Observation of discrepancy between the degradation of polymer scaffolds in vitro and in vivo according to high-resolution ultrasound technique

Biocompatible, biodegradable polymers are actively used as drug delivery systems and as tissue engineering scaffolds. The hydrothermal aging of polymers, including degradation of the microstructure and changes of mechanical properties directly depends on environmental conditions. In vitro studies in a model media cannot contain and describe all the factors influencing the polymer degradation in a living organism. It seems promising to study the processes of changes in the microstructure and elastic properties of polymer implants in vivo in dynamics. Here, we present data from the application of new experimental equipment for high-resolution ultrasound imaging of polymer degradation in vivo. Ultrasonic results include images of the transformation of volumetric microstructure and changes in elastic properties in dynamics. The method was verified on a rapidly degradable polymer poly(D,L-lactide-co-glycolide). We assess and compare the evolution of volume microstructure, elastic properties and molecular weight of the polymer weekly for 1.5 months of incubation in vitro and in vivo. We found that the in vivo degradation process occurs with a delay of 2 weeks compared to the hydrothermal aging in vitro.