Summary
Laser-light scattering was used to observe and quantify the dynamics of human blood
platelet aggregation in platelet-rich plasma (PRP). Aggregation was performed in a
controlled shear environment by placing the PRP in the annular space between a rotating
cylindrical rod and a stationary cylindrical tube. The instrument was capable of very
sensitive continuous semi-quantitative measurements of chemically-induced microaggregation.
As a demonstration of the technique, results are presented for ADP-induced aggregation
at doses of 10, 1, and 0.1 μM and collagen-induced aggregation at a dose of 5 μg/ml,
each at shear rates of 1,000 s-1 and 500 s-1. Extensive aggregation was observed in response to ADP at even the low dose of 0.1
μM, indicating a high sensitivity to microaggregates. The sensitivity of the ultimate
size of the ADP-induced aggregates to ADP concentration was shear dependent. The formation
of microaggregates by collagen stimulation was shown to be almost immediate, as contrasted
with a 10-20 s typical lag when observed turbidometrically. Disaggregation was observed
with 1 μM ADP, but this was only partial, as contrasted with the complete recovery
of transmittance observed in the turbidometric technique. Electronic particle sizing
and counting was employed to semiquantitatively verify the aggregate size distributions
found from mathematical conversion of the laser-light scattering data.
