Every surgeon knows the frustration. You're trying to repair a beating heart, blood washing over the wound site, and your sutures keep slipping. Traditional stitches work beautifully on dry, still tissue—but the human body is neither dry nor still. It's a wet, moving, hostile environment for anything trying to stick.

Nature, however, solved this problem millions of years ago. Mussels cling to wave-battered rocks. Slugs leave trails that bond to wet leaves. Sandcastle worms build underwater homes using biological cement. Bioengineers are now reverse-engineering these adhesives, creating surgical glues that can seal wounds in beating hearts, patch leaking blood vessels, and hold together tissues too delicate for needles.

The problem with gluing wet tissue isn't just the water—it's what water does at the molecular level. When you try to stick something to a wet surface, water molecules form a barrier, preventing the adhesive from making direct contact. Traditional surgical glues either can't displace this water layer or lose their sticking power entirely when submerged.

Mussels solved this by evolving proteins rich in an unusual amino acid called DOPA (dihydroxyphenylalanine). DOPA molecules can push water aside and form direct chemical bonds with surfaces—including the proteins and sugars that coat our cells. Even more remarkably, DOPA can form crosslinks within the adhesive itself, creating a tough, water-resistant network. Bioengineers have synthesized DOPA-containing polymers that mimic this chemistry, creating adhesives five times stronger than fibrin glue on wet tissue.

But mussels aren't the only inspiration. The Dusky Arion slug secretes a defensive mucus that becomes incredibly sticky when disturbed—strong enough to glue a predator's mouth shut. Researchers at Harvard analyzed this slime and discovered it works through a double-network system: one polymer network dissipates energy and absorbs stress, while another forms covalent bonds with tissue surfaces. Their slug-inspired adhesive successfully sealed holes in pig hearts—even while the hearts were beating and filled with blood.

Takeaway

The key to wet adhesion isn't fighting water—it's engineering molecules that can push water aside and form direct chemical bonds with living tissue.

Sticking to tissue is only half the challenge. The adhesive also needs to play nice with the immune system. Foreign materials in the body trigger inflammation, scar tissue formation, and sometimes dangerous immune reactions. A surgical glue that seals a wound but causes chronic inflammation has solved one problem while creating another.

Bioengineers approach this through careful material selection. Many successful bio-adhesives use proteins and polymers the body already recognizes—modified versions of collagen, gelatin, or polysaccharides like chitosan (derived from crustacean shells). These materials degrade into components cells can metabolize harmlessly. The challenge is maintaining adhesive strength while keeping the chemistry familiar enough that immune cells don't sound the alarm.

Some newer designs go further, incorporating bioactive signals that encourage tissue integration. Researchers have added growth factors that stimulate cell migration into the adhesive matrix, essentially turning the glue into temporary scaffolding for new tissue. Others include antimicrobial peptides that prevent infection at the wound site. The adhesive becomes more than passive sealant—it becomes an active participant in healing.

Takeaway

True biocompatibility means the adhesive doesn't just avoid triggering rejection—it actively supports the healing process before quietly disappearing.

A permanent adhesive in the body would be a disaster. As wounds heal, the tissue architecture changes. Cells divide, migrate, and remodel the extracellular matrix. An adhesive that sticks around too long interferes with this process, potentially causing scarring or preventing proper tissue restoration. But one that dissolves too quickly leaves the wound vulnerable before healing completes.

Bioengineers control degradation timing by adjusting the chemical crosslinks that hold the adhesive together. Ester bonds, for instance, hydrolyze slowly in body fluids—the more ester crosslinks, the longer the adhesive persists. Enzyme-cleavable sequences can be built in, allowing the body's own proteins to break down the material at a controlled rate. Some adhesives incorporate pH-sensitive bonds that remain stable during initial healing but break down as the local chemistry changes.

The ideal degradation profile matches tissue healing kinetics. A cardiac patch might need to hold strong for four to six weeks while heart muscle regenerates, then gradually transfer mechanical load to the new tissue. A corneal adhesive might need only days. Bioengineers are developing "smart" adhesives that respond to local healing signals—degrading faster in areas with more cell activity, slower where healing lags.

Takeaway

The best surgical adhesive isn't just strong—it knows when its job is done and gracefully exits, transferring responsibility to healed tissue.

We're entering an era where surgery's oldest tools—needles and thread—may finally have real competition. Bioinspired adhesives promise faster procedures, less tissue trauma, and access to anatomical regions where sutures simply can't reach. Early versions are already in clinical use for ocular surgery and wound closure.

The broader lesson extends beyond operating rooms. When engineering meets biology, the most elegant solutions often come from studying organisms that already solved the problem. Mussels, slugs, and worms spent millions of years perfecting wet adhesion. We're just learning to read their notes.