Research on tactile sensing technology has been actively conducted in recent years to pave the way for the next generation of highly intelligent devices. Sophisticated tactile sensing technology has a broad range of potential applications in various fields including: (1) robotic systems with tactile sensors that are capable of situation recognition for high-risk tasks in hazardous environments; (2) tactile quality evaluation of consumer products in the cosmetic, automobile, and fabric industries that are used in everyday life; (3) robot-assisted surgery (RAS) to facilitate tactile interaction with the surgeon; and (4) artificial skin that features a sense of touch to help people with disabilities who suffer from loss of tactile sense. This review provides an overview of recent advances in tactile sensing technology, which is divided into three aspects: basic physiology associated with human tactile sensing, the requirements for the realization of viable tactile sensors, and new materials for tactile devices. In addition, the potential, hurdles, and major challenges of tactile sensing technology applications including artificial skin, medical devices, and analysis tools for human tactile perception are presented in detail. Finally, the review highlights possible routes, rapid trends, and new opportunities related to tactile devices in the foreseeable future.
artificial skin; human tactile perception; robot-assisted surgery; soft robotics; tactile sensing.
Conflict of interest statement
The authors declare no conflicts of interest.
Description of mechanoreceptors in human hand skin.
a) Schematic illustration demonstrating the working mechanism of the sensor. Tunnel current occurs when the pressure is applied to the device; ( b) output curves showing the difference in pressure sensitivity according to the sensor structure (reprinted with permission for Figure 2a,b from Ref.  Copyright 2014 American Chemical Society); ( c) schematic illustration demonstrating the sensor fabrication method by using the liquid-driven transfer technique; ( d) image of the skin-conformal sensor array; ( e) gauge factor and maximum stretchability according to the number of transferred layer (reprinted with permission for Figure 2c–e from Ref.  Copyright 2017 John Wiley and Sons).
a) Image of the special spider organ for detecting external stimuli (left) and the magnified image of the organ (right); ( b) the relative output resistance change versus strain, including theoretical data; the inset shows the results of no cracks; ( c) image of crack sensor onto violin for detection of sound wave (left). The intensity versus frequency, when Elgar’s ‘Salut d’Amour’ was played (right) (reprinted with permission for Figure 3a–c, from Ref.  Copyright 2014 Springer Nature); ( d) SEM image shows the stretched graphene woven fabric (GWFs) depending on the strain (left). Optical image of the GWF on Si/SiO 2 substrate (right); ( e) data showing the relative output resistance under different strain levels. (Reprinted with permission for Figure 3d,e from Ref.  Copyright 2015 American Chemical Society); ( f) finite element modeling (FEM) simulation data including conventional flat film structure and auxetic metamaterial structure under 15% tensile strain; ( g) the normalized displacement at the transverse direction under different levels of longitudinal tensile strain; ( h) auxetic strain sensor and human wrist with sensor (left). The signal-to-noise ratio data in case of auxetics and flat sensors (right) (Reprinted with permission for Figure 3f–h from Ref.  Copyright 2018 John Wiley and Sons).
a) Illustration of the tactile sensor array with active matrix circuitry; ( b) photographic image showing the tactile sensor array (left). The mapping data by pressure of the ring (right) (reprinted with permission for Figure 4a,b from Ref.  Copyright 2013 Springer Nature); ( c) photograph of silicon membrane tactile sensor with active matrix circuitry; ( d) real-time monitoring of the fractional change in voltage versus the pressure levels in real time; ( e) data and image showing the movement of stylus tip (reprinted with permission for Figure 4c–e from Ref.  Copyright 2015 AIP Publishing); ( f) photograph showing active matrix array sensor based on the graphene; ( g) sensitivity performance of graphene transistor (GT) strain sensor including region I and II; ( h) the image and output data under different bending states (left) (reprinted with permission for Figure 4f–h from Ref.  Copyright 2015 John Wiley and Sons).
