Mechanical and contact characteristics of foam materials within wound dressings: Theoretical and practical considerations in treatment
December 23, 2022
International Wound Journal 2022 doi:10.1111/iwj.14056 [Epub ahead of print]
Gefen, A., Alves, P., Beeckman, D., Lázaro-Martínez, J.L., Lev-Tov, H., Najafi, B., Swanson, T., Woo, K.
Introduction
- The lack of data in regards to the clinical and cost-effectiveness of foam dressing results in care specialists not
understanding the differences in wound management properties between foam dressings and, thus, make
treatment decisions that result in suboptimal care. Therefore, it is necessary to understand the material behavior
of foam dressings to achieve optimum performance through wound dressing design and manufacturing.
Aims
- Review the mechanical and contact characteristics of foam in foam dressings.
- Outline key practical and theoretical considerations relevant to the design, development and efficacy of testing
standards of foam wound dressings.
Key findings/recommendations
The stiffness of foams and how they relate to foam density and porosity
- Foam dressings are comprised of a solid polymer and a dispersed air phase of microscopic pores. The pores
provide storage for excess exudate and allow dressings to be light weight and absorb mechanical energy. - Foam dressing stiffness should match the stiffness of the skin, even under mechanical strain (i.e. dressing strain
due to compression), to avoid dressings imprinting on the peri-wound skin and compromising tissue viability. - Porosity is defined as the ratio of the volume of pores in the foam sample to the total volume of the foam sample.
- Foam density and porosity are affected by compressive mechanical forces which collapse the air spaces.
- Foam stiffness increases with density as dense foam has less air and so compressive forces deform the solid
polymer more. However, typically, there is a non-linear increase in stiffness with decrease in porosity. - Scanning electron microscopy (SEM) is useful for determining pore diameter, aspect ratio (function of the largest
diameter and smallest diameter orthogonal to it), shape factor (pore circularity) and struts (pore wall thickness). - Pore size and wall thickness effect porosity which in turn affects the stiffness, strength and, therefore, the level
of resistance to mechanical forces foams can sustain.
The stiffness of foams and how they relate to foam density and porosity
- Foam dressings are comprised of a solid polymer and a dispersed air phase of microscopic pores. The pores
provide storage for excess exudate and allow dressings to be light weight and absorb mechanical energy. - Foam dressing stiffness should match the stiffness of the skin, even under mechanical strain (i.e. dressing strain
due to compression), to avoid dressings imprinting on the peri-wound skin and compromising tissue viability. - Porosity is defined as the ratio of the volume of pores in the foam sample to the total volume of the foam sample.
- Foam density and porosity are affected by compressive mechanical forces which collapse the air spaces.
- Foam stiffness increases with density as dense foam has less air and so compressive forces deform the solid
polymer more. However, typically, there is a non-linear increase in stiffness with decrease in porosity. - Scanning electron microscopy (SEM) is useful for determining pore diameter, aspect ratio (function of the largest
diameter and smallest diameter orthogonal to it), shape factor (pore circularity) and struts (pore wall thickness). - Pore size and wall thickness effect porosity which in turn affects the stiffness, strength and, therefore, the level
of resistance to mechanical forces foams can sustain.
Conclusions
The mechanical performance of foams in wound dressings strongly depends on the microstructure of the foam.
- Compressive and tensile stiffness, strength, bending stiffness and the ability of dressings to mechanically protect
the wound all depend on the relative density and porosity of foam materials. - Due to a lack of published work describing the microarchitecture of foams in wound dressings and variability in
pore sizes between manufacturers and products, the optimal porosity for foam dressings is currently unknown. - Currently, there are no test standards or target values for COFs, peeling forces, foam porosity, shape of pores
and variations in pore shape and size of foam dressings for manufacturers to optimize dressing performance.
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