A biomechanical comparative study of passive stomach tissue from pigs and humans

The prevalence of gastric problems, which are associated with high economic costs and medical complexity, is soaring worldwide. In biomedical research, porcine models have been widely used to investigate the gastrointestinal tract in preclinical studies due to their similar functionality and macrostructure. Despite their widespread acceptance, there is insufficient research on whether porcine gastric tissue accurately reflects the biomechanics and microstructure of the human stomach. Hence, the present study aims to characterize the human stomach wall and investigate inter-species differences and similarities through a comparison with a preceding study. For this purpose, quasi-static mechanical tests were performed in several deformation modes, i.e., planar biaxial extension, radial compression, and simple shear. The cyclic experiments were complemented by stress-relaxation tests to examine the viscoelastic behavior. Samples from two main layers of the stomach, i.e., mucosa and muscularis, as well as the complete stomach wall were tested from all gastric regions, i.e., fundus, body, and antrum. Through this strategic testing approach, considerable softening effects and various region- and layer-specific variations in the mechanical behavior of the stomach wall were observed. Complementary histological investigations highlighted the heterogeneous stomach wall architecture and its influence on the mechanical tissue response. The present study revealed significant regional, layer-, and sex-specific differences in the human stomach of patients undergoing bariatric surgery. The male stomach wall was thicker, more extensible in the antrum, and stiffer under radial compression in the fundus compared to the female cohort. Furthermore, notable differences were observed between porcine and human tissue, such as a significantly softer tissue response to radial compression and simple shear of the human muscularis and the complete stomach wall due to a higher collagen and elastin content and smaller muscle bundles.