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Which Metals can be 3D Printed?

Which Metals can be 3D Printed?

When three-dimensional (3D) components need to be printed, it is important to ensure the most appropriate materials are being used for the application. Several metals can go through the 3D printing process, and each metal provides a range of properties that might make them more suitable than others. In this blog post, we will highlight what metals can be 3D printed and what properties each metal possesses.

Which Metals can be 3D Printed?

Metals must be used in metal powder form to manufacture components via 3D printing. The metals that are available in powder form and are suitable for 3D printing include aluminum, cobalt chrome, pure copper, nickel alloys, stainless steel, titanium alloys, tungsten and also precious metals such as gold and silver.
The mechanical properties of some of the metals mentioned will be listed below. As you will see, there are many similar properties between them but others that make them a more suitable metal in specific applications, such as aluminum being lightweight or steel having high ductility.
  • Titanium alloys: Low weight combined with high strength, excellent corrosion resistance, and high fatigue resistance compared to other lightweight alloys
  • Nickel: good tensile, fatigue, creep and rupture strength
  • Pure copper: excellent thermal conductance
If a metal is available in the appropriate powder form, it can be used for 3D printing. However, it is worth noting that if a metal is more likely to burn at a high temperature, instead of melting, it will need to be processed via extrusion through a 3D printing nozzle.

3D Metal Printing with JEOL

JEOL is making headway in the 3D printing industry with our unique additive manufacturing technology. JEOL has designed and manufactured an electron beam metal additive manufacturing machine called the JAM-5200EBM. This machine will enhance the 3D printing metal process with higher speeds than other available laser beam options and a range of other features.

JAM-5200EBM

The JAM-5200EBM has been developed by JEOL’s team, who have over 50 years of experience designing and manufacturing automated electron beam control technology. See our blog and video “Why JEOL developed a new 3D Printer”. With innovation at the front of our designs, the new JAM-5200EBM metal printer allows for lighter parts to be manufactured cleanly and efficiently.

Key features

The key features of the JAM-5200EBM e-beam metal additive manufacturing system include being environmentally friendly, as it is helium-free and eliminates any smoke produced during manufacturing. Additional features include the following:

Automatic electron beam correction

If the focus and spot shape of the electron beam are inaccurate, the system will automatically correct them based on the irradiation position. JEOL’s experience in electron beam lithography systems for semiconductor manufacturing played a key role in developing this technology in-house which allows parts to be produced with higher quality and reproducibility.

Long-life cathode

The cathode in the e-beam system can operate for over 1,500 hours, which significantly reduces the need for downtime and allows processes to run smoothly. Because of the helium-free environment of the system, the surface of the cathode is protected from damage and thus improves the already high performance of the electron beam. These features help to reduce manufacturing costs whilst increasing product quality.
Contact us today for more information on our products or 3D printing and we’ll be happy to schedule a call or virtual demonstration.

EMD-13906

How Cryo-EM is Revolutionizing Structural Biology

Removing the need for cumbersome and often near-impossible crystallization attempts for imaging biological samples has had such a dramatic impact on structural biology that the 2017 Nobel Prize was awarded to Jacques Dubochet, Joachim Frank, and Richard Henderson for their development of cryo-electron microscopy (cryo-EM).1

Standard transmission electron microscopy (TEM) methods often rely on the staining or dehydration of biological samples to image them.2 While one advantage is that proteins do not need to be crystallized for structural analysis, sample preparation techniques can distort the biological structure from what it would be in its natural environment. Furthermore, staining techniques limit the resolution achievable by these methods.

Cryo-EM involves flash-freezing a sample to cryogenic temperatures. While the freezing process in cryo-EM means that a biological molecule, or “particle”, is trapped in a single configuration, the ability to image thousands of individual particles allows compiling these single “snapshots” into a single high-resolution 3D structure, or multiple structures if a biological sample is dynamic.
The huge drive for understanding structure and dynamics of biomolecules comes from the relationship between structure and function. Many proteins have sites with specific geometric constraints for the selective binding of ligands. Understanding the structural configuration of those sites and how they adapt dynamically to the binding of ligands can help refine drug design leading to the development of potent therapeutics.

New Structures

The impact of cryo-EM has been so profound that it is predicted to surpass X-ray crystallography as the predominant structural biology method by 2024.3 There have already been 10,000 new structures solved by cryo-EM, making it possible to look at new classes of proteins, such as membrane proteins, that were previously impossible.

