In the medical industry, it is of utmost importance to purchase cryostats capable of providing immediate results while preserving sample integrity. Moreover, it should have the right size, capable features, and can be set to section specimens into precise, ultra-thin sections without the unwanted morphological distortions. These factors pave the way for an efficient workflow and a high throughput rate.
LabEquipment has gathered the necessary information to guide you through buying the ideal cryostat for your needs. Through this guide, you will discover the different cryostat types, the distinct functionality of its parts, its various roles in the medical field, and recommended temperature ranges for each sample type. All-in-all, these are aimed at helping you purchase the cryostat unit that will serve you best.
1. Cryostat Types
When choosing which cryostat type to purchase, it is vital to take note of what each type can offer you, so you can match these with the requirements that have to be met to perform your lab applications effectively. Below is the list of each cryostat type, together with a brief description of each type’s capabilities.
Some single compressor cryostats use one compressor for controlling both the temperature within the cooling chamber and the freezing plate. An evaporator system is usually used in this process. In doing so, the cooling chamber and freezing plate can attain a temperature that falls under the range of 0° and −35° C. One of the drawbacks to using single compressor cryostats is you cannot control the freezing plate’s temperature separately, since it is integrated with the cooling chamber’s refrigeration system.
Double compressor cryostats are equipped with two separate compressors used to separately control the temperature of the cooling chamber and freezing plate. Given it has two compressors, it is capable of freezing samples at a faster rate and can achieve lower chamber temperatures. More so, compressor failures are less likely to occur since the unutilized compressor is programmed to automatically maintain the selected temperature, hence refrigeration becomes uninterrupted.
A number of rotary cryostats are equipped with a handwheel on the right side of the instrument. By turning the handwheel clockwise, the sectioning process commences. Sections are produced as sample specimens are brought down by the handwheel. In addition, the trimming thickness will also be carried out in the upper reversal point of the cutting movement. An important reminder when using manual sectioning cryostats is to keep the rotating area of the handwheel clear and to also keep enough distance from the rotating handwheel handle.
Motorized sectioning cryostats come with a motorized cutting drive used to perform sectioning. The cutting drive facilitates routine work and makes it a point that an even cutting speed is applied for harder sample specimens, since harder materials are recommended to be sectioned at a slower cutting speed rate. Cutting speed can be set and controlled from 0.5 - 250 mm/s. The return cutting speed is enhanced in line with the cutting speed, to pave way for a time-efficient sectioning process.
2. Cryostat Parts & Their Distinct Functions
Before purchasing any lab equipment, you should have a grasp of how to operate the parts you’ll be needing most in your lab applications. The cryostat is equipped with five parts that play an important role in various experiments: freezing shelf, microtome, blade holder, anti roll guides, & specimen holders.
The freezing shelf functions as an area for holding sample tissues that are stored and frozen in preparation for sectioning. Freezing shelves are positioned close to the compressor system, therefore having an average working temperature −10°C lower than the set chamber temperature. Newer cryostat units are equipped with a peltier freezing stage: a thermoelectric device increasing heat diffusion upon activation. This results in a higher cooling rate and ultimately, a faster freezing process. In addition, it is recommended that the sample tissues be small and thin (around 3mm - 4mm) to hasten the process and prevent ice crystal formation.
The microtome is an immensely sharp cutting instrument mounted inside a cryostat unit. Microtomes provide a mechanism for advancing sample tissues towards a fixed blade (with a section thickness range of approximately 1–100µm), which will section them into thin, microscopic pieces. Earlier cryostat units are equipped with a wheel mounted outside the chamber to manually control the microtomes. The wheel is utilized for minimizing unnecessary and unwanted conditions of the sample tissues to be sectioned. On the other hand, newer cryostat units come equipped with microtomes controlled by an electric push-button. These cryostat units also allow for slicing adjustments in micrometers: a unit of measurement determining cutting precision.
The blade holder is positioned in front of the microtome and is either fixed to the microtome base or the cabinet. Blade holders are used in clamping either a disposable blade, or a reusable blade in position.
Disposable vs Reusable Steel Blades
Disposable blades are cutting blades that can be used for a limited time before eventually being replaced. When clamping disposable blades, the clamping pressure must be maintained evenly across the disposable blade’s entire length. If damage is dealt to either the front or rear pressure plate, it will alter the clamping pressure, eventually putting sectioning efficiency and quality at risk. The benefit to using disposable blades is that they no longer require re-sharpening. In addition, disposable blades suit every cryosectioning application and support all common microtome systems, meaning there’s no need to buy different blade units for different functions.
An alternative to disposable blades is a reusable steel blade. They rest on a support bar positioned between two pillars of the standard knife holder. At the top of each pillar is a securing screw to ensure that the blade is clamped firmly. Reusable steel blades are manufactured from top-of-the-line carbon or tool grade steel and contain anti-corrosives. Given these, reusable steel blades are more likely to be rust-resistant and free from impurities as compared to disposable blades. Fully-hardened steel blades perform well in sectioning sample tissues.
