title: An analytical calculation of the fluid load support fraction in a biphasic material: an alternative technique.
abstract: BACKGROUND
  The fluid load support fraction (W(F)/W(T)) can be used to define the mechanical contribution of the interstitial fluid (W(F)) to the total force (W(T)) in the deformation of cartilage. Traditionally, W(F)/W(T) is calculated using complex experimental setups or time-consuming micromechanical poroelastic Finite Element (FE) simulations.
  
  
  OBJECTIVE
  To define and validate a fast and efficient technique to predict W(F)/W(T) using an analytical approach that can be applied without micromechanical detail or experimental measurement.
  
  
  METHODS
  Poroelastic FE simulations defined accurate values of W(F)/W(T) for a range of loading configurations and were used to validate subsequent predictions. The analytical prediction of W(F)/W(T) used elastic contact mechanics to calculate W(F), and viscoelastic FE representation to calculate W(T). Subsequently, these independent calculations of W(F) and W(T) provided values of W(F)/W(T) that were compared with the poroelastic FE calculations.
  
  
  CONCLUSIONS
  The analytical prediction of W(F)/W(T) proved effective and suitably accurate (mean difference S<0.05). This technique demonstrated how W(F) and W(T) can be determined independently, without a biphasic constitutive model. Here we used viscoelasticity to calculate W(T) as an example, however, W(T) could be measured experimentally or predicted computationally.
authors.affiliation: Institute of Medical and Biological Engineering, Department of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: A J F
authors.initials: AJ
authors.lastname: Stops
authors.forename: R K
authors.initials: RK
authors.lastname: Wilcox
authors.forename: Z
authors.initials: Z
authors.lastname: Jin
mesh_terms: D001696:Biomechanical Phenomena; D002356:Cartilage / Q000166:cytology* / Q000502:physiology*; D004548:Elasticity; D045604:Extracellular Fluid / Q000378:metabolism*; D020342:Finite Element Analysis; D055595:Mechanical Phenomena; D014783:Viscosity; D016474:Weight-Bearing