title: Probing multi-scale mechanical damage in connective tissues using X-ray diffraction.
abstract: The accumulation of microstructural collagen damage following repetitive loading is linked to painful and debilitating tendon injuries. As a hierarchical, semi-crystalline material, collagen mechanics can be studied using X-ray diffraction. The aim of the study was to describe multi-structural changes in tendon collagen following controlled plastic damage (5% permanent strain). We used small angle X-ray scattering (SAXS) to interrogate the spacing of collagen molecules within a fibril, and wide angle X-ray scattering (WAXS) to measure molecular strains under macroscopic loading. Simultaneous recordings of SAXS and WAXS patterns, together with whole-tissue strain in physiologically hydrated rat-tail tendons were made during increments of in situ tensile loading. Results showed that while tissue level modulus was unchanged, fibril modulus decreased significantly, and molecular modulus significantly increased. Further, analysis of higher order SAXS peaks suggested structural changes in the gap and overlap regions, possibly localising the damage to molecular cross-links. Our results provide new insight into the fundamental damage processes at work in collagenous tissues and point to new directions for their mitigation and repair.
  
  
  
  This article reports the first in situ loading synchrotron studies on mechanical damage in collagenous tissues. We provide new insight into the nano- and micro-structural mechanisms of damage processes. Pre-damaged tendons showed differential alteration of moduli at macro, micro and nano-scales as measured using X-ray scattering techniques. Detailed analysis of higher order diffraction peaks suggested damage is localised to molecular cross-links. The results are consistent with previous X-ray scattering studies of tendons and also with recent thermal stability studies on damaged material. Detailed understanding of damage mechanisms is essential in the development of new therapies promoting tissue repair.
authors.affiliation: Institute of Biomedical Engineering (IBME), Department of Engineering Science, University of Oxford, UK.
authors.forename: Fabio
authors.initials: F
authors.lastname: Bianchi
authors.affiliation: Department of Engineering Science, University of Oxford, UK.
authors.forename: Felix
authors.initials: F
authors.lastname: Hofmann
authors.affiliation: Diamond Light Source, Didcot, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Smith
authors.affiliation: Institute of Biomedical Engineering (IBME), Department of Engineering Science, University of Oxford, UK. Electronic address: mark.thompson@eng.ox.ac.uk.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Thompson
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003238:Connective Tissue / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000503:physiopathology; D055119:Elastic Modulus; D008297:Male; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical; D013710:Tendons / Q000473:pathology / Q000503:physiopathology; D014961:X-Ray Diffraction
keywords: Collagen; Damage; Tendon; X-ray diffraction