A sequential tape stripping approach for the assessment of the impact of personal cleansing products on the stratum corneum surface layers' acid mantle properties and antimicrobial defense.

BACKGROUND: Stratum corneum (SC) plays a critical role in skin barrier function for protection and defense in nature. The acidic skin pH, which is also known as the acid mantle, is very important in fighting against outer environmental threats, especially, bacteria. Furthermore, recent research has shown that the transient bacteria could potentially penetrate into deeper layer of the SC down to a few micrometers while posing an additional threat to the deeper layers of the skin. AIM: To develop a sequential tape stripping method for assessing the impact of personal cleansing product on the SC surface layers' acid mantle properties and antimicrobial defense against transient bacteria. METHODS: Fifty-five subjects were recruited. High pH soap-based Product 1 and low pH synthetic surfactant-based Product 2 were applied on the left and right forearms of each subject. Sequential tape stripping was performed on the same spots to access multiple layers of the skin SC. Both antimicrobial defense property and skin pH of different skin layers were evaluated at baseline and 12 h after treatment. RESULTS: The skin's antimicrobial defense was significantly higher 12 h after treatment of the low pH Product 2 as compared to the treatment of high pH Product 1. In fact, this trend was consistent across all three skin layers (Layer 1 to Layer 3) as measured in this study (p < 0.01). Furthermore, the skin surface pH of Layer 1 and Layer 3 were also lower 12 h after the treatment of low pH Product 2 as compared to that of the high pH Product 1 (p < 0.01). CONCLUSION: The results of this investigation demonstrated the benefits of 12-h long lasting and deeper protection of SC acid mantle properties and antimicrobial defense using a low pH skin cleansing product as compared to a high pH product.

Multiscale Observations of Inhomogeneous Bilayer SEI Film on a Conversion-Alloying SnO2 Anode.

SnO2 , storing Li through conversion and alloying reactions, has been regarded as one of the most typical anode materials and has been widely studied for both mechanism exploring and performance tuning. However, the structure of the solid electrolyte interphase (SEI) formed on the SnO2 electrode and its evolution process are rarely focused and still poorly understood. Herein, time of flight secondary ion mass spectrometry is used to observe the bilayer hybrid structure of SEI formed on a SnO2 film. Multiscale observations reveal the SEI accumulation after alloying reactions and distinct dissolving of the organic layer at potentials above de-conversion reactions, which results in the inorganic layer being directly exposed to the electrolyte and thus becoming thick and inhomogeneous. The broken and thick SEI causes rapid capacity decay and low Coulombic efficiencies (CEs) of 97.5%. Accordingly, it is demonstrated that, as the SnO2 is precoated with LiF or Li2 CO3 , a robust and thin SEI layer is induced to form and is stabilized in the continuous cycles, resulting in enhanced cycling stability and promoted CEs to 99.5%. This work adds new insights to the SEI evolution mechanisms on SnO2 -based anodes and suggests an effective strategy to create high performance metal oxide anode for Li-ion batteries.