title: Artefacts in the mechanical characterization of porcine articular cartilage due to freezing.
abstract: Many experimental protocols for investigating articular cartilage mechanics have involved the use of a freeze-thaw cycle for storage or tissue manipulation. It was hypothesized that mechanical properties are altered due to freeze-thaw cycling. The aim of this study, therefore, was to examine the possibility of protocol-induced artefacts in the mechanical properties of porcine articular cartilage specimens related specifically to freeze-thaw events. Twenty-eight osteochondral specimens [14 from the femoral condyles (FCs) and 14 from the patella-femoral (PF) groove] were tested in confined compression before and after being frozen at -20 degrees C for 7 days. The fluid-independent and fluid-dependent mechanical properties (aggregate modulus of the solid phase and the half-life of stress relaxation respectively) were determined and compared. The aggregate modulus decreased by 13.5 per cent and 20.1 per cent for the PF and FC regions respectively (p = 0.002) and the half-life of the stress relaxation at 10 per cent strain decreased by 6.4 per cent and 12.6 per cent for the PF and FC specimens respectively (p = 0.0341). In conclusion, it has been shown that the protocol used, which involved freezing to -20 degrees C and thawing after 7 days, caused artefacts in the mechanical properties of porcine osteochondral specimens. It is suggested that protocols requiring freezing must be critically reviewed to eliminate such artefacts.
authors.affiliation: Human Mobility Research Centre, Queen's University, Kingston, Canada. twillett@dal.ca
authors.forename: T L
authors.initials: TL
authors.lastname: Willett
authors.forename: R
authors.initials: R
authors.lastname: Whiteside
authors.forename: P M
authors.initials: PM
authors.lastname: Wild
authors.forename: U P
authors.initials: UP
authors.lastname: Wyss
authors.forename: T
authors.initials: T
authors.lastname: Anastassiades
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000379:methods; D002358:Cartilage, Articular / Q000166:cytology* / Q000502:physiology*; D015925:Cryopreservation / Q000379:methods*; D004548:Elasticity; D005615:Freezing; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D013314:Stress, Mechanical; D013552:Swine