www.advmatinterfaces.de FULL PAPER 1800635 (1 of 8) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Melt-Compounded Keratin-TPU Self-Assembled Composite Film as Bioinspired e-Skin Huan Li, Tridib K. Sinha, Jinho Lee, Jeong Seok Oh, Youngjoon Ahn, and Jin Kuk Kim* DOI: 10.1002/admi.201800635 stimuli from the external environment. [1,2] Because of the promise in advanced humanoid robotics, biomedical pros- theses, surgical electronic gloves, etc., [3–11] immense interests are being motivated for mimicking the human skin by devel- oping stable, flexible, and biocompatible artificial skin of human skin like rheology, tribology, and tactile sensing capability. However, the tactile sensing artificial skin is precisely known as electronic-skin (e-skin). [6,7] Although silicone rubber is being used to develop artificial skins or e-skins for different applications, [3–7] because of its elastic property, durability, shape- ability, nontoxicity, and skin like refractive index, [12] it is cost-intensive and non-bio- degradable. [13] Due to hydrophobic nature of silicone rubber, limitations also exist in simulating the tribomechanical perfor- mance of human skin properly over the full range of conditions. [14] Solution-based processing technique can be considered as another disadvantage of silicone rubber. Different biopolymers viz., cytoskeletal keratinocytes, tis- sues, cells, collagens are being potentially employed for devel- oping bio-inspired artificial skins and organs. [8–11] Apart from the biocompatibility and biodegradability, these biopolymers provide skin like keratin–elastin composition, [8–11] a similar trend of viscoelastic properties, [15–17] and skin like porous mor- phology. [1] Isolation of the biopolymers, and/or its modifica- tions are required for fabrication of artificial skin. The methods are mainly solution based, tedious and time-consuming. Tactile sensing capability is one of the major concerns of artificial skin (alias e-skin). In this recent years, different kinds of sensors based on different working principles, such as tri- boelectric nanogenerators (TENGs) are being fabricated using various flexible polymers, which not only perform as effective tactile sensors but also harvest abundant mechanical energy being wasted during our daily life movement, simply by contact electrification and electrostatic induction method. [4–6,18–20] Most of the TENGs have relatively complex structures consisting of pair of triboelectric surfaces with adequate patterning and texturing, and two induction electrodes, which require tricky operation mode and large working space. It is noteworthy to mention that human skin shows positive triboelectric property, whereas maximum polymers used in TENG fabrication are negative triboelectric material. [5,21] Inspired by the keratin–elastin composition of human skin, here an artificial skin (alias electronic (e)-skin) is developed through solvent-free extrusion based melt mixing of thermoplastic polyurethane (TPU) with the biowaste human hair keratin. Self-assembled composite film of TPU and keratin (i.e., PUK) shows leg skin equivalent coefficient of friction value of 0.26 ± 0.05, cheek skin equivalent average surface roughness (Ra) of 0.047 ± 0.07 μm, cytoskeletal keratin intermediate filament network like rheological behavior, porous morphology, and skin like positive triboelectric property, when the keratin content is 10 wt%. H-bonded self-assembled network and lubri- cating behavior of cysteine-rich keratin provide such tribological and rheo- logical behaviors of the PUK. Single electrode triboelectric nanogenerator (STENG) made of PUK containing 10 wt% keratin (i.e., 10% PUK) not only shows clear discrimination between the touch feeling sensations of bare, and glove protected human finger, by producing output voltage of ≈1 and ≈16 V cm -2 , respectively, but it also can discriminate the tactile sensations of different objects viz., aluminum foil, cotton glove, wood, polyimide, and poly(tetrafluoroethylene) by producing different output voltages, resembling that the PUK composite film is well fitted for e-skin applications. H. Li, Dr. T. K. Sinha, Prof. J. K. Kim Department of Materials Engineering and Convergence Technology Gyeongsang National University 501 Jinju-daero, Jinju 52828, South Korea E-mail: rubber@gnu.ac.kr Prof. J. Lee The Research Institute of Natural Science and Department of Physics Education Gyeongsang National University 501 Jinju-daero, Jinju 52828, South Korea Prof. J. S. Oh School of Materials Science and Engineering Polymer Science and Engineering Engineering Research Institute Gyeongsang National University 501 Jinju-daero, Jinju 52828, South Korea Dr. Y. Ahn Gangrim Fueltech Co., Ltd. 61-106 Hwangma-ro, Anwui-myeon, Hamyang-gun, Gyeongam 50007 South Korea Bioinspired Electronic Skin 1. Introduction Human skin, mainly having the keratin–elastin composition, protects the interior organs and transduce various mechanical Adv. Mater. Interfaces 2018, 1800635