Measurement of Average Aggregate Density by Sedimentation and Brownian Motion Analysis.
The spatially averaged density of protein aggregates is an important parameter that can be used to relate size distributions measured by orthogonal methods, to characterize protein particles, and perhaps to estimate the amount of protein in aggregate form in a sample. We obtained a series of images of protein aggregates exhibiting Brownian diffusion while settling under the influence of gravity in a sealed capillary. The aggregates were formed by stir-stressing a monoclonal antibody (NISTmAb). Image processing yielded particle tracks, which were then examined to determine settling velocity and hydrodynamic diameter down to 1 μm based on mean square displacement analysis. Measurements on polystyrene calibration microspheres ranging in size from 1 to 5 μm showed that the mean square displacement diameter had improved accuracy over the diameter derived from imaged particle area, suggesting a future method for correcting size distributions based on imaging. Stokes' law was used to estimate the density of each particle. It was found that the aggregates were highly porous with density decreasing from 1.080 to 1.028 g/cm3 as the size increased from 1.37 to 4.9 μm.
['Cavicchi|Richard E|RE|', 'King|Jason|J|', 'Ripple|Dean C|DC|']
D000911:Antibodies, Monoclonal D004058:Diffusion D004867:Equipment Design D057446:Hydrodynamics D007091:Image Processing, Computer-Assisted D008853:Microscopy D008863:Microspheres D009038:Motion D010316:Particle Size D011137:Polystyrenes D016062:Porosity D066329:Protein Aggregates
protein aggregates flow imaging image analysis microscopy particle sizing physical characterization