Thermal Transport Characteristics of Human Skin Measured In Vivo Using Ultrathin Conformal Arrays of Thermal Sensors and Actuators

• Published in: PloS one Vol. 10; no. 2; p. e0118131
• Main Authors: Webb, R. Chad, Pielak, Rafal M., Bastien, Philippe, Ayers, Joshua, Niittynen, Juha, Kurniawan, Jonas, Manco, Megan, Lin, Athena, Cho, Nam Heon, Malyrchuk, Viktor, Balooch, Guive, Rogers, John A.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 06.02.2015; Public Library of Science (PLoS)
• Subjects: Actuators; Algorithms; Analysis; Anisotropy; Cheek; Complex systems; Correlation; Electric properties; Electrical impedance; Electrical resistivity; Engineering; Epidermis; Flow velocity; Forearm; Heat conductivity; Humans; Hydration; In vivo methods and tests; Infrared heating; Infrared lasers; Laboratories; Laser beam heating; Lasers; Materials science; Measurement; Microscopy; Models, Theoretical; Moisture content; Multivariate statistical analysis; Optical Coherence Tomography; Physical properties; Regional Blood Flow; Sensor arrays; Sensors; Skin; Skin Physiological Phenomena; Spectrum analysis; Statistical analysis; Stratum corneum; Systems analysis; Temperature; Thermal Conductivity; Thermal diffusivity; Thermal properties; Thermoelectricity; Thermography; Thermoregulation; Thermosensing; Transport properties; Water content; Wrist; San Francisco California; California; United States > US; Illinois; New Jersey
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0118131

Measurements of the thermal transport properties of the skin can reveal changes in physical and chemical states of relevance to dermatological health, skin structure and activity, thermoregulation and other aspects of human physiology. Existing methods for in vivo evaluations demand complex systems for laser heating and infrared thermography, or they require rigid, invasive probes; neither can apply to arbitrary regions of the body, offers modes for rapid spatial mapping, or enables continuous monitoring outside of laboratory settings. Here we describe human clinical studies using mechanically soft arrays of thermal actuators and sensors that laminate onto the skin to provide rapid, quantitative in vivo determination of both the thermal conductivity and thermal diffusivity, in a completely non-invasive manner. Comprehensive analysis of measurements on six different body locations of each of twenty-five human subjects reveal systematic variations and directional anisotropies in the characteristics, with correlations to the thicknesses of the epidermis (EP) and stratum corneum (SC) determined by optical coherence tomography, and to the water content assessed by electrical impedance based measurements. Multivariate statistical analysis establishes four distinct locations across the body that exhibit different physical properties: heel, cheek, palm, and wrist/volar forearm/dorsal forearm. The data also demonstrate that thermal transport correlates negatively with SC and EP thickness and positively with water content, with a strength of correlation that varies from region to region, e.g., stronger in the palmar than in the follicular regions.