Soft Tissue Mechanics

The intervertebral disc is subject to large complex loads under the physical demands of daily living. Water is forced out of the disc during diurnal loading and reimbibed during bed-rest. The daily fluctuations in water content alter the osmotic loading environment experienced by the tissues and cells, causing changes in disc mechanics. Current studies aim to understand tissue hydration on joint and tissue levels, and investigate the effects of intrinsic and extrinsic factors, including degeneration, injuries, and external osmotic pressure on disc joint mechanics.

Strain analysis of annulus fibrosus loaded to failure.

Fiber-reinforced tissues of the musculoskeletal system, such as the annulus fibrosus (AF) in the intervertebral disc, experience large, complex loads during daily activities. Repetitive or excessive loading of these tissues may initiate structural damage and lead to mechanical failure, causing debilitating pain and reduced mobility. Understanding failure mechanisms of tissues with limited self-healing capabilities is of particular importance as the increase in AF tears with age may cause a cascade of damage and degenerative.

Tears in the annulus fibrosus can result in disc herniation and progressive degeneration. Understanding tissue failure mechanics is important, as research moves towards developing biological repair strategies for herniated discs. Unfortunately, failure mechanics of fiber-reinforced tissues, particularly tissues with fibers oriented off-axis from the applied load, is not well understood, nor is the failure behavior of degenerated tissue. Our research employs a combined experimental and computational approach to evaluate the tissue-level failure mechanics of both healthy and degenerate annulus fibrosus tissue in tension. It is our hope that a better understanding of tissue failure dynamics will better inform injury-prevention and tissue-repair strategies.

Uniaxial tension test of annulus fibrosus until failure. A full thickness notch was created to effectively crate a dog-bone cross section, ensuring that failure would occur at the mid-substance, rather than at the grips. In this sample, failure starts at the outer annulus and continues into the inner annulus.

Strain analysis of annulus fibrosus loaded to failure.