title: Fracture and fatigue in osteocytes.
abstract: Fatigue is a common mode of mechanical failure which occurs when a material is subjected to repeated cycles at a strain level less than that needed for monotonic fracture. Fatigue has been observed and measured in many different materials but, until recently, not in cells. We devised a novel experiment which allowed us to create both monotonic failure and fatigue in the cellular processes of osteocytes within samples of bone (Dooley et al., European Cells and Materials 2014). In the present paper, we describe the results of further experiments and a computer simulation, which has allowed us to estimate the strain history of each sample tested and thus present, for the first time, strain/life data for cells. Failure occurred during the first cycle at strains of 0.1-0.2; at lower strains failure occurred after a number of cycles which depended inversely on the applied strain range. Scatter in the strain/life data was reduced when we allowed for the effects of mean stress using the Smith-Watson-Topper parameter. We confirmed that aspects of our experimental method (the types of microcrack used and the testing of fresh versus frozen samples) did not affect the results. Such information is useful because many cell types, including the cellular processes of osteocytes, experience cyclic strain in vivo.
authors.affiliation: Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland; Department of Industrial Engineering, University of Bologna, Bologna, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Mulargia
authors.affiliation: Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland; Centre for Microscopy and Analysis, Trinity College Dublin, Dublin, Ireland.
authors.forename: Clodagh
authors.initials: C
authors.lastname: Dooley
authors.affiliation: Department of Industrial Engineering, University of Bologna, Bologna, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Cristofolini
authors.affiliation: Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland; Department of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin, Ireland. Electronic address: dtaylor@tcd.ie.
authors.forename: David
authors.initials: D
authors.lastname: Taylor
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000473:pathology*; D002417:Cattle; D003198:Computer Simulation; D050723:Fractures, Bone; D005615:Freezing; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010011:Osteocytes / Q000473:pathology*; D013314:Stress, Mechanical; D013977:Tibia / Q000473:pathology*; D016474:Weight-Bearing
keywords: Cells; Failure; Fatigue; Osteocytes; Strain