title: Creep loading during degradation attenuates mechanical property loss in PLGA.
abstract: While absorbable materials and medical devices primarily degrade through hydrolysis, their degradation kinetics are sensitive to environmental conditions, including temperature, pH, and mechanical loading. While there is some consistent information in the literature suggesting that strain controlled loading accelerates strength loss, there is much more limited information on the interaction between degradation and mechanical load applied under force control. Force control conditions impose a different stress state on the material and therefore, may exhibit different effects on degradation. In this study, the interaction between loading and degradation rate for an exemplary absorbable polymer, poly(l-lactide-co-glycolide), was investigated. The results indicated that load during degradation results in significant polymer creep, which is associated with increased force loss, but decreased strength loss (i.e., stress based parameters such as ultimate stress). This study further identified that changes to the degradation kinetics from exposure to loading were not associated with alterations to polymer crystallinity but were associated with delayed loss of molecular weight. Overall, these results demonstrate the importance of investigating the interaction between loading and degradation and that physical changes, such as those induced by creep, rather than chemical changes offer the strongest explanation for alteration of degradation kinetics.
authors: Division of Solid & Fluid Mechanics, US Food & Drug Administration, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Silver Spring, Maryland, 20993.
authors: Maureen L
authors: ML
authors: Dreher
authors: Srinidhi
authors: S
authors: Nagaraja
authors: Jian
authors: J
authors: Li
mesh_terms: D020341:Absorbable Implants; D065966:Absorption, Physicochemical; D002021:Buffers; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000737:chemistry*; D008422:Materials Testing; D055595:Mechanical Phenomena; D008970:Molecular Weight; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011312:Pressure; D013314:Stress, Mechanical; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D016474:Weight-Bearing
chemical_list: D002021:Buffers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid
keywords: PLGA; absorbable polymer; degradation; load