The SED function demonstrates the strain energy of an object against a deformation gradient. In the study, the researches used this to see the strain in the area of the skin with the applied pressure. 

Ohio State University, Columbus

The researchers developed two anatomically accurate models of the human head. A model would serve as a control, while the other is placed in a prone position with the dressing between the skin and the resting surface. These models would provide quantitative information about facial skin and subcutaneous fat loading while in a prone position.


Methodology for testing effectiveness of prophylactic dressing

Peko, L, Barakat‐Johnson, M, Gefen, A. Protecting prone positioned patients from facial pressure ulcers using prophylactic dressings: A timely biomechanical analysis in the context of the COVID‐19 pandemic. Int Wound J. 2020; 1– 12. 
https://doi.org/10.1111/iwj.13435

Using prophylactic dressing to prevent facial pressure ulcers for COVID-19 patients

The researchers applied a 40 N force, about 4 kg, orthogonal to the back of the model head. This simulates the tissue loading weight for an average adult head. in a prone position. Therefore, the forehead and chin bear the weight of the forehead on the donut-shaped surface. 

Material interface conditions

The researchers measured the interface pressures between the skin and the surface for multiple patients. These measurements were done without applying the dressing. The pressure was applied for one minute and data regarding the peak and average pressure was collected.

Validation of facial pressure measurements

The researchers calculated the distributions of the stresses and strain in the skin and the subcutaneous fat tissues. They later calculated the volumetric exposure of the skin and fat layer (forehead and chin) to the stress and strain. Finally, the team calculated the percent reduction in the area under the tissue exposure curves for the treatment and control groups for both areas (forehead and chin).

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