Researchers at the University of Leeds have developed a new design for tendon-driven continuum robots (TDCRs) aimed at one of the hardest problems in minimally invasive medicine: reaching small, hard-to-access lesions deep in the lung. Their design, published in IEEE/ASME Transactions on Mechatronics, relies on a manufacturing approach that couldn’t be achieved with conventional machining or standard 3D printing — and it’s where BMF’s microArch S140 played a critical role.
The Problem: Reaching Peripheral Lung Nodules
Bronchoscopy is a first-line tool for diagnosing and treating lung disease, but conventional bronchoscopes struggle to navigate the tortuous, narrowing airways needed to reach nodules out at the periphery of the lung. Robotic-assisted bronchoscopy platforms already on the market improve reach and stability, but they typically rely on complex, costly mechanical assemblies that are difficult to reconfigure for different procedures or patient anatomy.
The Leeds team, led by Burak Ozdemir, Pietro Valdastri, and James Chandler, set out to build something simpler: a continuum robot that’s compact enough for distal airway navigation, modular enough to be reconfigured without a full redesign, and still capable of housing a camera, light source, and biopsy tool through an open central channel.
The Design: A Spring Backbone with Self-Anchoring Disks
Instead of building the robot’s body from discrete 3D-printed helical segments (a common approach in prior work), the Leeds design uses a continuous, off-the-shelf helical spring as the backbone, with custom-designed spacer disks threaded onto it to define tendon paths and segment boundaries.
The disks screw directly onto the spring using a matched thread pitch, locking into place through friction alone — no adhesives or fasteners required. That “self-anchoring” mechanism is what makes the design modular: disk spacing, segment length, and tendon layout can all be adjusted without redesigning the robot from scratch.
The team demonstrated this with a two-segment, seven-tendon prototype: a proximal segment built from disks that anchor to the outside of the spring, and a distal segment built from disks nested inside it, arranged concentrically. The result is a robot with a minimum outer diameter of just 4.2 mm, housing a 2.4 mm working channel large enough for a miniature camera, fiber-based light source, and biopsy needle.
Where Micro-Precision 3D Printing Came In
Making this concentric arrangement work depends entirely on how precisely the disks are manufactured. The inner (Type-1) disks needed to thread smoothly onto the spring’s mean diameter while leaving enough clearance to also accept an outer (Type-2) disk layer around them — all within a robot barely wider than a large-gauge needle. Get the tolerances even slightly wrong, and the disks either won’t seat correctly on the spring or won’t leave room for the tendon routing holes and central working channel.
The Leeds team manufactured these Type-1 disks using BMF’s microArch S140 micro-precision 3D printer, specifically citing the need for tighter dimensional tolerances to support concentric integration with the outer disk layer. This is a case where standard-resolution 3D printing or machining would struggle to hold the geometry needed at this scale, and where BMF’s Projection Micro Stereolithography (PµSL) technology’s combination of feature resolution and dimensional accuracy made the design achievable.
The team’s earlier attempts to produce these disks on a standard SLA platform ran into a real problem: the tendons would jam during actuation, a failure mode that would undermine reliable bending and tool delivery in a device meant to navigate delicate airways. Moving the Type-1 disks over to BMF’s microArch S140 resolved the jamming, since PµSL’s tighter tolerances kept the tendon routing geometry consistent enough for smooth, repeatable movement.
How the Robot Performed
With the prototype assembled, the team put it through a series of validation tests:
- Workspace characterization: tracking roughly 25,000 tip positions from randomized tendon actuation showed broad, near-omnidirectional bending capability, with the robot able to bend past 310° without losing structural integrity or tendon alignment.
- Model validation: a piecewise constant-curvature kinematic model predicted tip position with a mean error of about 4.0 mm — within one robot diameter.
- Phantom navigation: using a 3D-printed lung phantom derived from real patient CT data, the robot successfully navigated to four distinct targets at different airway generations, with an average positioning error of 2.35 mm and navigation times between 67 and 82 seconds. At each target, it successfully deployed a biopsy needle through its working channel to simulate tissue sampling.
Why It Matters
This work is a good example of how micro-precision manufacturing can unlock robot architectures that simply weren’t practical before — not by making existing designs smaller, but by making entirely new mechanical strategies (like self-anchoring, screw-fit disk assembly) viable at millimeter scale. For medical device teams working on continuum robots, steerable catheters, or other compact surgical tools, it’s a look at how tolerance-critical components can be a limiting factor long before actuation or control ever becomes the bottleneck.
Read the full paper, “Spring-Based Tendon-Driven Continuum Robots for Compact Modular Designs in Endoluminal Applications,” in IEEE/ASME Transactions on Mechatronics.
