A Reticulated Open Cell Foam Dressing with Through Holes Has a Unique Stress and Strain Profile Compared to Alternative Dressings Under Negative Pressure

Background: Slough and non-viable tissue in wounds present a physical barrier potentially limiting Negative Pressure Wound Therapy (NPWT) benefits, creating a favorable environment for bacterial growth, maintaining hyper-inflammation and impeding healing.  Although the mechanism of action is not fully elucidated, clinical evidence suggests that a reticulated open cell foam dressing with 1cm through holes (ROCF-CC*) used with NPWT with instillation and dwell (NPWTi-d†) helps remove slough and non-viable tissue, promoting wound healing and preparing the wound for closure.  Early publications assessing NPWT with ROCF dressings, via finite element analysis (FEA), reported that microscale deformations induced by the foam struts resulted in a stress profile that promoted wound healing.  Defined physically, applied NP deforms the wound bed, doing work, W, on the tissue. Work is related to elastic energy, ∆U, stored in deformed tissue as W=∆U for elastic materials like wound tissue.  Knowing elastic properties, FEA can be used to predict NP deformation, stress, and stored elastic energy in tissue treated with ROCF-CC. 

Methods: NPWT (continuous -125 mmHg) using ROCF-V‡ or ROCF-CC dressings was applied to a simulated wound model made from elastic Dermasol to generate deformations, frozen in state, quantified and used to calculate W and ∆U.  FEA modeled and compared NP dressing stress/strain profile.

Results: Deformations created under NP were not visible for ROCF-V and measured 2.18 ± 0.03 mm for ROCF-CC. For ROCF-CC, W and ∆U were calculated as approximately 7 mJ and 9 mJ, respectively.  FEA of the dressings under NP suggest differences in pattern and intensity of stress and strain imparted to a simulated wound bed.

Conclusion: Experimental data and FEA can aide in designing different ROCF-CC geometries and predicting work done on wounds by NP. Greater work done means greater elastic energy introduced to the tissue potentially impacting healing in the presence of slough and non-viable tissue.