Overcoming brittleness: New insights into bulk metallic glass

Nov. 15, 2013 — From the production of tougher, more durable smart phones and other electronic devices, to a wider variety of longer lasting biomedical implants, bulk metallic glasses are poised to be mainstay materials for the 21^st Century. Featuring a non-crystalline amorphous structure, bulk metallic glasses can be as strong or even stronger than steel, as malleable as plastics, conduct electricity and resist corrosion. These materials would seem to have it all save for one problem: they are often brittle, with a poor and uneven resistance to fatigue that makes their reliability questionable. The creation of multicomponent bulk-metallic glass composites is addressing this issue but the problem remains for monolithic metallic glasses, which are major components of bulk metallic composites.

A new study by a collaboration of Berkeley Lab and Caltech researchers may point the way to improving the fatigue resistance of monolithic bulk glasses. The collaboration found that a bulk metallic glass based on palladium displayed a fatigue strength as good as the best composite bulk metallic glasses and comparable to regular polycrystalline structural alloys, such as steel, aluminum and titanium. This study was led by Robert Ritchie, a materials scientist with Berkeley Lab's Materials Sciences Division and Caltech's William Johnson, one of the pioneers in the field of bulk metallic glass fabrication.

"We found that the unexpectedly high fatigue resistance in monolithic palladium-based bulk metallic glass arises from extensive shear-band plasticity that results in a periodic staircase-like crack profile," Ritchie says. "The ease with which shear bands form in this palladium-based glass generates highly serrated cracks that resemble interlocking gear teeth and provide crack-tip blunting and shielding to limit the opening and closing of cracks. The effect is somewhat like trying to speak with a doughnut in your mouth."

Palladium is a metal with a high "bulk-to-shear" stiffness ratio that counteracts the intrinsic brittleness of glassy materials because the energy needed to form shear bands is significantly lower than the energy required to turn these shear bands into cracks.

"The effect of multiple shear-banding is multifold," Ritchie says. "The formation of shear bands leads to extensive crack-tip blunting, which leads to intrinsic toughening, whereas the resulting crack deflections and closures lead to crack-tip shielding, which leads to extrinsic toughening. These mechanisms, together with the high fatigue threshold, provide the major contributions to the excellent fatigue endurance strength shown by the monolithic palladium-based bulk metallic glass."

The results of this study have been published in the Proceedings of the National Academy of Sciences. It is titled "Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism." Ritchie and Johnson are the corresponding authors. Other co-authors are Bernd Gludovatz, Marios Demetriou, Michael Floyd and Anton Hohenwarter.

Share this story on Facebook, Twitter, and Google:

Other social bookmarking and sharing tools:

---

Story Source:

The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory.

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

---

Journal Reference:

1. B. Gludovatz, M. D. Demetriou, M. Floyd, A. Hohenwarter, W. L. Johnson, R. O. Ritchie. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1317715110

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

View the original article here

New insights into the ribosome; important implications for disease

Sep. 19, 2013 — In molecular biology, the ribosome represents the machinery necessary to assemble proteins, the building blocks of life. In this process, information encoded in the genome's DNA is first transcribed to messenger RNA in the nucleus, then transported to the ribosome where protein-assembly instructions are put in motion to translate the code into actual proteins.

But in recent years, it has been demonstrated that the ribosome is far more than just a processing unit; indeed, current research points to an important role for this complex structure in actively regulating biological processes.

Now, in a first-of-its-kind study that broadly examines the composition of the riboproteome, a scientific team led by investigators at Beth Israel Deaconess Medical Center (BIDMC) reveals previously unappreciated components of the ribosome, uncovering a large and dynamic structure that, among other things, can be altered in cancer. Published in today's on-line issue of the journal Cell Reports, the study additionally describes the development of an analytic platform that can be widely applied to numerous biological systems to highlight the functional roles of possible disease genes associated with the riboproteome.

"A primary goal of our lab is to gain a better understanding of translation and its impact on cancer," explains senior author Pier Paolo Pandolfi, MD, PhD, Scientific Director of the Cancer Center at BIDMC and George C. Reisman Professor of Medicine at Harvard Medical School (HMS). "So a key focus of our work has been the role of the ribosome. While the conventional wisdom has been that ribosome composition is absolutely fixed, we have recently pursued the hypothesis that it is, in fact, flexible and dynamic. Moreover, it has become apparent during the course of our investigations that the functional deregulation of the ribosome is implicated in disease initiation and progression, and could serve as a potential target for therapeutic intervention."

In this new study, a scientific team led by Pandolfi lab members John Clohessy, PhD, and Markus Reschke, PhD, examined the ribosome on a large scale to get a clearer picture of the relationship and interactions between ribosomes and the associated proteins required for efficient and correct translation of messenger RNA (mRNA).

"We wanted to find out what was happening in the ribosome on a global scale," explains Clohessy. "So we incorporated into our analysis those proteins that associate with either the ribosome itself or with the mRNA being translated, and which could represent important regulators of translation."

Until recently a lack of high-throughput ribosomal analysis has limited researchers' abilities to characterize the ribosomal proteome, which consists of the ribosome itself and a host of other proteins that interact with this cellular machine to regulate translation. In this new study, the scientists optimized and adapted a SILAC-based mass spectrometry approach to probe this complex microscopic structure through the analysis of far more data than was ever available before.

