Nano-Structure of Collagen Fibrils in Human Intervertebral Discs and Its Correlation With the Tissue Mechanics

The intervertebral disc (IVD) consists of three major components: the gelatinous nucleus pulposus (NP) at the centre, surrounded by concentric layers of annulus fibrosus (AF), and the superior and inferior endplates sandwiching the AF and NP. Collagen fibrils are the main structural components in all three parts of the disc. The dry mass of collagen in the IVD is about 70% [1]. The outer AF is predominantly collagen I with minor traces of collagen II. A gradual replacement in the collagen I by collagen II occurs in the inner regions [2]. Lumbar disc degenerative disease or early-onset disc degeneration is a primary cause for sciatica and low back pain in young individuals. The most significant biochemical change that occurs in disc degeneration is the loss of proteoglycans in the nucleus pulposus [3]. The mechanical inability of collagen fibrils to withstand the load may be one of the factors causing the loss of proteoglycans. The reason why collagen degrades may be environmental or genetic [4,5]. Researchers are working on developing tissue engineered disc replacements, stem cell therapy etc. to treat disc degeneration. Understanding the disc environment at the nano level is essential in order for these techniques to be clinically successful, as it is well known that the environment in the extracellular matrix plays an important role in determining the stem cells’ fate [6]. Therefore, in order to gain a better understanding on the role played by these matrix proteins, this study aimed at evaluating the correlation between the nano scale properties of the disc collagens with the disc tissue’s macro mechanics.