Potential of Poly-(N-Isopropylacrylamide) hydrogel as a clamper of the microrobot in gastrointestinal tract

We successfully demonstrate that a thermally actuated reversible hydrogel, the poly N-isopropylacrylamide (PNIPAAm), based clampers holds the intestines of a pig during the inchworm motion of microrobot. Although there are no direct relationship between hydro affinity and friction force, we found the significant friction force difference according to the surface condition change of PNIPAAm hydrogel. On the small intestine of a pig, a clamping mechanism was realized based on simple switching hydrophobic/hydrophilic surface conditions of PNIPAAm due to heating/cooling. In order to estimate response time of the clamper, the characteristic transition time of PNIPAAm film from hydrophilic to hydrophobic condition was investigated. Water contact angle (WCA) was monitored to normalize the transition time characteristics of PNIPAAm film in the course of time. From these results, we calculated the minimum heating time of the various thickness of PNIPAAm film to the clamping after its change to the hydrophobic condition. The minimum heating time was 15 seconds until 1 mm thickness of PNIPAAm film had enough friction force