---
title: Modular Soft Robotic Catheter
url: https://www.emergentmind.com/topics/modular-soft-robotic-catheter
type: topic
---

# Modular Soft Robotic Catheter

A modular soft robotic catheter is a multifunctional endoluminal instrument engineered to integrate actuated modules for anchoring, sensing, manipulation, and targeted therapy delivery within a compliant, miniaturized (1.47 mm outer diameter) body. The system advances the domain of soft-robotic instrumentation by enabling customizable, independently controlled modules to optimize navigation and intervention in delicate, tortuous anatomies inaccessible to standard catheters. Through wireless magnetic actuation, tendon-driven manipulation, closed-loop sensing, and in-situ therapeutic release, this platform supports precision therapies with enhanced compliance, safety, and functional scalability [2601.14837].

## 1. System Architecture and Modular Composition

The modular soft robotic catheter (mSCR) architecture consists of a monolithic silicone body (1.47 mm OD) designed to accommodate up to four functional units in series. Modules, sequentially embedded along the catheter's length, are connected by three 100 µm microchannels/lumens:

- A pneumatic lumen for balloon inflation
- A tendon lumen for gripper actuation
- A central lumen for camera cabling, LED fiber, and multicore FBG

Primary demonstrated modules comprise:

- **Anchoring balloon**: Hyperelastic, magnetically responsive, inflatable actuator to stabilize the catheter at target loci.
- **Manipulation gripper**: Tendon-driven, flexure-based L-arm gripper for compliant object retrieval and manipulation.
- **Sensing modules**: Onboard NanEye camera (250 × 250 px at 30 fps), FBG shape sensor (27 Hz interrogation), and inflation-pressure sensor (VSP1130, ±0.5 kPa accuracy).
- **Drug release shell**: Micropatterned, spin-coated PLA coating designed to fracture upon 1 MHz ultrasound, enabling on-demand payload delivery.

Mechanical compliance is preserved using low-modulus elastomer (DragonSkin 30) embedded with NdFeB powder and through the optimized geometry of each module (e.g., flexure and balloon wall thickness). The complete assembly is sleeved through a 0.9 mm ID PTFE tube (1.6 mm OD), maintaining flexibility comparable to standard soft catheters.

## 2. Materials, Fabrication, and Integration

The construction of the mSCR employs advanced materials and fabrication methods:

- **Elastomeric matrix**: A 1:1 mass ratio of NdFeB (5 µm) and DragonSkin 30, mixed in vacuum and injected into high-resolution molds (microArch S140).
- **Silicone and resin shells**: Two-part microfabricated HTL resin structures, defining precise air-channel cores and guides for integrated electronics and optics. These are assembled using sacrificial cores dissolved in acetone.
- **Gripper**: Ultra-high-resolution, 3D-printed (HTL resin) flexure structure, bonded around the imaging module.
- **PLA drug-release shell**: Spin-coated and micropatterned with 20 µm squares (5 µm depth, 10 µm spacing) by molding on a 3D-printed negative.
- **Sensing and transmission elements**: NanEye camera, LED fiber (Thorlabs), multicore FBG, nylon tendons (80 µm), and fine-ID/OD inflation tubing.
- **Assembly procedure**: Sequential demolding, camera/FBG installation, gripper bonding, PLA shell slip-fit, routing of actuator lines, and final coupling to control units.

This integration strategy enables monolithic compliance without local stiffening, supporting both module flexibility and dense packing of active elements.

## 3. Actuation Principles and Mathematical Modeling

### Magnetic Steering

Tip actuation is achieved wirelessly by an external permanent magnet (EPM, N52; 100 mm diameter, 100 mm thickness, remanence ≈1.45 T) mounted on a 7-DoF robot arm. The resulting field at the catheter tip ($|B_{EPM}|$) spans 16–25 mT, transmitting torques up to $\tau_{tip} \approx 6.7~\mathrm{N{\cdot}m}$. The EPM–mSCR interaction is described by a dipole–dipole physical model:

\[
B_{EPM}(p) = \frac{\mu_0}{4\pi|p|^3} \left[ 3(p\cdot m)\frac{p}{|p|^2} - m \right]
\]

\[
T(x) = \frac{\mu_0}{2\pi}|B_r||B_{EPM}|r^2(L-x)
\]

where $r$ is radius, $L$ is magnetized length, $B_r$ is remanence, $\mu_0$ the vacuum permeability, and $p$ is EPM pose. Maximal tip deflection ($\theta_{max}$) is modeled via Euler–Bernoulli theory:

\[
\theta_{max} = \left(3E\mu_0 r^2 \pi L^3\right)^{-1} |B_r||B_{EPM}|
\]

### Anchoring Ballon Actuation

Balloon expansion is pneumatically regulated (syringe pump up to $p_{in}=60$ kPa), with strain–pressure response modeled by a third-order Yeoh strain-energy density function:

\[
W = \sum_{i=1}^3 C_i (I_1 - 3)^i
\]

where $I_1$ is the Cauchy–Green invariant and $C_i$ are empirical constants. Measured anchoring force is $F_{anchor}=3.3 \pm 0.2$ N.