An acronym for stable isotopic labeling by amino acids in cell culture, SILAC utilizes non-radioactive isotope labeling to detect quantitative differences in protein abundance among cell samples. "A SILAC-based approach offers an elegant way of comparing two different cellular populations," explains Reschke. "The metabolic incorporation into the proteins of amino acids that have been differentially labeled with carbon and nitrogen isotopes results in a mass shift of the corresponding peptides, and it is this shift that can be detected by a mass spectrometer.

"The beauty of this system is that you're keeping the cells in their natural environment, you're simply substituting one amino acid with another," he adds. "This enables you to conduct a direct comparison without other chemical modifications."

Using a panel of cell lines, as well as genetic and pharmacological perturbations, the team embarked on their characterization of the prostate riboproteome. "Mass spectrometry enabled us to look at thousands of proteins at the same time," explains Clohessy. Through SILAC-based mass spec, the investigators were able to gain the first comprehensive overview of proteins within this space and examine how the riboproteome is altered in disease.

"We compared a number of different things," adds Clohessy. "We compared different cancer cell lines. We looked at changes to the riboproteome within a single specific cell line, both with and without use of a pharmacological inhibitor. And, we looked at a cell line in the context of genetic alteration. We essentially got a clear snapshot of which proteins were in this space at any particular time, and saw how they responded to cellular signals and stresses."

The authors then carried out a computational analysis on this extensive dataset to determine if there were specific protein networks or pathways that were highly represented in the data. Their survey revealed a number of exciting and surprising findings -- with important therapeutic implications.

"Among other things, our analysis uncovered a high incidence of genetic alterations to the riboproteome components in cancer, with a distinct bias towards genetic amplification, [whereby cells accumulate multiple copies of genes which can support cancer growth and survival]" explains Reschke, adding that it also revealed the presence of a significant population of RNA binding proteins (RBPs), important regulators of mRNA translation, some of which are also associated with disease.

"Changes in ribosome amounts have been shown to be associated with cancer for more than a century," notes Nahum Sonenberg, PhD, James McGill Professor of Biochemistry at McGill University. "However, the mechanism that links ribosomes and cancer is not well understood. This paper from the Pandolfi laboratory is a very important step towards the understanding of the full gamut of functions of the ribosome and its associated translation mRNA machinery in cancer."

This novel method additionally opens up a new direction in terms of how to study the ribosome in the context of both disease and therapy. "By now, we know a lot about the genes and pathways that converge on translation, and many of them are well-known oncogenes, including MYC and PI3K," explains Pandolfi. 'But the translational dimension we are now describing offers a new perspective on yet another layer of proteins that seem to be amplified in cancer. These findings provide us with a completely new set of proteins that may be used to better understand the process of translation in cancer, and help identify new targets for therapeutic intervention."

View the original article here

Study provides insights on protecting world's poor from climate change

Sep. 11, 2013 — The worst impacts of climate change on the world's poorest fishing communities can likely be avoided by careful management of the local environment and investing in the diversification of options for local people, according to the Wildlife Conservation Society and James Cook University.

Climate change is already putting pressure on fishers who depend on nature for their livelihoods. In a new study, scientists found large differences in the potential to adapt based on the local mixture of social and environmental characteristics, requiring a variety of management approaches for each situation.

The paper appears today in the online journal PLOS ONE. The authors include: Joshua E. Cinner, Cindy Huchery, Nicholas Graham, and Christina Hicks of the ARC Centre of Excellence for Coral Reef Studies, James Cook University; Emily Darling of Simon Fraser University and Austin Humphries of Rhodes University; Nadine Marshall of CSIRO; and Tim McClanahan of the Wildlife Conservation Society.

The study undertaken by an international team of scientists, focused on 12 poor fishing communities along the coast of Kenya -- a poor country that has been identified as one of the most vulnerable to the impacts of climate change. The scientists found that, even among the poor, there were considerable differences in how climate change was likely to affect the communities based on the existing social conditions and how each community cared for its marine resources.

"Despite the fact that all of the communities we studied were geographically close, they were vulnerable in very different ways," said lead author Dr. Joshua Cinner. "Some communities really lacked the assets to invest in new opportunities; others lacked the diversity of livelihood opportunities and skills to make a change, while some lacked the social networks and connections that people can rely on in times of need."

The team also looked at how the local coral reefs were holding up to a changing climate. "There are a number of studies that look at how climate change will affect either ecosystems or society, but in this study we really brought both of these together to get a more complete picture" says co-author Dr. Tim McClanahan, a Senior Conservation Zoologist from the Wildlife Conservation Society. "We conducted rigorous studies of reef ecology, the types of fish people were catching, and local socioeconomic conditions." Consequently, the study provides the most detailed and comprehensive examination of both social and ecological aspects of climate change impacts on coral reef fisheries to date.

The authors noted that climate change is already exerting significant pressure on the fishing communities of coastal Kenya; the 1998 El Nino Southern Oscillation resulted in widespread coral mortality along the coast. In areas where overfishing was rampant, communities lacked the potential to recover quickly from disturbances. These same areas tended to have fish species that were more sensitive to coral loss than areas that were protected from fishing by local communities and the government.

Overall, the authors found that communities and coastal managers can find ways of reducing the impacts of climate change on fragile coral reef ecosystems. Just as important, the authors maintain, will be formulating adaptation solutions combining ecological and socio-economic factors.

View the original article here