HIGH-PRECISION MEASUREMENT OF THE SWELLING OF MICROSPHERES

For controlled release of drugs and other uses, the accurate and preci se measurement of swelling of polymer microsphere carriers is often cr ucial. Most currently available techniques were designed to measure hi gh degrees of swelling. We explored the use of digital light microscop y for the high precision measurement of small degrees of swelling of i ndividual microsphere particles. By using a camera to acquire images o f microspheres in a sample cell filled with solvent, accurate, precise , measurements of swelling were obtained. The technique has a precisio n of 0.52% change in the swelling of the volume of a microsphere. We c ompared this technique with a state-of-the-art gravimetric technique. Comparison of the two techniques revealed that as much as 84% of swell ing as measured by the gravimetric method is excess fluid arising from confounding factors such as adsorption and capillary effects. Compute r modeling shows that the inaccuracies are due entirely to liquid brid ge formation between the microspheres. (C) 1996 John Wiley & Sons, Inc .