Variance Between Different Light Obscuration and Flow Imaging Microscopy Instruments and the Impact of Instrument Calibration

Subvisible Particulate Contamination in Cell Therapy Products—Can We Distinguish?

“…Using the flow imaging microscopy method, we found that SvP contaminationsdand cell debrisdcan be differentiated from actual cells in cell therapy products by the analyst. While the flow imaging microscopy method is currently not suggested for quality control purposes for traditional drug products, 17,22 the method may offer value in a process assessment related to minimizing potential particulate contaminations and support product development and the particle control strategy for cell therapy products.…”

Improving Diameter Accuracy for Dynamic Imaging Microscopy for Different Particle Types

“…Interest in using dynamic imaging (also referred to as flow imaging or flow microscopy) as a quantitative tool for particle size analysis in biopharmaceuticals, especially as supplemental to or complementary to light obscuration is growing. 1,2 Assessing the number of particles with a size greater than a designated limit requires accurate measurement of particle size. For computing particle sizes, the instruments' image processing and analysis software has been based on the use of polystyrene latex (PSL) microspheres as the only available particles for calibration.…”

“…By changing the index of refraction of the solution, differences have been observed on the results reported from dynamic imaging instruments. 1,5,[7][8][9][10] The apparent concentration of silica microspheres and protein aggregates is reported to disappear when the index of refraction of the solution, modified by sucrose, approaches that of the aggregates. 8 Observations of silica microspheres in solutions using glycerol or 2-pyridinemethanol to modify the index of refraction showed that as the difference in refractive index between the particle and bulk liquid Dn goes to zero, the measured size of the microspheres decreases and the reported concentration decreases.…”

“…12 In understanding the performance of dynamic imaging systems, it has been useful to characterize index of refraction and thresholdsetting effects by measuring calibrated microspheres, whose known size was obtained by a separate method, in solutions of different Dn. Matter et al 1 reported a comparison of an instrument calibrated using 10 mm microspheres in water (conventional) with calibration in a more closely index-matched solution of sucrose and report differences for counts in different size ranges. This might be regarded as a first step toward a more realistic calibration, although the effects of size errors grow with decreasing size down to 1 mm, and the correspondence between microspheres of known Dn with actual particles or droplets found in therapeutic products is not clear.…”