Hips that function better and last longer: Lubricant in metal-on-metal hip implants found to be graphite, not proteins

A team of engineers and physicians have made a surprising discovery that offers a target for designing new materials for hip implants that are less susceptible to the joint's normal wear and tear.

Researchers from Northwestern University, Rush University Medical Center, Chicago, and the University of Duisburg-Essen Germany found that graphitic carbon is a key element in a lubricating layer that forms on metal-on-metal hip implants. The lubricant is more similar to the lubrication of a combustion engine than that of a natural joint.

The study will be published Dec. 23 by the journal Science.

Prosthetic materials for hips, which include metals, polymers and ceramics, have a lifetime typically exceeding 10 years. However, beyond 10 years the failure rate generally increases, particularly in young, active individuals. Physicians would love to see that lifespan increased to 30 to 50 years. Ideally, artificial hips should last the patient's lifetime.

"Metal-on-metal implants can vastly improve people's lives, but it's an imperfect technology," said Laurence D. Marks, a co-author on the paper who led the experimental effort at Northwestern. "Now that we are starting to understand how lubrication of these implants works in the body, we have a target for how to make the devices better."

Marks is a professor of materials science and engineering at Northwestern's McCormick School of Engineering and Applied Science.

The ability to extend the life of implants would have enormous benefits, in terms of both cost and quality of life. More than 450,000 Americans, most with severe arthritis, undergo hip replacement each year, and the numbers are growing. Many more thousands delay the life-changing surgery until they are older, because of the limitations of current implants.

"Hip replacement surgery is the greatest advancement in the treatment of end-stage arthritis in the last century," said co-author and principal investigator Dr. Joshua J. Jacobs, the William A. Hark, M.D./Susanne G. Swift Professor of Orthopedic Surgery and professor and chair of the department of orthopedic surgery at Rush. "By the time patients get to me, most of them are disabled. Life is unpleasant. They have trouble working, playing with their grandchildren or walking down the street. Our findings will help push the field forward by providing a target to improve the performance of hip replacements. That's very exciting to me."

Earlier research by team members Alfons Fischer at the University of Duisburg-Essen and Markus Wimmer at Rush University Medical Center discovered that a lubricating layer forms on metallic joints as a result of friction. Once formed, the layer reduces friction as well as wear and corrosion. This layer is called a tribological layer and is where the sliding takes place, much like how an ice skate slides not on the ice but on a thin layer of water.

But, until now, researchers did not know what the layer was. (It forms on the surfaces of both the ball and the socket.) It had been assumed that the layer was made of proteins or something similar in the body that got into the joint and adhered to the implant's surfaces.

The interdisciplinary team studied seven implants that were retrieved from patients for a variety of reasons. The researchers used a number of analytical tools, including electron and optical microscopies, to study the tribological layer that formed on the metal parts. (An electron microscope uses electrons instead of light to image materials.)

The electron-energy loss spectra, a method of examining how the atoms are bonded, showed a well-known fingerprint of graphitic carbon. This, together with other evidence, led the researchers to conclude that the layer actually consists primarily of graphitic carbon, a well-established solid lubricant, not the proteins of natural joints.

"This was quite a surprise," Marks said, "but the moment we realized what we had, all of a sudden many things started to make sense."

Metal-on-metal implants have advantages over other types of implants, Jacobs said. They are a lower wear alternative to metal-on-polymer devices, and they allow for larger femoral heads, which can reduce the risk of hip dislocation (one of the more common reasons for additional surgery). Metal-on-metal also is the only current option for a hip resurfacing procedure, a bone-conserving surgical alternative to total hip replacement.

"Knowing that the structure is graphitic carbon really opens up the possibility that we may be able to manipulate the system in a way to produce graphitic surfaces," Fischer said. "We now have a target for how we can improve the performance of these devices."

"Nowadays we can design new alloys to go in racing cars, so we should be able to design new materials for implants that go into human beings," Marks added.

The next phase, Jacobs said, is to examine the surfaces of retrieved devices and correlate the researchers' observations of the graphitic layer with the reason for removal and the overall performance of the metal surfaces. Marks also hopes to learn how graphitic debris from the implant might affect surrounding cells.

The science of tribology is the study of friction, lubrication and wear. The term comes from the Greek word "tribos," meaning rubbing or sliding.

The National Institutes of Health (through American Recovery & Reinvestment Act of 2009 grant RC2-AR-058993) supported the research.

