Lyophilization, also known as freeze-drying, is a process used for preserving biological material by removing the water from the sample, which involves first freezing the sample and then drying it, under a vacuum, at very low temperatures. Lyophilized samples may be stored much longer than untreated samples.

Components of a lyophilizer

A lyophilizer consists of

  • A vacuum chamber containing product shelves which are capable of cooling and heating containers and their contents.
  • A vacuum pump, a refrigeration unit, which is associated controls are connected to the vacuum chamber.

Samples are generally placed in containers such as glass vials that are placed on the shelves within the vacuum chamber.

Cooling elements within the shelves freeze the product. Once the product is frozen, the vacuum pump evacuates the chamber and the product is heated. Heat is transferred by thermal conduction from the shelf, through the vial, and ultimately into the product.

Comparison with Liquid-Phase drying

Lyophilization avoid denaturation that is caused by heating the product, by maintaining it frozen throughout drying. This is the most obvious advantage over liquid-phase drying which cause the denaturation of proteins and other products.

Equally important is that in liquid-phase drying there is an undesirable shrinkage and concentration of active constituents that causes damage as well as a movement of these constituents to the surface of evaporation, where they form a dense, impermeable skin that inhibits drying, and later, rehydration. Such effects can be avoided by spray drying, but this requires brief exposure to temperatures around 100 degree C.

Advantages of the Lyophilization

Lyophilization has many advantages over the other drying and preserving techniques.

  1. It maintains food/ biochemical and chemical reagent quality because they remains at a temperature that is below the freezing-point during the process of sublimation.The use of lyophilization is particularly important when processing lactic bacteria, because these products are easily affected by heat.
  2. Food/biochemicals and chemical reagents which are lyophilized can usually be stored without refrigeration, which results in a significant reduction of storage and transportation costs.
  3. Lyophilization greatly reduces weight, and this makes the products easier to transport. For example, many foods contain as much as 90% water. These foods are 10 times lighter after lyophilization.
  4. Because they are porous, most freeze-dried products can be easily rehydrated. Lyophilization does not significantly reduce volume, therefore water quickly regains its place in the molecular structure of the food/ biochemicals and chemical reagents.

Lyophilizer Working Steps

Lyophilizer have 3 steps in freeze drying process, with an experienced operator, you can save energy and cost each batch.

Freezing stage

Is the most important step, also is the first step of a lyophilizer, thoroughly freezing the raw material to solid phase is the insurance of a success freeze drying. Freeze drying can be done in a lyophilizer (if shelves with freezing function) or in deep freezers. The key of freezing is to find out raw material’s eutectic point and make sure freezer temperature is lower than that. Freezing stage is the insurance of dried products’ physical shape.

Some material, especially fluid, the freezing stage may also involve annealing treatment (rapid freezing cause large ice crystals, proper raise its temperature allow ice crystal grow), which could help protect cells from broken as well as short the drying time.

Primary drying

Primary drying is the secondary step of a lyophilizer, mainly remove water by sublimation, in this stage, water in solid phase sublimate to vapor and move to ice condenser, freezing on condenser coils surface, in this stage >95% water have removed.

In this stage, gradually and proper increase the shelves temperature could speed up the sublimation, but too much energy supply may cause glass transition.

Secondary drying

Secondary drying is the last step of a lyophilizer, mainly remove the adsorption water. Higher temperature and vacuum needed in this step, after secondary drying, the shelves could reduce temperature and prepare harvest.

How lyophilization addresses sample storage challenges

Although it is a complicated process, lyophilization has become standard practice in many industries, including pharmaceutical, biotechnology, and agriculture. Given the adverse effects of heat and water, dehydration by lyophilization offers several advantages, from improved sample stability and purity to increased shelf life and reduced costs.

By removing the need to dehydrate by heating, lyophilization provides a convenient and safe method for long-term storage of lab samples and pharmaceutical products while preserving their activity.

As well as increasing shelf life, freeze-drying samples also reduces their weight and volume, helping cut down on shipping costs and environmental impact. Eliminating the need for shipping procedures designed to maintain sample stability, such as dry ice, also simplifies logistics and helps further reduce costs.

These benefits are especially advantageous when transporting samples and assays to developing countries with limited facilities and budgets. Long transportation distances and often hot and humid environments would otherwise put a substantial strain on cold chain transport and storage. With lyophilization, a temperature-controlled chain is not necessary.

An example of this can be found as long ago as World War II, which saw one of the first use cases of freeze-drying as a commercial technique(2). Lyophilization was used to render blood plasma and penicillin chemically stable and viable without refrigeration. As a result, both could be transported to their intended recipients regardless of cold chain transport availability. This process is still in use today.

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