---
title: Underwater Bio-Inspired Soft Robots
url: https://www.emergentmind.com/topics/underwater-bio-inspired-soft-robots
type: topic
---

# Underwater Bio-Inspired Soft Robots

Underwater bio-inspired soft robots are engineered systems that leverage the compliance, multifunctionality, and adaptive morphologies found in marine organisms to achieve enhanced performance, environmental compatibility, and novel operational capabilities in aquatic environments. These robots exploit architectural, actuation, and control paradigms inspired by fish, cephalopods, jellyfish, echinoderms, bacteria, and other aquatic life forms, and have emerged as an enabling technology for oceanexploration, ecological monitoring, environmental remediation, and complex manipulation in unstructured underwater settings [2601.12353], [2508.11883].

## 1. Fundamental Biological Inspirations and Biohybrid Principles

Marine organisms provide a diverse repertoire of locomotion, adhesion, manipulation, and sensory strategies for underwater robotics. Architectures such as muscular hydrostats (octopus arms), fin-and-body undulators (fish), soft-bell pulsers (jellyfish), jet-propelled mantles (squid), and flagella-driven bacteria are directly transposed into robotic analogues via compliant, distributed material systems.

- **Muscular hydrostat models:** Octopus arms exhibit unconstrained continuum bending, torsion, and telescopic extension through three orthogonally arranged muscle layers constrained at constant volume. Soft robotic manipulators replicate these through cable networks or embedded fluidic chambers in elastomeric matrices [2508.11883], [2401.13439].
- **Undulatory swimming and fin propulsion:** BCF (Body/Caudal Fin) and MPF (Median/Paired Fin) locomotion is emulated via elastomeric tails with antagonistic chambers (hydraulic or pneumatic), distributed smart-material "muscles" (e.g. HASEL, DEA, SMA), and sophisticated kinematic sequencing, enabling traveling or standing waveforms tailored for thrust or maneuverability [2601.12353], [2504.11377], [2310.11426].
- **Jet propulsion:** Cephalopod-inspired robots employ elastomeric mantles or combustion-driven chambers to realize pulsed-jet thrust and escape maneuvers, combining high instantaneous force with structural compliance [2302.08217], [2504.11722].
- **Flagellar and ciliary mechanisms:** Bacteria-analogues such as ZodiAq and BactoBot employ soft silicone helical flagella driven by distributed actuators, achieving omnidirectional, low-disturbance propulsion suited to delicate ecosystems [2509.20964], [2503.19556].
- **Soft adhesion:** Remora- and mollusk-inspired suction actuators employ bilayer doming, switchable negative pressure, and contact-compliant lips to adhere on wet, rough, or underwater surfaces, supporting amphibious climbing and biohitchhiking analogues [1804.08692].

## 2. Soft Material Platforms and Fabrication Methods

Material selection and characterization are critical for achieving biological fidelity and operational robustness:

- **Elastomers:** Ecoflex, DragonSkin, PDMS, and Mold Star silicones (E≈0.1–3 MPa) are ubiquitous for moderate modulus, extensibility, and stability [2511.09885], [2310.11426].
- **Hydrogels and LCEs:** Employed to mimic tissue-like softness and environmental responsiveness, enabling transparency, biocompatibility, and even self-healing [2601.12353], [2508.11883].
- **Smart materials:** HASEL and DEA actuators provide high strain rates, muscle-like contraction, and electrical tunability, while SMAs and SMPs afford thermal shape changes and high blocking force [2504.11377], [2310.11426].
- **Origami and composite laminates:** The Yoshimura fish-mouth gripper exemplifies crease-based mechanical intelligence for robust underwater manipulation, fabricated from patterned composite sheets (nylon–TPU, PETG) [2503.11049].
- **Modular casting and rapid prototyping:** Lost-wax, 3D printing, and soft lithography enable fast iterations on chamber layouts, stiffness gradients, and integration of electronics or sensors [2201.04098], [2511.09885].

## 3. Actuation Mechanisms and Kinematic Control

A diverse suite of actuation modes enables both biologically faithful and scalable robotic behaviors.

- **Fluidic actuation:** Pressurized pneumatic or hydraulic networks, including fiber-reinforced bellows and distributed antagonistic chambers, deliver large deflections and force outputs. Models typically relate pressure inputs to curvature via $κ = M/(EI)$, where $M$ is generated by chamber pressure, $E$ the Young's modulus, and $I$ the sectional inertia [2106.07011], [2201.04098].
- **Dielectric elastomer actuation:** DEAs convert Maxwell stress ($σ_M = ε_0 ε_r E^2$) into bending or extension for high-speed, low-inertia swimming and flapping [2310.11426], achieving >1 BL/s in compact manta-inspired robots.
- **Distributed artificial muscles:** Axial placement and independent control of HASELs in fish bodies enables traveling wave formation, higher thrust at elevated resonant modes, and embedded kinematic feedback [2504.11377].
- **Biohybrid and chemical actuation:** Autonomous gas generation, combustion-driven pulses, and even integrated living muscle tissue have been harnessed for swimming, gliding, and leaping behaviors [2303.08672], [2302.08217].
- **Origami transform mechanisms:** Single-DOF, force-amplifying folding architectures enable rapid, robust shape changes for gripping, crawling, or volume modulation [2503.11049], [2511.09885].
- **Adhesion actuators:** Positive-pressure, doming strategies with bilayer constructs deliver robust, reversible grip on surfaces in both air and under water, supporting amphibious climbing robots [1804.08692].

## 4. Sensing, Control, and Intelligent Behavior

Advanced underwater soft robots integrate proprioceptive and exteroceptive sensing with open-loop, closed-loop, and learning-based control strategies.

