Novel titanium alloy produces infection-resistant implants
A novel surgical implant developed by researchers at Washington State University (WSU) was able to kill 87% of the bacteria that cause staph infections in laboratory tests, while remaining strong and compatible with surrounding tissue, just like current implants.
The work, reported in a paper in the International Journal of Extreme Manufacturing, could someday lead to better infection control in many common surgeries, such as hip and knee replacements, that are performed daily around the world. Bacterial colonization of implants is one of the leading causes of failure and bad outcomes after surgery.
“Infection is a problem for which we do not have a solution,” said Amit Bandyopadhyay, professor in WSU’s School of Mechanical and Materials Engineering and corresponding author of the paper. “In most cases, the implant has no defensive power from the infection. We need to find something where the device material itself offers some inherent resistance -- more than just providing drug-based infection control. Here we’re saying, why not change the material itself and have inherent antibacterial response from the material itself?”
The titanium materials used for hip and knee replacements and other surgical implants were developed more than 50 years ago and are not well suited to overcoming infections. Although surgeons often treat preemptively with antibiotics, life-threatening infections can occur right after surgery, or weeks or months later as a secondary infection.
Once an infection sets in as a fuzzy, fine film on an implant, doctors try to treat it with systemic antibiotics. In about 7% of implant surgery cases, though, doctors have to perform a revision surgery: removing the implant, cleaning the area, adding antibiotics and putting in another implant.
Using 3D-printing technology, the WSU researchers added 10% tantalum, a corrosion-resistant metal, and 3% copper to the titanium alloy typically used in implants. When bacteria come into contact with this material’s copper surface, almost all of their cell walls rupture. The tantalum, meanwhile, encourages healthy cell growth with surrounding bone and tissue, leading to expedited healing for the patient.
The researchers spent three years on a comprehensive study of their implant, assessing its mechanical properties, biology and antibacterial response, both in the lab and in animal models. They also studied its wear to make sure that metal ions from the implant won’t wear off and move into nearby tissue, causing toxicity.
“The biggest advantage for this type of multifunctional device is that one can use it for infection control as well as for good bone-tissue integration,” said Susmita Bose, a professor in the School of Mechanical and Materials Engineering and co-author of the paper. “Because infection is such a big issue in today’s surgical world, if any multifunctional device can do both things, there’s nothing like it.”
The researchers are continuing this work, hoping to increase the bacterial death rate to the standard of more than 99% without compromising tissue integration. They also want to make sure that the materials can sustain a good performance under the real-world loading conditions that patients might experience, such as when hiking in the case of a knee replacement.
This story is adapted from material from Washington State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
Two molecules needed to address recombination problem
Researchers at Northwestern University have again raised the standards for perovskite solar cells with a new development that has helped the emerging technology hit new records for efficiency.
In a paper in Science, the researchers report a dual-molecule solution to overcoming losses in efficiency as sunlight is converted to energy. This solution involves incorporating a molecule to address something called surface recombination, in which electrons are lost when they are trapped by defects — missing atoms on the surface – and then a second molecule to disrupt recombination at the interface between layers. In this way, the researchers were able to achieve a National Renewable Energy Lab (NREL) certified efficiency of 25.1%, where earlier approaches reached efficiencies of just 24.09%.
“Perovskite solar technology is moving fast, and the emphasis of research and development is shifting from the bulk absorber to the interfaces,” said Ted Sargent at Northwestern University. “This is the critical point to further improve efficiency and stability and bring us closer to this promising route to ever-more-efficient solar harvesting.”
Sargent is the co-executive director of the Paula M. Trienens Institute for Sustainability and Energy (formerly ISEN) and a multidisciplinary researcher in materials chemistry and energy systems. He has appointments in the department of chemistry in the Weinberg College of Arts and Sciences and the department of electrical and computer engineering in the McCormick School of Engineering.
Conventional solar cells are made of high-purity silicon wafers that are energy intensive to produce and can only absorb a fixed range of the solar spectrum. In contrast, the size and composition of perovskite materials can be adjusted to ‘tune’ the wavelengths of light they absorb, making them a favorable and potentially lower-cost, high-efficiency emerging tandem technology.
Historically, perovskite solar cells have been plagued by challenges over improving their efficiency because of their relative instability. Over the past few years, however, advances from Sargent’s lab and others have brought the efficiency of perovskite solar cells to within the same range as can be achieved with silicon solar cells.
