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Proc. Natl. Acad. Sci. USA, First published November 30, 2020| https://doi.org/10.1073/pnas.2001055117 Fingerprint ridges allow primates to regulate grip

Seoung-Mok Yum^a,1 , In-Keun Baek^a,1,2, Dongpyo Hong^a, Juhan Kim^a, Kyunghoon Jung^a, Seontae Kim^a, Kihoon Eom^a, Jeongmin Jang^a, Seonmyeong Kim^a, Matlabjon Sattorov^a,b,c, Min-Geol Lee^d, Sungwan Kim^e, Michael J. Adams^f,3 , and Gun-Sik Park^a,b,c,g,3

^aCenter for THz-Driven Biomedical Systems, Department of Physics and Astronomy, College of Natural Sciences, Seoul National University, Seoul 08826, Republic of Korea; ^bCenter for Applied Electromagnetic Research, Advanced Institute of Convergence Technology, Suwon 16229, Republic of Korea; ^cR&D Department, Seoul-Teracom, Inc., Suwon 16229, Republic of Korea; ^dCutaneous Biology Research Institute, Department of Dermatology, College of Medicine, Yonsei University, Seoul 03722, Republic of Korea; ^eDepartment of Biomedical Engineering, College of Medicine, Seoul National University, Seoul 03080, Republic of Korea; ^fSchool of Chemical Engineering, University of Birmingham, Birmingham GL51 9RE, United Kingdom; and ^gInstitute of Applied Physics, Seoul National University, Seoul 08826, Republic of Korea

¹S.M.Y. and I.K.B. contributed equally to this work.
²Present address: Mechatronics R&D Center, Samsung Electronics Co., Ltd., Hwasung 18448, Republic of Korea.y
³To whom correspondence may be addressed.

Abstract

Fingerprints are unique to primates and koalas but what advantages do these features of our hands and feet provide us compared with the smooth pads of carnivorans, e.g., feline or ursine species? It has been argued that the epidermal ridges on finger pads decrease friction when in contact with smooth surfaces, promote interlocking with rough surfaces, channel excess water, prevent blistering, and enhance tactile sensitivity. Here, we found that they were at the origin of a moisture-regulating mechanism, which ensures an optimal hydration of the keratin layer of the skin for maximizing the friction and reducing the probability of catastrophic slip due to the hydrodynamic formation of a fluid layer. When in contact with impermeable surfaces, the occlusion of the sweat from the pores in the ridges promotes plasticization of the skin, dramatically increasing friction. Occlusion and external moisture could cause an excess of water that would defeat the natural hydration balance. However, we have demonstrated using femtosecond laser-based polarization-tunable terahertz wave spectroscopic imaging and infrared optical coherence tomography that the moisture regulation may be explained by a combination of a microfluidic capillary evaporation mechanism and a sweat pore blocking mechanism. This results in maintaining an optimal amount of moisture in the furrows that maximizes the friction irrespective of whether a finger pad is initially wet or dry. Thus, abundant low-flow sweat glands and epidermal furrows have provided primates with the evolutionary advantage in dry and wet conditions of manipulative and locomotive abilities not available to other animals.

epidermal ridge function, finger pad friction, moisture regulation, capillary evaporation

논문정보

형식Research article
게재일2020년 11월 (BRIC 등록일 2020-12-07)
연구진국내(교신)+국외 연구진
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