Tuesday, October 11, 2011

Radiation boost for artificial joints

 A blast of gamma radiation could toughen up plastic prosthetic joints to make them strong enough to last for years, according to researchers in China writing in the current issue of the International Journal of Biomedical Engineering and Technology.

Whole joint replacement, such as hip and knee replacement, commonly use stainless steel, titanium alloys or ceramics to replace the damaged or diseased bone of the joint. Non-stick polymer or nylon is usually used to coat the artificial joint to simulate the cartilage. However, none of these materials are ideal as they produce debris within the body as the joint is used, which leads to inflammation, pain and other problems.

Now, Maoquan Xue of the Changzhou Institute of Light Industry Technology, has investigated the effect of adding ceramic particles and fibers to two experimental materials for coating prosthetic joints, UHMWPE (ultra-high-molecular-weight polyethylene) and PEEK (polyether ether ketone). Alone neither UHMWPE nor PEEK is suitable as a prosthetic cartilage materials because both crack and fracture with the kind of everyday stresses that a hip or knee joint would exert on them. The problem is that the long polymer chains within the material can readily propagate applied forces causing tiny fractures to grow quickly and the material to fail.

Xue has now demonstrated that by adding ceramic particles to the polymers and then blasting the composite with a short burst of gamma-radiation it is possible to break the main polymer chains without disrupting the overall structure of the artificial cartilage. There is then no way for microscopic fractures to be propagated throughout the material because there are no long stretches of polymer to carry the force from one point to the next. The resulting treated material is thus much tougher than the polymer alone and will not produce the problematic debris within a joint that might otherwise lead to inflammation and pain for the patient.

Xue adds that the treated composite materials might also be more biocompatible and so less likely to be rejected by the patient's immune system on implantation. He suggests that the particular structure of the composites would also be receptive to addition of bone-generating cells, osteocytes or stem cells, that could help a prosthetic joint be incorporated more naturally into the body.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Inderscience Publishers, via EurekAlert!, a service of AAAS.

Journal Reference:

Maoquan Xue. Research on polymer composites of replacement prostheses. International Journal of Biomedical Engineering and Technology, 2011; 7 (1): 18 DOI: 10.1504/IJBET.2011.042495

Catching molecular motion at just the right time: Theorists overcome loss of entropy and friction in computational simulations

 University of Oregon researchers have devised a mathematically rich analytic approach to account for often-missing thermodynamic and molecular parameters in molecular dynamic simulations.

The new approach, which returns atomistic-level data into the time frame of the macroscopic world, is detailed in a paper appearing online ahead of regular publication in the journal Physical Review E. The method is all about timing, says Marina G. Guenza, professor of theoretical physical chemistry, and may help reduce trial-and-error experimentation required in manufacturing when such information is missing.

Molecular dynamic simulations are indispensable tools -- a natural partner of experiments and theory -- that help scientists understand the properties of new materials and processes by providing a view at the resolution of atoms. Simulations expedite the development of new materials by showing how those with a specific atomistic structure behave in various conditions, for example when they are strained or frozen.

Simulations of polymers and biological systems have been used since the 1990s. That effort has focused on the short-time motion of macromolecules described in atomistic detail, which, in addition to plastics and glasses, also applies to DNA and proteins, Guenza said.

However, modelers remove critical pieces of information, such as atom-level activity, to scale back simulations to cover only generic components and access longer times in an accessible simulation run. This technique provides helpful but incomplete data about behavioral responses, Guenza said. Simulations in which atomistic information is withheld are called coarse-grained models.

"These are big molecules," she said. "They move slowly. It is difficult to set up a simulation where the atomistic definition is included and still be able to see things happen on the long time scale, which can be really important. Coarse-graining allows one to simulate macromolecules for longer time, but, because some information is eliminated, the motion measured is unrealistically fast."

Entropy -- a loss of thermodynamic energy -- and surface friction are lost in these simulations, she said. Simulations at the atomistic level depict motion occurring in femtoseconds. (A femtosecond is a millionth of a nanosecond; a nanosecond, a billionth of a second.)

To understand what happens in macroscopic systems, you have to look at movement over longer periods of time -- over seconds, says Ivan Lyubimov, a UO doctoral student in chemistry and lead author. "When you try to simulate a second's worth of information at the atomistic level, with all the details included, it might take one or two years for the computer to run the simulation, and you'd still have errors due to numerical algorithms," he said.

Guenza and Lyubimov looked at simulations where thousands of macromolecules of polyethelene are represented as interacting soft particle, i.e. a coarse-grained model, and applied an original theory that refocuses the information missing in the simulations.

Guenza -- a member of the UO's Institute of Theoretical Science, Materials Science Institute and Institute of Molecular Biology -- and Lyubimov first detailed the basics of their theoretical formula in 2010 in the Journal of Chemical Physics.

Their "first-principle" approach looks at the loss of energy, due to the change in entropy, caused by the coarse-graining of the molecule in simulations. Coarse-graining also affects the surface of molecules in simulation, so the formalism accounts for the loss of friction as well.

"We were able to show that if you run your simulation with less detail, we can correct for these factors, and you'll produce the correct motion -- the dynamics -- of the real system," Guenza said. "We have done a lot of tests with different experiments and simulations, and our method works pretty well. No one else has been able to do this with a theoretical solution."

The method, the authors wrote, is different from others currently in use, because it is analytical rather than numerical. It removes the need for separate, time-consuming atomistic simulations to account for missing information obtained from coarse-grained simulations.

"Parameters can be varied for different systems, depending on the molecule size, density and temperature," Lyubimov said. "You can make realistic predictions for the type of material you want to study, at much less expense. You don't have to know all of the details, but you do need a certain number of parameters based on the chemical structure that you want to study."

