Materials Connect

Pathological Mineralization: How Materials Science Aids Medicine

Materials scientists are seeing a growing career in the field of medicine, which endeavors to employ physical principles common to challenges in areas, for instance, in biomedical engineering with advanced technology for biomedical applications. Advances in materials science have given new designs; synthesized materials; and aid in learning chemical, biological, physical, and biomolecular compositions of biomaterials. A specific area of support is disease diagnosis and progression. Materials science methods can give insights hidden at a molecular level.

The heart works like a doorway, maintaining blood movement throughout the organ by four valves. Each valve is made up of flaps, or leaflets (called cusps), that open and close to control blood flow. When impacted by a condition or disease, valves can stop opening fully, partially open, or not open at all. This results in reduced blood flow to the heart and other parts of the body. It also weakens the heart, making it work less effectively than normal. In addition, because the heart has limited regenerative capacity, certain diseases can lead to loss of function, therefore having to surgically remove and replace the heart.

Chambers and Valves of the Heart. Source: Mayo Clinic    A Normal Heart and Heart Valve Problems. Source: Mayo Clinic

However, there are occasions where the heart develops abnormalities, linked to birth defects (congenital heart disease), age-related, or caused by another condition. Hence, the heart will develop issues regarding its functions. A diseased or damaged aortic valve can interfere with blood flow and force the heart to work harder to transmit blood to the rest of the body. For instance, an example of this is Calcific Aortic Valve Disease (CAVD). The aortic valve differentiates the lower left heart chamber (left ventricle) and the body's main artery (aorta, the body’s largest vessel).

CAVD is a degenerative process in which heart valve leaflets progressively stiffen and calcify. Additionally, it is characterized by an active remodeling process accompanied by valve pathological mineralization on soft tissue. This process causes a progressive aortic valve narrowing, and disruption in the proper valve function. Moreover, CAVD is the most common valve disease worldwide. Epidemiological studies show that 2.8% of adults over 75 years old have some CAVD degree, and as many as 25% of adults over 65 years old have at least valvular sclerosis (calcification and thickening of a trileaflet aortic valve in the absence of obstruction of ventricular outflow).

Pathological Mineralization most often results from the deposit of phosphocalcic crystals in the final form of hydroxyapatite within the extracellular matrix (ECM, involved in cellular communication and growth) deposited by the cells involved. The minerals participating in calcification have not been directly analyzed as comprehensively. Materials science methods, for instance electron microscopy, diffraction, spectroscopy (infrared and Raman), thermal analysis, and others have been recently integrated to be applied in biology for the study of hard tissues and biomaterials.

These methods offer unique insights into the structure and composition of tissues and cells at molecular level. While being able to understand the origin of these mineral deposits. These techniques can be applied across a broad range of ECM imaging applications. In addition, they can provide insight on the composition and structure of the biomineralization that occurs within these valves. Being able to understand the biocomposition involved in these types of diseases will aid in providing medical treatments, appropriate therapy, within other remedies. 

Comparison of a Normal Aortic Valve View with a Calcified Aortic Valve. Source: Mayo Clinic

However, there is a deficiency of effective pharmacological approaches for lessening and recovery for CAVD; there are no therapies to slow this disease progression. The merely possible therapy choice is open-heart or transcatheter aortic valve replacement. Heart replacement surgery consists of removing a defective or damaged valve and replacing it with a new valve made from synthetic materials or animal tissue. This surgical treatment can increase blood flow, decrease symptoms, and extend life expectancy.

Furthermore, scientists are researching the knowledge of the roots of CAVD by understanding the multiple pathways for pathological calcification in the human body. By utilizing materials science, researchers have a better comprehension of the type of compounds and molecules found within the cardiovascular tissues of the heart, eventually being able to combat different types of heart diseases, specifically CAVD. Thus, implying further findings in stopping its development worldwide.

 

1. Bertazzo, S., Gentleman, E., Cloyd, K. L., Chester, A. H., Yacoub, M. H., & Stevens, M. M. (2013). Nano-analytical electron microscopy reveals fundamental insights into human cardiovascular tissue calcification. Nature materials, 12(6), 576–583. https://doi.org/10.1038/nmat3627
2. Di Vito, A., Donato, A., Presta, I., Mancuso, T., Brunetti, F. S., Mastroroberto, P., Amorosi, A., Malara, N., & Donato, G. (2021). Extracellular Matrix in Calcific Aortic Valve Disease: Architecture, Dynamic and Perspectives. International journal of molecular sciences, 22(2), 913. https://doi.org/10.3390/ijms22020913
3. Hunt, D. (2016). How materials science is forging a new path in medicine. Silicon Republic. https://www.siliconrepublic.com/innovation/materials-science-diania-technologies
4. Kim, J. (2021). Heart regeneration after reprogramming of cardiac muscle cells. Max-Planck-Gesellschaft. https://www.mpg.de/17679417/heart-regeneration-after-reprogramming-of-cardiac-muscle-cells#:~:text=The%20human%20heart%20has%20only,lost%20their%20ability%20to%20divide.
5. Mayo Clinic Staff. (2022). Aortic valve repair and aortic valve replacement. Mayo Clinic. https://www.mayoclinic.org/tests-procedures/aortic-valve-repair-aortic-valve-replacement/about/pac-20385093
6. Mayo Clinic Staff. (2021). Heart valve disease. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/heart-valve-disease/symptoms-causes/syc-20353727
7. Prasad, Y., & Bhalodkar, N. C. (2004). Aortic sclerosis--a marker of coronary atherosclerosis. Clinical cardiology, 27(12), 671–673. https://doi.org/10.1002/clc.4960271202
8. Radisic, M., & Christman, K. L. (2013). Materials science and tissue engineering: repairing the heart. Mayo Clinic proceedings, 88(8), 884–898. https://doi.org/10.1016/j.mayocp.2013.05.003
9. Suvorova, E. I., & Buffat, P. A. (2005). Pathological mineralization of cardiac valves: causes and mechanism. Journal of long-term effects of medical implants, 15(4), 355–368. https://doi.org/10.1615/jlongtermeffmedimplants.v15.i4.30
10. Tsolaki, E., & Bertazzo, S. (2019). Pathological Mineralization: The Potential of Mineralomics. Materials (Basel, Switzerland), 12(19), 3126. https://doi.org/10.3390/ma12193126
11. University of Wisconsin-Madison. (2017). New hope for stopping an understudied heart disease in its tracks. ScienceDaily. www.sciencedaily.com/releases/2017/12/171226105132.htm
12. Virani, S. S., Alonso, A., Aparicio, H. J., Benjamin, E. J., Bittencourt, M. S., Callaway, C. W., Carson, A. P., Chamberlain, A. M., Cheng, S., Delling, F. N., Elkind, M. S. V., Evenson, K. R., Ferguson, J. F., Gupta, D. K., Khan, S. S., Kissela, B. M., Knutson, K. L., Lee, C. D., Lewis, T. T., Liu, J., … American Heart Association Council on Epidemiology and Prevention Statistics Committee and Stroke Statistics Subcommittee (2021). Heart Disease and Stroke Statistics-2021 Update: A Report From the American Heart Association. Circulation, 143(8), e254–e743. https://doi.org/10.1161/CIR.0000000000000950

