Multiscale modelling for the heterogeneous strength of biodegradable polyesters

Area of Science:

• Materials Science
• Polymer Science
• Biomaterials Engineering

Background:

• Medical polyesters such as polylactide (PLA) and polyglycolide (PGA) are susceptible to degradation via bulk erosion, affecting their mechanical properties.
• Understanding the evolution of mechanical strength during degradation is crucial for predicting the performance and lifespan of medical devices made from these polymers.

Purpose of the Study:

• To develop and validate a coupled multiscale strength model for calculating the mechanical strength of medical polyesters during bulk erosion.
• To investigate the roles of molecular weight, chain recrystallization, and cavity formation in the heterogeneous strength of degrading polymers.

Main Methods:

• A heterogeneous method discretizing macroscopic devices into mesoscopic cells, with polymer chains confined to individual cells.
• Introduction of three strength phases: amorphous, crystallinity, and strength vacancy, each related to specific material characteristics (molecular weight, crystallinity, voids).
• Coupling micro-scale chain scission and recrystallization with macro-scale oligomer diffusion to form a multiscale strength model.

Main Results:

• The model successfully simulates the evolution of strength phases, cell status, molecular weight, crystallinity, weight loss, and overall device strength during degradation.
• The proposed strength phases (amorphous, crystallinity, vacancy) effectively represent the heterogeneous strength structures and contributions within the degrading polymer.
• Model predictions showed a good fit with experimental data, validating its efficacy.

Conclusions:

• The developed multiscale strength model provides a robust framework for predicting the mechanical behavior of degrading medical polyesters.
• The heterogeneous strength approach, considering distinct phases, is essential for accurately modeling the complex degradation process.
• This model can aid in the design and optimization of medical devices fabricated from PLA, PGA, and their copolymers.