title: Characterization of load dependent creep behavior in medically relevant absorbable polymers.
abstract: While synthetic absorbable polymers have a substantial history of use in medical devices, their use is expanding and becoming more prevalent for devices where long term loading and structural support is required. In addition, there is evidence that current absorbable medical devices may experience permanent deformations, warping (out of plane twisting), and geometric changes in vivo. For clinical indications with long term loading or structural support requirements, understanding the material's viscoelastic properties becomes increasingly important whereas these properties have not been used historically as preclinical indications of performance or design considerations. In this study we measured the static creep, creep recovery and cyclic creep responses of common medically relevant absorbable materials (i.e., poly(l-lactide, PLLA) and poly(l-co-glycolide, PLGA) over a range of physiologically relevant loading magnitudes. The results indicate that both PLLA and PLGA exhibit creep behavior and failure at loads significantly less than the yield or ultimate properties of the material and that significant material specific responses to loading exist. In addition, we identified a strong correlation between the extent of creep in the material and its crystallinity. Results of the study provide new information on the creep behavior of PLLA and PLGA and support the use of viscoelastic properties of absorbable polymers as part of the material selection process.
authors.affiliation: US Food and Drug Administration, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Division of Solid and Fluid Mechanics, 10903 New Hampshire Avenue, Silver Spring, MD 20993, USA. Electronic address: Maureen.dreher@fda.hhs.gov.
authors.forename: Maureen L
authors.initials: ML
authors.lastname: Dreher
authors.forename: Srinidhi
authors.initials: S
authors.lastname: Nagaraja
authors.forename: Hieu
authors.initials: H
authors.lastname: Bui
authors.forename: Danny
authors.initials: D
authors.lastname: Hong
mesh_terms: D000042:Absorption; D019344:Lactic Acid; D008422:Materials Testing; D055595:Mechanical Phenomena; D011091:Polyesters; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer
chemical_list: D011091:Polyesters; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide)
keywords: Absorbable; Creep; Crystallinity; PLGA; PLLA; Viscoelasticity