The resolution achievable with electron microscopy has also helped propel cryo-EM on its runaway success leading to what many have coined a “resolution-revolution”. Structures currently are routinely solved at atomic resolution, mirroring the resolution possible by X-ray crystallography.4

Finally, what has made cryo-EM so important in structural biology is that it can resolve multiple conformational states in dynamic biomolecules. Proteins for example often undergo interconversion between several different conformations or have significant structural changes when interacting with ligands. As modern cryo-EM automated data collection software can help capture thousands of images containing millions of particles, data processing programs can distinguish between different conformation states leading to multiple structures and insights into a range of possible conformers. In this way, cryo-EM can be used for both structural and dynamical analysis of biomolecules.

JEOL cryo-EM instruments

At the heart of a successful cryo-EM experiment is the electron microscope itself. JEOL has extensive expertise in the design of electron microscopy for biological imaging applications.
Contact JEOL today to find out how their cryo-EM and electron microscopy instruments could help provide unparalleled structural information on your biological samples.
EMDB entry: EMD-13906
Resolution: 2.9 Å
Sample name: Cryo-EM structure of Tn4430 TnpA transposase from Tn3 family in complex with 100 bp long transposon end DNA
Data collected on JEOL cryoARM300
Reference: Shkumatov, A.V., Aryanpour, N., Oger, C.A. et al. Structural insight into Tn3 family transposition mechanism. Nat Commun 13, 6155 (2022). https://doi.org/10.1038/s41467-022-33871-z

References

  1. 1. Shen, P. S. (2018). The 2017 Nobel Prize in Chemistry: cryo-EM comes of age. Analytical and Bioanalytical Chemistry, 410(8), 2053–2057. https://doi.org/10.1007/s00216-018-0899-8
  2. 2. Ayache, J., Beaunier, L., Boumendil, J., Ehret, G., & Laub, D. (2010). Sample preparation handbook for transmission electron microscopy: techniques (Vol. 2). Springer Science & Business Media. 
  3. 3. Callaway, E. (2020). Revolutionary cryo-EM is taking over structural biology. Nature, 578(7794), 201. https://doi.org/10.1038/d41586-020-00341-9
  4. 4. Nwanochie, E., & Uversky, V. N. (2019). Structure Determination by Single-Particle Cryo-Electron Microscopy : Only the Sky ( and Intrinsic Disorder ) is the Limit. International Journal of Molecular Sciences, 20, 4186. https://doi.org/doi:10.3390/ijms20174186

FWS Mobile lab

New Mobile Forensic Lab Features DART Mass Spectrometer

JEOL mass spectrometers are widely used by forensic investigators – in science centers, government agencies, and now, a mobile crime lab. On November 3rd, the U.S. Fish and Wildlife Forensics Lab revealed “The Woodshed” a mobile forensic laboratory built to identify illegal timber milled from endangered species of trees around the world and brought into the US at ports of entry.
The US is one of 150 countries who have signed the United Nation’s CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), an international treaty governing the illegal trade in products (including timber) from endangered species. In support of this mission, this forensic lab will combat the illegal timber market by identifying and comparing physical evidence to link suspect, victim, and crime scene.

A Backlog of Forensic Evidence

Smugglers try to sneak CITES-protected wood past customs officials by labeling it as non-protected. Customs agents rely on this documentation, only sending samples to be examined if there’s probable cause. Illegal wood can enter the consumer marketplace in a variety of forms – for example, incense made from agarwood, one of the most expensive natural raw materials in the world, or musical instruments made from endangered Brazilian rosewood.
Because of the volume of smuggled goods, backlogs of cargo containers await inspection at ports of entry until the wood can be inspected for illegally traded timber. The “Woodshed” addresses this backlog by taking the laboratory directly to the ports, eliminating delays associated with collecting and shipping samples from the port to a central laboratory.
The search and collection of rare species of wood for these goods affects whole ecosystems and the living creatures that depend on them, leading to forest degradation. Consumers can unknowingly become part of these schemes – like in 2015 when Lumber Liquidators agreed to pay $13 million for illegally sourcing their hardwood from Russia. Forensic labs like the US Fish and Wildlife Mobile Lab help identify these bad actors, ultimately protecting endangered species of timber.

