Visco-Elastic-Plastic Properties of Suture Fibers Made of PLA-PCL

Abstract

Aliphatic polyesters, like PGA, PLA, PCL and PDO, among others, are biodegradable materials that find applications in many biomedical devices, from fibers for subcutaneous sutures to other regenerative surgery implants. The main concept among these applications is to use a biodegradable device that temporarily replace the biomechanical functions, avoiding this way the chirurgical procedures to remove the device. However, the dimensioning of these devices is complex, not only because the mechanical properties evolve during degradation, but also because these biodegradable materials cannot be assumed as elastic materials. In more precise terms, the response of an elastic material implies that the loading and unloading paths coincide, the material responds instantaneously to an applied load, its behavior is time-independent and the material returns to its former unloaded configuration upon the removal of external loads. In this work, fibers of non-degraded PLA-PCL were submitted to tensile testing at different rates, to load-unloading cycles at different load levels and with or without delay before reloading, creep and fatigue tests at different levels of load. These results elucidate the viscoelastic/viscoplastic nature of this class of materials. The load-unloading cyclic test results allow determining the different components of the strain: elastic, plastic and viscous. The visco-plastic nature was also reflected on the creep and fatigue results. The findings discussed in this work must be taken into account when designing biomedical devices, to avoid common causes of failure such as laxity or premature rupture.