In the present study, rather than trying to help the solar cell absorb more sunlight, the team focused on increasing efficiency by maintaining and retaining the generated electrons. When the perovskite layer contacts the electron transport layer of the cell, electrons move from one to the other. But the electrons can also move back outward and ‘recombine’ with holes in the perovskite layer.
“Recombination at the interface is complex,” said first author Cheng Liu, a postdoctoral student in the Sargent lab. “It’s very difficult to use one type of molecule to address complex recombination and retain electrons, so we considered what combination of molecules we could use to more comprehensively solve the problem.”
Past research from Sargent’s team had uncovered evidence that one molecule, PDAI2, does a good job at solving interface recombination. But they also needed to find a molecule that would work to repair surface defects and prevent electrons from recombining with them. This led them to narrow in on sulfur, theorizing that it could replace carbon groups — typically poor at preventing electrons from moving — to cover missing atoms and suppress recombination.
In a recent paper in Nature, the same researchers reported developing a coating for the substrate beneath the perovskite layer to help the cell work at a higher temperature for a longer period. This solution, according to Liu, can work in tandem with the findings detailed in the Science paper.
While the team hopes their findings will encourage the larger scientific community to continue moving the work forward, they too will be working on follow-ups.
“We have to use a more flexible strategy to solve the complex interface problem,” Cheng said. “We can’t only use one kind of molecule, as people previously did. We use two molecules to solve two kinds of recombination, but we are sure there’s more kinds of defect-related recombination at the interface. We need to try to use more molecules to come together and make sure all molecules work together without destroying each other’s functions.”
This story is adapted from material from Northwestern University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
Making batteries last longer with a little help from soap
A team of scientists in the US have developed a new type of electrolyte that could extend the life of lithium metal batteries based on how soap works. With such batteries seen as crucial for improving the performance of electric vehicles, smart phones and other devices, these electrolytes offer complex nanostructures to improve how much energy batteries can store per cycle and how many cycles they last.
Although lithium metal batteries have a much higher energy storage capacity than lithium-ion batteries, standard electrolytes – comprised of low-concentration salt dissolved in a liquid solvent – are not good at allowing an electrical charge to pass between the two terminals to make the necessary electrochemical reaction for converting stored chemical energy to electric energy.
When lathered, soap forms structures called micelles that trap and remove grease and dirt when flushed through with water, with the soap acting as bridge between the water and what is being cleaned. However, as reported in Nature Materials [Efaw et al. Nat. Mater. (2023) DOI: 10.1038/s41563-023-01700-3], a similar thing was shown to happen for a new type of electrolyte called a localized high-concentration electrolyte (LHCE).
There has been interest in LHCEs due to in-situ formation of a stable solid–electrolyte interphases layer on a lithium metal anode, although their microstructures are not well understood. The electrolytes were developed by combining high concentrations of salt in solvent with another liquid called a diluent, which helps to make the electrolyte flow better to maintain the power of the battery. The role of the soap or surfactant is played by the solvent that binds the diluent and the salt, wrapping itself around the higher concentration salt in the center of the micelle.
The micelle-like structures produced were predicted by simulations and then confirmed in experiments. As researcher Bin Li told Materials Today, “Based on the micelle structures and predicted ternary phase diagram, this work can help rational design of advanced electrolytes with complicated chemical interactions and shorten the time of searching for good electrolytes with stable [solid–electrolyte interphases] formed and wider operation temperature windows.”
The study therefore provides a guideline on the desired interactions from the salt, the solvent and the diluent in the electrolyte, what the concentrations should be and how they should be mixed. The team now hope to optimize the impact of electrolyte component choices in LHCEs to control the salt–solvent cluster size, shape and composition, as well as external parameters during operation.
This work can help rational design of advanced electrolytes with complicated chemical interactions and shorten the time of searching for good electrolytes with stable [solidelectrolyte interphases] formed and wider operation temperature windows.Bin Li
Defects engineer fracture resistance in 2D materials
Two-dimensional transition metal dichalcogenides (TMDs) are highly attractive for applications because of their electronic and optoelectronic properties, which can be fine-tuned by manipulating defects known as vacancies. Now researchers from Northwestern University, Argonne National Laboratory, and Rice University have shown how these vacancies affect the mechanical strength of one such TMD, hexagonal MoSe2, too [Nguyen et al., Materials Today (2023), https://doi.org/10.1016/j.mattod.2023.10.002].
