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)