Cryogenic Microscopy

By increasing the pressure to approximately 2000 bar results in 10x deeper layer of well preserved material as the pressure increase acts as a thermophysical cryoprotectant, i.e. water is about 1500x more viscous at 2000 bar than at ambient pressure. The samples can then be introduced to the electron microscope for analysis using SEM or TEM.

This freezing allows the analysis of a variety of sample types to be studied in detail using electron microscopy:

• Structured liquids (such as emulsions, gels etc), particularly applicable to personal care products such as moisturisers, deodorants, creams and conditioners.
• Food - specifically structured foods where texture and constincy are vital to creating the customer experience (e.g. ice creams, margarines and spreads)
• Microbiological material - the fast freezing preserves the structure of the cells allowing analysis of cells close to their native state.

This “vitreous state” of water reduces the growth in ice crystallisation on freezing, resulting in amorphous ice and a lack of the ice crystallisation network and material migration.

Allied to the increasing the pressure, is the reduction in cooling rates required to achieve vitrification. At atmospheric pressure, cooling rates greater than 100,000 K per second are required, while at 2000 bar rates between 1000 and 10,000 K per second are only necessary.

However, within the world of Home and Personal Care (HPC), many treatments used on substrates such as hair, fabrics, teeth, skin and hard surfaces are water based and often require structural analysis by microscopy to ascertain there functionality as well as interaction with their target substrate. These products may have as high 99% water content, so conventional plunge or slamming freezing techniques often result in high ice crystallisation, causing massive material migration, thus reducing any relationship to the true nature of the materials in situ.

So by employing a system that increases the pressure to approximately 2000 bar, and facilitates freezing rates > 12,000 K per second, allows detailed microscopy of high water content products without there fear of ice crystal damage and material damage.

To this end, Intertek NWTC has combined its many year of experience in examining HPC products using cryo SEM/TEM with the addition of high pressure freezing system. This will allow the examination of very dilute products (as used by the consumer) without the ice damage and material migration. As a consequence of the limited ice damage, not only cryo-SEM examination is vastly improved, but examination at much higher magnification, were ice damage would be more apparent, i.e. TEM becomes available via freeze fracture and cryo-section techniques, allied to freeze substitution.