Surface tension of artificial blood for assessing medical face masks

Surface tension of artificial blood for assessing medical face masks
Medical face masks are intended to resist liquid penetration from splashes or splatters of blood, body fluids and other potentially infectious materials. Many factors influence the wetting and penetration properties of body fluids. Consider surface tension, viscosity, polarity of the liquid, as well as the structure, properties of the material the mask is made of (hydrophilic or hydrophobic) and the design of the mask.

Blood-repellent surfaces (Blood repellent surfaces) can be made of different materials. However, to properly evaluate their performance, a fluid that resembles and/or has blood-like properties is needed. The surface tension for blood and other body fluids (excluding saliva) ranges from 42 to 60 mN/m. To simulate the wetting characteristics of blood and body fluids, the surface tension of the synthetic blood is adjusted to the lowest surface tension range. Hence, the surface tension of synthetic blood is 42 mN/m with an accuracy of +/- 2 mN/m.

The main component of synthetic blood is water with a thickener and a red dye to assess visual detection/inspection of penetration. 

By varying the droplet speed and drop height, the synthetic blood is sprayed onto the mask or mask material to assess its resistance to liquid penetration.

Standards must be followed when evaluating protective materials.

The ASTM F1670 standard describes the standard test method of how protective materials (clothing and face masks) can resist a certain penetration of synthetic blood. The method described in the standard is based on studies of blood-borne pathogens such as Hepatitis B and C, and HIV. These studies mainly took place in the last century (ca. 1980) when HIV infections were at their highest. A very important requirement within liquid penetration tests (ASTM F1670) is that the surface tension of the synthetic blood is measured according to the ASTM D1331 standard.

The ASTM D1331-standard describes the surface tension measurement to be performed with a so-called “Force Tensiometer” (balance tensiometer) and the du Noüy-Ring method. The ASTM D1331 particularly emphasizes the importance of cleanliness when performing Surface Tension measurements. At least two measurements should be taken to ensure repeatability of the measurement. The videos below shows the Du Noüy ring surface tension measurement in practice. 

For more information: Technex in Wormerveer

Source: Biolin Scientific
Susanna Lauren
Susanna is an Application Scientist at Biolin Scientific. In her PhD thesis, she developed fabrication methods for a new type of inorganic-organic polymers. Microfabricated polymer chips were utilized as a tool for biomolecule separation in analytical chemistry.