Direct Analysis in Real Time with JEOL DART

Scientists in the U.S. Fish and Wildlife Forensics Lab rely on forensic methods like morphology, DNA analysis, and chemical analysis to verify what species the sample is from and determine its origin. DNA analysis is highly specific, but it is expensive and takes time. Furthermore, DNA data is not available for all of the CITES-protected species. Identification by morphology is rapid and inexpensive but requires skilled wood anatomists to distinguish between some key species.

The AccuTOFTM DART® is an essential tool in this effort because of its near-instantaneous analysis and high specificity. JEOL’s DART relies on ambient ionization, a technology that enables real-time open-air analysis, to analyze samples with little or no preparation. The unique chemical composition of each wood species can be identified by passing the sample between the DART ion source and the AccuTOF mass spectrometer inlet. Scientists can identify the species of wood by searching the ForeST (Forensic Spectra of Trees) database compiled and distributed by the US Fish and Wildlife Lab.

Because it will analyze virtually anything put in front of its ion source, the AccuTOF™-DART is a fast and efficient way to achieve comprehensive chemical analysis and identify evidence. The AccuTOF-DART has gained widespread use at leading forensics labs.

To learn more about the mobile forensic lab, visit the U.S. National Fish and Wildlife website or our press release on its launch. To learn more about the instrument, visit the product page.

Additive Manufacturing 3D Metal Printing

What is 3D Metal Printing and How Does it Work?

3D metal printing is a term that is used to cover several processes in which metal objects are produced by technology. Simply put, a highly focused beam of energy is used to scan and melt metal powder particles, which bonds them together to manufacture a component layer by layer. Although machine manufacturing is still the preferred method for producing metal components, a more specialist approach is often required, which brings us to 3D metal printing. This post will aim to cover the basics of what 3D metal printing is and how it works.

What is 3D Metal Printing?

The term 3D metal printing covers several technologies used for printing metal. The standard process involves melting or sintering metal powders, although some powders can be combined with additional material. Typical metals and metal alloys used in powder form are aluminum, copper, nickel, steel, stainless steel, titanium, tungsten, and precious metals such as gold, palladium, platinum, and silver.
There are a few main metal printing types, such as selective laser melting (SLM), direct metal laser sintering (DMLS), electron beam melting (EBM), and some additional methods. However, some of the others have limited applications. Therefore, we won’t cover them in this article.

Selective Laser Melting (SLM)

One of the primary metal printing methods involves melting the material with a laser in an inert gas environment. The process is repeated layer by layer to create similar components and is often used for manufacturing parts in the aerospace, automotive and medical industries.

Direct Metal Laser Sintering (DMLS)

As the name suggests, this method sinters metal powder with a laser and forms an object layer by layer. DMLS is typically used for prototyping and producing finished components such as medical devices.

Electron Beam Melting (EBM)

EBM is a similar process to SLM, with the critical difference being that an electron beam is used instead of a laser. EBM is frequently used to produce components from nickel and titanium alloys, is suitable for the aerospace industry.

JEOL: 3D Printing

JEOL is making advancements in the world of 3D printing with our unique additive manufacturing technology and our electron beam metal AM machine. Our technology enhances additive manufacturing so lighter manufactured components can be produced more cleanly and efficiently for use in the aerospace, medical, and energy industries.
The JEOL electron beam metal AM machine, the JAM-5200EBM, provides several benefits for additive manufacturing. These advantages stem from JEOL’s decades of experience developing advanced electron optics technology and our current position as the market leader for electron microscopy instruments. 

JAM-5200EBM

The key features of this instrument include automatic electron beam correction, long-life cathode and a remote monitoring system. The cathode will run for over 1,500 hours, allowing total system uptime to be improved and manufacturing quality to remain high. The machine operates in a clean and helium-free environment. Other features and benefits include the following:

Automatic Correction

The automatic correction and alignment function was developed in-house by JEOL and will ensure the focus and spot shape of the electron beam are precise according to the irradiation position.

Eco-Friendly

The AM machine is helium-free, and the ‘e-shield’ component eliminates any smoke that may arise during the manufacturing process. Additionally, the machine can produce multiple parts in one run, reducing waste and run time for single products.

Remote Monitoring

It is possible to monitor the manufacturing status and the current system conditions remotely, allowing for efficient updates and reducing the time personnel would spend going to and from the machine. An alarm function is also available.
Contact us today for more information about our JAM-5200EBM or to request a virtual demonstration.