Antiroll guides are used by cryostats to take off sections, and as preventive measures to avoid the rolling or curling of sections being prepared. They are made up of a glass plates, supported in an aluminum frame. The frame creates a gap between the underside of the glass and the upper surface of the front pressure plate or knife surface allowing the section to slide under. Gap sizes of 50, 100, and 150µm are available depending on the section thickness required. For instance, if sections of <5.0µm were being collected, then it would be most suitable to use a gap size of 50µm.
If the cryostat unit doesn’t have antiroll guides, an alternative method referred to as the cooled brushed technique is used to collect and gather sections. With this method, the brush pulls or guides the section onto the pressure plate down onto the blade’s front surface as soon as the section’s leading edge begins to approach the blade edge.
Specimen Holders aka chucks
Specimen holders, also known as “chucks”, mount frozen specimens on the microtome for sectioning. They are designed with a crossing grid pattern of sharply-cut channels. These help maximize the required gripping power to hold the embedded sample tissues. Chucks are also manufactured using stainless steel, therefore withstanding large amounts of freezing power. They are available in a variety of shapes and sizes, made to accommodate multiple embedding requirements.
3. The Different Roles Of Cryostats in The Medical Industry
Essentially, the medical industry uses cryostats for freezing tissue samples and slicing (or sectioning) frozen samples into thin pieces using a microtome for observation. Sectioned samples should be suitable for microscopic observation, to achieve desirable results in the following:
The sectioned frozen tissue samples are used physicians to quickly diagnose its condition. Frozen sections are used as references for conducting rapid intraoperative diagnosis, as they help determine the extent of the excision needed in eliminating diseases such as skin tumor.
Study the margins of cancer
In determining if microscopic structures are contaminated with cancer, pathologists carefully examine frozen sections. In chemosurgery, cryostats are used in freezing and sectioning sample tissues for analytical use by the surgeon, to confirm whether the samples have been contaminated with skin cancer cells.
In the diagnosis and treatment of neuromuscular diseases, pathologists and neurologists rely on enzyme histochemistry. Staining and enzyme procedures are done on frozen sections. The samples to be sectioned should be frozen at a range of -12° C to -22° C.
Immunohistochemistry is utilized to inspect abnormal cells found in cancerous tumors. Tissue samples used for immunohistochemistry are sliced into sections of at least 3 µm.
4. Temperature recommendations for tissue type
A cryostat’s normal working chamber temperature is from 0℃ to -35℃. When freezing sample tissues, the temperature range may differ from one tissue type to another. Given this, it pays to know what temperature range your tissue types falls under. Below is a chart listing down the recommended temperature ranges for each tissue type:
|Tissue Type||-10°C – -15 °C||-15 °C – -25 °C||-25 °C – -30 °C|
|Breast - fatty||x|
|Breast - little fat||x|
|Heart and vascular||x|
|Skin with fat||x|
|Skin without fat||x|
|Spleenal or bloody tissue||x|
5. Recommended Micron Range For Sectioning
The micron range of most cryostat units reach up to 60 microns, but this does not necessarily mean it’s recommended for you to section at a range close to the maximum micron rate. Keep in mind that for medical and pharmaceutical purposes, it’s advised to section frozen tissue samples into thin sections that appear almost transparent. Therefore, the recommended micron range for sectioning frozen samples is 2 - 4 microns, to guarantee ultra-thin section. This makes it easier for the sectioned samples to be observed under a microscope. Anything above 5 µm is thick and may be counterproductive if utilized. Be sure to check the section thickness specifications of the cryostat you want to buy to see if it can accommodate your application’s sample thickness requirements.
6. Getting Cryostats At A Good Price
The price range of cryostats varies from one type to another, and if the unit is brand new or refurbished. If you’re the type who is looking for a unit equipped with the latest features and an extensive set of add-ons, the best way to go is to purchase brand new cryostat units.
On the other hand, if your budget is tight and you don’t require all the bells and whistles of a brand new line, then you might want to look at fully recertified cryostat units.They may not be equipped with the latest features, but rest assured they perform just as well as brand new cryostat units. After all, not all lab demands are in need of the latest features. However, it is recommended that you make more careful decisions if you decide to go for a recertified cryostat unit, since a number of companies have a tendency to short-change customers by offering refurbished cryostats without replacing the equipment’s insides with functioning parts.
If you aren’t comfortable buying a cryostat immediately, other distributors offer lease-to-own or simple rental options, which gives you the option to test out certain features, helping you determine the best cryostat unit for your lab demands. If ever you’re looking to upgrade from your old cryostat units, reach out to your distributor to get information regarding their available trade-up options.