- **Embedded strain and curvature sensing:** Liquid-metal, carbon-nanotube, or foil strain sensors are laminated or molded into soft spines, enabling real-time midline reconstruction and feedback for gait optimization [2504.11377], [2601.12353].
- **Hydrodynamic and tactile perception:** Lateral-line analogs, fiber Bragg gratings, and soft tactile arrays monitor flow, contact, or object properties, facilitating embodied interaction and adaptive manipulation [2508.11883].
- **Closed-loop model and model-free control:** Nonlinear model predictive control (NMPC) addresses wave-induced disturbances on soft manipulators, yielding up to 84% error reduction in set-point/trajectory tracking tasks [2401.13439]. Bang-bang logic and fluidic valves provide low-power, electronics-free feedback in gliders [2303.08672].
- **Embodied intelligence:** Distributed actuation and compliance enable robots to passively negotiate obstacles, exploit environmental forces, and simplify control requirements—seen in flagellum-driven redundancy, passively morphing appendages, and quick-return mechanisms [2503.19556], [2410.11764].
- **Learning and optimization:** Reinforcement learning and multi-criteria decision frameworks (G1-VIKOR) are used to automate design-choice mapping from biological behaviors to robotic hardware [2504.11722].

## 5. Locomotion Modes, Manipulation, and Functional Capabilities

Soft robots achieve a wide range of underwater behaviors, spanning propulsion, adhesion, object grasping, and environment-adaptive transformations.

**Locomotion Modes:**
| Bio-inspiration | Robotic Implementation | Performance Metrics            |
|-----------------|-----------------------|-------------------------------|
| Fish (BCF/MPF)  | Modular elastomer fish; DEA/HASEL fins; phasic drives | 0.25–0.81 BL/s [2310.11426], [2601.12353] |
| Jellyfish       | Bell-actuated pulsed swimmers          | 0.8 mm/s (IPMC), up to 300 m depths [2601.12353] |
| Cephalopod      | Jetting actuators: elastic mantles, combustion | Up to 1100 N peak thrust; 850 BL/s² accel [2302.08217] |
| Snake/Eel       | Soft continuum robot snakes, McKibben or SMA actuation| Smooth, undulatory motion; modeling only [1908.05250]|
| Flagella        | Dodecahedral flagella drones (ZodiAq, BactoBot) | 0.04–0.06 m/s; omnidirectional, safe interaction [2509.20964], [2503.19556] |
| Amphibious Climbing | Spiral-channel adhesion, doming actuators | ≥200 g load, 1.6 BL/min climbing speed [1804.08692] |

**Manipulation and Grasping:**
- Anthropomorphic multi-chamber water-hydraulic hands achieve forehand/backhand grasps under high pressure (up to 10 N five-finger force) with rapid response and compliance [2106.07011].
- Origami-based single-DOF fish-mouth grippers employ geometric closure for compliant, delicately adjustable grasping and scooping, with high success rates even on soft marine targets [2503.11049].
- Distributed soft tentacles and suction pads conform to substrates for both manipulation and reversible adhesion [1804.08692], [2508.11883].

**Multi-environment and Adaptive Morphing:**
- PuffyBot and related projects achieve seamless switching between terrestrial crawling, aquatic swimming, hovering, and submergence/resurfacing via shape-morphing scissor mechanisms and volume modulation [2511.09885].

## 6. Environmental Integration, Applications, and Challenges

Bio-inspired soft robots are uniquely adapted for underwater environments due to their compliance, minimal noise generation, and low harm to biological systems.

- **Applications:** Inspection and maintenance (ship hulls, aquaculture nets), ecological surveys, window cleaning, payload delivery, sampling fragile biota (corals, jellyfish), distributed environmental monitoring via low-cost swarms [2508.11883], [2511.09885].
- **Eco-friendliness:** Fluidic, dielectric and passive actuation regimes reduce acoustic footprints and physical disturbance, enabling interaction with sensitive fauna and habitats [2601.12353].
- **Endurance and autonomy:** Modular gliders with purely mechanical fluidic circuits demonstrate >150 m travel per CO₂ charge at 28 mW/m; soft glider and swimmer designs support distributed, disposable units for broad environmental coverage [2303.08672], [2509.20964].
- **Key limitations:** Energy density (battery and actuation), durability in deep sea (elastomer fatigue, aging), communications (acoustic and magnetic constraints), and integration of robust, multi-modal sensing. Autonomous navigation and manipulation in cluttered, high-disturbance environments remain open challenges [2601.12353], [2508.11883], [2511.09885].

## 7. Prospects and Design Guidelines

Emerging directions encompass:
- Hybridization of multiple locomotion and manipulation principles (BCF-MPF, undulation+jetting, tactile adhesion).
- Development of advanced, tunable, and self-healing material systems (dynamic crosslinkers, composite hydrogels).
- Freeform reversible embedding (FRE) and multi-material 3D printing for integrated actuator–sensor–structure modules.
- Adoption of “biouniversal” paradigms that abstract convergent solutions across taxa (log-spiral appendages, modular skeletons) for greater adaptability [2508.11883].
- Fusion of closed-loop model-based and data-driven control, onboard sensory intelligence, and decentralized swarm coordination.

Underwater bio-inspired soft robots thus represent a rigorously grounded, rapidly expanding research frontier. By leveraging nature's morphological, material, and behavioral paradigms, and by integrating advances in soft actuation, sensing, and computation, these systems are well positioned to enable transformative advances in marine science, technological innovation, and the direct testing of biological hypotheses [2601.12353], [2508.11883], [1804.08692].

Source: https://www.emergentmind.com/topics/underwater-bio-inspired-soft-robots