Wednesday, August 10, 2011

Heavy metal: Titanium implant safety under scrutiny

A new strategy to quantify the levels of titanium in the blood of patients fitted with titanium orthopaedic implants is presented in Analytical and Bioanalytical Chemistry, a Springer journal. Yoana Nuevo-Ordónez and colleagues of the Sanz-Medel research group from the University of Oviedo in Spain have developed a highly sensitive method to determine the levels of titanium in human blood, establishing a baseline for natural levels of titanium in untreated individuals as well as measuring levels in patients with surgical implants.

Titanium are routinely used for bone fractures as well as dental work. It has recently been shown that titanium-based implants both corrode and degrade, generating metallic debris. There is some concern over the increased concentrations of circulating metal-degradation products derived from these implants, and their potential harmful biological effects over a period of time, including hepatic injury and renal lesions. In order to assess the implications of these 'leaks', it is essential to accurately measure the basal, normal levels of in the bloodstream, as well as quantify how much higher levels are in patients with implants.

Nuevo-Ordónez and team collected blood from 40 healthy individuals and 37 patients with titanium implants - 15 had tibia implants, eight had femur implants, and 14 had humerus implants (eight internal and six external fixation implants). They used their new method, based on isotope dilution analysis and mass spectrometry, or IDA-ICP-MS, to analyze the blood samples.

They found that control individuals had very low levels of titanium in the blood whereas titanium concentrations were significantly higher for all the patients with implants. The sensitivity of the method was such that the researchers were also able to show significant differences in titanium levels for different types of bone fixation devices. The more invasive implants shed more metallic debris into the than the external, superficial designs. The work also identified how the titanium from the implants is transported in the bloodstream and potentially distributed and accumulated.

The authors conclude: "The simplicity of the methodology based on isotope dilution analysis and the accuracy and precision of the obtained results should encourage the use of the proposed strategy on a routine basis."

More information: Nuevo-Ordónez Y, Montes-Bayón M, Blanco-Gonzalez E, Paz J, Dianez Raimundez J, Tejerina Lobo J, Pena M, Sanz-Medel A (2011). Titanium release in serum of patients with different bone fixation implants and its interaction with serum biomolecules at physiological levels. Analytical and Bioanalytical Chemistry; DOI 10.1007/s00216-011-5232-8

Provided by Springer

Sugars can do it too: Protein-like oligomerization of carbohydrates

In order for enzymes and other proteins in our bodies to work correctly, it is often necessary for multiple protein units to gather together into a larger structure. Chains of sugar molecules cannot do this—at least that is what was thought until now. A team led by Thomas Heinze at the University of Jena (Germany) and Stephen E. Harding at the University of Nottingham (UK) has now proven the opposite.

In the journal Angewandte Chemie, the researchers have introduced their discovery: cellulose-like carbohydrates that can form defined aggregates from several subunits.

The individual subunits of functional proteins are not chemically bound to each other; they are held together by physical attractive forces and can separate again depending on the environmental conditions. It was previously assumed that molecules made of many sugar units, known as polysaccharides, never demonstrate such behavior. Defined, reversible aggregates of several such sugar chains have not previously been observed. A German–British team of researchers has now detected the protein-like aggregation of carbohydrates into defined oligomers—a novel and completely unexpected phenomenon.

The scientists studied a nitrogen-containing polysaccharide that resembles cellulose. Cellulose is the primary component of plant cell walls and is the most familiar representative of the polysaccharide family after starch. The researchers examined aminocelluloses by means of analytical ultracentrifugation. Ultracentrifuges rotate up to 500,000 times a minute. The correspondingly high centrifugal forces cause large molecules to sediment, or settle to the bottom. The sedimentation rate can be used to determine the approximate molar masses of macromolecules. In their study, the researchers found up to five different species present in their aminocellulose solutions. Their molar masses were found to be multiples of the mass of the monomer, clearly showing that they are aggregates of two to five polysaccharide units. The aggregates dissociate when the solution is diluted, indicating that the bonds are reversible.

The researchers believe that aminocelluloses not only interact with each other in this way, but also with certain other biomolecules. They could thus be interesting as boundary surface materials with biological recognition functionality, which could be used to immobilize proteins, for example to design analysis device outside a lab to identify toxins or pathogens without a few minutes. These are interesting for the on-site detection of animal diseases, food contamination as well as of biological warfare agents such as anthrax, ebola, and botulinus toxin.

More information: Thomas Heinze, Protein-Like Oligomerization of Carbohydrates, Angewandte Chemie International Edition, … ie.201103026

Provided by Wiley (news : web)

New spin on friction-stir

Researchers Zhili Feng, Alan Frederic and Stan David in Oak Ridge National Laboratory's Materials S&T Division have made significant progress toward a new metal processing technique, called friction-stir extrusion, that could represent a major advance in converting recyclable materials -- such as alloys of aluminum, magnesium and titanium alloys, and even high-temperature superconductors -- to useful products.

The process also represents a step forward in energy-efficient industrial processes in that it eliminates the melting step in conventional metal recycling and processing. The friction-stir method, as the name implies, derives its heat from spinning metal against metal, and direct conversion of mechanical energy to thermal energy as frictional heat generated between two surfaces.

