Developing Low-Viscosity Lubricants to Maintain Lubricity between Overtube and Enteroscope for Improved Maneuverability during Single-Balloon Enteroscopy

During enteroscopy, the hydrophilic coating on the inner surface of the overtube (OT) reduces the dynamic friction coefficient (DFC) between the endoscopic shaft (ES) and OT, allowing smooth insertion of the ES. However, endoscopists often encounter resistance to ES insertion and poor endoscopic manipulation during prolonged enteroscopy. We hypothesized that the reason is the degradation of the hydrophilic coating due to the continuous contact between the ES and OT and the associated increase in DFC. Focusing on single-balloon enteroscopy, we developed a unique model to continuously measure the DFC for 30 min while moving the ES in contact with the inner surface of the OT, which was applied with pure water or various lubricants. When pure water was applied, the initial DFC was 0.112 ± 0.001; however, it increased to 0.357 ± 0.002 over 30 min (219% increase). Meanwhile, the application of 0.1% carboxymethyl cellulose, 0.05% sodium alginate, 0.25% hydroxyethyl cellulose, and 0.04% xanthan gum solutions resulted in significantly lower initial DFCs of 0.073 ± 0.0004, 0.081 ± 0.0004, 0.079 ± 0.0004, and 0.063 ± 0.0003, respectively. Moreover, low DFCs were maintained even after 30 min, with DFC increase rates of +2.5%, -0.2%, -5.9%, and +5.6%, respectively. In addition, the injection pressures required for these optimal lubricants were extremely low. The optimal lubricants identified in this study successfully maintained lower DFCs than pure water, which is conventionally used to induce lubrication between the ES and OT; therefore, they may improve endoscopic manipulation.