COLUMBUS , Ohio – Ohio State University researchers have justcompleted the first comprehensive study of human hair on the nanometerlevel.
Special equipment enabled Bharat Bhushan and hiscolleagues to get an unprecedented close-up look at a rogue's galleryof bad hair days – from chemically overprocessed locks to curls kinkedup by humidity.
They used the techniques they developed to test a new high-tech hair conditioner.
Ultimately,the same techniques could be used to improve lipstick, nail polish andother beauty products, said Bhushan , Ohio Eminent Scholar and theHoward D. Winbigler Professor of mechanical engineering at Ohio State .
Hisspecialty is nanotribology – the measurement of very small things, suchas the friction between moving parts in microelectronics.
Atfirst, hair seemed like an unlikely study subject, he said. Then he wasinvited to give a lecture to scientists at Procter & Gamble Co.
“Itturns out that, for hair, friction is a major issue,” he said. Everydayactivities like washing, drying, combing and brushing all cause hairsto rub against objects and against each other, he explained. Over time,the friction causes wear and tear – two processes that he and hiscolleagues are very familiar with, though they're normally studying thewear between tiny motors and gears.
“We realized that beauty care was an emerging area for us and we should dive in,” Bhushan said.
Heconsulted for the company until P&G became an industrial partner inhis laboratory, supplying him with samples of healthy and damaged hair.The Ohio State engineers examined hairs under an atomic forcemicroscope (AFM), a tool that let them scratch the surface of hairs andprobe inside the hair shaft with a very tiny needle. They publishedtheir results in the journal Ultramicroscopy, in a paper now availableon the Web.
Among their findings: hair conditioners typically do not evenly cover the entire hair shaft.
P&Grecently developed a new formula with additives to make the conditionercoat the hair evenly. In tests, Bhushan found that the new conditionerdid coat hair more evenly.
Meanwhile, they examined healthy anddamaged hairs under an electron microscope and an AFM, and simulatedeveryday wear and tear by rubbing hairs together and againstpolyurethane film to simulate skin.
“We didn't know what we werelooking for,” Bhushan said. “People know a lot about hair, but nobodyhas used an AFM to really study the structure of hair. So we alreadyknew some things, but otherwise we didn't know what to expect.”
Underthe electron microscope, individual hairs looked like tree trunks,wrapped in layers of cuticle that resembled bark. In healthy hair, thecuticle edges lay flat against the hair shaft, but as hair gets damagedfrom chemical treatments or wear and tear, the cuticle edges begin topeel away from the shaft. That much was already known.
Theresearchers simulated what happens when damaged hair is exposed tohumidity; the hairs plump up, and the cuticles stick out even further,leading to frizz. More frizz meant more friction – a fact confirmed bythe AFM as researchers dragged a tiny needle across the surface.
Conditionertends to stick to the cuticle edges, and can make the hair sticky onthe nanometer scale. The researchers determined that by poking the hairshaft with the needle, and measuring the force required to pull it away.
Theyalso probed inside hairs to measure the hardness of different layers ofthe shaft. Hair has a very complex structure, Bhushan said, and thesefirst ultra-precise measurements of interior structure could one daylead to new products that treat hair from the inside.
In the future, he thinks his AFM techniques could be used to develop wear-resistant nail polishes and lipsticks.
Bhushanconducted this work with graduate student Carmen LaTorre andpostdoctoral researchers Nianhuan Chen and Guohua Wei, all of OhioState .
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