A control of friction characteristics between self-propelled robotic system and gastrointestinal tissues plays a key role in achieving active locomotion. Fabrication of micropatterns on soft polymers has been proposed to enhance frictional traction. In the present study, micropillar arrays with different diameters of 60-140 μm were prepared on polydimethylsiloxane (PDMS) by soft lithography, and a series of friction tests were performed between microscopically patterned/nonpatterned PDMS and rabbit small intestinal tract (SIT) on a universal material tester, with the record of friction coefficient under various experimental conditions (sliding speed: 0.25 mm/s; sliding distance: 40 mm; applied loading: 0.4-1.0 N). Surface morphology of microscopically patterned PDMS samples was evaluated by scanning electron microscopy (SEM) before and after the friction tests. It was demonstrated that micropillar arrays aligned regularly on the microscopically patterned PDMS samples and maintained the shape after friction tests. At 0.4 N, the friction coefficient of PDMS samples with the micropillar diameter from 80 to 140 μm presented a decreasing trend, which was significantly larger than that of nonpatterned PDMS samples. However, the smallest friction coefficient (∼0.12) was obtained for the 60 μm micropillar diameter PDMS samples. In addition, the friction coefficient of nonpatterned PDMS samples decreased as the applied loading varied from 0.4 to 1.0 N, whereas the 60 μm micropillar diameter PDMS samples showed an opposite trend. It is proposed that the enhancement in friction between PDMS and SIT, which is achieved through the introduction of micropillars, may be determined based on different lubrication mechanisms.
Keywords: biotribology; capsule endoscopy; friction; robotic system; surface texture.