The real cost of our batteries

Nowadays, it is difficult to imagine daily life without using mobile devices, such as cell phones, tablets, or laptops. While our phones are lightweight and capable of lasting throughout the day, this wasn't always the case. These advances are, to a large extent, due to the development of new battery technologies over the years.

The lithium-ion batteries and their widespread use

In mobile applications, lithium-ion batteries (LIBs) prevail due to their high energy density, high output voltage (~3.6 V), and low self-discharge rate (less than 3% per month) [1]. Thanks to these characteristics, most electric vehicles (EVs) use this type of battery. LIBs are also commonly used to support the application of renewable energies by auxiliary energy storage systems [2,3]. Thus, the role of LIBs in reducing greenhouse gas emissions cannot be denied.

The dominant battery chemistry uses lithium cobalt oxide (LCO) as cathode and graphite as anode, but it is not the only one. There are batteries on the market that also use manganese, nickel, and phosphorus, among others.

But what about their ethical implications? pollution, water crisis, and violence

However, the great success and widespread use of this technology are causing several problems around the world, both social and environmental, which represent an even greater challenge. One of them, of course, is to obtain the raw materials necessary for its manufacture, mainly lithium and cobalt, which are obtained, to a greater extent, through mining. These materials, of course, are not renewable.

Obtaining lithium can pose significant problems. For example, in Bolivia, Argentina, and Chile is located the so-called "Lithium Triangle", which contains more than 75% of the supply of this metal worldwide. For extracting lithium from its salt flats, it is necessary to drill into the ground and pump water in order to obtain a brine rich in minerals. Subsequently, this brine is left to dry in the sun; during this process, some substances are added, such as hydrochloric acid, then it is evaporated for up to 18 months to obtain lithium carbonate. This activity consumes enormous amounts of water in a region that is extremely arid on its own, exacerbating the water scarcity that the inhabitants of the area already have to face. On the other hand, leaks can happen in evaporation pools, which causes contamination of the water supply with toxic chemicals [4].

Salar de Uyuni. Image from Alexander Schimmeck, via Unsplash

In other places such as Sichuan province, China, where lithium extraction is done by mining (which is more energy inefficient), this activity has contaminated water bodies, causing the death of cattle and thousands of fish [4].

Cobalt extraction also implies ethical problems; about 60% of the world's cobalt production comes from the Democratic Republic of the Congo. The abundance of a coveted material that is quite scarce in the rest of the world leads, among other things, to a poorly regulated industry, few security measures, high rates of child labor, and an increase in violence [5].

And still, the demand grows

Despite the conflicts that can be generated by the use of these materials, it is expected that by 2050 the demand for lithium and cobalt will increase by 488% and 460% respectively, compared to 2018 [5]. This is due to the goal of decarbonization (using electrifying transportation and creating battery banks for electrical networks), among other factors.

Taking into account that the battery of a compact electric car (for example, the Tesla Model S) uses around 12 kilograms of lithium, it is easy to imagine the problem that we will face in the coming years to meet the demand for lithium and cobalt.

Present and future challenges

With this, another exceedingly important challenge becomes present: the disposal of batteries that have finished their life cycle. Lithium-ion batteries (even small ones, such as cell phone batteries) must be disposed of carefully and correctly, as when they are dumped or illegally disposed of, they can cause landfill fires that are particularly difficult to control, in addition to releasing toxic gases. Also, if a lithium-ion battery leaks, it can release heavy metals and substances such as hydrofluoric acid, which can seep into the subsoil and contaminate water bodies.

On the other hand, this disposition of the batteries does not allow us to recover their components to reuse them. That is why recycling is so important. However, current recycling methods are energy inefficient and use significant amounts of water, and also require storage, which greatly increases the risk of fire in warehouses.

Besides, these processes are economically inefficient, so there is not enough incentive for the industry to invest in infrastructure and make an effort to increase the number of recycled batteries. Currently, only 12% of LIBs in the European Union (one of the best-regulated markets) are recycled, due, among other things, the export of batteries towards Asia. Again, this problem looks set to increase in the coming years, as the first LIBs used in electric vehicles will soon reach the end of their life cycle, leaving behind a need for recycling capacity like never before [3].

What can we do?

Thus, the importance of lithium-ion batteries in our daily lives and the benefits they bring us is clear. However, we cannot ignore that its widespread use implies huge challenges that we must solve. As materials scientists, we can contribute to this by creating cathodic and anodic materials that use less polluting or problematic materials. We can also look for better ways to reuse and recycle them, as well as promote a circular economy that allows us to reduce these intense mineral demands. One exciting initiative is the US Department of Energy's ReCell Center, where academia, industry, and national laboratories collaborate to improve recycling technologies. It is desirable that similar efforts be made around the world, and that all sectors of society give this issue the importance it deserves.

