Biomechanical Performance of Multilayer Sacral Dressings

Introduction: Multilayer dressings to protect the sacrum have become a common tool in the arsenal against pressure ulcers. There are a variety of designs on the market, which share a few common characteristics. We are developing models for testing these dressings to determine if their performances are equivalent or vary in any substantial manner.

Materials and Methods: Commercially available multilayer sacral dressings were chosen to test their ability to reduce strain on a pseudo-tissue model by 1) strain relief and 2) by friction reduction. The pseudo-tissue is gelatin-based gel loaded with blue beads. A custom made digital image correlation (DIC) strain measurement device was created from extruded aluminum, a 300 mm linear rail with stepper motor, an EasyDriver motor controller, a digital camera, and a Raspberry Pi 3. A control program was written in Python 3 and the data were analyzed in ImageJ.

Results: In testing the two sacral dressings versus nothing, it was immediately apparent that the dressings did allow the load to begin sliding after a certain threshold strain. Between the two dressings, the load consistently slid smoothly across the Dressing 1, while the load entered a slip-and- stick mode of sliding with the Dressing 2. Despite those differences, both the sacral dressings provided a definite reduction in strain.  Student’s t-Test using the final frame revealed that the differences analyzed by maximum strain-per-frame lead to significant findings comparing Dressing 1 to control (65% reduction, p = 0.003) as did Dressing 2 vs. Nil (61% reduction, p = 0.004). The comparison between the two dressings remained a trend (p = 0.24).

Conclusions: The initial tests demonstrate that the system can measure strain in the pseudo-tissue and that strain mitigation can be measured and that two currently available dressings differed slightly, but that the differences didn't reach statistical significance.