Degenerative disc disease (DDD) continues to be a burden on the general population and economy both in the United States and worldwide. There is strong evidence from the literature that indicate that mechanical stress plays a role in the progression of DDD. However, the complex lamellar architecture of the disc and the zonal variation in cell phenotype have made it difficult to translate tissue level mechanics to the cellular micromechanical environment, which governs intervertebral disc (IVD) cell function. Understanding how cells respond to stimuli that can be characterized in detail is important for developing repair strategies where scaffolds can be tailored to provide the appropriate micromechanical cues. Based on observations from our previous animal studies and recently reported descriptions of the interlamellar (IL) matrix in normal and degenerate annulus fibrosus (AF), we have developed an hypothesis on the regulation of the IL space by mechanical stress. This central hypothesis states that radial and shear stress coordinately modulate the IL matrix through mechanoregulation of AF cells. In order to provide cells with both radial and shear stimuli in a uniform micromechanical environment, we propose to implement a novel collagen interface cell culture model. Cells will be cultured and deformed between a fibrillar collagen thin film (CTF) that mimics the microfibrillar structure of the IL matrix and its type-matched collagen gel. Using this interface culture model, Aim 1 will determine how AF cells respond to macrostructural shear. Specifically, it will characterize zonal- and substrate-dependent deformation of inner and outer AF cells, and investigate whether intrinsic or structural factors dominate their responses.
In Aim 2, our hypothetical mechanobiologic model of AF cell regulation by radial and shear stress will be tested using the interface culture model. A range of tension-compression stress and shear strain will be studied in the context of the healthy IL compartment. In parallel, a novel finite element model that explicitly incorporates an IL compartment will be developed, validated using optical coherence tomography, and implemented to predict the shear environment for IL cells. The mechanobiologic response obtained experimentally can then be spatially "mapped" to corresponding shear regions.
There is substantial evidence that matrix shear stresses are generated in the intervertebral disc, related to injury and degeneration. Results of this project will provide detailed insight into the effects of mechanical shear stresses on cell function. Such knowledge can aid the development of regenerative strategies against disorders such as degenerative disc disease.
|Labus, Kevin M; Han, Sang Kuy; Hsieh, Adam H et al. (2014) A computational model to describe the regional interlamellar shear of the annulus fibrosus. J Biomech Eng 136:051009|