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Scientists from the University of Sheffield, in collaboration with the University of Bayreuth in Germany and the Rutherford Appleton Laboratory in Oxford, have developed a water-based adhesive that can be turned on and off. The glue, which can lose and regain its stickiness at different pH levels, could have huge implications for administering drugs in the body.

The glue is made up of polyelectrolytes, which are polymers that are electrically charged and can change their shape in response to their environment. A polyelectrolyte can either stretch out, when at one pH level, or roll into a ball at another pH.
The researchers, led by Dr Mark Geoghegan in the Department of Physics and Astronomy at the University of Sheffield, showed that if oppositely charged polyelectrolytes are brought together in water they stick tightly. This was widely known, but until now the strength of this bond and the fact that the process can be reversed and repeated was a mystery.
The study showed that the adhesion was nearly as strong as epoxy glue. Not only that, but when the water was made acidic, the two materials came apart. The separation of the two could also be reversed by immersing them again in water.
The work is expected to have applications in nanotechnology where changes in pH levels can be used to control the not as yet invented nanoscale machines of the future. It is also thought it could aid in drug delivery.
Dr Mark Geoghegan said: "There are several advantages to this mechanism. It is strong, as good as epoxy glue, but reversible in the fact that it can be turned off and still be re-used. It is also water-based, and so environmentally friendly.
"Trying to identify where this will be used at this point is difficult. As scientists we have contributed what you might call the molecular tools of nanotechnology with our adhesive, but it is up to the engineers to decide how to use it. Drug delivery is always a possibility because different parts of the body have different pH values. A possibility is that the body´s natural pH could be used with the adhesive to allow drug release."