GCC 2022 Conference Review

Next Steps in GC-MS Petrochemical Analysis: Gulf Coast Conference 2022 Review

Gulf Coast Conference 2022 has officially come to a close and our JEOL Applications Team has returned from Galveston, TX with a wealth of new connections and new ideas for petrochemical analysis (). In case you missed it, read below to catch up on our two technical presentations and our in-booth activities.

Petrochemical Analysis using Soft- and Hard-Ionization: GCxGC-HRTOFMS

On Tuesday 10/11, Mass Spec Product Manager Dr. John Dane shared his research on The Analysis of Petroleum Samples Measured by Using GCxGC-HRTOFMS.
In this work, a high-resolution time-of-flight mass spectrometer (HRTOFMS) equipped with a thermal modulator GCxGC system was used to analyze petroleum samples by using an electron ionization/field ionization/field desorption (EI/FI/FD) combination ion source. Additionally, the GC-MS interface was modified to increase the temperature in this region, so that higher boiling point compounds are able to be analyzed by the GCxGC-HRTOFMS system.
More specifically, Dr. Dane demonstrated our GC-Alpha's capabilities by pairing our optional EI/FI/FD combo source with GCxGC separation as a unique and powerful characterization tool for petrochemical mixtures. The GCxGC-EI data provides library searchable MS data while the GCxGC-FI data provides molecular ion accurate mass information to allow full characterization of compound families present in petroleum samples.
The combination of GCxGC, high resolution MS, and soft ionization provides the information needed to effectively analyze complex petrochemical samples.

Automate Structural Analysis using AI and GC-HRTOFMS

Also on Tuesday, Dr. Masaaki Ubukata traveled from our headquarters in Japan to share his work on Automated Structural Analysis for Real Unknown Compounds by Combining Artificial Intelligence (AI) with GC-HRTOFMS.
Despite being the most popular method used in gas chromatography-mass spectrometry (GC-MS), electron ionization (EI) often results in weak or absent molecular ions in the mass spectral data, making it difficult to identify unknowns by EI alone. JEOL’s newly-developed automated structure analysis software, msFineAnalysis AI, uses AI in combination with high-resolution MS to predict chemical structures from EI and SI (soft ionization) data and assigns library matches when available. msFineAnalysis AI builds upon our most recent iteration of this software, msFineAnalysis iQ.
Automated library matching and structure analysis will reduce the time required to perform qualitative analysis on petrochemical samples that contain complex mixtures of structurally-similar compounds. This technology is exclusively available on our AccuTOF™ GC-Alpha, and is scheduled for release in December 2022.

Sample Prep-Free Analysis of Motor Oils

Due to the complexity of lubricating oils, identifying additives can require time-consuming sample preparation and analysis in order to characterize these compounds within a given sample. On the other hand, JEOL’s AccuTOF™ DART® (Direct Analysis in Real Time) can directly characterize the additives in a lubricating oil within seconds with no sample prep necessary.

Additionally, O2-• attachment chemical ionization with DART allows our system to provide complementary information about nonpolar components of the base oil, enhancing its analysis capabilities by providing additional information about the sample without the need for other complex analyses.

Users can save time and money by eliminating sample preparation, even with a material as complex as a lubricating oil. To see our application note, AccuTOF™ DART® Analysis of Motor Oils, click here.

JEOL Additive Manufacturing with 3D Printer

JEOL and Additive Manufacturing – why JEOL developed a new 3D Printer

JEOL and Additive Manufacturing – why JEOL developed a new 3D Printer

Additive manufacturing is a new and exciting direction for JEOL. We entered the AM market with the idea that we can develop the world's best Electron Beam Melting powder bed fusion solution by using JEOL's electron beam technology.
Many people already know JEOL for its electron microscopes and e-beam lithography systems. JEOL was established in 1949 and has many sales and service locations worldwide.
This was a natural evolutionary step for JEOL.
Since the first JEOL electron microscope was developed in 1949, we have greatly advanced electron beam generation and optics. The technology is widely used by scientists and engineers for imaging, metrology, material characterization and nanofabrication in both research and manufacturing.
In 1967, JEOL released the world’s first computer-controlled direct write E-Beam lithography system. This technology is used to write highly-accurate nanoscale patterns on substrates. This is one of the first crucial steps in producing integrated circuits and semiconductor chips.
We are pleased to bring JEOL’s new e-beam melting PBF technology to the growing field of Additive Manufacturing. This new system significantly improves the productivity, quality, and reliability needed in an additive manufacturing machine. Ultimately it produces stronger and lighter parts for aerospace and other industries.
JEOL began this new venture in 2014, and we are now prepared to be an integral part of the additive manufacturing industry with our established production, applications, and service and support capabilities. Our goal is to apply our unique technologies to leading edge, reliable products that empower our customers to fulfill their own objectives and missions.

