Stochastic Interdigitation as a Toughening Mechanism at the Interface between Tendon and Bone

Abstract

Reattachment and healing of tendon to bone poses a persistent clinical challenge and often results in poor outcomes, in part because the mechanisms that imbue the uninjured tendon-to-bone attachment with toughness are not known. One feature of typical tendon-to-bone surgical repairs is direct attachment of tendon to smooth bone. The native tendon-to-bone attachment, however, presents a rough mineralized interface that might serve an important role in stress transfer between tendon and bone. In this study, we examined the effects of interfacial roughness and interdigital stochasticity on the strength and toughness of a bimaterial interface. Closed form linear approximations of the amplification of stresses at the rough interface were derived and applied in a two-dimensional unit-cell model. Results demonstrated that roughness may serve to increase the toughness of the tendon-to-bone insertion site at the expense of its strength. Results further suggested that the natural tendon-to-bone attachment presents roughness for which the gain in toughness outweighs the loss in strength. More generally, our results suggest a pathway for stochasticity to improve surgical reattachment strategies and structural engineering attachments.

Allometry of the Tendon Enthesis: Mechanisms of Load Transfer Between Tendon and Bone

“…At the micrometer length scale, the interface between the mineralized and unmineralized tissues exhibits a waviness or interfacial roughness. In silico models have shown that a wavy interface between two dissimilar materials can serve to increase interfacial toughness at the cost of interfacial strength [42]. An increase in peak height (A) versus peak width (k), as measured by the A/k ratio, increases the magnitude of stress concentrations, leading to a decrease in strength.…”

“…1). In silico studies examining interdigitating interfaces indicated that the waviness of an interface affects both its strength and toughness [5]. Uniformly increasing amplitude and frequency of the interfacial waviness results in a decrease in interfacial strength due to an increase in stress concentrations.…”

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

“…[1,25,164] The native enthesis contains a dense network of collagen fibers interdigitated into bone that aid in tensile and compressive load transmission. [165–168] The loading environment of the enthesis provides mechanical cues to cells that instruct matrix production and remodeling. Lack of loading during native development results in impaired mineral deposition and disorganized fiber distribution.…”

Integrated multiscale biomaterials experiment and modelling: a perspective

“…Interactions between collagen and mineral are central to the mechanics and resilience of bone [20,21] and its interfaces with soft tissues [22,23]. A range of phenomenological and mechanistic models exist for the strength and toughness of bone, as reviewed by Jasiuk et al [24].…”