The National Science Foundation supported the research.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Oregon.

Journal Reference:

I. Lyubimov, M. Guenza. First-principle approach to rescale the dynamics of simulated coarse-grained macromolecular liquids. Physical Review E, 2011; 84 (3) DOI: 10.1103/PhysRevE.84.031801

Reducing costs of metal casting with plasma technology

 Tecnalia Research & Innovation is undertaking the innovation of casting processes with its "plasma torch." This new system enables great precision when heating the metal, thus reducing operational costs, enhancing metallurgical quality and saving energy.

To achieve this end, Tecnalia made use of a High-Powered Thermal Plasma, enabling heating the necessary quantity of metal at the required temperature and at the precise moment of casting, when the molten metal has to be poured from the furnace or ladle. Precision in this process is fundamental, as overheated metal oxidises easily and can lose its characteristics to the point of invalidating it for the production of parts. This is why the temperature of fusion has to be controlled to the maximum.

The "plasma torch" enables programming the range of temperature at which it is desired to cast the metal and maintain this automatically over the whole period of the casting process. Besides, the exclusive characteristic that the plasma provides is that this operation can be undertaken using an external heating element, separate from the furnace itself, facilitating maintenance tasks and thus reducing general costs of casting.

The success of the system was quickly evident thanks to the marketing efforts of SERT Metal, the company which has been licensed to commercially exploit the patent. The Bizkaia-based blast furnace company Fuchosa and the Valladolid-based Lingotes Especiales already have this equipment at their installations and underline its high performance.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Elhuyar Fundazioa, via AlphaGalileo.

Lessons to be learned from nature in photosynthesis

Photosynthesis is one of nature's finest miracles. Through the photosynthetic process, green plants absorb sunlight in their leaves and convert the photonic energy into chemical energy that is stored as sugars in the plants' biomass. If we can learn from nature and develop an artificial version of photosynthesis we would have an energy source that is absolutely clean and virtually inexhaustible.

"Solar energy is forecasted to provide a significant fraction of the world's energy needs over the next century, as sunlight is the most abundant source of energy we have at our disposal," says Graham Fleming, Vice Chancellor for Research at the University of California (UC) Berkeley who holds a joint appointment with Lawrence Berkeley National Laboratory (Berkeley Lab). "However, to utilize solar energy harvested from sun¬light efficiently we must understand and improve both the effective cap¬ture of photons and the transfer of electronic excitation energy."

Fleming, a physical chemist and authority on the quantum phenomena that underlie photosynthesis, is one of four international co-authors of a paper in Nature Chemistry, entitled "Lessons from nature about solar light harvesting." The other co-authors are Gregory Scholes, of the University of Toronto, Alexandra Olaya-Castro, of London's University College, and Rienk van Grondelle, of the University of Amsterdam. The paper describes the principles behind various natural antenna complexes and explains what research needs to be done for the design of effective artificial versions.

Solar-based energy production starts with the harvesting of the photons in sunlight by the molecules in antenna complexes. Energy from the photons excites or energizes electrons in these light-absorbing molecules and this excitation energy is subsequently transferred to suitable acceptor molecular complexes. In natural photosynthesis, these antenna complexes consist of light-absorbing molecules called "chromophores," and the captured solar energy is directed to chemical reaction centers -- a process that is completed within 10-to-100 picoseconds (a picosecond is one trillionth of second).

"In solar cells made from organic film, this brief timescale constrains the size of the chromophore arrays and how far excitation energy can travel," Fleming says. "Therefore energy-transfer needs and antenna design can make a significant difference to the efficiency of an artificial photosynthetic system."

Scientists have been studying how nature has mastered the efficient capture and near instantaneous transfer of the sun's energy for more than a century, and while important lessons have been learned that can aid the design of optimal synthetic sys¬tems, Fleming and his co-authors say that some of nature's design principles are not easily applied using current chemical synthesis procedures. For example, the way in which light harvesting is optimized through the organization of chromophores and the tuning of their excitation energy is not easily replicated. Also, the discovery by Fleming and his research group that the phenomenon of quantum coherence is involved in the transport of electronic excitation energy presents what the authors say is a "challenge to our understanding of chemical dynamics."

In their paper, Fleming and his international colleagues say that a clear frame¬work exists for the design and synthesis of an effective antenna unit for future artificial photosynthesis systems providing several key areas of research are addressed. First, chromophores with large absorption strengths that can be conveniently incorporated into a synthetic protocol must be developed. Second, theoretical studies are needed to determine the optimal arrangement patterns of chromophores. Third, experiments are needed to elucidate the role of the environment on quantum coherence and the transport of electronic excitation energy. Experiments are also needed to determine how light-harvesting regulation and photo protection can be introduced and made reasonably sophisticated in response to incident light levels.

"There remains a number of outstanding questions about the mechanistic details of energy transfer, especially concerning how the electronic system interacts with the environment and what are the precise consequences of quantum coherence," Fleming says. "However, if the right research effort is made, perhaps based on synthetic biology, artificial photosynthetic systems should be able to produce energy on a commercial scale within the next 20 years."

Support for this work was provided by the U.S. Department of Energy (DOE) Office of Science, the Natural Sciences and Engineering Research Council of Canada, the Engineering and Physical Sciences Research Council of the United Kingdom, and the Netherlands Organization for Scientific Research, and the European Research Council.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Gregory D. Scholes, Graham R. Fleming, Alexandra Olaya-Castro, Rienk van Grondelle. Lessons from nature about solar light harvesting. Nature Chemistry, 2011; 3 (10): 763 DOI: 10.1038/nchem.1145