overview of electron beam lithography

An overview of electron beam lithography

An overview of electron beam lithography

Electron beam lithography uses a focused electron beam to pattern the surface of a material. As electron beams can be very tightly focused and small beam sizes achieved, electron beam lithography can be used to create very intricate structures for a wide variety of nanofabrication applications.1

What is the electron beam lithography process? 

The electron beam lithography process involves covering the surface of the substrate with a resist. Certain areas of the sample are then exposed to the incident beam of electrons that allow for the pattern's direct writing into the resist layer.
The sample is exposed by the electron beam in very fine steps to create the pattern. At each step, the resist must be exposed for sufficient time for the beam to activate the resist. Determining the optimal time for this in electron beam lithography is one of the steps in the process automation of the technique.
Once the resist layer has been exposed, the remaining resist is developed through chemical treatment of the sample, often with solvents such as acetone or alcohols that will dissolve the resist layers. Polymers such as PMMA (positive tone) and HSQ (negative tone) are popular choices for electron beam lithography resists and can be spun in very thin layers on top of the substrate of choice for the electron beam lithography process.

What is electron beam lithography used for?

Nanofabrication is one of the biggest applications for high-resolution direct-write methods like electron beam lithography.2 Many technologies, from new metalens structures toquantum computing, rely on techniques such as electron beam lithography to create the complex surface structures that these applications demand. One of the biggest challenges to be overcome with many new nanotechnology developments is reliable fabrication techniques for creating devices, and electron beam lithography is one potential solution for that.
Other applications of electron beam lithography include creating complex structures such as metal-organic frameworks (MOFs) that are now of interest for the miniaturization of solid-state devices.3 There are industrial applications using EBL for production of communication devices, due to the beam position’s nanometer-level accuracy and small linewidth capabilities.

What is the advantage of e-beam lithography over photolithography?

Photolithography involves the use of optical beams. As the diffraction limit of visible light is on the order of hundreds of nanometers, this limits the spatial resolution achievable with photolithography. While electron beam lithography is also diffraction limited, the diffraction limit of the high energy electrons that can be produced in various electron beam lithography experiments is on the order of nanometers or even sub-nanometer.
The improved spatial resolution of electron beam lithography means much more detailed, and complex structures can be created than with photolithography methods, though the latter has the advantage of higher throughput.

JEOL Solutions

JEOL are world leaders in electron beam technologies and has a number of products available to support electron beam lithography processes. Contact JEOL today to see how your direct-write processes could benefit from JEOL’s expertise in the development and optimization of electron beam lithography experiments.

References

  1. Nagashima, K., Zheng, J., Parmiter, D., & Patri, A. K. (2011). Biological Tissue and Cell Culture Specimen Preparation for TEM Nanoparticle Characterization. In S. E. McNeil (Ed.), Characterization of Nanoparticles Intended for Drug Delivery (pp. 83–91). Humana Press. https://doi.org/10.1007/978-1-60327-198-1_8
  2. Chen, Y. (2015). Nanofabrication by electron beam lithography and its applications : A review. Microelectronic Engineering, 135, 57–72. https://doi.org/10.1016/j.mee.2015.02.042
  3. Tu, M., Xia, B., Kravchenko, D. E., Tietze, M. L., Cruz, A. J., Stassen, I., Hauffman, T., Teyssandier, J., Feyter, S. De, Wang, Z., Fischer, R. A., Marmiroli, B., Amenitsch, H., Torvisco, A., Velásquez-hernández, M. D. J., Falcaro, P., & Ameloot, R. (2021). Direct X-ray and electron-beam lithography of halogenated zeolitic imidazolate frameworks. Nature Materials, 20, https://doi.org/10.1038/s41563-020-00827-x
  4. Smith, D. J. (2008). Ultimate resolution in the electron microscope? Materials Today, 11, 30–38. https://doi.org/10.1016/S1369-7021(09)70005-7
  5. JEOL (2022) Scanning Electron Microscopes, https://www.jeolusa.com/PRODUCTS/Scanning-Electron-Microscopes-SEM, accessed April 2022
  6. Arenal, F. L., A., D., & R., M. (2015). Advanced transmission electron microscopy. Springer

