Swelling behavior of soft and biological materials

Injuries or other ailments can cause swelling of tissues in the body, or of ligaments and tendons surrounding the bones. Such inflammation can lead to discomfort, pain, or even serious illness. Knowledge of the biomechanics of soft tissues is essential for correct prognosis and diagnosis. This requires good modeling and simulation of soft skeletal tissues, which cannot be carried out without experimental material characterization. Behavior of organic tissues is quite similar to that of elastomeric materials that swell when immersed in certain fluids. This work investigates the effect of swelling on compression and bulk properties and the polymeric structure of a water-based elastomer. A drastic change in mechanical and structural properties is observed during the initial swelling period. Elastic and shear moduli decrease by nearly 90% within a few days, and then exhibit almost no change. An opposite trend can be observed for Poisson's ratio; dramatic increase in the beginning, then a near-constant behavior. Variation in bulk modulus is somewhat fluctuating, but the general trend is a decrease due to swelling. After ten days of swelling, value of Poisson's ratio becomes approximately 0.5. A sharp decrease in the first week of swelling can be observed in chain density, while cross-link average molecular weight shows the opposite trend of an increase with swelling (with minor fluctuations). Results of this study can provide the material input values for modeling and simulation of the behavior of tissues and other soft biological materials. This, in turn, can form a basis for more detailed analytical and computational studies in biomechanics and biomedical engineering.