The ORNL team produced a solid wire of a magnesium-aluminum alloy from machined chips, eliminating the energy and labor intensive processes of melting and casting.

"This process is very simple. You get the product form that you want by just using the frictional heat," said Stan David, an ORNL retiree and consultant who once led the division's Joining group.

The new approach provides an opportunity to efficiently produce highly engineered structural and functional materials. Friction extrusion can be developed into metal recycling process of steels, Al alloys, and other recyclable metals. It is suitable to produce a variety of bulk nano materials such as nano engineered ODS alloys. It also has the potential to produce nano grain structure bulk materials. The impact of economically producing nano engineered creep resistance Al conductors in large quantity will be enormous for the power transmission industry.

Friction-stir extrusion could also represent a new route to the fabrication of extremely specialized materials, such as high-temperature superconducting wires and mechanical alloyed materials.

"The process of melting and casting can destroy the properties of a highly ordered, novel material such as an oxide dispersion strengthened materials or a high-temperature superconductors. Because friction-stir only takes the material up to 'plasticizing' temperatures, the properties of the material are not affected as much," said Zhili Feng, who now leads the ORNL group.

The extrusion process follows the same principle of the friction-stir welding, in which a rapidly spinning tool is applied to the metal, heating it until it becomes soft, but not melted. Because the material is still in its solid state when it is extruded, it suffers none of the degradation and transformation that would occur with actual melting.
"The process of melting is very detrimental to those properties," said Feng.

Wayne Thomas, who pioneered the stir technology at The Welding Institute in England, says ORNL has proved the basic principle of a new technique that could be key to working with advanced alloys, including high-temperature superconductors.

"It is very difficult to mix silicon, titanium, magnesium and other materials in to alloys and turn them into molten metals. If you can mix them in the solid phase, it is much better, and there are mixtures you can't even consider outside a solid phase," Thomas said.

One such application is the fabrication of mechanically alloyed magnesium alloys into components. Friction-stir extrusion has potential to be a low-cost way to produce product forms with this lightweight and high-performance metal. ORNL is extensively involved in the magnesium alloy R&D and technology transfer and commercialization.

The energy savings of this process are significant: The process requires only 10 to 20 percent of the energy required for conventional melting with potential saving of more than 80 percent.

The team credits DOE's Industrial Technologies Program for a capital equipment investment and programmatic funding that enabled them to establish the prototype friction-stir work station at ORNL. The ORNL team is already seeing industry interest in what they've accomplished so far with the technology. One of the companies is Southwire Company, a major international electric cable company, that is currently working with ORNL on the technology development.

Provided by Oak Ridge National Laboratory (news : web)

Computational chemistry shows the way to safer biofuels

Replacing gasoline and diesel with plant-based bio fuels is crucial to curb climate change. But there are several ways to transform crops to fuel, and some of the methods result in bio fuels that are harmful to health as well as nature.

Now a study from the University of Copenhagen shows that it is possible to predict just how toxic the fuel will become without producing a single drop. This promises cheaper, faster and above all safer development of alternatives to fossil fuel.

Solvejg Jorgensen is a computational chemist at the Department of Chemistry in Copenhagen. Accounts of her new computational prediction tool are published in acclaimed scientific periodical The A.

Among other things the calculations of the computer chemist show that bio fuels produced by the wrong synthesis path will decompose to compounds such as health hazardous , carcinogenic particles and toxic . Previously an assessment of the environmental impact of a given method of production could not be carried out until the fuel had actually been made. Now Jorgensen has shown that various production methods can be tested on the computer. This will almost certainly result in cheaper and safer development of bio fuels.

"There is an almost infinite number of different ways to get to these fuels. We can show the least hazardous avenues to follow and we can do that with a series of calculations that take only days", explains Jorgensen.

Chemically bio fuel is composed of extremely large molecules. As they degrade during and afterwards in the atmosphere they peel of several different compounds. This was no big surprise. That some compounds are more toxic than others did not come as a revelation either but Jorgensen was astonished to learn from her calculations that there is a huge difference in toxicity depending on how the molecules were assembled during production. She was also more than a little pleased that she could calculate very precisely the degradation mechanisms for a bio fuel molecule and do it fast.

"In order to find the best production method a chemist might have to test thousands of different types of synthesis. They just can't wait for a method that takes months to predict the degradation mechanisms", explains Jorgensen who continues: "On the other hand: For a chemist who might spend as much as a year trying to get the synthesis right it would be a disaster if their method leads to a toxic result".

It seems an obvious mission to develop a computational tool that could save thousands of hours in the lab. But Solvejg Jorgensen wasn't really all that interested in bio fuels. What she really wanted to do was to improve existing theoretical models for the degradation of large in the atmosphere.

To this end she needed some physical analysis to compare to her calculations. Colleagues at the Department of Chemistry had just completed the analysis of two bio fuels. One of these would do nicely. But Jorgensen made a mistake. And instead of adding just another piece to a huge puzzle she had laid the foundation for a brand new method.

"I accidentally based my calculations on the wrong molecule, so I had to start over with the right one. This meant I had two different calculations to compare. These should have been almost identical but they were worlds apart. That's when I knew I was on to something important", says Solvejg Jorgensen, who has utilised her intimate knowledge of the theoretical tool density functional theory and the considerable computing power of the University of Copenhagen.

Provided by University of Copenhagen