In the freezing step, the cooling technique enables the tissue to harden quickly, making it possible to cut in the cryostat within minutes. The main problem during the freezing of a sample is the formation of ice crystals, which can destroy or damage the sample’s structure, thereby complicating diagnosis. Conventional methods include:
• direct freezing in the cryostat. This method is simpler and more cost-effective, but there are some limitations regarding cryostat temperature reduction. Consequently, the freezing process takes longer and this leads to a higher likelihood of ice crystal formation.
• liquid nitrogen (-200°C). It poses risks of room saturation and is not entirely safe.
• dry ice (-70°C)
• cold isopentane (-70°C). It is both flammable and toxic.
None of these methods allow for precise temperature control of the block. Additionally, the challenging orientation and uneven sample surfaces lead to longer cutting times as a consequence.
PrestoCHILL, is Milestone solution to enhance the quality of frozen sections. This advanced cryoembedding system works at -40°C and reduces the freezing time to 30 seconds, preventing ice crystal formation. The sample is frozen with a face-down technique, that consists in the direct contact of the sample with the cold metal, giving the fastest freezing possible. The freezing workflow is further enhanced using Milestone’s Cryoembedding Compound (MCC), specially formulated with a lower viscosity that flows easily into the cryomolds and improves adhesion to the cryostat chuck.

After cutting the frozen block in the cryostat, the staining of tissue sections is essential for revealing cell structure under the microscope. One approach to enhance the diagnosis of a frozen section could be to process the slide to emulate a paraffin section, which pathologists are more familiar to. Another effective method for enhancing frozen section quality is to automate and standardize the staining process. In most instances, the current practice for staining frozen sections is a manual and operator-dependent process, leading to inconsistent and substandard visualization of nuclear and cytoplasmic details.
In order to optimize this important step of the process, Milestone has introduced PRESTO PRO, an innovative processor-stainer providing a standardized and automated approach to process and stain up to 6 frozen slides simultaneously. The automated arm moves the rack with slides into and out of the vessels on a circular platform. In the initial step, the slide is immersed in heated FineFIX, Milestone’s reagent able to fix, dehydrate and clear the tissue. Thanks to the section’s thinness and the heated FineFIX, the tissue undergoes a process within seconds that mirrors the preparation of a paraffin section, which typically takes hours. Subsequently, the rack is automatically moved to next vessels for the staining step, according to the selected protocol. At the end of staining, the slide must be cover-slipped and is then ready for diagnosis.