ORGANISATION AND MECHANICAL ROLE OF ELASTIC FIBRES IN TENDON
Tyler Grant (1), Mark Thompson (1)
1. Department of Engineering Science, University of Oxford, UK
Introduction
Tendon is capable of withstanding large tensile
loads, but the microstructural origin for the superb
mechanical properties of this complex material is
poorly understood. Elastic fibres are present in
tendon [Ritty, 2002], but there remains a lack of
understanding of their organisation and mechanical
role in this hierarchical tissue. The objective of this
study was to characterise the organisation of elastic
fibres in tendon through a histological investigation
and define their mechanical role by performing
enzyme treatments combined with mechanical
testing. Understanding the structure-function
relationship of tendon will help elucidate
deformation mechanisms and improve the current
understanding of tendon disease and regeneration.
Methods
Basic histology, immunohistochemistry, and
multiphoton microscopy (MPM) were used to
investigate the elastic fibre organisation of bovine
flexor tendon. Paraffin sections were stained with
Miller’s elastic stain and fresh-frozen sections were
immunostained with anti-elastin, fibrillin-1 and -2
antibodies to reveal elastic fibre components.
MPM enabled second harmonic generation (SHG -
collagen, blue) and two photon fluorescence (TPF -
elastin, green) emission spectra to identify elastin
fibre structure. An elastase treatment was used to
degrade elastin fibres and failure and hysteresis
tensile tests were conducted to characterise their
mechanical contribution through comparison of
material properties with two-way analysis of
variance.
Results
Immunostaining and MPM, confirmed by Miller’s
staining, showed that elastin fibres were present in
tendon (Fig 1a,b,c; green) and ran longitudinally
along collagen fibrils, conforming to fibril crimp
(Fig 1b; blue). Transverse sections indicated that
fibrillin-1 and -2 bridged collagen fascicles at
oblique angles (Fig 1d) and little elastin was found
between fascicles. Elastic fibres were distributed
parallel to tenocytes and sometimes showed a close
association with cells. Tensile tests following
elastase treatment suggested that elastin did not
contribute to the low stress-strain response or
elastic recoil of tendon (Fig 2) contrary to previous
hypotheses.
Figure 1: Elastic fibre organisation of tendon
Figure 2: Stress-strain response of tendon
Discussion
This study shows the detailed microstructure of
elastic fibres in tendon for the first time, in small
numbers mirroring collagen fibril arrangement and
in the vicinity of tenocytes. With the enzyme
digested tissue testing, this suggests that they do not
affect the macroscopic deformation of tendon, but
may influence tenocytes’ local mechanical
environment. As in cartilage and bone, knowledge
of the pericellular matrix will be key to
understanding cell-level deformations and
mechanotransductive mechanisms of tendon.
Although elastic fibres have a sparse distribution,
their specific organisation suggests that they
contribute to the microstructural deformation of
tendon.
References
Ritty et al, Anatomical Record, 268:430-440, 2002.
Presentation 1254 − Topic 30. Ligament and tendon S399
ESB2012: 18th Congress of the European Society of Biomechanics Journal of Biomechanics 45(S1)