Story Source:

The above story is reprinted from materials provided by Northwestern University. The original article was written by Megan Fellman.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Y. Liao, R. Pourzal, M. A. Wimmer, J. J. Jacobs, A. Fischer, L. D. Marks. Graphitic Tribological Layers in Metal-on-Metal Hip Replacements. Science, 2011; 334 (6063): 1687 DOI: 10.1126/science.1213902

Note: If no author is given, the source is cited instead.

Keeping beer fresh longer

Researchers are reporting discovery of a scientific basis for extending the shelf life of beer so that it stays fresh and tastes good longer. For the first time, they identified the main substances that cause the bitter, harsh aftertaste of aged beer and suggest that preventing the formation of these substances could help extend its freshness. Their findings appear in ACS' Journal of Agricultural and Food Chemistry.

Thomas Hofmann and colleagues point out that beer can develop an unpleasant, bitter aftertaste as it ages. Unlike wine, scotch whiskey, and bourbon, beer tastes best when consumed fresh. Experts estimate that the average beer goes bad after 6 to 12 months of storage. Scientists have identified several dozens of the key bitter-tasting substances formed during beer manufacturing — mostly so-called "prenylated polyketides" derived from hops. Until now, however, nobody had solid information about the bitter substances that form as beer ages.

The scientists analyzed a variety of commercial beers both before and after storage. They identified 56 substances that contribute to beer's bitter taste, including five that appear to be largely responsible for its harsh flavor after aging. "The present study offers the scientific basis for a knowledge-based extension of the shelf life of the desirable beer's bitter taste and the delay of the onset of the less preferred harsh bitter aftertaste by controlling the initial pH value of the beer and by keeping the temperature as low as possible during storage of the final beverage," the study concludes.

Provided by American Chemical Society (news : web)

Why many historians no longer see alchemy as an occult practice

 lchemy is making a comeback. No, wizards have not learned how to transmute lead into gold and they haven't found any rejuvenating elixir of life. But the scholars who write the history of science and technology no longer lump alchemy in with witchcraft as a pseudo-science.Instead they see alchemy as the proper precursor to modern chemistry. The modern word "alchemy" comes from the Arabic word "al kemia," which incorporated a spectrum of knowledge of chemical properties and practices from ancient times. Chemist and historian Lawrence Principe of Johns Hopkins University in Maryland believes that the hardworking alchemists of the late Middle Ages and the Renaissance, a period stretching across the 14th to the 17th centuries, were defamed by being lumped in with charlatans of the 19th century, quacks that were often depicted wearing eccentric costumes and casting spells. "We're in an alchemical revolution," said Principe during a meeting of the American Association for the Advancement of Science in February. Principe said that just in the past 30 years articles about alchemy were being accepted into Isis, one of the leading journals devoted to the history of science. Before that a prohibition on alchemical subjects had been in place.The reason for this change is that historians are now recognizing the huge role alchemists had in producing valuable things, even if the alchemists never succeeded in turning lead into gold. By the way, making new gold was of great concern to kings since it would have interfered with the valuation of coins. This is why transmutation was considered a crime and why alchemists often had to do their research in secret. Alchemists did something more important than make new gold. They were instrumental in the development of many technologies during pre-modern times in Europe. For example, alchemists could be considered as an early form of industrial researcher. William Newman of the University of Indiana points out that alchemists "integrated a host of pursuits that can be loosely labeled 'chemical technologies' with an experimental practice that was linked to various theories about the nature and operations of minerals and metals."Newman provides plenty of examples. Alchemists, he says, were active in assaying metals, refining salts, making dyes and pigments, making glass and ceramics, artificial fertilizers, perfumes, and cosmetics. An alchemists' shop was often the place in a town where you would go for medicine. Even today in many parts of Europe you go to "the chemist," for medicine, rather than to a "drug store."Principe said that alchemists perfected the process of distillation, in which a mixed substance is boiled in such a way as to separate out one component by letting a vapor collect in a portion of the apparatus where it can be drawn off. Distillation is of course well known as the means of making spirits like whiskey. But it was also used by alchemists to make powerful acids, which in turn were important for a variety of industrial purposes, such as for separating metals from their ores. The career of Robert Boyle illustrates the new, more respectful, view of alchemy. Boyle was long considered to be the first major modern chemist, one whose quantitative and careful laboratory practice made him the supposed antithesis of alchemy. But some 17th century documents, fully interpreted by Principe for the first time, show that Boyle was an avid alchemy practitioner. So was the man often cited as the father of modern physics, Isaac Newton. Provided by Inside Science News Service (news : web)Move the slider to adjust rank threshold, so that you can hide some of the comments.

