How Come?: Velcro can get tired of hanging on

How come Velcro stops sticking? Can Velcro be fixed to stick again? asks reader Myron Rushetzky.

Take your dog for a walk through an overgrown field, and you'll probably return with some unwanted hangers-on: bristly brown burrs attached to your pants, socks and shoelaces (and matted tightly into your poor dog's fur). If you've ever tried to pull tiny burr bristles out of twisted shoelaces, you might be tempted to try Velcroed sneakers. But you'll soon find the Velcro matted with dog hair. Hmmm . . . Burr, meet Velcro.

In fact, in the 1940s, George de Mestral came up with the idea of Velcro after a hike with his dog, a similarly burr-infested adventure. Finding himself covered with the prickly seed pods, the Swiss inventor decided to put a burr under his home microscope. What he found was an array of bristling hooks, armed and ready to snare in fur or the woven threads of clothing. By the 1950s, de Mestral was collaborating with a French textile weaver, first using cotton and then sturdy nylon to create a working hook-and-loop fastener.

And by the 1960s, NASA was using de Mestral's Velcro in its manned space flights, in fasteners for spacesuits and to keep objects from floating off in free fall. In the 1970s, hook-and-loop strips were adopted by the clothing industry - and the rest is sticky history. Inventor George de Mestral died in 1990 at age 82. By then, Velcro had become a popular stand-in for all kinds of fasteners, from shoelaces to buttons, buckles to zippers.

Clothing's version of AstroTurf is a match made in heaven for fumbling fingers. Instead of a single hook and eye, Velcro is a bristling array of barbs and loops, which, when pressed together, catch and hold on tight. And no need to unfasten each hook and loop, either - just let 'er rip.

But as handy as Velcro is, its stick-to-itiveness doesn't last forever. Look closely at any well-used Velcro fastener and you'll see a tangled mass of hair, lint and unidentifiable debris. With its hooks and loops clogged with stuff, Velcro's sticking power wanes. Up for a round of Velcro spring cleaning? Manufacturers suggest using a strip of fresh Velcro to clean old Velcro, peeling off accumulated hair and dirt with a single, satisfying rip.

No spare Velcro lying around? Try cleaning the softer looped side with a piece of duct tape. Then use a fine-toothed comb (such as a plastic flea comb) to rake through the field of hooks. Although cleaning your Velcro should improve its clinginess, once the loops are stretched out or broken, it's time to replace the fastener.

Ordinary plastic Velcro is surprisingly strong. But researchers have also created a hook-and-loop material made out of steel. A strip of the steel fastener, though less than a hundredth of an inch thick, can be used at temperatures that would melt plastic (more than 1,400 degrees F.). Its inventors say the metal strips, with barbed spikes hooking onto steel brushes, could be used as fasteners in factories, cars and homes. Each square meter of the steel "Velcro" can support a load of more than 38 tons, or about 77,000 pounds.