Tissue Ingrowth into Foam but Not into Gauze during Negative Pressure Wound Therapy

Ola Borgquist, MD; Lotta Gustafsson, MSc, PhD; Richard Ingemansson, MD, PhD; Malin Malmsjö, MD, PhD


Wounds. 2009;21(11) 

In This Article

Abstract and Introduction


Background. Foam and gauze are two types of wound fillers used for negative pressure wound therapy (NPWT). Differences in the wound healing effects of foam and gauze have been observed clinically. The aim of the present study was to examine the effects of NPWT on the wound bed using foam and gauze.
Methods. A porcine peripheral wound model was treated with NPWT at 0, −75 mmHg, or −125 mmHg for 72 hours. The effects of foam and gauze on the wound bed were compared, and the force required to remove the dressings was measured. Sections of biopsies from the wound bed with an overlying dressing were stained with hematoxylin-eosin and Giemsa and were examined histologically.
Results. The force ratio needed to remove the wound filler from the wound bed after treatment with negative pressure was greater for foam than for gauze. NPWT caused the wound bed tissue to grow into the foam, while there was no such ingrowth into gauze. Furthermore, beneath the foam there was more leukocyte infiltration, tissue disorganization, disruption of contact among cells, and differences in size among cells. The results were similar regardless of the level of negative pressure.
Conclusion. More force was required to remove foam compared to gauze following NPWT, which may have been due to greater ingrowth into foam. These findings may explain the patient discomfort and wound bed disruption upon removal of foam. The observed differences in wound bed tissue morphology under foam and gauze are in accordance with the clinically observed differences in quality of granulation tissue formation.


The use of negative pressure wound therapy (NPWT) has evolved over the last decade due to its remarkable effects on the healing of chronic and difficult wounds.[1,2] Although the precise mechanism by which NPWT brings about wound healing is not known, it has been shown that it promotes a moist wound healing environment,[3] reduces bacterial colony counts,[4] increases granulation tissue formation,[4] removes edema,[5] stimulates cell-mediated immune response,[6] induces mechanical deformation of the wound edge tissue,[1,4,7] decreases the permeability of blood vessels,[8] and stimulates angiogenesis and blood flow to the wound margins.[9,10]

NPWT consists of a wound filler material covered with an adherent airtight drape that is connected to a negative pressure pump. The wound filler material is either foam or gauze. Paglinawan et al[11] showed that both gauze and foam result in increased granulation tissue formation, yet it is believed that there are differences in the granulation tissue formed by foam and gauze. In clinical practice it has been observed that the granulation tissue formed after NPWT using foam is thick but fragile, whereas the granulation tissue is thinner and denser following NPWT using gauze. Furthermore, foam tends to adhere to the wound. Upon removal, the patient may experience pain, the tissue in the wound bed may be disrupted, and pieces of the foam may remain in the wound. Morykwas[12] showed that granulation tissue grows into the wound filler during NPWT using foam and that this effect may be responsible for the clinically observed problems. No study has yet been performed to examine the effects of gauze on tissue ingrowth. Furthermore, the difference in structure of the wound bed after NPWT using foam and gauze has not been elucidated.

The aim of the present study was to evaluate features of the wound bed after treatment with NPWT using either foam or gauze. Continuous negative pressure therapy was applied for 72 hours in a porcine peripheral wound model. First, the force needed to remove the wound dressing after NPWT was determined. Second, the amount of ingrowth of tissue into the dressing was evaluated in hematoxylin-eosin and Giemsa stained sections of biopsies from the wound bed with the overlying dressing. Third, the wound bed was examined histologically regarding morphology, leukocyte infiltration, and tissue disorganization.