Sticking with silicon micromushrooms.

Sticking with silicon micromushrooms

Need to suture a broken blood vessel or securely mount an integrated-circuit chip? The answer to many such sticky problems may lie in new mechanical fasteners consisting of silicon sheets packed with orderly arrays of microscopic structures resembling mushrooms. Just aligning and pressing two such surfaces face-to-face interlocks the mushroom caps to produce a tough, permanent bond.

"It's a very simple idea," says Michael L. Reed of Carnegie Mellon University in Pittsburgh, who is spearheading the fasteners' development. "It isn't hard to make them, and it seems like they just might have a lot of applications."

Reed and his co-workers prepare these novel fasteners by applying the same techniques now widely used for manufacturing dense webs of electronic devices on silicon chips. By selectively etching away portions of a silicon surface initially covered by a thin layer of silicon dioxide, they fabricate an array of silicon dioxide caps perched on silicon pedestals about 5 microns tall.

In one type of fastener, the structures have smooth caps, allowing them to interlock easily. These fasteners provide a way of joining extremely small mechanical objects without using an adhesive. The resulting seals readily survive temperature extremes and chemical attack. Because they practically align themselves, such fasteners may also prove useful in the automated assembly of electronic circuitry.

In contrast, structures designed for biological applications have caps with sharp points -- which readily pierce tissue -- and flared bottoms that prevent retraction. These microscopic barbs, fabricated on opposite sides of a silicon wafer, provide an ideal mechanism for joining tissues without causing extensive cellular damage, the researchers say.