Fluid bed film coating of fine ibuprofen particles

Fine pharmaceutical powders pose significant challenge in fluid bed (FB) film coating due to their high cohesion. Ibuprofen powders, considered as model Geldart group C powders with Sauter mean diameters of 41 μm (coarse) and 22 μm (micronized), could not be fluidized due to severe agglomeration, solid-bridging, and poor flowability. Dry coating, applied as a pre-processing method that coats nano-silica on the surface of ibuprofen, enabled sufficiently improved flow, hence fluidization via reduced cohesion. Resulting coarse and micronized ibuprofen powders were successfully polymer film coated in a top spray fluidized bed. As a major novelty, apart from pre-processing through 20 nm silica surface coating that enabled fluidization, agglomeration during FB processing was minimized by introducing 180 nm colloidal silica particles that were pH stabilized in polymer spraying suspension using NaOH. In contrast, lack of or poorly stabilized colloidal particles led to significant agglomeration. Spray rate and fluidization velocity were both investigated to understand their effect on agglomeration of the coarse ibuprofen powders. Increased spray rate led to increased agglomeration due to the overly wet conditions, while increased fluidization velocities unexpectedly led to increased agglomeration resulting from electrostatic charging. To simplify the experimental design, a simple scaling relationship was introduced to estimate the coating conditions for the micronized ibuprofen powders based on the processing conditions of the coarse ibuprofen powders. This relationship, based on the minimum fluidization velocity, led to comparable agglomeration levels for powders with Sauter mean diameters of 21 and 42 μm. To the author's knowledge these are the first successful results where micronized pharmaceutical powders were polymer coated in a traditional top spray fluidized bed.