Hong Kong University of Science and Technology Team Develops Helical Scaffold for Stable Bronchoscopic Imaging and Intervention

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Helical brace helps robots resist respiratory interference.

A robot needs to perform precise imaging and intervention deep within the bronchus, yet the lungs continuously move with breathing, and the distal end of the catheter may also shift accordingly. For a robot, this is like standing on a constantly rocking ship, trying to aim a needle at a constantly moving target.

More challenging is that the instrument needs a structure to stabilize itself; however, improper support may increase the mechanical load on the airway wall, while a structure that is too large may obstruct airflow.

Can we find a "temporary anchor point" for the robot, which can stabilize the instrument without interfering with lung ventilation?

Professor Ren Hongliang and Professor Yuan Wu from the Chinese University of Hong Kong designed a

hydraulically shape-changing helical brace.

In a simulated bronchus model with intense breathing, it reduced catheter displacement from 2.97 millimeters to within 0.12 millimeters, a reduction of about 96%. At the same time, the airway's airflow transmission capability remained above 97.4% of the baseline level.

This study was recently published in the international robotics journal Science Robotics, with the title "Stabilizing telerobotic endobronchial imaging and interventions in breathing lungs with a helical brace".

Researchers not only tested whether the brace could stabilize the catheter, but also integrated it with a remote-controlled robotic system, performing bronchial puncture, liquid delivery, and aspiration operations in a live pig model, and verified its assistance in fine imaging.

01.

How does breathing-induced displacement affect robotic operations?

For a lung intervention robot, having the catheter reach the target area is just the first step.

The lung airway is not a static tube. With breathing, lung tissue and airways continuously move, and the position of the catheter distal end may also change. For puncture operations requiring precise positioning, this displacement can alter the relative position between the needle and the target tissue.

Imaging is also affected. If the probe keeps moving with breathing, the continuously captured images may show motion artifacts, affecting the observation and measurement of tissue structures.

The research team first needed to solve the problem of

how to provide a stable support point for the instrument.

Traditional solutions have their limitations.

Rigid shape-locking structures

can provide support, but in a curved airway, some designs require continuous axial tension to maintain shape, which may impose additional mechanical load on the tube wall. Some electrothermal driving solutions also involve temperature rise and electrical safety issues.

Balloon stents

rely on inflation to expand and press against the tube wall for fixation, but they occupy lumen space and may obstruct airflow.

Variations in airway dimensions further increase the difficulty.

The paper points out that the diameter of the main bronchus is about 10 millimeters, while the diameter of more distal bronchi can shrink to about 3 millimeters. A fixed structure must adapt to different tube diameters while balancing stability and ventilation capability.

What researchers needed was not simply to make the instrument tighter, but to give the robot sufficient anchoring force while minimally interfering with the normal function of the airway.

02.

A helical brace, with a diameter that can be adjusted nearly 10 times

The most distinctive feature of this device is that it can actively change its shape.

Researchers designed a

helical brace composed of multiple asymmetric stiffness tubular modules

. In simple terms, different parts of each module have different stiffness, and they bend when subjected to liquid pressure. By stacking these modules at a certain angle, the entire structure can gradually reconfigure from a relatively straight state into a helical shape as hydraulic conditions change.

Once the helical structure contacts the tube wall, it can provide support for the catheter; adjusting its shape allows it to adapt to different lumen sizes. In terms of driving method, the research team used water pressure rather than air pressure to avoid control losses caused by the compressibility of gas.

After structural and material optimization, researchers created a tubular brace that is 50 millimeters long with an initial outer diameter of 3 millimeters. When using the optimized S70/S90 material combination, its diameter can expand from 3.0 millimeters to 29.3 millimeters, with a maximum diameter approximately 9.77 times the minimum diameter.

This nearly 10-fold adjustment range provides the basis for it to adapt to bronchi of different diameters.

Of course, the brace cannot solely pursue expansion capability. Insufficient support force cannot effectively fix the catheter; excessive support force may damage airway tissue. The research team therefore tested the radial and axial forces of different material combinations, ultimately selecting a solution that balances support capability and structural deformation characteristics.

Notably, the helical brace does not completely occupy airway space. Its design advantage lies in

achieving anchoring through reconfigurable helical morphology while preserving as much airflow passage as possible, rather than relying on overall expansion like a balloon.

03.

Catheter displacement reduced by 96%, airway still maintains normal ventilation

To verify the effectiveness of this design, researchers first simulated normal resting breathing and intense breathing in a dynamic bronchus model, comparing catheter movement before and after the helical brace was applied.

Under simulated conditions of intense breathing, without stent fixation, the catheter displacement was approximately 2.97 millimeters; after enabling the stent, the displacement dropped to within 0.12 millimeters,

a decrease of about 96%.

This means that the spiral stent can significantly reduce the impact of respiratory motion on catheter position, providing a more stable operating foundation for distal instruments.

