Two surfaces stick together, separate, and stick together again—on command. This discovery by a team of researchers from the Universities of Sheffield (UK) and Bayreuth contradicts our day-to-day experience.
In the animal kingdom, geckos can climb up vertical inclines, displaying an incredible switchable adhesion as they do so. Insects also use another form of switchable adhesion to sit on your ceiling and then fly off before you climb up on your chair with a rolled-up newspaper.
How these animals can switch off and on adhesion is not yet understood in detail. But the scientists led by Mark Geoghegan reveal the secret of their “intelligent” adhesion in the journal Angewandte Chemie.
One of the surfaces involved consists 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.
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. 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.
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.
Citation: Mark Geoghegan, Controlling Network–Brush Interactions to Achieve Switchable Adhesion, Angewandte Chemie International Edition, doi: 10.1002/anie.200701796
Source: Angewandte Chemie
Related stories:
Switchable bio-adhesion
(PhysOrg.com) -- Researchers have developed a new type of property-changing polymer: It is water-repellent at 37°C, which makes it an ideal culture substrate for biological cells. At room temperature it attracts water, allowing the cells to be detached easily from the substrate.
MIT crafts bacteria-resistant films
Having found that whether bacteria stick to surfaces depends partly on how stiff those surfaces are, MIT engineers have created ultrathin films made of polymers that could be applied to medical devices and other surfaces to control microbe accumulation.
The first autism disease genes
The autistic disorder was first described, more than sixty years ago, by Dr. Leo Kanner of the Johns Hopkins Hospital (USA), who created the new label 'early infantile autism'. At the same time an Austrian scientist, Dr. Hans Asperger, described a milder form of the disorder that became known as Asperger Syndrome, characterised by higher cognitive abilities and more normal language function. Today, both disorders are classified in the continuum of 'Pervasive Developmental Disorders' (PDD), more often referred to as Autism Spectrum Disorders (ASD).
Researchers Find Oldest Gecko Fossil Ever Discovered
(PhysOrg.com) -- Scientists from Oregon State University and the Natural History Museum in London have announced the discovery of the oldest known fossil of a gecko, with body parts that are forever preserved in life-like form after 100 million years of being entombed in amber.
Silver is the key to reducing pneumonia associated with breathing tubes
People have long prized silver as a precious metal. Now, silver-coated endotracheal tubes are giving critically ill patients another reason to value the lustrous metal. In a study published in the Aug. 20, 2008 issue of the
Journal of the American Medical Association, researchers at Washington University School of Medicine in St. Louis and the NASCENT Investigation Group, report that the silver-coated tubes led to a 36 percent reduction of ventilator-associated pneumonia (VAP).
Nothing stops an expert in the art of living
There are few things more irritating than a fly buzzing around the house. South African's have an unconventional solution to the problem. They hang up a bunch of Roridula gorgonias leaves. Attracted to the shiny adhesive droplets on the leaf's hairs, the hapless pest is soon trapped by the natural flypaper.
Researchers identify gene responsible for rare childhood disease
The chromosomal abnormality that causes a rare, but often fatal, disorder that affects infants has been identified by researchers at the University of California, San Diego School of Medicine, who happened to treat two young children with the disease in San Diego – two of perhaps a dozen children in the entire country diagnosed with the disorder.
Discovery of a mechanism that regulates cell movement
A study performed by researchers at the Institute for Research in Biomedicine (IRB Barcelona), in collaboration with researchers at the Instituto de Biología Molecular of the CSIC, reveal a mechanism that controls the movement of cells in a tissue by regulating cell adhesion. This same mechanism may be defective in diseases such as cancer and its metastasis, when tumour cells lose their adhesion to neighbouring cells and migrate through the organism. The results of this research have been published in this week's
Nature Cell Biology.