Paperweight for platinum: Bracing catalyst in material makes fuel cell component work better and last longer

A new combination of nanoparticles and graphene results in a more durable catalytic material for fuel cells, according to work published online at the Journal of the American Chemical Society. The catalytic material is not only hardier but more chemically active as well. The researchers are confident the results will help improve fuel cell design.

"Fuel cells are an important area of energy technology, but cost and durability are big challenges," said chemist Jun Liu. "The unique structure of this material provides much needed stability, good electrical conductivity and other desired properties."

Liu and his colleagues at the Department of Energy's Pacific Northwest National Laboratory, Princeton University in Princeton, N.J., and Washington State University in Pullman, Wash., combined graphene, a one-atom-thick honeycomb of carbon with handy electrical and structural properties, with metal oxide nanoparticles to stabilize a fuel cell catalyst and make it better available to do its job.

"This material has great potential to make fuel cells cheaper and last longer," said catalytic chemist Yong Wang, who has a joint appointment with PNNL and WSU. "The work may also provide lessons for improving the performance of other carbon-based catalysts for a broad range of industrial applications."

Muscle Metal Oxide

Fuel cells work by chemically breaking down oxygen and hydrogen gases to create an electrical current, producing water and heat in the process. The centerpiece of the fuel cell is the chemical catalyst -- usually a metal such as platinum -- sitting on a support that is often made of carbon. A good supporting material spreads the platinum evenly over its surface to maximize the surface area with which it can attack gas molecules. It is also electrically conductive.

Fuel cell developers most commonly use black carbon -- think pencil lead -- but platinum atoms tend to clump on such carbon. In addition, water can degrade the carbon away. Another support option is metal oxides -- think rust -- but what metal oxides make up for in stability and catalyst dispersion, they lose in conductivity and ease of synthesis. Other researchers have begun to explore metal oxides in conjunction with carbon materials to get the best of both worlds.

As a carbon support, Liu and his colleagues thought graphene intriguing. The honeycomb lattice of graphene is porous, electrically conductive and affords a lot of room for platinum atoms to work. First, the team crystallized nanoparticles of the metal oxide known as indium tin oxide -- or ITO -- directly onto specially treated graphene. Then they added platinum nanoparticles to the graphene-ITO and tested the materials.

Platinumweight

The team viewed the materials under high-resolution microscopes at EMSL, DOE's Environmental Molecular Sciences Laboratory on the PNNL campus. The images showed that without ITO, platinum atoms clumped up on the graphene surface. But with ITO, the platinum spread out nicely. Those images also showed catalytic platinum wedged between the nanoparticles and the graphene surface, with the nanoparticles partially sitting on the platinum like a paperweight.

To see how stable this arrangement was, the team performed theoretical calculations of molecular interactions between the graphene, platinum and ITO. This number-crunching on EMSL's Chinook supercomputer showed that the threesome was more stable than the metal oxide alone on graphene or the catalyst alone on graphene.

But stability makes no difference if the catalyst doesn't work. In tests for how well the materials break down oxygen as they would in a fuel cell, the triple-threat packed about 40% more of a wallop than the catalyst alone on graphene or the catalyst alone on other carbon-based supports such as activated carbon.

Last, the team tested how well the new material stands up to repeated usage by artificially aging it. After aging, the tripartite material proved to be three times as durable as the lone catalyst on graphene and twice as durable as on commonly used activated carbon. Corrosion tests revealed that the triple threat was more resistant than the other materials tested as well.

The team is now incorporating the platinum-ITO-graphene material into experimental fuel cells to determine how well it works under real world conditions and how long it lasts.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Pacific Northwest National Laboratory.

Journal Reference:

Rong Kou, Yuyan Shao, Donghai Mei, Zimin Nie, Donghai Wang, Chongmin Wang, Vilayanur V Viswanathan, Sehkyu Park, Ilhan A. Aksay, Yuehe Lin, Yong Wang, Jun Liu. Stabilization of Electrocatalytic Metal Nanoparticles at Metal-Metal Oxide-Graphene Triple Junction Points. Journal of the American Chemical Society, 2011; 110208101227051 DOI: 10.1021/ja107719u

Note: If no author is given, the source is cited instead.

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