5% w/w micronized talc in ethanol:water mixture (9:1 w/w). This formulation served as a discriminating coating system to compare the standard Wurster and Wurster Pro processes due to its significantly tacky nature. The Wurster Pro formulation was the same as the standard process except that the talc was applied in a dispersed powder form. The talc was added at a rate of 0.67 g/min and 0.82 g/min for VFC-Lab 3 and VFC-15M trials, respectively. The process was considered complete when theoretical weight gain of 5%w/w was achieved. The coated pellets were dispersed in DI water and aliquots were subjected to loss-on-drying for evaluation of %solids released over a period of time to evaluate comparative coating efficiency between the two processes. The talc powder used for Wurster Pro was dispersed into a fine mist by supplying compressed air (accelerator air) to further improve coating efficiency and reduce agglomeration.

Results: The main difference between the standard Wurster process and the Wurster Pro set-up was the method of application for the talc. The Wurster Pro process in a VFC-Lab 3 allowed a spray rate of 26 g/min compared to 19 g/min for the standard process which was 31% faster and reduced processing time by 24%. Similarly, the Wurster Pro trials conducted in the VFC-15M allowed for 20% faster spray rates than the standard Wurster and reduced the processing time by 18%. Both the processes produced comparable coating efficiencies.

Conclusion: The Wurster Pro provided two major advantages over the standard Wurster process. It allowed anti-tacking agent, talc, to be removed from the coating solution and added in a powder form. It also permitted to process at increased spray rates and thus, reduced the overall processing time. The Wurster Pro process was scalable and highly reproducible.

Acknowledgements: The authors would like to thank Colorcon (Shawn Engels) for providing the raw materials for the presented work.