Lyophilisation specialist Lyofal, part of the Synerlab Group, explains the benefits of this freeze-drying process in the production of ‘active’ dressings, which can release drugs to act directly on wounds while maintaining the basic properties of a dressing.

The primary goal of lyophilised medical devices must of course be to create a moist environment for wound healing while at the same time being a barrier to bacteria. However, they must also have the characteristics of modern therapeutic dressings. These are increasingly more technical and complex. Their formulation must be constantly refined to better meet market demands such as the treatment of bedsores and ulcers, re-epithelialisation of severe burns, treatment of chronic wounds, use in surgery and so on.

Lyophilisation and medical devices

Lyophilisation adds value to the product by giving it some very specific properties. The manufacturing process can be performed in a totally sterile environment.

Lyophilisation allows, for example, the development of ‘active’ and specialised dressings, which can release drugs that act directly on the wound while maintaining the dressing’s basic properties. These include being occlusive but permeable to gas exchange, and adhering to the skin without adhesives. A biopolymer matrix is selected for its wound-healing and haemostasis properties, among others. The agent is added directly to the matrix without any problem of stability or formulation. Active ingredients in these products may be bacteriostatic agents, moisturisers, re-epithelialisation facilitators or enzymes. This range of and freedom in the choice of matrix and active ingredients answer the needs of an ideal modern dressing and give lyophilisation its capability for specific specialised uses.

Lyophilised dressings and compresses are suitable for different types of wounds due to their adaptable shape and texture, which improves patient comfort. It is possible to work on moulded products in their liquid form before drying. The shape will become fixed at the moment of freezing or it can be cut after lyophilisation.

Moreover, the absence of water in the product gives it an extraordinary liquid-absorbing capacity for blood, exudates and so on. This capacity is much greater than that of a conventional dressing: 1g of lyophilised biomatrix is very hygroscopic and can absorb more than 30g of water.

This characteristic, conferred by lyophilisation, also ensures stability and allows an initial formulation with no preservatives. Dressings and compresses are thus quite suitable for atopic or injured skin.

It is important to note that, depending on the selected initial biomatrix, lyophilised dressings can be totally resorbable – a valuable property of interest for internal use in surgery. Lyophilised dressings can also be nonresorbable. In this case, the carrier is a biomatrix with mechanical properties that can protect the wound or provide support. It is also possible to make composite biomatrix/synthetic structures. It is thus possible to work on nonwoven, more flexible substrates or on much more rigid substrates such as polyethylene.

Biomatrices and the manufacturing process

It is possible to work from matrices of different origins. Thus, work has been done on matrices of animal origin, such as collagen, and on matrices of vegetable origin, such as polysaccharides (for example, galactomannans, chitosans and alginates).

The resultant mixture is then poured into moulds, with or without a carrier, if a shape has been specified in advance and moulded; or into trays, which will yield a raw product to be further processed with later cutting. This allows different shapes to be made from the same starting material. After lyophilisation and the optional cutting step, sponges are packed in a blister package and/or in heat-sealed bags. The finished product is then put into cases to be delivered directly to the customer.

In the case of nonresorbable matrices, it is also possible to provide an active ingredient solution with the product that will allow impregnation of the sponge just prior to use.