title: Dynamic changes of macaque cancellous bone following head-down bed rest.
abstract: BACKGROUND
  Skeletal unloading during a spaceflight could result in bone loss and osteopenia, ultimately leading to poor bone strength. The purpose of the present study was to investigate the influence of bone loss on the dynamic behavior of cancellous bone.
  
  
  METHODS
  Microgravity-induced bone loss and osteopenia were simulated in a macaque head-down bed rest (HDBR) model, in which 20 macaques were laid on a bed tilted by -6 degrees from the horizontal. These macaques were randomly divided into control (Con) and head down bed rest (HDBR) groups. After 28 d, 5 macaques chosen at random from each group were tested for bone density and mechanical properties, and the obtained data was used to develop a density-based constitutive equation; the remaining animals were tested only for bone density in order to attain statistical power. A split Hopkinson bar was used to monitor the dynamic response of cancellous bone. Cancellous bone deformation under high strain rate conditions was recorded by high-speed videos.
  
  
  RESULTS
  Compared with the Con group, the Young's modulus of cancellous bone from HDBR macaque lumbar vertebrae were decreased by 6.03%. Based on the static and dynamic experimental results, parameters in the Maxwell nonlinear viscoelasticity material model were estimated.
  
  
  CONCLUSIONS
  This model of cancellous bone under high strain rate was useful to establish the medical tolerance and evolution criteria of impact-related trauma by finite element method calculations.
authors.affiliation: China Astronaut Research and Training Center, Beijing, China. mahlei@163.com
authors.forename: Honglei
authors.initials: H
authors.lastname: Ma
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: Guanghan
authors.initials: G
authors.lastname: Kan
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Jin
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: King H
authors.initials: KH
authors.lastname: Yang
authors.affiliation: China Astronaut Research and Training Center, Beijing, China.
authors.forename: Albert I
authors.initials: AI
authors.lastname: King
mesh_terms: D000818:Animals; D001510:Bed Rest / Q000009:adverse effects*; D015519:Bone Density; D001851:Bone Diseases, Metabolic / Q000209:etiology / Q000503:physiopathology*; D001862:Bone Resorption / Q000209:etiology / Q000503:physiopathology*; D055119:Elastic Modulus; D018475:Head-Down Tilt / Q000009:adverse effects*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008251:Macaca; D013026:Space Flight; D014893:Weightlessness / Q000009:adverse effects