A Multi-Vine Soft Robot Enabling Accessible Working Channel and Steering

Technical Summary: A Multi-Vine Soft Robot Enabling Accessible Working Channel and Steering

Problem Statement
Soft eversion robots, or "vine robots," offer significant potential for navigation in complex, confined environments like the human colon due to their ability to grow with minimal friction via tip-growth. However, their navigation performance is heavily dependent on environmental interactions, and sharp directional changes often exceed the capabilities of passive growth, necessitating active steering mechanisms. Furthermore, existing applications requiring payload delivery (e.g., microsurgical tools) face limitations with current designs. Prior attempts to integrate working channels within the vine body constrain tool size, introduce friction, and restrict environmental access strictly to the robot's tip. There is a need for a system that enables active steering and facilitates the delivery of tools without embedding the channel within the growing vine structure.

Methodology
The authors propose a multi-vine architecture consisting of two vine robots coupled to an externally integrated working channel via soft mounting tips. The system is fabricated using low-density polyethylene (LDPE) sheets (0.06 mm thickness) ultrasonically welded into rectangular tubes, which expand to diameters of 10 mm and 20 mm upon pressurization. The working channel is a 6 mm outer diameter silicone tube anchored externally, while soft fabric caps link the two vines and the channel.

The control strategy relies on independent actuation of the two vines:

• Straight Growth: Both vines are inflated at the same pressure, allowing the working channel to advance freely.
• Steering: To achieve a turn (e.g., a left turn), the vine on the right side is pressurized while the working channel is locked. This asymmetric actuation induces structural buckling, resulting in a sharp directional change. The process is reversed for opposite turns.
• Growth Control: The advancement speed of the working channel is manually controlled to regulate the system's growth speed and ensure the soft caps remain in their intended positions.

Key Contributions

• Multi-Vine Architecture: The introduction of a dual-vine system coupled to an external working channel, decoupling the steering mechanism from the payload delivery path.
• External Working Channel: A design that preserves a working channel from the base to the tip without embedding it within the vine bodies, thereby reducing friction and tool size constraints.
• Active Steering Mechanism: A method utilizing asymmetric pressurization to induce buckling, enabling sharp turns (nearly 90 degrees) during growth.

Results
Experimental characterization demonstrated that the addition of soft caps did not noticeably alter the growth pressure requirements. While smaller diameter vines (10 mm) required higher growth pressures due to increased friction, these pressures remained well below the burst pressure, indicating a sufficient safety margin.

• Open Environment: The multi-vine system successfully grew forward and performed controlled turns, accurately locating and entering pipe openings.
• Confined Environment: In a silicone colon phantom with realistic dimensions, the 10 mm diameter system successfully navigated a 90° bend while carrying the working channel. This was achieved despite the phantom material being less slippery than a real colon, which increased friction.

Significance and Claims
The paper claims that this architecture significantly improves the navigation performance of eversion robots in both open and confined environments. By maintaining an externally integrated working channel, the system addresses a key limitation of existing designs by enabling less restricted tool delivery. The authors state that the multi-vine robot demonstrates sufficient maneuverability to grow through a colon phantom, offering a potential solution for scenarios where a single, smaller vine might rely on wall contact forces that could cause discomfort. The work highlights the potential of this architecture for versatile medical and non-medical applications, with future work planned to quantitatively characterize steering performance gains and develop the working channel to allow tool access along the entire length of the robot body, not just at the tip.