Nature's Engineers - Part 3: Shark Skin and the Art of Doing Nothing

The Counterintuitive Discovery

For decades, engineers assumed that smooth surfaces were the key to reducing friction. If you want something to slide easily, make it as polished as possible. Remove every bump, fill every groove, achieve mirror-like perfection.

Nature disagrees.

The fastest swimmers in the ocean—sharks—have skin that feels like sandpaper when rubbed the wrong way. Lotus flowers stay immaculately clean in murky ponds not despite their bumpy surface, but because of it. Gecko feet stick to walls without any glue, using nothing but texture.

These discoveries launched a revolution in surface engineering. The emerging field reveals that the right micro-texture, at the right scale, can achieve effects that seem almost magical:

• Surfaces that clean themselves when it rains

• Coatings that repel bacteria without antibiotics

• Textures that reduce drag better than any lubricant

• Materials that stick and unstick on command

And the most remarkable thing? These surfaces do nothing. They have no moving parts. They consume no energy. They just work, passively, because of how they’re shaped at the microscopic level.

Shark Skin: Nature’s Drag Reducer

Sharks are apex predators, and speed is their advantage. A great white shark can burst to 56 km/h when attacking prey—faster than any human swimmer by a factor of ten.

This performance depends partly on muscle power and body shape. But there’s another secret: shark skin.

The Myth of Smoothness

Most fish are covered in smooth, overlapping scales that secrete mucus to reduce friction. Sharks took a different evolutionary path. Their skin is covered in dermal denticles—tiny tooth-like scales that point backward, toward the tail.

Run your hand from nose to tail, and shark skin feels almost smooth. Run it the other direction, and it’s like stroking sandpaper. This asymmetry is intentional.

How Denticles Work

When a shark swims, water flows over its body from nose to tail. The denticles have a specific geometry:

1. Ribbed structure — Each denticle has tiny parallel ridges running lengthwise

2. Aligned orientation — The ridges are parallel to the direction of water flow

3. Optimal spacing — The grooves between ridges are precisely sized to control turbulence

This pattern does something remarkable: it channels the water into organized streams.

Without denticles, water flowing over a moving body creates chaotic vortices—spinning pockets of turbulence that create drag. These vortices pull backward on the shark, slowing it down and wasting energy.

The denticle ridges prevent this chaos. They guide the water into parallel lanes, like highway dividers controlling traffic. Small vortices still form, but they’re tiny and contained—too small to create significant drag.

The result: up to 10% reduction in skin friction compared to smooth surfaces.

The Anti-Fouling Bonus

Denticles have another unexpected property: bacteria can’t stick to them.

In the ocean, every surface becomes colonized by microorganisms within hours. This “biofouling” can add significant drag to ships and underwater structures. It also creates health risks—bacteria form protective biofilms that resist antibiotics and cleaning.

But sharks don’t have this problem. Their skin stays remarkably clean despite decades in bacteria-rich water.

The reason is geometry. The denticle pattern creates an environment hostile to bacterial attachment. The ridges are spaced so that bacteria can’t find stable purchase—it’s like trying to stand on a surface made of knife edges. Any organisms that do manage to attach are swept away by water flow.

Speedo’s Experiment

In 2000, Speedo introduced the Fastskin—a full-body swimsuit designed to mimic shark skin. The fabric had tiny V-shaped ridges printed on its surface, modeled on denticle geometry.

The results were controversial but dramatic. At the Sydney Olympics, swimmers wearing Fastskin suits won 83% of all medals and set 13 of 15 new world records.

Did the suit actually work? The biomimetics community debated this intensely. Critics pointed out that human bodies are nothing like sharks—different shapes, different swimming motions, different scales. The drag reduction from a textile pattern seemed implausible.

But something was happening. Between 2008 and 2009, when the suits were still permitted, swimmers set over 300 world records—an unprecedented burst that suggested technology, not just talent, was at work.

In 2010, FINA (swimming’s governing body) banned high-tech bodysuits. But the principle had been demonstrated: even an imperfect copy of shark skin could enhance human performance.

Lufthansa’s Coating

The aerospace industry is now applying the same principle to aircraft.

In 2013, Germany’s Lufthansa airline began testing shark-skin-inspired coatings on Airbus A340-300 jets. Researchers at the Fraunhofer Institute had developed a ribbed polymer film that could be applied to aircraft surfaces.

The challenge is immense: airplane wings are far larger than shark bodies, and air behaves differently than water. But early results suggest that a 40-70% coverage of ribbed coating could reduce fuel consumption by about 1%.