1.     Wu, Y. Lithium-ion batteries : fundamentals and applications. (CRC Press, 2015).
2.     Raw materials for a truly green future. Nature Reviews Materials vol. 6 455 Preprint at https://doi.org/10.1038/s41578-021-00333-9 (2021).
3.     Mrozik, W., Rajaeifar, M. A., Heidrich, O. & Christensen, P. Environmental impacts, pollution sources and pathways of spent lithium-ion batteries. Energy and Environmental Science vol. 14 6099–6121 Preprint at https://doi.org/10.1039/d1ee00691f (2021).
4.     Katwala, A. The spiralling environmental cost of our lithium battery addiction. Wired (2018).
5.     Herrington, R. Mining our green future. Nature Reviews Materials vol. 6 456–458 Preprint at https://doi.org/10.1038/s41578-021-00325-9 (2021).

 

The Silent Revolution in Electric Vehicles: From Silicon to Silicon Carbide

By Cullen Walsh

A Tesla vehicle can now travel over 300 miles on a single charge, matching the range of many combustion engine vehicles. One of the contributing factors that has helped make this possible was a relatively quiet decision by Tesla back in 2017 to start replacing silicon with silicon carbide in many of its power electronics. How could this seemingly simple change facilitate such drastic improvements, and what else could this material achieve?

Silicon Carbide Integrated Circuit Chip Developed by NASA. Source: NASA.

What is Silicon Carbide?

Silicon carbide is a crystalline compound made of silicon and carbon. It has been known about for over a century, having applications in abrasives and heating elements. Its use in solid-state devices began back in 1907 when it became the first material to reportedly demonstrate emission via electrical pumping. As a result, many of the first LEDs were made using silicon carbide. However, in the late 20th century, III-V materials, such as gallium nitride, became the dominant materials in LEDs due to their improved luminescence. Silicon carbide is now seeing a resurgence via its use in power electronics (electronics that process high voltages and currents). This is a result of recent improvements in its fabrication and its ability to handle high voltages, such as those coming from car batteries.

The Benefits of Silicon Carbide

One reason silicon carbide is able to operate under such high voltages is its wide bandgap (around 3x that of pure silicon). This imbues it with many beneficial qualities, one of which is a high breakdown voltage. Breakdown voltage is an important attribute of diodes, such as Schottky-barrier diodes, and field-effect transistors. It determines the maximum voltage that can be applied before atoms at the interface start to ionize. Once this occurs, electrons from the ionized atoms accelerate across the interface, striking and ionizing other atoms and creating an avalanche-type effect. This leads to reverse current in the diode, preventing it from operating properly, and can even result in permanent damage to the device. As a result, the breakdown voltage contributes to the upper limit of how much AC voltage a device can handle.

Silicon Carbide vs Silicon

Typical silicon-based Schottky-barrier diodes possess low breakdown voltages, limiting their use in high power electronics. In order to raise their breakdown voltage, the n-doped region of the diode needs to be made larger. However, this leads to increased resistance, causing heat dissipation and lower efficiency. In comparison, silicon carbide-based Schottky-barrier diodes have a smaller n-doped region and therefore generate less resistance, improving their efficiency and making them more compact. The same concept applies to silicon carbide-based MOSFETs where the drift layer can be made thinner, resulting in a lower internal resistance. These advantages provide silicon carbide-based devices with breakdown voltages in the range of 600-1000 V, allowing them to interface with typical electric car batteries. It also makes them smaller and more compact as well as more efficient energy converters. 

Another benefit of silicon carbide is its ability to operate under high temperatures. This material is an excellent thermal conductor, allowing it to efficiently dissipate heat even at high powers and with closely packed circuits. Its wide bandgap also helps prevent leakage current, which is current that flows across a diode in its ‘off’ state (when under reverse voltage), allowing it to act as a switch even at elevated temperatures. 

What’s Next?

These properties have made silicon carbide the go-to material in high power electronics. Currently, most silicon carbide used in commercial electronics goes into electric vehicles. However, this material has the potential to impact numerous industries via applications in HVACs, solar energy converters, 5G telecoms, and more. It is also being explored by NASA for use in future space compatible electronics due to its ability to function at elevated temperatures, powers, and radiation levels.

It is unusual for a material to go from the lab bench to industry and displace silicon. However, as we start to reach the limit of how small silicon transistors can become and how many we can fit on a chip, the desire to look beyond silicon is only increasing. Silicon carbide may just be the tip of the iceberg, kicking off a new era where new materials outcompete silicon in novel applications.

The world of regenerative medicine

What if I told you that certain types of blindness could be treated using adult stem cell therapy for corneal repair or that wound healing could be sped up using fish skin, would you believe me? Doctors in Brazil have successfully demonstrated the use of fish skin in the wound healing process. Welcome to the exciting world of regenerative medicine

Regenerative medicine is a very interesting and emerging interdisciplinary field of research and study. It focuses on the repair, replacement, or regeneration of cells, tissues, or organs. It restores impaired function which might have resulted from congenital defects, disease, and/or trauma. It uses a combination of several/different technological approaches that goes beyond the traditional transplantation and replacement therapies. These new approaches include stem cells, soluble molecules, tissue engineering, and genetic engineering.

The main goal of regenerative medicine is not just to replace what is malfunctioning, but also to provide the needed elements for in vivo repair, design, and develop replacements that seamlessly interact with the living body and stimulate the body´s intrinsic capacities for regeneration.

Although it is a new and emerging field, regenerative medicine has produced significant therapies. Typical examples include a tissue-engineered skin substitute, Apligraf, and the adult stem cell-containing bone regenerating treatment, Osteocel. The population that needs stem cell-based therapies exceeds a hundred million patients reports Stem Cells and the Future of Regenerative Medicine. These patients include people with conditions such as cancer, diabetes, cardiovascular diseases, burns, and neurodegenerative diseases. This clearly shows the importance of this new and exciting field.

