title: Effect of high-energy X-ray irradiation on creep mechanisms in bone and dentin.
abstract: Under long-term loading creep conditions, mineralized biological tissues like bone are expected to behave in a similar manner to synthetic composites where the creeping matrix sheds load to the elastic reinforcement as creep deformation progresses. To study this mechanism in biological composites, creep experiments were performed at 37 °C on bovine compact bone and dentin. Static compressive stresses were applied to the samples, while wide- and small-angle scattering patterns from high energy synchrotron X-rays were used to determine, respectively, the elastic strain in the hydroxyapatite (HAP) platelets and the strain in the mineralized collagen fibril, as a function of creep time. In these highly irradiated biological composites, the reinforcing hydroxyapatite platelets progressively transfer some of their stress back to the softer protein matrix during creep. While such behavior can be explained by damage at the interface between the two phases, it is not consistent with measurements of the apparent moduli--the ratio of applied stress to elastic HAP strain measured throughout the creep experiments by elastic unload/load segments--which remained constant throughout the experiment and thus indicated good HAP/protein bonding. A possible explanation is a combination of X-ray and load induced interfacial damage explaining the shedding of load from the HAP during long term creep, coupled with interfacial re-bonding of the load-disrupted reversible bonds upon unloading, explaining the unaffected elastic load partitioning during unload/load segments. This hypothesis is further supported by finite element modeling which shows results mirroring the experimental strain measurements when considering interfacial delamination and a compliant interstitial space at the ends of the HAP platelets.
authors: Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA. a.black@wustl.edu
authors: Alix C
authors: AC
authors: Deymier-Black
authors: Anjali
authors: A
authors: Singhal
authors: Fang
authors: F
authors: Yuan
authors: Jonathan D
authors: JD
authors: Almer
authors: L Catherine
authors: LC
authors: Brinson
authors: David C
authors: DC
authors: Dunand
mesh_terms: D000818:Animals; D002417:Cattle; D019245:Compressive Strength / Q000502:physiology / Q000528:radiation effects; D003198:Computer Simulation; D003804:Dentin / Q000502:physiology* / Q000528:radiation effects*; D055119:Elastic Modulus / Q000502:physiology / Q000528:radiation effects; D005269:Femur / Q000502:physiology* / Q000528:radiation effects*; D066298:In Vitro Techniques; D008954:Models, Biological; D011829:Radiation Dosage; D014783:Viscosity / Q000528:radiation effects; D014965:X-Rays