That sounds small—until you realize that Lufthansa burns over 9 million tonnes of jet fuel annually. A 1% reduction represents 90,000 tonnes of fuel saved, worth hundreds of millions of dollars and eliminating roughly 280,000 tonnes of CO2 emissions.

The Lotus Effect: Cleaning Without Effort

In Hindu and Buddhist traditions, the lotus flower symbolizes purity. It rises from muddy water yet remains unstained, its petals pristine white even in polluted ponds.

For centuries, this was considered mystical—a spiritual quality beyond scientific explanation. Then botanist Wilhelm Barthlott pointed an electron microscope at a lotus leaf.

The Micro-Bump Architecture

What Barthlott discovered was astonishing. The lotus leaf is not smooth at all. Its surface is covered with tiny bumps, or papillae, about 10-20 micrometers tall and spaced about 10-20 micrometers apart. On top of each bump are even smaller protrusions—nano-crystals of waxy material.

This two-level architecture creates a surface with extreme properties:

Superhydrophobicity — Water drops bead up into nearly perfect spheres rather than spreading out. The contact angle (how steeply the drop meets the surface) exceeds 150°. On a normal surface, it’s typically 70-90°.

Self-cleaning — When water droplets roll across the surface, they pick up any dirt particles they encounter and carry them away. The lotus doesn’t need to be washed; it washes itself.

Why Bumps Beat Smoothness

The physics is elegant. A water droplet on a truly smooth surface makes contact across its entire base. The surface tension of water and the chemistry of the surface determine how much it spreads.

But on the lotus leaf, water doesn’t contact the actual leaf. The droplet sits on top of the micro-bumps, with air trapped in the spaces between. It’s like a marble resting on a bed of tiny nails—only the tips touch.

Because so little surface is actually in contact, there’s almost no adhesion. The slightest tilt causes the droplet to roll away. And as it rolls, it encounters dirt particles that are also perched precariously on the bump tips. The droplet absorbs the dirt and carries it off.

The result: a surface that cleans itself every time it rains.

Commercial Applications

The “Lotus Effect” was patented by Barthlott’s team in 1994, and products followed quickly:

• Lotusan — A self-cleaning paint for building facades that stays clean for years without washing

• NeverWet — A superhydrophobic spray coating for consumer products

• Hydrobead — Anti-fog and self-cleaning coatings for windshields and glasses

The technology is especially valuable for solar panels, which lose efficiency when covered in dust. Self-cleaning surfaces can maintain power output in desert environments where water for cleaning is scarce.

Gecko Feet: Sticking Without Glue

If shark skin and lotus leaves work by rejecting contact, gecko feet work by embracing it—but in a way that seems to violate physics.

Geckos can walk up glass walls and across ceilings. They can support their entire body weight with a single toe. They can attach and detach their feet 15 times per second while running. And they do all this without any sticky substance—their feet are dry.

The Forest of Setae

A gecko’s toe pad is covered with approximately 500,000 hair-like structures called setae. Each seta is about 100 micrometers long—roughly the diameter of a human hair. But each seta splits at the tip into hundreds or thousands of even finer branches called spatulae, each only 200 nanometers wide.

This gives each gecko foot somewhere between 500 million and 2 billion points of contact with any surface.

Van der Waals Forces

The adhesion comes from van der Waals forces—weak electromagnetic attractions between molecules that are extremely close together. Individually, these forces are trivial. But multiply them by billions of contact points, and the result is extraordinary grip.

A gecko’s two front feet can support about 40 newtons of force—enough to hold 4 kilograms. Theoretically, if all four feet were optimally attached, a gecko could hold nearly 130 kg. The adhesion is strong enough that researchers have used gecko-inspired pads to climb glass buildings.

The Attachment-Detachment Problem

What’s truly remarkable is that geckos can release their grip instantly. If the adhesion were permanent like glue, the gecko would be stuck. But gecko feet are directional—they stick when pulled in one direction and release when pulled in another.

The spatulae are curved, and they only make full contact when the foot is pulled downward and backward. When the gecko lifts its toe, the spatulae peel away sequentially, like removing tape. The release requires almost no force.

Gecko Tape

Researchers have created synthetic versions called “gecko tape” that mimic this capability:

• NASA is developing gecko-inspired grippers for catching debris in space, where suction cups don’t work and magnets only attach to metal

• Stanford University created pads that allow humans to climb glass walls

• Medical researchers are developing gecko-inspired bandages that stick firmly to skin but peel off painlessly

The challenge is manufacturing. Those billions of spatulae need to be precisely shaped and oriented, at scales approaching the limits of current production technology. But progress is rapid.