Typical example – Wound healing fibrinogen scaffolds

The main focus of tissue engineering is to find alternative ways of producing artificial tissues using cell and molecular biology together with materials and mechanical engineering to mimic the environment of native ECM, structurally and functionally, to replace damaged or diseased organs and tissues. A perfectly engineered scaffold has the same morphology, shape, and similar biochemistry as the natural scaffold that serves as an architectural sustenance for cells to attach, proliferate, and synthesize new tissue to heal a wound. The scaffold should be able to provide the appropriate environment for cells to attach and perform their task efficiently.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/smll.202101384

Although a variety of synthetic and protein-based polymer scaffolds for preparation of biomimetic scaffolds exist, such as collagen, gelatin, elastin, proteoglycan, hyaluronan, laminin, silk fibroin, soybeans, another reasonable way is to use fibrin or its soluble precursor fibrinogen since they can provide a permanent solution to damaged tissue and organs by their non-immunogenicity (autograft) and have the potential to mimic the organization of original tissue structures.

Even though fibrin-based materials exhibit outstanding qualities of native fibrin and are suitable for wound treatment, the latest focus of tissue engineering has been on the materials achieved from the fibrin precursor molecule, fibrinogen. Additionally, to produce fibrin we need thrombin, which makes the process more expensive. Fibrinogen has great potential as a material in biomedical engineering applications due to its biocompatibility and biodegradability. It offers major healing advantages by providing a suitable surface for cellular attachment and proliferation, a three-dimensional (3-D) fibrous structural support, and nanotextured surfaces, which consist of a fibrous network for cell signaling, and cell−matrix and cell−cell interactions. Moreover, its intrinsic ability to induce cellular interaction, easy degradability, non-immunogenic nature, and the promotion of increased cell migration make fibrinogen a good candidate material for the development of a tissue-engineered scaffold.

Fibrinogen can be purified into nanofibrous biomaterials either by electrospinning or by different self-assembly methods. Recently, the extrusion process has been introduced as a new method of forming fibrinogen scaffolds. This method is used to fabricate nanofibers through hydrophilic aluminum oxide nanopores from different biopolymers including fibrinogen. However, due to the low fiber density of the fibrinogen scaffold formed and the inability to prepare a large-scale 3D nanofibrous fibrinogen scaffold, this method is not ideal. Another way of producing fibers is electrospinning. It is a well-established technique that is widely used for electrostatic fiber formation. It uses electrical forces to produce polymer fibers with diameters ranging from 2 nm to several micrometers using polymer solutions. The major disadvantage of this method is the use of organic solvents which can lead to conformational changes in native protein structure and high electric field which can degrade fibrinogen and change its biological function.

Fibrinogen does not only form fibrin networks in the presence of thrombin but also exhibits self-assembly in dilute aqueous solutions in the absence of thrombin by various techniques in vitro. One method of producing fibrinogen nanofibers without thrombin in solution is by incubation of fibrinogen either in acidic pH of 2 or in an 80% ethanol solution. However, a major disadvantage of these methods is the alteration of the native structure of proteins. In addition, another method of self-assembly of fibrinogen was to decrease the ionic strength of fibrinogen and NaCl solution, which lead to aggregation of fibrinogen in the solution.

The latest approach toward assembling fibrinogen into dense three-dimensional nanofibrous scaffold resembling native ECM protein fibers was introduced by a salt-induced self-assembly technique. Fibrinogen nanofibers were obtained in the presence of a salt-containing buffer combined with a drying step under physiological conditions, without the use of high voltage, organic solvents, or enzymatic activity.

The role of material scientists in regenerative medicine

The role of material scientists in this field is very crucial. This is because they have to produce different biomaterials that will suit different situations. A biomaterial is defined as a substance that has been engineered to interact with biological systems for a medical purpose, either a therapeutic or a diagnostic one. Biomaterials are important components in tissue engineering and regenerative medicine applications,  which has the intended purpose of reducing the burden of disease and enhancing the quality of life of a large number of patients. The successful application of many regenerative medicine strategies, such as cell-based therapies, artificial organs, and engineered living tissues, is highly dependent on the ability to design or produce suitable biomaterials that can support and guide cells during tissue healing and remodeling processes. These biomaterials, which include polymers, ceramics, and nano-biomaterials are normally produced by material scientists.  The different types of biomaterials are illustrated in the diagram below. These materials are categorized into synthetic and biological biomaterials.

https://www.researchgate.net/figure/Classification-of-biomaterials_fig1_335144989

These designed biomaterials must also meet the biocompatibility test. It is therefore imperative that material scientists develop materials that can satisfy the different requirements. As illustrated in the figure below, it is important that these biomaterials satisfy all the criteria.

D.F. Williams: Definitions in Biomaterials. Proceedings of a Consensus Conference of the European Society for Biomaterials, Chester, England March 3-5, 1986, Vol. 4, Elsevier, New York

Challenges

Despite the immense benefits to be derived from this field, there seems to be a lack of interest from developing countries. These low- and middle-income countries have made very little effort to systematically understand how this new field can improve the quality of life. This is because they seem to have other priorities  Although, chronic illness or disease i.e. which are primary targets, of regenerative medicine affect people in poor countries more than rich ones, the rich countries spend more on such research. This is not to suggest that this new field presents easy solutions to the complex healthcare problems facing developing countries, but it is a plea to researchers and policymakers to consider this new technological advancement

Combating CO2 Emissions: Iron and Steel Industry Going Green

Iron and steel have always been at the center of world technological advancement. The products of iron and steel are interwoven into human history and lifestyles. The production processes of these materials are usually massive, ubiquitous, and operate around the clock. The products of iron and steel range from the cutlery on our dining tables to knives in our kitchens, to some bed frames in the bedrooms, lamp-holders all around the house, door hinges, railings, and even our vehicles. This unending list extends to innumerable pieces of machinery and equipment in different industries around the globe. The iron and steel-making industry, as one of the top contributors to global greenhouse gas (GHG), emits about 8% of global CO₂ (carbon dioxide)⁽¹⁾.

