Calibration Framework for Modeling Nonlinear Viscoelastic-Plastic Behavior of Bioresorbable Polymers in Finite...

Area of Science:

• Biomedical Engineering
• Materials Science
• Computational Mechanics

Background:

• Finite element analysis (FEA) is vital in biomedical engineering for device design and material development.
• Accurate FEA model validation is critical for predicting material behavior, especially for medical devices like stents.
• Manufacturing simplified geometries, such as 2D substructures, is often necessary for efficient stent development and testing.

Purpose of the Study:

• To establish a methodology for validating FEA models used in stent development.
• To evaluate the performance of different constitutive models (LEP, PRF, TN) for predicting the behavior of polymers used in stents.
• To enable efficient material screening and stent design optimization through a simplified 2D validation approach.

Main Methods:

• Injection-molded planar 2D substructures of a stent design were created using poly(l-lactide) (PLLA) and poly(glycolide-co-trimethylene carbonate) (PGA-co-TMC).
• Specimens were subjected to quasi-static and cyclic mechanical testing, including loading, stress relaxation, unloading, and strain recovery.
• Material model coefficients for FEA were calibrated using three constitutive models: linear elastic-plastic (LEP), Parallel Rheological Framework (PRF), and Three-Network (TN).

Main Results:

• FEA validation using planar stent segment expansion (PSSE) demonstrated strong agreement with experimental deformation patterns.
• The PRF and TN models showed superior accuracy in predicting material behavior compared to the LEP model.
• The PRF model was particularly effective for PLLA, while all tested models had limitations for PGA-co-TMC behavior.
• Model accuracy was sensitive to the congruence between calibration and load cases, with phenomenological models like PRF showing greater robustness.

Conclusions:

• A robust methodology for material modeling in stent development was proposed, utilizing a simplified 2D validation setup.
• The study highlights the importance of selecting appropriate constitutive models and ensuring calibration-load case congruence for accurate FEA predictions.
• The developed approach facilitates efficient material screening and optimization of stent designs, improving the development process for biomedical devices.