Directional Micro-Fibrillar Adhesives
For more information, see the General Gecko-hair fabrication page.

Introduction: The small fibers that allow the gecko to cling and climb on smooth surfaces exhibit directional properties, gripping in one direction, and releasing effortlessly in the other. This allows strong grip and efficient releasing behaviors.

Here we mimic the directional characteristics of the natural gecko adhesive using synthetic polymer fibers, while also maintaining a high level of adhesion strength in the gripping direction. By controlling the tip angle of each microfiber during fabrication, we can design the adhesives to vary their gripping and releasing behavior. Furthermore, by controlling the fiber tip size, we can design the adhesives to adhere with more or less adhesion strength.

The results of characterization of these directional adhesives indicate that on smooth surfaces, the synthetic directional adhesives perform very similarly to the gecko's foot hairs in both magnitude and directional properties. In a photo on the right, a large weight is supported by a single square centimeter of synthetic fibrillar adhesive in the `gripping direction.' When the direction is reversed and loaded in the `releasing direction,' the structures only support 200 grams, in other words, they are removed from the surface easily.

In addition, with these structures, it is possible to control the level of adhesion by altering the drag distance during the loading phase (when the material is pressed against a surface). If it is dragged in the releasing direction or not dragged at all, no adhesion will be present. If it is dragged in the gripping direction, adhesion is present during separation, as seen in the figure on the right.

Benefits: Repeatable directional dry adhesives have many potential applications including:

• Advanced ultra-mobile robots.
• Diagnostic tool anchoring inside the body.
• Clothing closures to replace bulky and noisy Velcro.
• Ultra gripping gloves for sports applications.

Videos: Available online.

Media Appearances: MIT Technology Review Article

Past Members: Mike Murphy, Burak Aksak, Metin Sitti

Papers:

• M. Murphy, B. Aksak, and M. Sitti, "Gecko Inspired Directional and Controllable Adhesion" Small, 5, 170-175, 2009. available online