Achieving Pristine Cross Sections of Battery Samples for SEM

Achieving Pristine Cross Sections of Battery Samples for Scanning Electron Microscopy

Achieving Pristine Cross Sections of Battery Samples for Scanning Electron Microscopy

Lithium-ion batteries present unique challenges for sample preparation prior to imaging and analysis with the Scanning Electron Microscope (SEM). Batteries consist of layers of thin films that form multiple solid−solid interfaces and are sensitive to air when the inner structures are exposed. The ultrathin layers of cathode materials, separators, anode materials, metal current collectors, and electrolyte – all in the form of powders, sheets, and fluids – are each of different compositions and hardnesses. This layered composite of varying and sensitive materials requires special preparation techniques.
Broad beam ion milling is a robust method for obtaining pristine cross sections of such a complex system. Other, more traditional mechanical polishing tools introduce various artifacts, such as scratches and embedded polishing media, that obscure the original microstructure, crystallographic information and precise layer thickness measurements.
Figure 1. Scanning Electron Microscope image of Cross sectioned battery layers.
Figure 1. Scanning Electron Microscope image of Cross sectioned battery layers.
The JEOL Ion Beam Cross Section Polisher (CP) is widely used for preparing pristine samples prior to high resolution imaging and elemental analysis with the SEM. It produces pristine cross sections of samples – hard, soft, or composites – without smearing, crumbling, distorting, or contaminating them in any way.
The JEOL CP uses an Argon ion beam to mill cross sections or polish virtually any material that is affixed to the continuously rotating sample holder. During milling, the sample is rocked automatically to reduce creating beam striations on the cross-sectioned surface.
Figure 2. JEOL Ion Beam Cryo Cross Section Polisher
Figure 2. JEOL Ion Beam Cryo Cross Section Polisher
With the emergence of increased research on batteries, JEOL developed a special Cooling Cross Section Polisher (CCP) for preparation and polishing of materials that are sensitive to exposure to air or thermal damage. This new configuration is designed for cryo-preparation (down to LN2 temperature) and air-isolated transfer for atmosphere sensitive specimens The CCP allows long cooling periods while conserving liquid nitrogen.
The CCP is integrated into JEOL’s air-isolated workflow using a sample transfer vessel for air and heat-sensitive samples. The sample is initially prepared in an inert gas environment (such as in a glove box) then safely transferred to the Cryo Cross-section Polisher, and subsequently into the SEM (or Focused Ion Beam preparation and Transmission Electron Microscope) using the special air-isolated sample holder.
Figure 3. JEOL air-isolated workflow for battery sample preparation and imaging in the SEM.
Figure 3. JEOL air-isolated workflow for battery sample preparation and imaging in the SEM.
Using this technique, it is possible to examine morphological (surface) details and compositional characterization of battery materials without any air exposure. Every layer of detail can be examined clearly in the SEM. Ultra-low voltage imaging combined with signal filtering in the SEM allows direct imaging and analysis of battery constituents (anode and cathode) with nanometer resolution.
Figure 4. Scanning Electron Microscope image showing cross section of Lithium Ion Battery cathode. Larger image is magnified at 7500X for details of precise cross sectioning.
Figure 4. Scanning Electron Microscope image showing cross section of Lithium Ion Battery cathode. Larger image is magnified at 7500X for details of precise cross sectioning. 
Figure 5. Scanning Electron Microscope image showing cross section of Lithium Ion Battery separator.
Figure 5. Scanning Electron Microscope image showing cross section of Lithium Ion Battery separator.

Also See:

Further Reading:

cryo-electron microscopy images and microscope

What is Cryo-Electron Microscopy Used for?

What is cryo-electron microscopy used for?

What is cryo-electron microscopy used for?

Cryo-electron microscopy, or cryo-EM, is an imaging method that has revolutionized imaging of macromolecular complexes.1 Numerous atomic structures solved purely by cryo-EM and single particle analysis (SPA) have been deposited into data banks.