 

Photo by Markus Distelrath on Pexels (For illustration purposes only)

CO₂ is mainly produced as a by-product when carbon is used to extract metallic iron from its ores. Iron ores usually exist as oxides. Since carbon is easily accessible and readily reacts with oxygen, it is used as a reducing agent to separate (metallic) iron from its oxides. Not only that, a network of CO₂-emitting facilities is used at the mining field down to the factory. Considering the quantity of greenhouse gas that may be emitted during the mining operations⁽²⁾ and production stages, the iron and steel industry could be one of the key players in combatting global warming. 

In order to tackle these huge challenges of CO₂ emissions, the iron and steel industry is setting up various regulatory procedures and supports for helpful research. Avenues employed to combat CO₂ emissions involve reducing the quantity of carbon used during production, capturing the CO₂ emitted during production, substituting carbon with more environmentally friendly chemicals, or completely avoiding carbon use during most of the production processes. 

In the decarbonization of production processes, the most common strategy is the adoption of low-emission programs. The low-emission programs encourage the use of low-emission equipment. An example is the industrial shift from blast furnaces to electric furnaces. The traditional blast furnace is coal-fired, with high CO₂ emission. It is encouraging to know that giants in steel production, such as ArcelorMittal and Baowu Steel Group top the Green Steel Tracker⁽¹⁾ program list - declaring their commitments to the global net-zero goals⁽³⁾⁽⁴⁾.

Carbon capture, utilization, and storage (CCUS)⁽⁵⁾ is another program for decarbonizing production processes. This program basically targets the recovery of CO₂ from gaseous waste. Hence, it is also called the carbon-negative initiative. It extends to the direct/indirect use (or storage) of generated CO₂. Various strategies are employed to convert CO₂ to valuable materials⁽⁶⁾ like polymers, fertilizers, proteins, and foams. CO₂ can be stored safely underground⁽⁷⁾ for many years – in rock reservoirs under the sea, empty oil fields, or empty gas fields. In fact, researchers claim that stored CO₂ can transform into solid minerals (carbonates) if it comes in contact with certain rocks rich in very reactive metallic elements such as calcium, iron, and magnesium.

Interestingly, one cutting-edge method of combatting CO₂ emission in iron and steel production is Molten Oxide Electrolysis, a net-zero steel production technique. It is a result of research works⁽⁸⁾ that began in the early 1980s by Professors Donald Sadoway and Antoine Allanore at the Massachusetts Institute of Technology (MIT)⁽⁸⁾. This concept prevents the production of CO₂. It involves the utilization of electrolysis in the iron and steel-making process with O₂ as the by-product. This technique is being championed by a company called Boston Metal⁽⁹⁾, situated in Massachusetts, USA. Already there is news about BMW and  BHP Ventures partnering with Boston Metal.

Through multiple avenues of combatting CO₂ such as decarbonization of production processes, carbon capture, utilization, and storage, the iron and steel industry is working determinedly, championing the global net-zero emission plans. Many are joining this drive daily; if we keep it going, we will be a few years less in actualizing the net-zero goals. Then, our beautiful Earth would have less CO₂ to struggle with!

The benefits of having a third party: ternary organic solar cells

Organic photovoltaics

Global energy demand is one of the great concerns of today. The amount of usable solar energy is huge. In fact, it is the largest of all alternatives and power sources, which is why it attracts so much interest in many fields of research. Photovoltaics is a discipline that provides access to renewable and clean electrical energy through devices that can be installed and adapted according to consumption needs. However, the photocells that prevail in the market are limited in investment and manufacturing. Organic solar cells exhibit several advantages over conventional solid-state technologies, such as light weight, flexibility, semi-transparency, large area coverage and low cost/waste of materials. The development of interfaces that fulfill the role of photogeneration and charge transport in an organic solar cell implies the constant search for new strategies that allow improvement in the system architecture and in its net performance for the conversion of solar energy into electricity. The nature of the materials used in the photoactive film of the device in question lies in their electron donating and accepting properties and in their ability to transport charge carriers resulting from hole-electron pair dissociation.

 

Ternary organic solar cell structure. Source: Ossila

 

Bulk heterojunctions 

Bulk heterojunctions (BHJs) have represented, for some years, the most successful option in terms of overall photovoltaic performance of the photocell. A BHJ has a structure such that the mixture of materials with donation and electronic acceptance characteristics facilitates and increases the effective interactions between both and at the same time decreases the interface that distinguishes them at the nanometric/mesoscopic scale. It is important to highlight that in organic and polymeric compounds the phenomena that occur along the interface govern the excitonic separation and the subsequent transport by the corresponding surface. The tendency and the custom has been, then, the elaboration of donor/acceptor binary mixtures.

 

The role of the third party in the device 

The incorporation of a third material in the heterojunction can represent, in principle, a drastic change in the configuration of the device itself, as well as the arrangement of interface sections, substrates and contacts. Some of the benefits of introducing this new component to the usual donor/acceptor combination are the increase in stability with respect to its binary counterparts via morphological ordering, the extension of the optical absorption characteristics due to the modification of the energy levels of the semiconductors involved and the capture of light in broader regions of the solar spectrum (which stimulates photogeneration and the consequent obtaining of a higher short-circuit current density, Jsc), a superior character for charge transport dissociated, the effective breaking of the hole-electron bound pair and, of course, the improvement in efficiency.

What happens when having two electron acceptors and a donor moiety (D-A-A) or two electron donors and an acceptor (D-D-A) in the heterojunction is to facilitate the interactions characteristic of charge transfer between both subunits of the optically active film, such as donor/acceptor coupling through from the improvement in the distribution of the crystalline structure, a greater coverage as far as the absorption of electromagnetic radiation is concerned, the better solubility of the mixture with the solvent used to prepare the photoactive layer and the miscibility between the components.

