(726e) Unified Polymer Erosion Model

Hydrolytically degradable polymers have become standard in many applications and are being enthusiastically investigated for many more. When modeling the erosion of these polymers, they are typically first categorized as either bulk-eroding or surface-eroding, then modeled with assumptions tied to that assumed behavior. In fact, these are simply the extremes in a continuum of erosion behavior dictated by the polymer’s hydrolysis rate, moisture permeability, and thickness, along with modifying factors such as autocatalysis. Few polymers actually erode with perfect bulk- or surface- behavior, particularly among newer copolymers, blends, and composites. Moreover, some applications require not only bulk property information, but detailed information regarding the polymer’s structure—particularly when used as a barrier for controlled release applications.

This presentation introduces a stochastic, Monte-Carlo style model which calculates the erosion profile of a degradable polymer monolith based on its moisture diffusion coefficient, monolith thickness, and hydrolytic degradation rate constant, generating erosion profiles spanning the continuum from strongly bulk-eroding to strongly surface-eroding without any a priori assumptions about the erosion behavior. The location of the polymer on this surface-to-bulk erosion continuum is quantified by the Bulk Erosion Factor, which compares the polymer’s mean erosion time to the pure surface- and bulk-eroding ideals. The model generates time-evolving surface roughness parameters and the monolith’s average percolation time. Finally, it is applied to controlled release applications in calculating the release profile for an underlying drug layer.