title: Characterizing local collagen fiber re-alignment and crimp behavior throughout mechanical testing in a mature mouse supraspinatus tendon model.
abstract: BACKGROUND
  Collagen fiber re-alignment and uncrimping are two postulated mechanisms of tendon structural response to load. Recent studies have examined structural changes in response to mechanical testing in a postnatal development mouse supraspinatus tendon model (SST), however, those changes in the mature mouse have not been characterized. The objective of this study was to characterize collagen fiber re-alignment and crimp behavior throughout mechanical testing in a mature mouse SST.
  
  
  METHODS
  A tensile mechanical testing set-up integrated with a polarized light system was utilized for alignment and mechanical analysis. Local collagen fiber crimp frequency was quantified immediately following the designated loading protocol using a traditional tensile set up and a flash-freezing method. The effect of number of preconditioning cycles on collagen fiber re-alignment, crimp frequency and mechanical properties in midsubstance and insertion site locations were examined.
  
  
  RESULTS
  Decreases in collagen fiber crimp frequency were identified at the toe-region of the mechanical test at both locations. The insertion site re-aligned throughout the entire test, while the midsubstance re-aligned during preconditioning and the test's linear-region. The insertion site demonstrated a more disorganized collagen fiber distribution, lower mechanical properties and a higher cross-sectional area compared to the midsubstance location.
  
  
  CONCLUSIONS
  Local collagen fiber re-alignment, crimp behavior and mechanical properties were characterized in a mature mouse SST model. The insertion site and midsubstance respond differently to mechanical load and have different mechanisms of structural response. Additionally, results support that collagen fiber crimp is a physiologic phenomenon that may explain the mechanical test toe-region.
authors: McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA 19104-6081, USA.
authors: Kristin S
authors: KS
authors: Miller
authors: Brianne K
authors: BK
authors: Connizzo
authors: Elizabeth
authors: E
authors: Feeney
authors: Louis J
authors: LJ
authors: Soslowsky
mesh_terms: D000818:Animals; D003094:Collagen / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D013312:Stress, Physiological / Q000502:physiology*; D013710:Tendons / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D003094:Collagen