Have you ever wondered why glue doesn't stick to the inside of the bottle, or why the sticking plaster covering your injured finger falls off when you wash your hands?

To be sticky, good glue needs two things; adhesion (the ability to stick to the surface to which you are applied) and cohesion (the ability to stick to yourself). When your sticking plaster falls off your wet hands, it's because the water caused the glue to lose its ability to stick to your skin, this is adhesion failure. When you spread jam on one piece of bread, add another slice to make a sandwich then peel apart the two to find jam on both slices, this is cohesion failure, or the inability of jam to stick to itself better than to bread.

Humans' use of natural glue dates back to 4000BC; archaeologists have found sticky tree sap was used to repair broken pottery and ivory eyeballs were glued into eyesockets in Babylonian temples.

The first animal based glue patents were filed in the 1700s, with boiled up fish, animal bones and milk protein recipes being used. It wasn't until the industrial revolution that glues made from plastics were developed, resulting in the commercial adhesives we know today.


Glue research is far from complete though, with many challenges including how to make strong and reliable underwater glue. This week, that sticky problem took a step forward thanks to Otago and Canterbury researchers and a South Pacific brown seaweed species.

The researchers noticed the seaweed Durvillaea Antarctica, also known as "the strongest kelp in the world" stuck firm while it was being battered by waves at the bottom of a cliff during an Otago Peninsula walk, and set to work researching the chemistry of how it adheres.

They are not the first group to try and understand how underwater superglues work, a discovery which could help the marine and medical industries. Nature seems to have it all figured out, as any boat owner who has tried to clean barnacles or mussels off the bottom of their boat will tell you. Trying to mimic how sea creatures are able to firmly stick to surfaces in wet environments could result in glue that far exceeds any synthetic product that exists today.

Science has shown that mussels cling to rocks and other surfaces using L-Dopa amino acid rich proteins which they secrete through their feet in the form of silky threads. Barnacles secrete a tiny drop of oil on to the surface they want to stick to which repels water, giving them a "dry" region to stick to. Sandcastle worms store their biological glue internally at a low pH until they need it then use the higher pH of seawater to slowly cause the glue to solidify.

This new seaweed research, published in the Journal of the Royal Society, shows how the Kiwi kelp secretes an initial meshwork thread coating which sticks first, then secretes a secondary adhesive which crosslinks and cures the glue over time.

With this combined information, moves towards biomimetic or glues copied from nature can be made, all thanks to a curious tramp along one of New Zealand's scenic walks.

So why doesn't glue stick to the inside of the bottle? Well, glue needs air to set - white glue needs air for water evaporation and superglue requires air moisture to cause a chemical reaction. As glue bottles are designed to minimise the amount of air inside, those reactions don't occur as long as you leave the top on.