Novel Application of Finite Element Technique to Simulate In-Vitro Deterioration and Estimation of Fracture Toughness of Biodegradable Polymer

摘要

Material is the most important factor in today's technological advancements. New materials are discovered and invented to help facilitate the advancement and hence in the betterment of the mankind. Material properties and its behavior, therefore, is very important in designing and manufacturing a certain part or a system.;Polymer is the key material in many implantable medical devices. It is easily available. It gives structural stability, electrical insulation and biocompatibility. The stability and functional integrity during intended and desired use is very important while at the same time, the opposite, degradation and disappearance of the polymer is also required.;Poly lactide-co-glycolide (PLGA 85:15) is a polymer which has been used quite intensively in medical science as fixation devices. Their growing usage inside the human body have always been a tough challenge for orthopedic doctors and material scientists to understand the behavior of the polymer, that is, its physical, chemical and mechanical properties. This significant jump in the usage is due to the fact that they are easily available and manufactured, help in quick healing etc. However, there are instances where the recipients of the implant, made from such biodegradable polymers suddenly complained about excruciating pain during recovery period. Upon diagnostic checkup, it was revealed that the implant had cracked. Biodegradable polymers such as PLGA 50:50, PLGA 85:15 etc. undergo degradation due to physiological processes inside the human body while the fractured bone, subjected to kinesiological stresses, is being healed. To avoid any complication due to premature fracture of the implant, a prior knowledge of its behavior should be known to orthopedic doctors. As per the surveyed literature, so far research studies have been conducted on physical and chemical aspects of the degradation. No study has ever been conducted on the mechanical aspect of the degradation. In order to understand how such biodegradable polymers lose mechanical strength during its intended use, an investigation into the influence of degradation process on Mode-I fracture toughness of Poly (lactide-co-glycolide) 85:15, material was initiated.;The objective of this study was to build an improved understanding of the deterioration of this biodegradable polymer's mechanical properties during in-vitro degradation and how this change may affect long term performance of the implants made from such biodegradable polymers. A simple mathematical relationship was established for Mode-I fracture to understand change in the Young's modulus of PLGA 85:15 during the degradation process. Compact tension specimens were designed and molded for Mode-I fracture criterion and then put in 3% concentrated H2 O2 to simulate the change in the internal structure of the polymer and how that change is affecting its mechanical properties. Fracture toughness, a key mechanical property which resist fracture as it deteriorates was the main component of this study.;Extended Finite Element Method (xFEM), an extension of Finite Element Method (FEM) technique was used in this study. It is a numerical method, developed based on Linear Elastic Fracture Mechanics (LEFM) to study fracture at each stage of the degradation. xFEM models were built and analyzed at each stage of degradation. The result from xFEM analysis was then compared against the physical test result. This study inferred that with the help of physical test and xFEM analysis, biodegradable polymer, PLGA 85:15 became extremely brittle and porous as degradation progressed and hence, the fracture toughness decreased.