Interestingly, ternary organic solar cells have a history that already exceeds a decade in the research field (actually, since 2009), but the specific application of the techniques and principles linked to this configuration is relatively recent. The reason for this time lag is mainly due to the transition from fullerene-type acceptors to small molecules and non-fullerene acceptors (NFAs). The main limitation of fullerenes is the absorption of light, which in turn affects the photocurrent and the use of the incident power. Since the advent of NFAs, the possible options for ternary organic solar cells have diversified remarkably. The opportunities for synthesis and combination are enormous today.

 

Let's talk about efficiency

In an ideal case, the enhancement in power conversion efficiency (PCE) is estimated to be 35% for a device that has a wide range of light absorption ranging from 200 nm to 400 nm in wavelength (where, in most cases, deficiencies are shown despite the large flux of photons that can be exploited), that is, the insertion of a third component with absorptive sensitivity in that range could increase the PCE of the photocell to beyond of 25% (considering that the current record is close to 19% for mixtures of two components). This estimation reveals the importance of the compatibility between the spectra of the participating molecules in order to maximize the assimilation of radiation and the great benefit that the third donor or acceptor subunit brings.

 

How to choose the third component?

The choice of the third component of the solar photocell is not such a simple matter, much less trivial. It depends, in the first place, on the very identity of the molecule to be used. That is, if it is a primarily electron-donating semiconductor or if, on the contrary, an electron acceptor character dominates in it. In addition, the third component must have good light absorption regardless of whether it is a donor or an acceptor, since the reason for its use lies precisely in the expansion of the capacity to capture the available radiation. Another point to consider is the nature of this third component in the processing of the mixture, since it can be another organic semiconductor, an inorganic fragment, a polymer, a dye, a quantum dot (particles with semiconducting properties) and so on. This implies that the morphological and electronic complement with the two original systems must be carried out in a suitable way.

In summary, the central objective of ternary organic solar cells is to take advantage of the absorption, transport, thermal stability, solubility and versatility properties of a new material to overcome or mitigate the deficiencies exhibited by the original semiconductors without sacrificing mobility or aspects related to the D-A behavior of the interpenetrating regions of the heterojunction. Future views indicate that the trend in the use of this alternative to cause “energy cascades” that accelerate the injection and transport of charge as well as to expand the characteristics of optical absorption will continue in the coming years. And why not think of a fourth?

If you want to characterize small molecules, sometimes you need duck sauce

Single crystal X-ray diffraction (XRD) is the basis for the field of crystallography, a technique that has been so helpful in characterizing molecules, large and small, from DNA and proteins to pharmaceuticals. These methods rely on ‘single’ crystals of a large enough size to study in an X-ray beam, typically 100 μm on all sides. Large molecules in crystals produce data with thousands of diffraction spots, enough spots that you can resolve the structure with a little hard work. However, crystal growing is a dark art, and sometimes nature puts a variety of impediments in the way of growing nice, large crystals for XRD. These impediments give experimental scientists a major headache, and sometimes causing years of delay between the discovery of a new material or molecule and its eventual structural characterization.

One solution to this problem is Serial Femtosecond Crystallography (SFX), a technique that involves firing a jet of smaller crystals, suspended in a liquid, into the path of an X-ray free-electron laser (XFEL), an extremely bright coherent X-ray source generated from free electrons produced by a particle accelerator. This method packs incredible brightness into an extremely short (40 fs) pulse. Since the time of exposure of any one crystal is so short, it is a good choice for any crystal that is too small or too sensitive to ionizing radiation to study by traditional methods.

The SFX technique was first developed to solve crystal structures of big molecules: proteins. Hitting these crystals with the XFEL beam produces rich datasets with thousands of spots,  or as Nate Hohman from the University of Connecticut put it, “You have spots for days”. But what Nate is interested in is metal-organic chalcogenolates (MOChas), hybrid semiconductors that self-assemble into small crystals that are just a few microns across. The crystals are too small for traditional characterization; single crystals that are large enough to be characterized using standard X-ray diffraction techniques can be difficult to produce and create a lot of chemical waste, each example consuming many long months of effort. What Nate wants is a method to solve structures from an easysynthesis method that produces small molecules.

Nate’s graduate student, Elyse Schriber, suggested using SFX to characterize their tiny MOCha crystals, however, there was a major conundrum: any single hit of a crystal might only produce about twelve diffraction spots, too few to use existing methods to interpret the data.

 

Schematic of the Serial Femtosecond X-ray crystallography set-up, taken from the original publication*
a) Tiny crystals in solution are passed through the collimated X-ray beam (XFEL). b) When an X-ray strikes a crystal it diffracts. c) The diffraction pattern hits the detector and diffraction spots are seen in different locations depending on the orientation of the crystal.

 

When beamtime allocation for Nate and Elyse to use XFEL SFX came up at the Linac Coherent Light Source in California, they had another problem: the crystals wouldn’t stay in solution. Pressed for time and needing a quick solution, Nate had a nifty trick up his sleeve. Dish detergent helps stabilize the chalcogenolates in solution. “Go for the one with the duck on it”, he told his team. With their small molecules now in the duck sauce solution, they could start collecting data.

 

Data analysis (big time!)

Although SFX requires careful calibration and sensitive equipment, it sounds like this might have been the easy part of the experiment. The data still need to be analyzed; there are only a few diffraction spots for each small molecule, and the random orientation of each molecule as it passes through the beam isn’t known. They also have a huge volume of data to wade through.

Aaron Brewster, research scientist at the Lawrence Berkeley National Laboratory, came up with an algorithm based on graph theory to determine the orientation of each crystal and then aggregate this information to compile diffraction patterns from crystals. Further data analysis can reveal the crystal structure of these small molecules (sm) so the technique as a whole is given the acronym smSFX.

Aaron developed his novel algorithm way back in 2015, but it stayed largely on the shelf until Nate’s team came along with the perfect problem: samples where there are enough crystals of the right size, a size too small for usual crystallographic methods.

