A study on the response of PLGA 85/15 under compression and heat-treatment testing cycles

Poly(lactic-co-glycolic acid) (PLGA) is one of the most prominent bioresorbable materials, currently used in several medical applications (screws, craniofacial plates etc.). Looking to extend the knowledge about the thermomechanical behavior of bioresorbable medical materials, this research presents a series of experiments and results based on nonhomogeneous compression tests for the polymer PLGA 85/15. Instead of focusing on tensile and bending conditions for compression-molded products, such as usually presented in the literature, attention is given to compression tests and samples machined from injection-molded parts. Additionally, PLGA strain rate sensitivity, which is an issue less discussed in the literature, is analyzed. In the current study, this material is tested by observing the main features related to resorbable medical materials. The effects of a material heat treatment that are associated with PLGA shape-memory properties are investigated. Differential scanning calorimetry (DSC) was also employed in the thermal characterization. A finite element analysis of the compression testing provides a complementary overview of the mechanical behavior of PLGA 85/15. Results indicate that PLGA has a linear rate-insensitive response for small strains but presents a strong rate dependence for strains beyond the material yielding. PLGA shows a remarkable post-yielding strain-softening behavior, with a steep descent slope. Samples present significant mechanical changes after heat treatment at temperatures above T-g, with reduction of 35% in the material elastic modulus and 30% in the upper-yielding stress and no significant changes for further heat-treatment procedures. DSC analysis confirmed the existence of significant residual stress in PLGA specimens. Mechanical deformation and manly heat treatment seem to reduce this residual stress caused by molecular orientation and rapid solidification. Finally, finite element simulations show that the limit of the homogeneity hypothesis is associated with the yield strain, after which highly non-uniform stresses develop.

Automated summary

This research presents a series of experiments and results based on nonhomogeneous compression tests for the polymer PLGA 85/15 to extend the knowledge about the thermomechanical behavior of bioresorbable medical materials. The study explores PLGA strain rate sensitivity, shape-memory properties, heat treatment effects, and residual stress, revealing linear rate-insensitive response for small strains and strong rate dependence for strains beyond yielding. Differential scanning calorimetry and finite element simulations are utilized to provide a comprehensive overview of the mechanical behavior of PLGA.