title: Thermal transport characteristics of human skin measured in vivo using ultrathin conformal arrays of thermal sensors and actuators.
abstract: 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.
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: R Chad
authors: RC
authors: Webb
authors: L'Oréal California Research Center, San Francisco, California, United States of America.
authors: Rafal M
authors: RM
authors: Pielak
authors: L'Oréal Research and Innovation, Aulnay sous Bois, France.
authors: Philippe
authors: P
authors: Bastien
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: Joshua
authors: J
authors: Ayers
authors: Tampere University of Technology, Department of Electronics and Communication Engineering, Korkeakoulunkatu 3, Tampere, Finland.
authors: Juha
authors: J
authors: Niittynen
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: Jonas
authors: J
authors: Kurniawan
authors: L'Oréal Early Clinical, Clark, New Jersey, United States of America.
authors: Megan
authors: M
authors: Manco
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: Athena
authors: A
authors: Lin
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: Nam Heon
authors: NH
authors: Cho
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: Viktor
authors: V
authors: Malyrchuk
authors: L'Oréal California Research Center, San Francisco, California, United States of America; L'Oréal Digital Incubator, Clark, New Jersey, United States of America.
authors: Guive
authors: G
authors: Balooch
authors: Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
authors: John A
authors: JA
authors: Rogers
mesh_terms: D000465:Algorithms; D006801:Humans; D008962:Models, Theoretical; D012039:Regional Blood Flow; D012879:Skin Physiological Phenomena; D013696:Temperature; D013814:Thermal Conductivity; D013697:Thermosensing