Abstract: A spiral inertial microfluidics device has been designed for use as a microfluidic sorting device. The device includes a spiral microchannel in which particles or cells of different sizes go through regions having different magnitudes of inertial and/or drag forces and equilibrate at different lateral positions in the microchannel so that those particles or cells of different sizes are separated. Using different focusing characteristics of larger versus smaller particles/cells in the spiral microchannel, adventitious agents (AAs) such as bacteria, virus, mycoplasma, etc. can be selectively removed from cells such as those producing therapeutic enzymes or monoclonal antibodies or those comprising the product itself.