The microstructure and micromechanics of the tendon–bone insertion

Abstract

The exceptional mechanical properties of the load-bearing connection of tendon to bone rely on an intricate interplay of its biomolecular composition, microstructure and micromechanics. Here we identify that the Achilles tendon-bone insertion is characterized by an interface region of ∼500 μm with a distinct fibre organization and biomolecular composition. Within this region, we identify a heterogeneous mechanical response by micromechanical testing coupled with multiscale confocal microscopy. This leads to localized strains that can be larger than the remotely applied strain. The subset of fibres that sustain the majority of loading in the interface area changes with the angle of force application. Proteomic analysis detects enrichment of 22 proteins in the interfacial region that are predominantly involved in cartilage and skeletal development as well as proteoglycan metabolism. The presented mechanisms mark a guideline for further biomimetic strategies to rationally design hard-soft interfaces.

Tendon injury and repair – A perspective on the basic mechanisms of tendon disease and future clinical therapy

“…This article focuses almost exclusively on the ''tendon proper", and leaves aside a detailed consideration of the highly specialized muscle-tendon [27][28][29] and tendon-bone junctions [30][31][32][33][34]. Nonetheless, the structure of tendon proper is tightly coupled to the architecture and function of the muscle to which it is attached.…”

Next generation tissue engineering of orthopedic soft tissue-to-bone interfaces

“…[23,29] Similar to ligament and tendon, aggrecan in the meniscus is located in the inner portion of the meniscus, which is subject to more compressive loads, and the entheseal attachments. [30,31] The large “bottle brush” structure and negative charge of aggrecan helps to bind and retain water, which contributes to the ability of the tissue to resist compression. [32] Small leucine-rich proteoglycans (SLRPs) such as fibromodulin, decorin, and biglycan are known to bind to collagen and help to regulate collagen fiber formation and maintenance.…”

“…[33–35] SLRPs are prevalent in association with highly organized collagen bundles of tendon, ligament, and meniscus. [31,36] Aggrecan is often found in regions of soft tissue-to-bone interfaces under compressive loading, while SLRPs are found in regions with large fibers experiencing tensile loads. [31] …”

“…[31,36] Aggrecan is often found in regions of soft tissue-to-bone interfaces under compressive loading, while SLRPs are found in regions with large fibers experiencing tensile loads. [31] …”

The fibrous cellular microenvironment, and how cells make sense of a tangled web

“…However, as we probe deeper into the hierarchical structures of tissue systems, many tissues no longer appear continuous, but rather present discrete fibrous structures. For example, fibrous networks appear to drive the mechanics of the attachment of tendon to bone (20,21) and the pericellular environment (22).…”