Fine grade engineered microcrystalline cellulose excipients for direct compaction: Assessing suitability of different dry coating processes

Recent work showed that contrary to conventional wisdom, fine surface engineered excipients outperform their larger counterparts in blends of highly loaded blends of cohesive drug powders in terms of their packing, flowability and tablet tensile strength. Here, two continuous devices, fluid-energy mill (FEM) and conical mill (Comil), are compared with LabRAM, a batch device used in previous work, for nano-silica dry coating of microcrystalline cellulose (MCC) excipients, 20 and 30 μm. Coated MCCs from all three devices had higher bulk densities and flow function coefficients (FFCs) compared with Avicel PH-102. Silica coating quality was best with LabRAM, but also good with FEM and Comil, although Comil was less effective for the finer MCC. However, the better coating quality of LabRAM had a downside of having poorer compaction properties. The most surprising outcome was that multi-component blends of 17 wt% coated MCC with 60 wt % Ibuprofen 50 had higher bulk density, higher or similar flowability, higher tablet tensile strength, and comparable Ibuprofen dissolution from tablets, compared to those with Prosolv 50, a silicified excipient. The FEM dry coated MCC blends, having only 0.17 wt% silica, performed the best, having desirable bulk density, FFC, and tensile strength that could facilitate high-speed direct compression tableting. In summary, considering that achieving best coating quality need not be the primary objective, FEM may be the best option for producing desired sized dry coated fine excipients.