However, stability is only half the story. The other half is ensuring that it does not interfere with pulmonary ventilation. To this end, researchers measured changes in airway pressure under different conditions in simulated bronchi with diameters of 10 millimeters and 5 millimeters.

The results showed that after stent fixation, the relative pressure changes under all test conditions did not exceed 2.6%

and the airway's airflow conductivity remained above 97.4% of the baseline level

. In contrast, fixed-state balloon stents can cause significant bronchial obstruction.

In addition, the research team also conducted tissue safety tests.

In an ex vivo rat bronchus experiment, researchers applied a radial force of 1 Newton to the stent for 2 hours, then observed tissue changes using optical microscopy, optical coherence tomography (OCT), and histological analysis.

No significant surface or deep tissue damage was found, with an average thickness change of no more than 6 micrometers. However, the mucosal layer still showed statistically significant changes, indicating that the tissue's response to mechanical load cannot be completely ignored.

In the in vivo pig experiment, during stent fixation, the animal's expiratory tidal volume was 866±15 milliliters, close to the ventilator's set value of 875 milliliters, and peripheral blood oxygen saturation was maintained at 100%. Histological examination also did not reveal clear stent pressure damage.

04.

It's not just about stabilizing the catheter; robots have already begun performing puncture operations

With the catheter stabilized, it still needs to be determined whether the robot can complete more precise interventional procedures.

The research team integrated the spiral stent with a remote-controlled robotic catheter system.

The catheter's tip integrated a fluid-driven robotic arm, capable of carrying interventional needles, endoscopic cameras, and OCT probes to perform turning, positioning, and operations within the bronchus.

Here, the term 'remote robot' refers to a system operated by the operator through a control console, not a robot that autonomously judges and executes surgery.

In an ex vivo pig lung experiment under simulated breathing conditions, researchers allowed the robotic arm's tip to move along a pre-set path. Without stent fixation, the average positioning error under intense breathing conditions exceeded 3 millimeters; after enabling the stent, the average positioning error dropped to within 1 millimeter.

Subsequently, the team validated three types of bronchoscopic needle insertion procedures in a live pig model.

The first type was drug delivery.

Researchers used blue dye to simulate drugs and delivered the liquid to the target location through the needle.

The second type was bronchial puncture.

The robot adjusted the needle's direction and position, then advanced the needle to the bronchial wall.

The third type was liquid aspiration.

After repositioning the needle at the target branch, the needle performed rotational and retraction operations to aspirate tissue fluid containing blue dye.

These experiments demonstrate that the spiral stent not only stabilizes the position of instruments but also provides mechanical support for needle positioning and interventional procedures.

However, these results come from a live pig model and do not mean that this system is ready for direct use in human lung surgery. Whether it can improve clinical sampling accuracy and reduce complications still requires further research.

05.

Imaging is also more stable, but there is still a distance to clinical application

In addition to interventional procedures, researchers also tested the assistance of the spiral stent for OCT imaging.

OCT uses near-infrared light to obtain microscopic structural information of tissues, which can assist in observing the bronchial wall and its internal tissues. However, in a dynamic pulmonary environment, probe displacement may affect the stability of continuous scanning.

In an ex vivo pig lung experiment, an unfixed OCT probe had an average radial displacement of approximately 57 micrometers under simulated resting breathing and 116 micrometers under intense breathing conditions. After stent fixation, the average displacement under both conditions dropped to approximately 15 micrometers.

In the in vivo pig lung experiment, without fixation, the probe's average radial displacement was 141 micrometers; after stent fixation, the displacement dropped below 40 micrometers, a reduction of about 71.9%.

This means that

the spiral stent not only stabilizes interventional needles but also helps reduce respiratory motion interference on imaging probes, providing conditions for more stable bronchial imaging.

However, imaging is not completely unaffected by motion. Researchers still observed some scanning jitter and residual respiratory-related motion. The paper also points out that this device still needs improvement. For example, the current stent's radial and axial support forces are still insufficient to directly apply to scenarios requiring greater force, such as cardiac interventions. Additionally, the efficiency of needle force transmission by the robotic arm decreases at larger bending angles.

Next, the research team still needs to evaluate its safety, positioning accuracy, and interventional effectiveness through human studies and compare it with traditional bronchoscopes and other approaches.

The design concept of the spiral stent may also be extended to other tubular systems with similar physiological movements, such as the gastrointestinal and urinary tracts

. However, these applications still require separate validation.

The inspiration from this study is that

the precision of minimally invasive robots is not only determined by whether the robotic arm can accurately execute commands but also by whether it can obtain a stable operating foundation in real physiological environments.

As robots enter deeper and more complex internal spaces, how to stabilize the instruments without interfering with the normal function of organs will be a worthwhile issue to continue researching.

Paper link: https://www.science.org/doi/10.1126/scirobotics.aed1960

END

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