快猫短视频

GERM-FREE toys, cellphones, computer keyboards, clothes and even medical
implants are promised by a new molecular saw that tears stubborn germs
apart.

Antimicrobial materials are normally made by impregnating substances with
chemicals that leach out bacteria and poison them. But these substances work
best in solution. Even if the surface stays moist enough to kill bugs, the
chemical will eventually run out.

So Alexander Klibanov at MIT and his colleague Kim Lewis from nearby Tufts
University wondered if they could make surfaces that would go on killing bugs
indefinitely. What they finally created looks like a miniature saw blade. The
backbone of the saw is a carbon chain a few hundred atoms long. The
鈥渢eeth鈥濃�攕hort chains of carbon atoms containing an internal positive
charge鈥攋ut out from alternate carbon atoms. The positively charged saw
blade, they reasoned, would be attracted towards the negatively charged surface
membrane of the bacteria, rupturing the cells.

In tests, short-toothed saws with points 3 to 6 carbon atoms long made very
efficient weapons. Treated glass killed 94 per cent of Staphylococcus aureus,
the scourge of hospitals, and more than 99 per cent of three other bacterial
species. But saws with longer teeth worked no better than untreated
glass鈥攑robably because long teeth become entangled and can鈥檛 attack
germs.

The team believe the bugs won鈥檛 develop resistance because the saws probably
kill the bugs by mechanical disruption. And because the chemistry of the saws is
so simple, they could be attached to any material, from steel to cotton, making
even teddy bears virtually germ-free. The saws are safe to touch because the
teeth are too short to harm larger, mammalian cells.

Linda Stetzenbach, a microbiologist at the University of Nevada, says the
results look exciting. But she questions the wisdom of widespread use of any
antimicrobial agent when there is a risk of bacterial resistance developing. And
some scientists think the modern obsession with hypercleanliness may be behind
the rapid increase of asthma and other allergies
(快猫短视频, 18 July 1998, p 26).
鈥淏ut in a hospital environment, the additional benefit to sterility might
be worthwhile,鈥� she says.