Space for the Foam

Many of us still learned from our parents that wounds should be kept as dry as possible – especially to minimize the risk of wound infection. However, even if many lay people and some doctors hold this to be true, numerous studies have since shown that a moist, warm wound environment actually accelerates wound healing. Heat and humidity stimulate cell growth without increasing the risk of infection.

This concept can be realized with silicone-coated foam dressings. Like all hydroactive wound dressings, they regulate moisture in the wound, prevent it from cooling, avoid scab formation, and protect it from environmental influences, thereby creating optimal conditions for healing. Particularly for the treatment of chronic and open wounds – the dreaded pressure ulcer – nursing staff regularly turn to silicone-coated foam dressings.

In a silicone-coated foam dressing, several layers of different materials are built up in a laminar structure. The bottom layer of this laminate, a silicone adhesive layer, fixes the dressing to the skin. An absorbent foam material combined with a water-impermeable but breathable backing film regulates the moisture in the laminate. The absorbent material is often a solid open-cell polyurethane foam. This foam layer absorbs the watery wound secretion – known as exudate – produced during wound healing, thereby preventing the wound edges from becoming softened and bacteria from colonizing the wound. The backing film, in turn, ensures that the wound does not dry out.

Freudenberg Performance Materials, a global manufacturer of technical textiles, has now developed a process for applying the liquid silicone directly to a polyurethane foam. This technology, known as direct coating, is patented. It significantly simplifies the structure and manufacturing process of the silicone-coated foam layer; unlike the conventional process, with this new technology carrier films are no longer necessary.

The new technology yields dressings comprising three layers. Because they do not contain a carrier film, they are much more flexible than conventional products and move with the body. A significant advantage for wound healing is that the foam can swell into deeper wounds as soon as it absorbs exudate. “The foam can rest snugly on the contours of the wound, effectively preventing the formation of exudate pooling. This can also reduce bacterial colonization and thus reduce the risk of infection,” explains the Freudenberg expert.

Because fewer process steps are required for production than with conventional technology, the new technology has a positive effect on the sustainability of the dressings: The waste that inevitably results during transfer coating and perforation is eliminated. Fewer intermediate products have to be transported to the production plants, and energy requirements are reduced. In addition, the risk of impurities being introduced into the process chain is lowered.

The developers at Freudenberg also paid special attention to the adhesion properties of the dressing. After extensive testing, Freudenberg Performance Materials opted for high-purity medical-grade silicone adhesive gels such as those offered by WACKER’s SILPURAN^® portfolio.

“Silicone adhesives are the materials of choice for the adhesive layer of hydroactive wound dressings,” says Dr. Thomas Gröer, who is responsible for silicone adhesives in WACKER's Applications Technology department. Conventional adhesives stick so strongly that skin cells remain attached to the dressing and are pulled off during peeling, injuring the wound and surrounding skin. This traumatization not only delays healing, but can also cause severe pain – for people with chronic wounds, dressing changes then become an ordeal.

Silicone adhesives are different: As hydrophobic materials, they only adhere to healthy, dry skin, but not to moist wounds. Since they don’t adhere to wound edges or fuse with newly formed tissue, and can be pulled off without great effort, they make low-pain wound care possible.

Silicone adhesives are two-component formulated transparent silicone products that come in a liquid, ready-to-use form, and crosslink at room temperature in a platinum-catalyzed addition reaction to form soft materials with a gel-like consistency. The crosslinked adhesive gels are highly flexible and pliable, but are also elastic. “Together with the low surface energy typical of silicones, the compliance ensures that the adhesion between dry skin and crosslinked silicone gel is built up,” says silicone expert Gröer. “The elasticity of the silicone gel means that the adhesive layer can be easily removed without leaving any residue on the skin.”

The laminate sheets, which are manufactured without an adhesive border, are suitable for further processing into wound pads. These pads are designed to be held in place with a gauze bandage or other secondary fixation during wound care. In these cases, the silicone adhesive layer merely serves as an application aid to make dressing changes easier for the nurse: Like a helping third hand, the adhesive layer holds the pad in situ on the wound so that the nurse has both hands free to apply the secondary fixation. A silicone gel with relatively weak adhesion is used for the adhesive layer of such pads.

Border dressings, on the other hand, are applied without secondary fixation. Here, the silicone gel used at the adhesive edge with its high adhesive strength ensures a long wearing time. “In border dressings manufactured with our technology, the foam island is coated with a weaker-adhesive silicone gel. This means the dressing can be removed very gently from the wound, despite the stronger adhesive edge,” says the Freudenberg expert.