Right now SFX is only available at five facilities in the world. Factor in Aaron’s novel algorithm and it seems that this new technique isn’t very accessible. Nate wants to change that too. With further work he wants to turn smSFX into a mail-in service. One reason that the technique generates large volumes of data, of the order of terabytes, is that for every shot of the x-ray beam only about 10% of the jets of liquid would contain a crystal (even after the concentration of the duck sauce has been fine-tuned) and of that 10%, only 8-10% of these successful shots could capture enough information to be useful to the algorithm. Since just 1% of the data that are collected contain truly useful information, this means you have to collect data for longer. Some SFX facilities deliver 120 shots per second while others deliver 3600 shots per second. Since the small molecules are easy to make, Nate knows that it’s straightforward to “squirt more duck sauce through there” and use a high rate of shots to minimize instrument time.

The terabytes of data were analyzed on a supercomputer, and it took a few years to perfect the algorithm using this set of samples that were the perfect problem for Aaron to solve. Now that the technique has been developed and proven to work, it can be made more accessible, and now structural solutions can be solved in real time during the experiments.

 

Materials synthesis and some cool photo-physical properties

The chalcogenolates self-assemble to create 2D materials, in this case inorganic polymers that are supported by organic ligands. They also don’t exhibit nano-scale size effects: their properties are the same as for the 3D material. Self-assembly is a much more straight forward way of creating 2D materials than techniques, such as exfoliation, which are used to create graphene. This could be a more cost effective way of creating materials that don’t exhibit nanoscale effects. The high exciton binding energy of these chalcogenolates means that these materials have applications for semiconductors, photovoltaic cells that might be more efficient that silicon-based ones, and for photo-catalysis. They may even have applications in quantum computing.

 

Scanning electron micrographs of the crystals, taken from the original publication*.
Scale bars are 5 μm. Left: Thiorene. Center: Mithrene. Right: Tethrene.

 

Nate’s long-term interest has been to create these layered materials with organic spacers. With the  calcogenolates there are three components that can be varied: the metal atom; the organic molecule, or; the chalcogen atom (group 16 in the periodic table – Nate mainly works with sulphur, selenium and tellurium).

Nate very quickly hit on a silver-benzene-selenolate compound known as mithrene (AgSePh) with unusual properties: it glows blue which indicates a high energy photo-physical state. In contrast, swapping in sulfur (thiorene AgSPh) led to a compound without any photo-physical properties while using tellurium (tethrene: AgTePh) led to the emission of light at broader wavelengths when compared to mithrene.

 

Suspended microcrystals, taken from the original publication*
a) Thiorene, b) mithrene, c) Thethrene

 

The reasons for these differences were unknown until now and there wasn’t any agreement of the structure of thiorene. The new analytical technique, smSFX (recently published in Nature), showed that the 2D nature of the bonds in mithrene is broken in thiorene i.e. the silver atoms in thiorene form 1D chains while in mithrene they form 2D chains.

 

Side and top views of crystal structures from smSFX, taken from the original publication*
d) Thiorene, e) Mithrene, f) Tethrene.
Thermal ellipsoids for Ag (blue), S (yellow), Se (orange) and Te (magenta) are drawn at the 50% probability level.
Hydrogen atoms and one position of disordered C₆H₅ (for mithrene) are omitted for clarity.
g-i are models of thiorene (g), mithrene (h) and tethrene (i) with the view oriented down the c axis of the unit cell.

 

Final thought

This breakthrough in understanding the photo-physical properties of chalcogenolates came about through the passion and hard work of many people. Although Nate has been working on small molecules for years, and Aaron developed a novel algorithm, they may not have come together if it weren’t for the inspiration of Elyse who was working on her PhD and had an idea that led to a leap forward in materials science.

 

* All images from Elyse, Nate and Aaron's (and the rest of the team) recent article: "Chemical crystallography by serial femtosecond X-ray diffraction", Nature 601, pp 360-365 (2022). Published under a creative commons licence CC BY 4.0.

MRS Blogger Sebastián Suárez Schmidt

Hi all,

    I am Sebastián Suárez Schmidt, a Material Scientist and writer for the MRS Bulletin. My scientific research is stationed at the University of Puerto Rico – Río Piedras, where I have recently specialized in the development of metal phthalocyanine nanostructures for gas sensing and monitoring applications at trace amounts. Aside from my research, I also enjoy the dissemination of written content within the general public or the scientific community and aspire to eventually dedicate my career to writing.

    This year, our team of writers will bring you closer to the presenters as well as encourage discussions by summarizing the overall experience in each event that we attend. From my part, I am specially excited to cover the varied presentations focusing on their social impacts, characterization techniques and energy efficiency. During this virtual portion of the Hybrid MRS Spring Meeting & Exhibit, we can also look forward to diverse networking opportunities with colleagues from all over the world. So feel free to reach out or message other researchers when the opportunity presents itself.

    We encourage the attendants to find topics that pique their interest from the broad array of symposium sessions in our virtual catalog. Or for a more open discussion, share your thoughts using the #S22MRS over on Twitter. I hope to connect with as many presenters as possible and that everyone enjoys this year’s 2022 Hybrid MRS Spring Meeting & Exhibit.

Kind regards.

10-minute writing: Reaching into our “poetic” selves

The purpose of this exercise is to heighten our science writing as we develop our individual voices.

In her book The Alchemy of Us, materials scientist Ainissa Ramirez writes a chapter called “Connect” (p. 27). She opens the chapter with a story about US President Abraham Lincoln’s funeral procession in the 1860s, where a train carries his coffin across a number of states so people may “attend” his funeral before his body is laid to rest in Illinois. She relates this story to materials science through the materials that make up the tracks (iron, steel, metal alloys). She also makes an analogy between Lincoln and the train tracks as “connectors of the country.”

She could have used the word “connect” over and over again, which would have been mediocre writing. Instead, she uses verbs like bridge and link, and ones that carry metaphorical meanings: threaded, stitched, and circulatory system of the nation. The opposite term she uses is splintered, a powerful term that snaps – we can hear it.

