Tissue ingrowth into foam but not into gauze during negative pressure wound therapy

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.

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.

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.

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.