A viscoelastic framework for inflation testing of gastrointestinal tissue.

Gastrointestinal (GI) diseases are often associated with hypertrophy of the layers of the GI wall, along with dilatation and a denervation of smooth muscle cells which alters the biomechanical properties of the tissue. 'Balloon distension' is a specialised experimental protocol performed on hollow organs to investigate their biomechanical properties. A balloon is inserted and pressurized during this procedure and the change in external diameter is monitored as a function of the applied pressure. A hyperelastic framework is often used in this context to evaluate the stresses in the wall after inflation. However, this only gives an idea about the final equilibrium state of the tissue, whereas the intermediate states of deformations are overlooked. GI soft tissues are viscoelastic, thus, the stress values during inflation are loading rate dependent and are higher than the equilibrium state values. Therefore, it is necessary to consider the time- and rate-dependent material properties during a balloon distension test. The aim of this work was to develop a viscoelastic framework for interpreting balloon distension experiments under finite deformation. To demonstrate the efficacy of the framework, it was used to recreate experimental results from intestinal and colonic tissue segments. In all cases, the simulation results were well matched (R>0.9) with the experimental data.