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This method utilizes lipstick formulation drawn down on the BIOSKIN substrate using a 25µm or 75µm drawdown bar. The sample dries for about one to two hours at 37°C and 35%RH. Once dry, the BIOSKIN substrate is stretched twice manually in both the X and Y directions. A visual assessment of the sample for cracking is made.

Figure 1.7 demonstrates what would classify as performing well with the stretch test (left), as compared to that which performed poorly (right). This test is used to mimic consumer experience through the movement of their lips to determine if the deposited film would result in cracks and other undesirable visual effects. Such movements may include talking, yawning, and smiling which could result in the lipstick wearing off. Cracking is rated on a scale from 1 to 5 depending on the severity of crack formations that were observed.

Figure 1.7 Lipstick stretch test results indicating no cracking (left) and severe cracking (right) after manual stretching.