### Tendon-Driven Gripper Dynamics

The compliant gripper is modeled with a shifted Legendre polynomial curvature expansion:

\[
\kappa(s)=a_0 + a_1 P_1(s) + a_2 P_2(s)
\]
and tip response is determined by tendon force ($f_{tendon}$). Pre-twisting elevates fundamental resonance above 2 MHz, avoiding 1 MHz actuation cross-talk. Maximum tip gripping force is $1.28 \pm 0.16$ N when anchored ($0.43 \pm 0.06$ N unanchored, a $\sim 300\%$ increase).

## 4. Sensing Modalities and Real-Time Calibration

Onboard sensing subsystems are fundamental for navigation precision and autonomous feedback.

- **FBG Shape Sensing**: A three-core FBG records distributed strain ($\epsilon_i$) at 27 Hz. Curvature conversion: $\kappa=(\epsilon_{+}-\epsilon_{-})/d$, $d$ core spacing; tip orientation $\psi(s)=\int_0^s \kappa(u)du$. Calibration errors are under $2^\circ$ relative to ground-truth.
- **Balloon Pressure Sensing**: A VSP1130 sensor provides balloon pressure with $\pm 0.5$ kPa accuracy; PID-based closed-loop—$u(t) = K_p[e(t) + (1/T_i)\int e + T_d\,\dot{e}(t)]$, managing actuation within safe limits ($p_{in}\leq150$ kPa burst pressure).
- **Visual Marker Tracking**: Two heat-shrink markers and papilla (anatomical landmark) are detected by YOLOv8 at 30 fps (precision 0.81, recall 0.76, F1 = 0.78). Angular correction:

\[
\Delta\psi = \arccos\left( \frac{v_{tip} \cdot v_{goal}}{|v_{tip}||v_{goal}|} \right)
\]

where $v_{tip}$ and $v_{goal}$ are inter-marker and target vectors, respectively.

## 5. Closed-Loop Control and Automation

The mSCR employs a closed-loop, ROS-integrated pipeline combining perception, model-based planning, and actuation:

1. Endoscopic video analyzed via YOLOv8 for marker and target detection, yielding $\Delta\psi$.
2. Magnetic model computes desired tip curvature $\kappa_{des}=f_{model}(\Delta\psi)$.
3. Inverse field solver translates $\kappa_{des}$ to a desired EPM pose increment ($\Delta p$).
4. 7-DoF robot manipulates the EPM accordingly.
5. FBG shape sensing confirms execution ($|\psi_{FBG}-\psi_{model}| < 2^\circ$).
6. Catheter is advanced using an external feed unit.

Control architecture features PID regulation for balloon inflation, damped least-squares for magnet Cartesian control, and curvature-to-field mapping ($\Delta B \propto EI\kappa_{des}$). Human override is enabled at all times.

## 6. In Vivo Validation and Performance Evaluation

Key procedural validation was performed in two Yorkshire–Landrace porcine subjects (33 kg, 35 kg) via standard duodenoscopes, with the following protocol:

- Papilla cannulation using duodenoscope
- Semi-autonomous magnetic tip alignment and 75 mm navigation into pancreatic duct (depth not accessible with conventional catheters)
- Balloon deployment to anchor mSCR
- Object retrieval via gripper
- Ultrasound-triggered (1 MHz) drug release

Performance metrics:

| Task                                   | Quantitative Metric                | Comments                                            |
|----------------------------------------|------------------------------------|-----------------------------------------------------|
| Navigation depth                       | 75 mm                              | Pancreatic duct; inaccessible to standard devices   |
| Autonomous cannulation time            | $t_{auto}=223\pm3$ s               | 12% faster vs. manual ($t_{manual}=253\pm23$ s)     |
| Anchored gripper force                 | $1.28\pm0.16$ N                    | $0.43\pm0.06$ N unanchored                         |
| Balloon holding force                  | $3.3\pm0.2$ N                      | Enough for robust actuation                         |
| Drug release (T$_{80}$)                | $104\pm22$ s                       | 80% payload after 1 MHz insonation                  |
| Tip orientation error                  | $<2^\circ$                         | FBG vs. model                                       |
| Clinical complications                 | None                               | No papilla damage, no bleeding                      |

The platform demonstrated compatibility with duodenoscope, gastroscope, and bronchoscope access, underscoring generalizability.

## 7. Clinical Significance, Limitations, and Future Directions

The modular mSCR supplies a scalable architecture for hospital-based and research endoluminal interventions, achieving expanded functionalization of compliant catheters without sacrificing mechanical softness. Key clinical benefits include first-person visualization, reduced X-ray exposure, semi-autonomous tip navigation (shortening the procedural learning curve), and stimulus-triggered drug delivery precisely at target sites.

Identified limitations include unresolved depth estimation (addressable via miniaturized localization modalities), lack of multi-dose capability (potentially via multi-resonant segmented PLA shells), and the need for distal tip biohybrid actuators to further enhance manipulation accuracy. Long-term biocompatibility for chronic deployment remains under investigation. 

Through integration of wireless magnetic steering, pneumatic anchoring, compliant manipulation, onboard feedback, and ultrasound-mediated drug release, the mSCR defines a new standard for precision therapies in anatomies and disease states where conventional catheters lack efficacy [2601.14837].

Source: https://www.emergentmind.com/topics/modular-soft-robotic-catheter