The Namib Beetle: Harvesting Water from Air

In the Namib Desert of southwestern Africa, rainfall averages less than 15 millimeters per year. It’s one of the driest places on Earth. Yet life persists—including the Namib Desert beetle, which has evolved a remarkable way to harvest water from thin air.

The Fog-Catching Shell

Each morning, fog rolls in from the Atlantic Ocean. The beetle climbs to the crest of a sand dune, faces the wind, and tilts its body upward. Tiny water droplets from the fog condense on its shell and roll down into its mouth.

The shell’s surface makes this possible. It has a pattern of hydrophilic (water-attracting) bumps surrounded by hydrophobic (water-repelling) troughs. Water from the fog condenses preferentially on the bumps, and when the droplets grow large enough, they roll off into the channels, which guide the water toward the beetle’s head.

Artificial Fog Harvesting

Engineers have copied this design for fog harvesting systems in water-scarce regions:

• Mesh structures with alternating hydrophilic and hydrophobic regions

• Building facades that collect water from coastal fog

• Textile coatings that could harvest moisture from the air in emergency situations

In Chile and Peru, where coastal fog is common, experimental fog-harvesting installations based on the beetle’s principles are providing drinking water to remote communities.

The Thorny Devil: Water Against Gravity

Australia’s thorny devil lizard takes water harvesting even further. This desert reptile can drink through its skin.

The lizard is covered in grooved scales arranged in a network that functions as a capillary system. When any part of the thorny devil’s body contacts moisture—even just damp sand—the water wicks along the grooves toward the lizard’s mouth, traveling against gravity through capillary action.

The lizard essentially uses its entire body as a drinking straw.

Engineers are exploring similar capillary networks for:

• Passive water transport in cooling systems

• Moisture management in athletic clothing

• Medical devices that wick fluids without pumps

Stomatex: Breathing Fabrics

The stomata of leaves are tiny pores that regulate gas exchange—allowing CO2 in for photosynthesis while controlling water loss. Each stoma is surrounded by two guard cells that open and close based on the plant’s needs.

British company Stomatex developed a fabric that mimics this mechanism. The material has small dome-shaped chambers with pores that flex in response to pressure and movement. When the wearer exercises, body heat and motion cause the domes to expand and contract, pumping air through the pores.

The result is a breathable insulation layer that regulates temperature without batteries or power. When you’re cold and still, the pores stay closed, trapping warmth. When you’re hot and active, the pores pump air, removing heat.

The fabric is used in high-performance athletic wear, diving suits, and medical garments.

The Future of Surfaces

We’re only beginning to understand nature’s surface tricks. Current research is exploring:

Anti-ice surfaces — Inspired by the skin of certain Antarctic fish, which produce antifreeze proteins that prevent ice crystal formation

Anti-reflection coatings — Moth eyes have nanostructures that eliminate reflection, making them nearly invisible to predators (and inspiring coatings for solar cells and displays)

Friction control — Snake scales can be smooth in one direction and grippy in another, enabling efficient locomotion

Anti-bacterial surfaces — Dragonfly and cicada wings have nano-pillars that physically rupture bacterial cell walls—no chemicals needed

Each of these represents a potential revolution in materials science. And each was developed by evolution over millions of years, perfected by the ruthless optimization of natural selection.

We’re just learning to read the library.

The Lesson

The surfaces that evolution has produced share a common theme: they solve problems passively.

Shark skin doesn’t require energy to reduce drag. Lotus leaves don’t need maintenance to stay clean. Gecko feet don’t run out of adhesive. The Namib beetle doesn’t operate a water pump.

In a world of active systems—motors, electronics, chemicals—these passive solutions are revolutionary. They work continuously, require no maintenance, and last as long as the underlying structure holds.

For engineers trained to add complexity, biomimetic surfaces offer a different lesson: sometimes the best solution is just the right texture.

References

• Bixler, G.D. and Bhushan, B. “Bioinspired Surface Characterization.” Philosophical Transactions of the Royal Society A, 2012.

• Barthlott, W. and Neinhuis, C. “Purity of the Sacred Lotus.” Planta, 1997.

• Autumn, K. et al. “Adhesive Force of a Single Gecko Foot-Hair.” Nature, 2000.

• Kapsali, V. Biomimicry for Designers. Thames & Hudson, 2016.

• Dean, B. and Bhushan, B. “Shark-Skin Surfaces for Fluid-Drag Reduction.” Philosophical Transactions of the Royal Society A, 2010.

Next in the series: Why Geckos Walk on Ceilings — A deeper dive into the physics of sticking without glue, and the race to manufacture gecko-inspired adhesives.