title: Effects of gamma radiation sterilization and strain rate on compressive behavior of equine cortical bone.
abstract: OBJECTIVE
  Gamma radiation has been widely used for sterilization of bone allograft. However, sterilization by gamma radiation damages the material properties of bone which is a major clinical concern since bone allograft is used in load bearing applications. While the degree of this damage is well investigated for quasi-static and cyclic loading conditions, there does not appear any information on mechanical behavior of gamma-irradiated cortical bone at high speed loading conditions. In this study, the effects of gamma irradiation on high strain rate compressive behavior of equine cortical bone were investigated using a Split Hopkinson Pressure Bar (SHPB). Quasi-static compression testing was also performed.
  
  
  METHODS
  Equine cortical bone tissue from 8year old retired racehorses was divided into two groups: non-irradiated and gamma-irradiated at 30kGy. Quasi-static and high strain rate compression tests were performed at average strain rates of 0.0045/s and 725/s, respectively.
  
  
  RESULTS
  Agreeing with previous results on the embrittlement of cortical bone when gamma-irradiated, the quasi-static results showed that gamma-irradiation significantly decreased ultimate strength (9%), ultimate strain (27%) and toughness (41%), while not having significant effect on modulus of elasticity, yield strain and resilience. More importantly, contrary to what is typically observed in quasi-static loading, the gamma-irradiated bone under high speed loading showed significantly higher modulus of elasticity (45%), ultimate strength (24%) and toughness (26%) than those of non-irradiated bone, although the failure was at a similar strain.
  
  
  CONCLUSIONS
  Under high speed loading, the mechanical properties of bone allografts were not degraded by irradiation, in contrast to the degradation measured in this and prior studies under quasi-static loading. This result calls into question the assumption that bone allograft is always degraded by gamma irradiation, regardless of loading conditions. However, it needs further investigation to be translated positively in a clinical setting.
authors.affiliation: Department of Mechanical Engineering, Süleyman Demirel University, 32260 Isparta, Turkey. Electronic address: kenantufekci@sdu.edu.tr.
authors.forename: Kenan
authors.initials: K
authors.lastname: Tüfekci
authors.affiliation: Department of Mechanical Engineering, Süleyman Demirel University, 32260 Isparta, Turkey. Electronic address: ramazankayacan@sdu.edu.tr.
authors.forename: Ramazan
authors.initials: R
authors.lastname: Kayacan
authors.affiliation: Department of Mechanical Engineering, İstanbul Medeniyet University, Göztepe Kadıköy - İstanbul, Turkey. Electronic address: cahit.kurbanoglu@medeniyet.edu.tr.
authors.forename: Cahit
authors.initials: C
authors.lastname: Kurbanoğlu
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology / Q000528:radiation effects*; D004548:Elasticity; D005720:Gamma Rays / Q000009:adverse effects*; D006736:Horses; D006801:Humans; D008422:Materials Testing; D013242:Sterilization; D013314:Stress, Mechanical
keywords: Equine bone; Gamma radiation sterilization; High strain rate compression; Mechanical properties; Quasi-static compression; Split Hopkinson pressure bar