Region-media coupling in characterization and modelling of the disc annulus single lamella swelling.

The annulus fibrosus (AF) swelling property, which is correlated with its rheological and viscoelastic properties, plays a significant role in disc nutrition and mechanical loading justification during daily activities as well as designing scaffolds for tissue engineering applications. The objective of this study was twofold: firstly to characterize the AF single lamella swelling kinetics in different regions and solutions at the temperature range of 35-40 °C and secondly to use the swelling results as a baseline to model (independent to swelling media and anatomic region) the AF single lamella swelling. It was found that the AF single lamella swelling kinetics (equilibrium swelling ratio and swelling rate) depends on anatomic region and swelling media; however, its trend for different swelling media (ionic and molecular solution) is similar and the majority of hydration occurs during first 20% of equilibrium swelling time (about 20 min). Change in swelling rate constant in circumferential direction depends on the solution type. It decreases from anterior to lateral regions for water, PBS and glucose solution and remains constant-or its change is negligible-from lateral to posterolateral regions. The effect of temperature (in the range of 35-40 °C) on swelling kinetics was seen to be negligible. It was also understood that it is possible to present a model (independent to swelling media type) to predict the swelling kinetics of posterior and posterolateral AF single lamella, as these locations are less sensitive to the swelling media.