How Nature's Glue Is Inspiring an Underwater Adhesion Revolution
From the stubborn grip of a mussel to the ingenious building habits of a worm, scientists are uncovering the secrets of nature's underwater superglues.
A remarkable contradiction exists just beneath the ocean's surface. While a standard commercial glue completely fails when submerged, countless marine organisms perform daily feats of underwater adhesion. Today, researchers are turning to these aquatic creatures as master instructors to create a new generation of synthetic underwater adhesives that are transforming the impossible into the achievable 1 .
The Formidable Challenge of Sticking Underwater
A layer of water molecules coats any surface submerged in water, creating a hydration layer that acts as a physical barrier. This prevents an adhesive from making the intimate molecular contact with the substrate necessary for a strong bond 6 .
Water actively works against the cohesiveness of the adhesive material. For many adhesives, water can seep into the polymer network, acting as a plasticizer and weakening the material over time through swelling, hydrolysis, or degradation 6 .
Nature's Blueprint for Underwater Adhesion
Barnacle
Secretes proteinaceous cement for permanent attachment.
Key Organisms and Their Adhesive Strategies
| Organism | Adhesive Mechanism | Key Functional Feature | Inspiration for Synthetic Materials |
|---|---|---|---|
| Mussel | Proteinaceous glue (Byssus) | DOPA / Catechol chemistry | Polymers functionalized with catechol groups |
| Sandcastle Worm | Complex coacervation | Oppositely charged polymers | Synthetic coacervates for water-displacement |
| Barnacle | Proteinaceous cement | Strong interfacial bonding | Recombinant cement proteins |
| Remora | Mechanical suction | Structured disc with spinules | Soft robotic grippers for wet environments |
Adhesive Mechanism Comparison
Catechol Chemistry
Versatility: 95%Coacervation
Water Resistance: 85%Mechanical Suction
Reusability: 75%A Closer Look: Engineering a Remora-Inspired Medical Device
A recent groundbreaking experiment exemplifies how biological principles can be translated into functional devices. The research team, led by Giovanni Traverso from MIT, sought to create a device that could adhere to the wet, dynamic, and soft lining of the gastrointestinal (GI) tract for sustained drug delivery or sensing 3 .
Development Process
Biological Analysis
The team first extensively studied the remora's suction disc, focusing on how the arrangement of lamellae and the tiny spinules enable adhesion to soft, dynamically shifting surfaces 3 .
Device Fabrication
Using silicone rubber and temperature-responsive smart materials, they fabricated the MUSAS disc with tilted lamellae and integrated microneedles made of a shape-memory alloy 3 .
Functionalization
For drug delivery, they either integrated an HIV drug into the device material for slow release or loaded RNA into the microneedles for injection into the tissue 3 .
Testing
The device was tested on a variety of soft surfaces underwater, including pig stomach tissue and a swimming tilapia, to evaluate its adhesive strength and utility 3 .
Results and Analysis
- Robust adhesion to soft, wet surfaces
- Aquatic environmental monitoring
- Reflux sensing in medical applications
- Oral delivery of biologic drugs
Performance of Different Synthetic Underwater Adhesive Strategies
| Adhesive Strategy | Example Material | Reported Adhesive Strength | Key Advantages |
|---|---|---|---|
| Catechol Chemistry | Poly(catechol-styrene) 6 | ~3 MPa (on aluminum) | Versatile adhesion to multiple surfaces |
| Isocyanate Curing | Polyurethane adhesive 4 | Up to 2.44 MPa (on steel) | Self-curing in water; stable in harsh conditions |
| Natural Hydrogel | Gelatin-Tannic Acid-Stearic Acid 7 | ~80 kPa (on various substrates) | Biocompatible, biodegradable, antibacterial |
| Mechanical Suction (MUSAS) | Remora-inspired disc 3 | N/A (Mechanical adhesion) | Reversible, works on soft, wet tissues |
The Scientist's Toolkit: Building the Next Generation of Underwater Adhesives
| Tool / Component | Function | Biological Inspiration |
|---|---|---|
| DOPA / Catechol Derivatives | Forms strong, versatile bonds with substrates; can crosslink the adhesive | Mussel foot proteins 2 |
| Isocyanate Groups (-NCO) | Reacts with water to form polyurea networks, enabling autonomous underwater curing | Synthetic curing strategy 4 6 |
| Tannic Acid | Plant-derived polyphenol that provides catechol/pyrogallol groups for dynamic hydrogen bonding and cohesion | Simpler, cheaper alternative to DOPA 7 |
| Complex Coacervation | Creates a water-immiscible adhesive phase that displaces water and bridges surfaces | Sandcastle worm cement 2 9 |
| Stearic Acid / Fatty Acids | Imparts hydrophobicity, helping to repel interfacial water from the substrate | Biomimicry of water-repellent surfaces 7 |
| Shape-Memory Alloys | Used in microneedles to enable mechanical interlocking with soft tissues upon activation | Remora's spinules 3 |
Catechol chemistry, inspired by mussel foot proteins, enables versatile adhesion through multiple mechanisms including strong hydrogen bonding, metal coordination, and covalent bonding upon oxidation 2 . This allows the adhesive to displace water molecules and bind tightly to virtually any surface.
Inspired by the sandcastle worm, complex coacervation involves the phase separation of oppositely charged polymers to form a dense, water-immiscible liquid that spontaneously displaces water from substrate surfaces 2 9 . This "3C" adhesive mode—constraint, contact, and crosslinking—ensures the glue is not washed away before it sets.
Taking inspiration from the remora's suction disc, mechanical underwater soft adhesion systems (MUSAS) use structured surfaces with lamellae and microneedles to create suction compartments that interlock with soft tissues 3 . This approach is particularly valuable for medical applications where reversible adhesion to wet, soft tissues is required.
The Future of Underwater Adhesives
The field of underwater adhesion is riding a wave of innovation. The global market for underwater glue and adhesive, valued at over USD 20 billion in 2024, is projected to grow significantly, driven by demand in marine, medical, and industrial sectors 8 .
Dynamic Water Environments
Developing adhesives that work not just in calm lab conditions but in real-world dynamic water environments 9 .
Smart, Responsive Adhesives
Creating adhesives that can be debonded on demand using light or heat, allowing for reworkability and recycling 9 .
Biocompatibility
Push for biocompatibility and biodegradability, especially for medical applications like wound sealing and tissue engineering 2 7 .
Sustainability
Developing environmentally friendly adhesives from renewable resources with minimal ecological impact.
As scientists continue to delve into the mysteries of natural adhesives and refine the synthetic counterparts, the once "impossible" task of sticking things together underwater is becoming a routine engineering feat. The lessons learned from mussels, worms, and remoras are not only enabling us to build and repair in watery environments but are also sticking us together in ways that are profoundly changing medicine and technology.