Vacancies play a complex role in TMDs: depending on the type and density, vacancies can reduce crack resistance rendering devices less reliable or they can trigger the formation of phases that improve toughness and fracture behavior.
“[We wanted to know] would defects… alter the mechanical behavior of TMDs? And, if so, what are the mechanisms and can these defects be designed to engineer the mechanical properties of TMDs,” explains first author of the study, Hoang Nguyen.
The team, led by Horacio D. Espinosa, used controlled electron irradiation doses in a high-resolution transmission electron microscope to create different types and densities of vacancies. At low dose rates, zero dimensional (0D) isolated Se (iSe), Se2 (iSe2), and Mo (iMo) vacancies are formed, while at higher dose rates 1D Se line (lSe) vacancies form. The effect of these vacancy types on the mechanical behavior of MoSe2 was modelled using molecular dynamics (MD) simulations.
“We used the types and densities [of] observed defects to make predictions about their interaction with cracks to see how they affect one another,” says Nguyen. “These predictions were analyzed and explained using a series of mechanical-chemical tools.”
By comparing experimental results and first principle calculations, the researchers reveal that three vacancy types affect the interaction of cracks and defects while one type does not. Isolated metal monovacancies (iMo) and chalcogenide divacancies (iSe2) arrest the motion and development of crack tips, increasing toughness and resistance to fracture. High-dose chalcogenide line vacancies (lSe) also affect cracks but in a different way. This type of 1D defect attracts propagating cracks, altering the propagation direction and leading to kinking. Isolated chalcogenide monovacancies (iSe), meanwhile, have no significant effect on crack behavior.
“This study shows that defect engineering using controlled electron dose rate or other methods could be feasible… [to] bring about promising enhancement of TMDs’ ductility, a material that is notorious for its brittleness,” points out Nguyen.
Designing patterns of defects could offer a means of controlling fracture behavior in TMDs, at the same time as optimizing optical and electronic properties, say the researchers.
Recyclable nanosheets as high-performance barrier material
New self-assembling and recyclable nanosheets for electronics, energy storage, and health and safety applications have been developed by researchers led by Lawrence Berkeley National Laboratory. The 2D nanosheets could significantly improve the shelf life of consumer products, as well as reducing the amount of single-use packaging and electronics being thrown away.
As reported in Nature [Vargo et al. Nature (2023) DOI: 10.1038/s41586-023-06660-x], this is the first time that a multipurpose, high-performance barrier material from self-assembling nanosheets has been successfully developed. It is hoped the nanosheets could significantly increase the rate of development of functional and sustainable nanomaterials. To develop such materials the various pieces need to combine for the nanomaterial to grow big enough for use.
Although stacking nanosheets into a product is straightforward, gaps between the nanosheets cannot be avoided. However, this nanosheet material circumvents the problem of stacking defects by missing the serial stacked sheet approach by combining blends of materials that can self-assemble into small particles with alternating layers of the component materials, suspended in a solvent.
The complex blend needed two ideal properties, that in addition to having high entropy to drive the self-assembly of a stack of nanosheets formed simultaneously, the system would be minimally affected by different surface chemistries. This means the same blend can form a protective barrier on many surfaces, including the glass screen of electronic devices.
The performance of the material as a barrier coating was tested by mapping out how each component comes together. Barrier coatings were then made by applying a dilute solution of polymers, organic small molecules, and nanoparticles to a range of substrates, with the rate of film formation being controlled.
When the solvent evaporates, the small particles coalesce and spontaneously organize coarsely templating layers, before solidifying into dense nanosheets. As the small pieces are only required to move short distances to get organized and close gaps, the problems of moving larger tiles and the inevitable gaps between them is avoided.
As principal investigator and study leader Ting Xu told Materials Today, “Self-assembly prizes precision and naturally connects precision with clean systems. Yet, real material synthesis and applications aren't. I believe our study shows […] there are room for both if we are willing to think outside of the box.”
Although the research remains at an early stage, and the blends have significantly enhanced miscibility that needs to be investigated at the molecular level, which is a challenge because of the size differences involved. The team also want to improve the material’s recyclability and add color tunability.
Self-assembly prizes precision and naturally connects precision with clean systems. Yet, real material synthesis and applications aren't. I believe our study shows  there are room for both if we are willing to think outside of the box.Ting Xu