Quantitative method for the evaluation of biomicrocapsule resistance to mechanical stress

A quantitative method has been developed for the evaluation of biomicrocapsule resistance to mechanical stress. Fluorescein isothiocyanate-labelled dextran (M.W. 2 x 10(6)) was microencapsulated in alginate-poly-L-lysine membranes. Microcapsules of 302.0 +/- 3.2 microns were mixed with 3 mm glass beads and continuously agitated for 0 to 144 h. The percentage of broken capsules was calculated by measuring the fluorescence in the supernatant and in the residual intact capsules after the latter were dissolved. The fluorescence method was validated by comparison with a manual method (handpicking under a stereomicroscope). The highest percentage of broken capsules was obtained with a ratio of 225 +/- 25 glass beads per 1000 microcapsules. The percentage of broken capsules increased linearly from 7.3% at 12 h to 48.3% at 72 h of continuous agitation. The applicability of the method was evaluated by studying microcapsules of potentially different levels of resistance. The results confirmed that capsule resistance is improved by increasing poly-L-lysine concentrations and incubation times. Microcapsules made with guluronic acid-rich alginate were stronger than those made with mannuronic acid-rich alginate. In conclusion, this is a simple, precise and sensitive method for the quantification of biomicrocapsule resistance to mechanical stress.