Scientists unravel secrets of geckos, mosquitoes switchable adhesion

Ever wondered how geckos stick to a vertical incline and move away effortlessly at the slightest provocation, or how mosquitoes cling on to ceilings and walls and fly away at the slightest hint of danger. The trick, as a team of scientists from the Universities of Sheffield (UK) and Bayreuth found, is in switchable adhesion.

Stuttgart, July 25 : Ever wondered how geckos stick to a vertical incline and move away effortlessly at the slightest provocation, or how mosquitoes cling on to ceilings and walls and fly away at the slightest hint of danger. The trick, as a team of scientists from the Universities of Sheffield (UK) and Bayreuth found, is in switchable adhesion.

One of the surfaces involved, as the team of scientists led by Mark Geoghegan discovered, consisted of a polyacid gel, a three-dimensionally cross-linked polymer containing many acid groups. This polymer network is so heavily soaked in liquid that it forms a solid, gelatinous mass.

The second surface is a silicon chip onto which a polybase has been deposited. This polybase consists of polymer chains that stretch brush-like from the support and contain many basic groups.

In water or slightly acidic solution, the acidic groups carry a positive charge while the basic groups are negatively charged; this causes them to attract each other. In addition to this electrostatic attraction, hydrogen bonds are also formed, which causes the two surfaces to be tightly stuck together.

However, if the surrounding solution is made more strongly acidic (a pH value of about 1), the bonds break up, the basic groups lose their charge, and the electrostatic attraction lets up.

The two surfaces can then be slowly and carefully separated from each other without any damage.

According to the study in the scientific journal Angewandte Chemie, this detachment is reversible: If the pH value is raised again, making the solution less acidic, the gel and "brush" stick to each other once again.

This cycle can be repeated many times by simply changing the pH value, the scientists further wrote in their study.

According to the researchers, possible applications for such "smart" surface pairs include microelectromagnetic components (actuators), components for microfluidic systems, or carriers for pharmacological agents that could release their cargo under specific physiological conditions.

ANI