Surface engineered excipients: II. Simultaneous milling and dry coating for preparation of fine-grade microcrystalline cellulose with enhanced properties.

A solventless process for simultaneously milling and dry coating microcrystalline cellulose (MCC) was investigated for producing fine excipients in five different sizes (∼20, 25, 30, 35, 40 µm) having high bulk density (BD), good flow function coefficient (FFC), and excellent compaction. Avicel PH-102, used as the starting material, was milled and coated with two grades of silicas, hydrophobic and hydrophilic (R972P and A200), using a fluid energy mill (FEM). Through judicious selection of the FEM feed rate, feeding pressure, and grinding pressure, five desired milled sizes were produced. The bulk density of all the milled-coated (1 wt% A200) excipients was significantly better than uncoated-milled MCC, Avicel PH-102, and Prosolv 50 and 90. Whereas the FFC values were greater than uncoated-milled MCC, Avicel PH-102, and Prosolv 50 (latter for ∼30, 35, and 40 µm sizes). The tablet compaction testing was used to evaluate compactibility (tensile strength vs tablet porosity), compressibility (tablet porosity vs compaction pressure), and tabletibility (tensile strength vs compaction pressure). The results indicate that all finer grade milled and A200 coated MCC had lower porosity and higher tablet strengths than Prosolv 50 and 90 at all compaction pressures. Surprisingly, the BD and FFC were better for A200 than for R972P coated-milled MCCs; explained through analyzing inter-particle contact models. Finally, milling did not increase the moisture content but coating with silica led to a slight increase; A200 higher than R972P. It is hoped that these engineered excipients would help formulators with a multitude of options for finer excipients without loss of flow and bulk density.