| STUDY |
FIGS. 1 and 3 demonstrate the erosion curves for PCPM matrices without any cholic acid in phosphate buffer at 37.degree. C. and 60.degree. C. respectively. The weight of the matrices tested at each temperature weighed 23 and 18 milligrams; it is noted that the rate of surface erosion as much slower at 37.degree. C. than when placed at 60.degree. C. FIGS. 3 and 4 illustrate the effect of preeroding PCPM matrices at 60.degree. C. for 50 hours prior to being placed in 37.degree. C. and 60.degree. C. environments for a more extended time. The matrices tested at 37.degree. C. and 60.degree. c. weighed 74 and 25 milligrams respectively. It will be noted that the polymer erosion in each and every instance was 100% of the total mass of the matrix regardless of the time required for such surface erosion to be complete. In all instances as well, each matrix decreased in size and maintained their physical integrity throughout the entire duration of the test demonstrating that only surface erosion of the matrix occurred. It is also appreciated that in all instances the erosion rate is characterized by an induction period which is then followed by a linear loss of mass at a constant rate. All the empirical evidence thus demonstrates that a zero-order erosion reaction is in effect
|