Professor and songwriter Pat Pattison from Berklee College of Music in Boston presents a 5-minute video about verbs: Electrify your writing with verbs. He refers to verbs in terms of “wattage.” The average writer, he says, relies on a string of adjectives and verbs with a low wattage. The great writer, however, leverages powerful action verbs (200 Watts).

One way to reach these powerful verbs is to use a thesaurus.

However, to actually dig into ourselves and strengthen our own writing by developing our own voice, we have to do much more. One way is to practice object writing. Here is a 3.5-minute pivotal video on that topic by Pat Pattison.

In his book Writing Better Lyrics, Pattison implements object writing as a 10-minute writing exercise (p. 3). The way this works is you take an object, then without lifting your pen from paper (or fingers from keyboard), you write non-stop for 10 minutes on how the object looks (see), sounds (hear), tastes, smells, feels (touch), how your body reacts to it (organic – heartbeat, pulse, muscle tension, stomachache, cramp, breathing, etc.), and how your body moves in response to it (kinesthetic – sense of motion, dizzy, balance, embrace, shrink in fear, etc.). When free-writing, you won’t write in full sentences but you’ll put down words as quickly as they come.

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My 10-minute writing sample (11:50-Noon) -

Kate spade, spade symbol, deck of cards, mom is the queen of spades, queen of hearts, queen of cards, she wins our game while she’s half asleep in the hospital, Mom, Mom, It’s your turn. She wakes up and makes her play then sleeps during mine. Mom, Mom, it’s your turn, she plays & wins the game and I’m flabbergasted. Mom - what this does to my ego, I lose while you’re recovering and I’m fine. Wow. Queen of 500-Rum. Teaches us all to play Bridge as kids, I have no patience, bidding, bidding, bidding, I tense up, how high to bid, someone could out-bid me, or I can’t meet my bid, I set aside Bridge and play Pinochle instead, more my style, I relax, bid once, take it or leave it, no more decisions. Decision out of choice of 3 is great; out of multitudes of choices due to internet, how ppl do it? Tensing at the endless possibilities need to make a decision, go back to the eye glass case, skyblue cover, biking along the GAP trail, riding a horse through Cook Forest, skyblue with clouds writing across the sky: kate spade, New York - and dark green grass below, dark green grass on bottom of eye glass case, wow, sky blue top and deep dirty green, muddy, horse slips downhill at cook forest, no worries horse has 3 more legs, the green smells of weeds composting, not cool but not bad, bad, not like pollution from steel mills of Pittsburgh – when Mom was growing up, when I grew up, pollution level makes me nauseous on the way to school. Sometimes so bad, what did it smell like? Not dirt, that’s organic like composting weeds, but a smell worse than bus fumes. I want to head home – or back to the eye glass case – the green turns me off, muggy, humid, a green I wouldn’t use in a daily painting, I like the sky blue top of the case, shines from the sun coming through the window, kitchen-counter smooth case, brings me calmness like a weekend riding horses in Cook Forest, no worries back home, no covid, no delta variant. Mom, queen of hearts, her sweater smells like her perfume, what we wear when we need our Mom-hug, grandma-hug.

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How the exercise improves our writing is to do this every day, first thing in the morning, and stick to the 10-minute limit. If we go beyond 10 minutes, the next day we’ll say we have no time. The 10-minute writing will not yield a piece of writing we want to use. Its purpose, through daily practice, is to help us more quickly access those words and metaphors that are uniquely us when we do our regular writing.

My suggestion:

Set aside one week to do the 10-minute writing at the same time each day. After 7 days, assess how it’s working. The first day I pretty much guarantee will be difficult. By the 7^th day, I pretty much guarantee you’ll note a difference in how much more quickly your mind takes you somewhere you didn’t expect!  

-Judy Meiksin

Explaining Sensors

A sensor can be broadly defined as a device that receives a stimulus and emits a signal.¹ For example, a fire alarm is an acoustic sensor that emits a loud noise to alert bystanders that there is a fire nearby. This changed the state of silence to a state of a loud noise. A chemical sensor based on changes of acidity, like a litmus paper, uses the chemical changes in the paper to emit an optical signal; changing the color from red to blue as the acidity decreases or maintaining the original color of the litmus paper if the substance is of neutral acidity (like pure water). And an electrical sensor works by changing the electric current of a circuit (by a specific amount) when in the presence of a particular substance. This can further be imagined by a circuit connected to a multimeter that is set to measure current from a source while adding different resistances and observing the change in current (Figure 1).

Most of today’s research depends considerably on electric sensors. Generally, “there are two types of electric sensors; direct and complex. A direct sensor converts a stimulus into an electrical signal or modifies an electrical signal by using an appropriate physical effect. On the other hand, a complex sensor also needs one or more transducers of energy (to change from one form of energy to another) before a direct sensor can measure the electrical output.”¹ By understanding how sensors can be organized, it’s possible to enhance their measurements and maximize their use within the system; thus, allowing us dive deeper and farther into the unknown.

Figure 1: Diagram of an electrical circuit that depicts a change in current when a substance is added to a substrate.

 

The hands, nose, mouth, ears and eyes are the sensors which our bodies use to understand our surroundings. And with the aid of modern sensors, we can enhance our ability to detect changes that  would otherwise elude us, such as slight variations in hardness of metals or miniscule alterations in atomic structures that can greatly impact experimental procedures and lead to discoveries that pave the future. But it is important to note that this field has its obstacles to overcome, such as increasing the precision, maintaining functionality in extreme conditions and reducing single-use materials. Therefore, material researchers have the responsibility to not only meet the demands of society’s needs, but also be conscious of the repercussions their developments can have on the environment in the short- and long-term future.

Reference: 

Fraden, J. Chapter 1 - 2. In Handbook of modern sensors physics, designs, and applications; Springer New York: New York, NY, 2010; pp. 1–25.