Controlled induction of distributed microdeformation in wounded tissue via a microchamber array dressing

A Comparison of the Biomechanical Performance of 3 Negative Pressure Wound Therapy Foams

PURPOSE

The purpose of this study was to compare 3 foam dressings to (1) determine the biomechanical performance of existing negative pressure wound therapy (NPWT) foams and (2) to determine if a test foam is possibly suitable as an antimicrobial "white" foam alternative for use in NPWT.

DESIGN

A comparison of mechanical performance of 3 foams used for vacuum-assisted NPWT.

SUBJECTS AND SETTING

Preclinical laboratory study using an in vitro model.

METHODS

The performance of a "white" foam (polyvinyl alcohol [PVA]), an antimicrobial "black" foam (polyurethane [PU]), and an antimicrobial white foam alternative (test PVA) were tested and compared using 3 mechanically relevant criteria. First, the fluid removal rate was measured for 72 hours. Next, the pressure input was compared to the pressure directly beneath the center of the foam. Finally, the spread of negative pressure beneath the foam was measured and compared.

RESULTS

Significant differences were found in fluid removal rates; specifically, the PU foam removed fluids faster than the PVA and test PVA foams, and the currently available PVA foams performed similarly. Both the PU and test PVA foams were able to transmit the negative pressure through the center of the dressing, while the typical PVA foam began failing at 140 mm Hg, with 50% of the samples failing at 200 mm Hg. All PU replicate foams evenly distributed the pressure, while 47% to 60% of the test PVA foams and 7% of the typical PVA foams distributed pressures evenly.

CONCLUSIONS

Study findings suggest that the test PVA foam does not mechanically interfere with NPWT and performs equivalently to currently used foams. These results suggest that the test PVA may be modified and incorporated into a vacuum-assisted NPWT device. In addition, the methods employed in these experiments provide a reproducible means to compare biomechanical compatibility of various NPWT foams, dressings, and subdrape devices.

The role of mouse mast cell proteases in the proliferative phase of wound healing in microdeformational wound therapy

BACKGROUND

Stored in the secretory granules of cutaneous mouse mast cells are mouse mast cell proteases (mMCP-4, -5, and -6). Using transgenic mouse lines that lacked these enzymes, it was shown that mMCP-4 and mMCP-5 modulate the outcome of burn-induced skin injury. Whether or not these proteases also play a role in the repair of surgically damaged skin, with or without microdeformational wound therapy, remains to be determined.

METHODS

Wild-type C57BL/6 mice and transgenic C57BL/6 mouse lines lacking mMCP-4, -5, or -6 were subjected to surgical wounding of their skin. Wounds were splinted with a stabilizing patch, and the mice received either microdeformational wound therapy (n = 5) or occlusive dressing (n = 5) for 7 days. Wound healing parameters were assessed in the proliferative phase.

RESULTS

Cell proliferation in the wounded wild-type mice receiving microdeformational wound therapy was 60 ± 3 percent. Cell proliferation was only 35 ± 5 percent, 25 ± 5 percent, and 45 ± 4 percent for the treated mMCP-4-, mMCP-5-, and mMCP-6-null mice, respectively (p = 0.005). Blood vessel sprouting was higher in the control mice with microdeformational wound therapy (170 ± 40 vessels/high-power field) compared with mouse mast cell protease 6-null mice with microdeformational wound therapy (70 ± 20 vessels/high-power field; p = 0.005), and higher in the control mice with occlusive dressing (110 ± 30 vessels/high-power field) compared with mMCP-4-null mice with occlusive dressing (50 ± 20 vessels/high-power field; p = 0.01). Qualitatively, the granulation tissue of all the protease-deficient groups receiving microdeformational wound therapy was disrupted.

CONCLUSION

Results suggest that mouse mast cell proteases 4, 5, and 6 are mediators of the critical role mast cells play in microdeformational wound therapy in the proliferative phase of healing.

Negative pressure wound therapy: past, present and future

Negative pressure wound therapy (NPWT), which was introduced as a commercial product (V.A.C. Therapy, KCI USA, Inc., San Antonio, TX) less than 20 years ago, has revolutionised the treatment of complex wounds. Indicated for wide variety of wound types, NPWT is an adjunctive therapy that can be used safely in a range of care settings. Current research indicates that there are four primary NPWT mechanisms of action: macrodeformation, microdeformation, fluid removal and environmental control of the wound. The interaction of the primary mechanisms results in secondary effects through cell signalling (e.g. granulation tissue formation, cell proliferation and modulation of inflammation). Better understanding of the mechanisms of action also provides insight into future directions for NPWT research that could create better solutions for patients with complex wounds.