Human Stress Monitoring Skin Patches Fabricated on a Novel Porous PDMS Layer with the Moisture Permeability Improved for Skin Trouble Reduction

Abstract

The present research proposes a novel porous PDMS layer fabrication process to enhance pore uniformity and water vapor transmission rate for skin trouble reduction. The novel porous PDMS is applied on the development of a stress monitoring skin patches and is experimentally characterized in the human physiological signal range.The conventional porous PDMS layer form pores by mixing sugar and PDMS followed by sugar dissolution using water. The conventional porous PDMS is hard to apply on the human skin attachable device due to the two problems of: i) pore forming difficulty inside the PDMS due to the low water permeability of PDMS

ii) spin-coating difficulty due to the large size and the low size uniformity of the sugar particles.The present porous PDMS layer form pores by citric acid crystallization in PDMS followed by the citric acid crystal dissolution using ethanol. The present porous PDMS layer enables forming pores inside the PDMS by using the ethanol having high PDMS permeability. The citric acid is used for pore forming material instead of sugar due to the high solubility to ethanol. The citric acid crystallization process of the present porous PDMS layer enables spin-coating by reducing the pore size and improving the pore size uniformity, thereby enabling the human skin attachable device application.The present porous PDMS layer form pores stably in the condition of the ethanol and the toluene solvent evaporation temperature (te = 150 °C) and the weight mixing ratio of citric acid and PDMS (WMR = 0.5). The present porous PDMS layer, fabricated at te =150 °C and WMR = 0.5, shows 92.5 %p decreased and 200 %p increased pore size and pore size uniformity, respectively, compared to the non-crystallized porous PDMS layer, fabricated by citric acid mixing and dissolution. Thus the present porous PDMS layer enables membrane fabrication in the thickness range of 21 ~ 300 µm by spin-coating process. The present porous PDMS layer reduces the skin trouble by having the water vapor transmission rate of 770 ± 7.1 g/day∙m2 which is 1.8 times of the human skin requirement (432 g/day∙m2). As a result of the 7 days of human skin attachment test, the conventional PDMS layer causes skin trouble of the skin redness and the itchiness, whereas the present porous PDMS layer does not cause skin trouble.The stress monitoring skin patches integrates three sensors of skin temperature, skin conductance and arterial pulsewave sensor on the present porous PDMS layer. The stress monitoring skin patches are experimentally characterized in the human physiological signal range. The stress monitoring patches reduces the skin trouble by having the 4.34 times higher water vapor transmission rate (817 ± 4.2 g/day∙m2) than the conventional skin attachable device’s water vapor transmission rate (188 g/day∙m2).The present porous PDMS layer is appropriate to integrate physiological sensors and reduce skin troubles, thereby applicable to the development of the daily stress monitoring skin patch.