transporting products in the frozen state is costly, while freezer
breakdown may result in the complete loss of valuable product
[1]. Alternatively, biological specimens can be dried to increase
their shelf life. Traditional drying processes typically result in
marked changes in the physical and chemical properties of the
product by high solute concentration or thermal inactivation and
are more appropriate for dehydrating low-cost products such as
foodstuffs. Freeze-drying combines the benefits of both freezing
and drying to provide a dry, biologically active, shelf-stable product
that can be readily rehydrated into a solution or suspension [2, 3].
Operationally, we could define freeze-drying as a controllable
method of dehydrating labile products by vacuum desiccation.
Earlier accounts of freeze-drying suggested that ice was only
removed by sublimation and defined this step as primary drying.
The cycle was then described as being extended by secondary
drying or desorption. Although these definitions are applicable to
ideal systems, they incompletely define the process for typical systems that form an amorphous matrix or glass when cooled [4].
1.2 History
The principles of low-temperature drying can be traced back to
prehistoric times and was used by the Aztecs and Arctic peoples for
preserving foodstuffs. Toward the end of the 1880s, the process
was used on a laboratory scale and the basic principles understood
at that time. Practically, the method remained a laboratory technique until the 1930s when there was the need to process heatlabile antibiotics and blood products. At this time, refrigeration and
vacuum technologies had advanced sufficiently to enable production freeze-dryers to be developed, and since then, the process has
been used industrially in both the food and pharmaceutical
industries [5].
1.3 Applications
of Freeze-Drying
in the Pharmaceutical
and Biological Sectors
Freeze-drying offers a stable and robust format with significantly
reduced weight to facilitate storage and shipment; it provides stabilization for materials not readily stabilized by conventional drying
technologies, which tend to use higher temperatures; the product
can be sealed under vacuum or an inert gas, which can reduce
oxidative denaturation; it can accommodate the need to separately
dry two or more components that would be incompatible if dispensed together as a solution within a single container. In the case
of the latter, freeze-drying can enable this to be practically achieved
by filling and freezing one component before adding the other and
completing the freezing process; an example being dual-layer collagen implants for surgical use.
A wide range of products are freeze-dried even within the
biologicals and healthcare sectors, including: small molecules,
where the process is used to dehydrate or concentrate reactive or
heat-sensitive chemicals/pharmaceuticals; biologically active molecules including enzymes, hormones, antibiotics, vitamins, blood
100
Kevin R. Ward and Paul Matejtschuk
breakdown may result in the complete loss of valuable product
[1]. Alternatively, biological specimens can be dried to increase
their shelf life. Traditional drying processes typically result in
marked changes in the physical and chemical properties of the
product by high solute concentration or thermal inactivation and
are more appropriate for dehydrating low-cost products such as
foodstuffs. Freeze-drying combines the benefits of both freezing
and drying to provide a dry, biologically active, shelf-stable product
that can be readily rehydrated into a solution or suspension [2, 3].
Operationally, we could define freeze-drying as a controllable
method of dehydrating labile products by vacuum desiccation.
Earlier accounts of freeze-drying suggested that ice was only
removed by sublimation and defined this step as primary drying.
The cycle was then described as being extended by secondary
drying or desorption. Although these definitions are applicable to
ideal systems, they incompletely define the process for typical systems that form an amorphous matrix or glass when cooled [4].
1.2 History
The principles of low-temperature drying can be traced back to
prehistoric times and was used by the Aztecs and Arctic peoples for
preserving foodstuffs. Toward the end of the 1880s, the process
was used on a laboratory scale and the basic principles understood
at that time. Practically, the method remained a laboratory technique until the 1930s when there was the need to process heatlabile antibiotics and blood products. At this time, refrigeration and
vacuum technologies had advanced sufficiently to enable production freeze-dryers to be developed, and since then, the process has
been used industrially in both the food and pharmaceutical
industries [5].
1.3 Applications
of Freeze-Drying
in the Pharmaceutical
and Biological Sectors
Freeze-drying offers a stable and robust format with significantly
reduced weight to facilitate storage and shipment; it provides stabilization for materials not readily stabilized by conventional drying
technologies, which tend to use higher temperatures; the product
can be sealed under vacuum or an inert gas, which can reduce
oxidative denaturation; it can accommodate the need to separately
dry two or more components that would be incompatible if dispensed together as a solution within a single container. In the case
of the latter, freeze-drying can enable this to be practically achieved
by filling and freezing one component before adding the other and
completing the freezing process; an example being dual-layer collagen implants for surgical use.
A wide range of products are freeze-dried even within the
biologicals and healthcare sectors, including: small molecules,
where the process is used to dehydrate or concentrate reactive or
heat-sensitive chemicals/pharmaceuticals; biologically active molecules including enzymes, hormones, antibiotics, vitamins, blood
100
Kevin R. Ward and Paul Matejtschuk