One of the older techniques in structural biology, protein x-ray crystallography, uses high energy photons that are diffracted from a high-quality crystal from different angles to build the 3D structure. However, not every protein can be crystallized and, although the drive to better beamlines allowed researchers to solve structures from ever smaller crystals, many samples are out of reach of this method
Cryo-EM by virtue of sub-millisecond vitrification does offer a way to obtain true or near-atomic resolution structures without requiring crystals. This approach has been highly successful on samples such as membrane proteins, reaction intermediaries, complexes that are fleeting, or those that exist in a mixture that can be heterogeneous in conformational and/or compositional in nature.

The field of structural biology was revolutionized with the advent of direct detectors cameras and highly stable and automated cryo-electron microscopes in cryo-EM. This resolution revolution propelled cryo-EM into becoming one of the most widely used tools in structural biology. In 2017 the Nobel prize in Chemistry was rightly awarded to Dr. Henderson, Dr. Dubochet and Dr. Frank for each of their contributions to the field of cryo-EM. Cryo-EM is currently applied to study variants of the SARS-CoV-2 virus, various membrane proteins and the immune system. 1 Understanding the structure of these species is key in understanding how some of these protein systems function, or malfunction in the case of disease, as well as in identifying potential drug-binding targets for therapies.

What is cryo-electron microscopy

Cryo-EM involves vitrifying the sample and imaging the vitrified, or frozen-hydrated specimen in the electron microscope under cryogenic conditions in transmission mode. The electrons that are scattered by the sample form an image modulated by phase contrast, which is magnified onto a camera. Although electrons have a much shorter wavelength than visible light photons, the final resolution in cryo-EM is governed by many factors, some of which are the aberrations in the entire system, both optically and environmentally; others are the radiation sensitivity of the sample2.

In SPA workflows, thousands of images of a macromolecular complex are recorded under low-dose conditions as movies on preferably a direct detector camera. Hundreds of thousands or even millions of particles are selected from motion-corrected movies and subjected to rounds of alignments, classification, and intermediate 3D model builds. After the final 3D reconstruction is scrutinized for correctness and resolution, the task is to try to understand the complex structure in terms of its functionality.
In tomography workflows, around 100 images are acquired under low-dose conditions from the same area of a vitrified sample at various tilts in the electron microscope. These images are recombined after corrections for tracking and focus changes into a 3D volume using a weighted-back projection scheme or a variant thereof. The resulting volume can be annotated and analyzed, but also subjected to sub-tomogram averaging techniques, whereby selected sub-volumes from the tomogram are processed using SPA techniques. Given that typically fewer sub-volumes are available the resulting 3D model of a complex is often obtained at a slightly lower resolution.

The biggest challenge in imaging vitrified specimens is radiation damage from the electron beam. This can show up in various forms, most easily recognizable as a loss of Bragg reflections of 2D crystalline samples, like catalase or purple membrane. However, other effects include charging as a result from secondary electron emission, bond breakage and even mass loss. Specimen charging is most often visible as beam-induced specimen motion and, in extreme cases, doming of the sample. These effects severely restrict any attempt to acquire a high resolution structure.4 Pioneering efforts at the MRC point to a new type of grid for SPA, hexafoils, to combat these effects with great efficacy5.

The success of cryo-EM applied to a macromolecular complex depends on many factors, some of which are biochemical in nature, others related to the vitrification process and yet others related to the automation on the microscope. Since many images are required to solve the structure of a complex, the best possible approach is to have as many images of the complex of interest as possible. Automation, gauged by the number of high resolution images per hour is important in any setting. A substantial fraction of the cycle time, i.e. the time to go from one area on the sample to the next, is taken up by either moving the stage and waiting for drift to settle, or simply the process of recording the movie. The current state-of-the-art puts this number around 20,000 movies/day. A clinical evaluation of all steps that factor into any throughput number is critical in the choice of equipment and imaging strategy. 

JEOL cryo-electron microscopes

Performing successful cryo-EM means having the right microscope set up. JEOL offers the CRYO ARM 300 II, a dedicated instrument for highthroughput, automated cryo-EM using either SPA or tomography. The CRYO ARM 300 II will achieve this throughput via high levels of instrument stability and automated data collection through SerialEM or JADAS.3  With an ever expanding arsenal of experimental techniques and the availability of commercial cryo-electron microscopy instruments like the CRYO ARM 300 II, cryo-EM is projected to become the leading technique in Life Sciences in the coming years1.

References

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