Improving practical steerability of a bidirectional steerable catheter for ERCP by non-straight wire routing

Endoscopic retrograde cholangiopancreatography (ERCP) requires reliable bile duct cannulation, yet steerability of wire-driven steerable catheters (SCs) can deteriorate when the shaft is constrained, partly because actuation may induce unintended shaft-side deformation and transmission loss. This study evaluated whether non-straight wire-routing architectures could improve practical steerability of a bidirectional SC for ERCP. Three prototypes were developed: a conventional straight-wiring design (SC#0), a non-straight, non-crossed design (SC#1), and a non-straight, crossed design (SC#2). Steerability was assessed by incremental wire-pulling tests under straight-shaft and loose-shaft conditions and by a mock ERCP study using an actual duodenoscope. Outcomes included the handle displacement and pulling force required to reach 85° distal bending (HD₈₅, HPF₈₅) and target-angle reachability. In the straight-shaft condition, SC#1 and SC#2 reduced HD₈₅ and HPF₈₅ by 54-63% and 63-65%, respectively, compared with SC#0. Under the loose-shaft condition, SC#0 reached 85° in only 1/5 trials, whereas SC#1 and SC#2 reached 85° in all trials. In the mock ERCP study, the proposed designs reduced HD₈₅ and HPF₈₅ by 57-71% and 57-62%, respectively, in both bending directions. These findings indicate that non-straight wire-routing architectures can be practically implemented in a bidirectional SC for ERCP and may improve steerability under ERCP-relevant constraints.