Lay Title: Rapid Freezing for Advanced Electron Microscopy of Wet Materials
Nontechnical explanation: Using microscopes to see the structure of a material provides very important information that helps scientists and engineers understand how to make new materials with better properties. While many microscopes use light to form images, electron microscopes can reach much higher magnifications and resolve finer detail in a material's structure. However, unlike light microscopes, electron microscopes require a vacuum (the air inside the microscope must be removed )so that the electrons will not collide with gas molecules from the air. Vacuum isn't a problem when studying dry materials, but it is a big problem when studying wet materials, because water quickly evaporates in a vacuum. This research team is developing new materials that all contain water. These materials are being designed to help regrow human tissue, to make biomedical implants more resistant to infection, and to deliver drugs where and when they are needed within the human body. These new materials can be studied in an electron microscope if they are frozen and kept cold, because then the water is solid rather than liquid and it doesn't evaporate. However, the freezing has to be done in a special way, otherwise the material gets damaged just like a sealed bottle of milk will break if it freezes. So, this research project is using a new tool called a high-pressure freezer, which eliminates expansion of the liquid water when it freezes. Consequently, the team is able to study wet materials and gather information about structure at levels of detail that no one has previously achieved. Because this approach is so new and significant, the research team is working with an electron-microscope manufacturer to help share these developments with other microscope users. And, because this freezing tool can also be used to study everyday materials like cosmetics, food, plants, and insects, the research team is partnering with an all-girls school in New Jersey to use this new technology to help dozens of young women get exposed to some of the excitement associated with science and engineering.
While the average morphology of many hydrated materials can often be determined by scattering (neutron, X-ray, light), these techniques can not match the ability of electron microscopes to collect site-specific, high-resolution, real-space, image data. The high vacuum required for both scanning (SEM) and transmission electron microscopy (TEM), however, precludes the direct observation of hydrated specimens, and this limitation is only partially mitigated by variable-pressure microscopes and environmental/liquid microscope stages. The long-standing solution has been to freeze the specimens and study them in the electron microscope under cryogenic conditions. Simply quenching specimens in a liquid cryogen is, however, no longer adequate for the imaging problems being addressed by this research team. This team is pursuing six externally funded inter-related projects centered on polymer and nanoparticle self-assembly, microfluidic 3-D tissue models, advanced scaffolds for tissue engineering, and hierarchical surface nano-patterning for infection control. These projects all involve advanced materials with high levels of hydration, which inhibits high-resolution morphological studies using conventional cryo-EM techniques. The goal of this project is thus to exploit the new technique of high-pressure freezing to prepare highly hydrated materials for advanced electron microscopy, both SEM and TEM, as well as for 3-D imaging using slice-and-view focused ion beam (FIB-SEM) microscopy. High-pressure freezing mitigates artifacts created by water crystallization and solute segregation during conventional freezing. Incorporating this state-of-the-art technology is enabling the research team to assess the detailed morphology of emerging materials and material systems in their native hydrated state at pioneering levels of image resolution.
