title: Thermal, creep-recovery and viscoelastic behavior of high density polyethylene/hydroxyapatite nano particles for bone substitutes: effects of gamma radiation.
abstract: BACKGROUND
  High Density Polyethylene (HDPE) is one of the most often used polymers in biomedical applications. The limitations of HDPE are its visco-elastic behavior, low modulus and poor bioactivity. To improve HDPE properties, HA nanoparticles can be added to form polymer composite that can be used as alternatives to metals for bone substitutes and orthopaedic implant applications.
  
  
  METHODS
  In our previous work (BioMedical Engineering OnLine 2013), different ratios of HDPE/HA nanocomposites were prepared using melt blending in a co-rotating intermeshing twin screw extruder. The accelerated aging effects on the tensile properties and torsional viscoelastic behavior (storage modulus (G') and Loss modulus (G")) at 80°C of irradiated and non-irradiated HDPE/HA was investigated. Also the thermal behavior of HDPE/HA were studied. In this study, the effects of gamma irradiation on the tensile viscoelastic behavior (storage modulus (E') and Loss modulus (E")) at 25°C examined for HDPE/HA nanocomposites at different frequencies using Dynamic Mechanical Analysis (DMA). The DMA was also used to analyze creep-recovery and relaxation properties of the nanocomposites. To analyze the thermal behavior of the HDPE/HA nanocomposite, Differential Scanning Calorimetry (DSC) was used.
  
  
  RESULTS
  The microscopic examination of the cryogenically fractured surface revealed a reasonable distribution of HA nanoparticles in the HDPE matrix. The DMA showed that the tensile storage and loss modulus increases with increasing the HA nanoparticles ratio and the test frequency. The creep-recovery behavior improves with increasing the HA nanoparticle content. Finally, the results indicated that the crystallinity, viscoelastic, creep recovery and relaxation behavior of HDPE nanocomposite improved due to gamma irradiation.
  
  
  CONCLUSIONS
  Based on the experimental results, it is found that prepared HDPE nanocomposite properties improved due to the addition of HA nanoparticles and irradiation. So, the prepared HDPE/HA nanocomposite appears to have fairly good comprehensive properties that make it a good candidate as bone substitute.
authors.forename: Othman Y
authors.initials: OY
authors.lastname: Alothman
authors.affiliation: Applied Medical Science Department, Riyadh Community College, King Saud University, Riyadh, Saudi Arabia. menhfefnew@hotmail.com.
authors.forename: H
authors.initials: H
authors.lastname: Fouad
authors.forename: S M
authors.initials: SM
authors.lastname: Al-Zahrani
authors.forename: Ayman
authors.initials: A
authors.lastname: Eshra
authors.forename: Mohammed Fayez
authors.initials: MF
authors.lastname: Al Rez
authors.forename: S G
authors.initials: SG
authors.lastname: Ansari
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry / Q000528:radiation effects; D018786:Bone Substitutes / Q000737:chemistry* / Q000528:radiation effects; D002151:Calorimetry; D017886:Durapatite / Q000737:chemistry* / Q000528:radiation effects; D005720:Gamma Rays; D053761:Nanocomposites / Q000737:chemistry* / Q000528:radiation effects; D053758:Nanoparticles / Q000737:chemistry* / Q000528:radiation effects; D020959:Polyethylene / Q000737:chemistry* / Q000528:radiation effects; D014783:Viscosity
chemical_list: D001672:Biocompatible Materials; D018786:Bone Substitutes; D020959:Polyethylene; D017886:Durapatite