A freeze dryer, or lyophilizer, is used to preserve samples by removing moisture from them via sublimation, which is a direct phase change from a solid to a gas. Dry ice being exposed to normal ambient temperature is a great example of this phenomenon. By forcing the solvent (the substance that the sample is suspended in) to sublimate directly into vapor, thus skipping the liquid phase, samples can be preserved very well as no chemical bonds are broken or formed in the process. This makes freeze drying a vital process in many applications, especially research applications.
Freeze dryers are used in many different disciplines, from preserving fragile archaeological artifacts to extending the shelf-life of fruit and vegetables. Their most common application in laboratories is preserving organic samples, like blood, that have yet to be analyzed.
How does a freeze dryer work?
According to Labconco, one of the largest manufacturers of laboratory freeze dryers, samples undergoing lyophilization are put through three stages: pre-freezing, sublimation (or primary drying), and adsorption (or secondary drying). Let's dive into the details of each stage.
As its name suggests, the first step in the lyophilization process prepares the samples to be sublimated. This is achieved by cooling the samples down past the melting point of the solvent (that which the sample is dissolved in) to ensure that it is completely frozen, or else it will be damaged during primary drying. Thus, pre-freezing is a vital part of the lyophilization process.
Sublimation (Primary Drying)
Once the sample is completely frozen, the second stage of lyophilization, primary drying, can begin. In this stage, the vacuum pump is powered on and begins pulling a vacuum in the sample chamber, which lowers both the chamber's pressure and, in turn, the sample's boiling point. The sample is then heated (either through ambient heat transfer from the environment or through a heat source built into the chamber; manifold dryers employ ambient heating while shelf dryers use a physical heat source), thus sublimating the solvent. Without lowering the pressure within the sample chamber, it'd be virtually impossible to skip the liquid phase as the sample's boiling point would be much higher.
Adsorption (Secondary Drying)
The final stage in the lyophilization process is adsorption, or secondary drying. Primary drying can't remove 100% of the moisture, so secondary drying evaporates the residual moisture so the sample is sufficiently dry for storage or study.
What types of freeze dryers are there?
Freeze dryers are unique machines in that they have a place in so many different settings. There's consumer-level models used in home kitchens to preserve food, massive industrial-grade systems used in manufacturing processes, and finally there's the type we offer: research-focused laboratory models that, in terms of throughput, fall between home units and industrial units. Since we specialize in laboratory models, we'll focus on the variations in that category.
Manifold Freeze Dryers
Perhaps the most popular choice, manifold dryers make use of stainless steel manifolds, flasks, and valves to sublimate samples. When using a manifold dryer, users first pre-freeze their samples in glass flasks. They then attach the flasks to the valves branching off the manifold, initiate the sublimation process, and simply detach the flasks when the process is finished.
There are two main types of manifolds: tree, and drum. Tree manifolds are better suited for high-throughput applications, while drum manifolds save more space.
Most manifold dryers are modular. One can easily swap the manifolds out so they can always use the format that best suits their current application.
Shelf Freeze Dryers
Shelf freeze dryers have integrated sublimation chambers with, you guessed it, shelves. Typically, these shelves are adjustable so users can fit sample containers of varying sizes in. Shelf dryers are often used to develop freeze drying "recipes", or reproducible procedures with defined parameters for temperature, pressure, duration, etc. These systems are useful for development because they're designed to work with more precise parameters than manifold dryers. Because they can achieve such precision, shelf dryers are frequently used to process samples of especially low volumes since they're so sensitive.
Combination Freeze Dryers
Featuring both shelves and valves, combination freeze dryers allow users to have the best of both worlds. These systems are suited for labs that must address varying lyophilization needs while remaining budget-conscious.
The Anatomy of a Freeze Dryer
So what does a freeze dryer need to work? Let's go over some of the most vital components:
Maintaining and Troubleshooting a Freeze Dryer
Keeping a lyophilizer running smoothly can be tricky, but there are some tried and true methods for troubleshooting and maintenance to follow. Here are some links outlining some of that information:
While it may seem intimidating at first glance, freeze drying is an easier topic to wrap your mind around than you'd expect. Armed with this knowledge, you should now be able to delve even deeper into the topic and, hopefully, graduate from novice to slightly-less-of-a-novice.
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