Nondestructive Characterization of Biodegradable Polymer Erosion in Vivo Using Ultrasound Elastography Imaging

Significant advancements in biodegradable polymeric materials have been made for numerous biomedical applications including tissue engineering, regenerative medicine, and drug delivery. The functions of these polymers within each application often rely on controllable polymer degradation and erosion, yet the process has proven difficult to measure in vivo. Traditional methods for investigating polymer erosion and degradation are destructive, hampering accurate longitudinal measurement of the samples in the same subject. To overcome this limitation, we have utilized ultrasound elastography imaging as a tool to nondestructively measure strain of poly(lactic-co-glycolic acid) (PLGA) phase sensitive in situ forming implants (ISFI), which changes with progressive loss of structural integrity resulting from polymer erosion. Using this tool, we investigated erosion kinetics of implants comprised of three different PLGA molecular weights (18, 34, and 52 kDa) in vitro and in vivo. The in vitro environment was created using a novel polyacrylamide based tissue mimicking phantom while the in vivo experiment was performed subcutaneously using a rat abdominal model. A strong linear relationship independent of polymer molecular weight was found between average strain values and erosion values in both the in vitro and in vivo environment. Results support the use of a mechanical stiffness-based predicative model for longitudinal monitoring of material erosion and highlight the use of ultrasound elastography as a nondestructive tool for measuring polymer erosion kinetics.