Kellie K. Sluga*, Grace May Alba, Minhthi Bui, Paroma Chakravarty, Hao Helen Hou.

Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, United States

Purpose. Dry particle coating with nano-silica is commonly used to improve the flowability of cohesive active pharmaceutical ingredients (APIs). This work assesses one element of nano-silica coating that remains understudied—its impact on the compaction properties of the coated materials. 

Methods. Eight cohesive proprietary APIs with varying particulate and bulk properties were dry coated with two different grades of Aerosil using an acoustic mixer.  The coated APIs specific surface area, surface energy, and flowability were characterized. Their compaction properties were assessed by compressing tablets on a compaction simulator at pressures ranging from 50-250MPa. 

Results. Aerosil coating led to higher surface area and lower surface energy for all tested APIs.  While no significant effect of Aerosil coating was observed on the compressibility, residual die-wall pressure, elastic recovery, and plastic energy of the coated APIs, its impact on the material compactability was more complex – materials coated with Aerosil R972 tended to have tensile strength that was marginally higher, if at all, than the uncoated counterparts, whereas those coated with Aerosil 200 were universally stronger than the uncoated samples. Interestingly, Aerosil coating also appeared to make some of the APIs less susceptible to tablet defects (e.g. lamination).  This suggests that the increase in inter-particle bonding following the increase in surface area may be sufficient to prevent these defects from occurring. 

Conclusions. Nano-silica dry coating resulted in comparable or improved compaction properties of cohesive APIs. As such, it can be utilized to improve the flowability of these materials without negatively impacting their ability to be tableted.