a) Schematic illustration of pressure-sensitive graphene FETs (left). Cross-sectional image unit cell with a graphene channel and an air dielectric layer (right); ( b) the characteristic of the air dielectric graphene transistors as a function of time at various pressure levels (left: maximum level of 267 kPa, right: maximum level of 3140 kPa) (reprinted with permission for Figure 5a,b from Ref.  under CC-BY 4.0 license); ( c) image of intrinsically stretchable transistor and illustration of unit cell with tactile sensor, electrodes, dielectric, and passivation layer; ( d) photograph showing the conformal transistor array with ladybug on palm (left), current mapping data resulting from the pressure of the six legs of a ladybug (right) (reprinted with permission for Figure 5c,d from Ref.  Copyright 2018 Springer Nature); ( e) schematic illustration showing fabrication steps of a flexible pressure sensor (left), the photographic image of the active matrix tactile sensor with 16 × 16 array; ( f) the current mapping data indicating pressure distribution at flat and bending states (radius of 60 mm) (reprinted with permission for Figure 5e,f from Ref.  Copyright 2018 American Chemical Society).
a) Photograph and optical microscopic image indicating the flexible three-axial shear force sensor; ( b) illustration and SEM image depicting the cross-sectional view of the sensor; ( c) output characteristics (sensitivity under normal and shear force/the different weight of 80 mg, 15 mg, and 10 mg) of flexible shear force sensor (reprinted with permission for Figure 6a–c from Ref.  Copyright 2014 John Wiley and Sons).
a) Photograph showing the fully fabricated sensor with 3 × 3 array (top) and unit cell (bottom); ( b) real applications of the device using normal force, shear force, and N 2 flow (reprinted with permission for Figure 7a,b from Ref.  Copyright 2014 American Chemical Society); ( c) schematic illustration demonstrating the unit cell of the flexible microfluidic tactile sensor, and working principle; ( d) illustration of texture sensing experiment and related output performances (rounded edges, softer material, and 80 μm) (reprinted with permission for Figure 7c,d from Ref.  Copyright 2017 John Wiley and Sons).
a) Magnified image showing the structure of a unit cell; ( b) schematic illustration showing the working mechanism; ( c) photograph of e-skin that fully covers the area of a human hand; ( d) changes in voltage under normal and shear loads (reprinted with permission for Figure 8a–d from Ref.  Copyright 2016 John Wiley and Sons).
a) Photographic image of silicon strain sensor and location of boron-doped silicon nanomembrane; ( b) the relative change in resistance versus strain (%) with modeling data (reprinted with permission for Figure 9a,b from Ref.  Copyright 2014 Springer Nature); ( c) image of strain gauge with the serpentine shape pattern and picture of device on tape without stress layer; ( d) photographic image showing e-skin applications on the finger and wrist (reprinted with permission for Figure 9c,d from Ref.  Copyright 2017 John Wiley and Sons).
a) Picture showing the transparent graphene strain gauge sensor; ( b) change in resistance versus stretched strain; ( c) the relative change in resistance during a stretching experiment of the device on the finger (reprinted with permission for Figure 10a–c from Ref.  Copyright 2012 Elsevier); ( d) photograph of the strain sensor array based on the nanographene film; ( e) the change in resistance rate with respect to applied strain (reprinted with permission for Figure 10d,e from Ref.  Copyright 2015 American Chemical Society); ( f) photographic and SEM image of graphene strain gauge sensor array on animal leather, the structural information of the unit cell; ( g) pressure distribution under gentle touch of 9 kPa (reprinted with permission for Figure 10f,g from Ref.  Copyright 2014 American Chemical Society); ( h) output curve variation and the gauge factor values, according to the strain applied to the sensor (top: no mesh, a low-density mesh, and a high-density mesh). The illustration of the working principle (bottom); ( i) the laser patterned graphene sensor attached onto the wristband, finger, face mask, and throat (reprinted with permission for Figure 10h,i from Ref.  Copyright 2017 Royal Society of Chemistry).
a) Picture and the optical microscopic image of flexible device consisting of single-layer MoS 2 flake; ( b) schematic illustration of the operating mechanism of single-layer MoS 2 piezoelectric device under strain (reprinted with permission for Figure 11a,b from Ref.  Copyright 2014 Springer Nature); ( c) image of conformal tactile sensor based on MoS 2 floating on the surface of water; ( d) the output resistance change versus compressive strain; ( e) fractional change in resistance of the tactile sensor as function of the applied tensile and compressive strain; ( f) monitoring of pressure distribution (reprinted with permission for Figure 11c–f from Ref.  Copyright 2016 John Wiley and Sons).
a) Description of the sensor structure (top), image showing the prosthetic hand that is covered with artificial skin. The inset indicates the stretchability of device; ( b) photograph of tapping keyboard by using prosthetic hand (top left). The changes in resistance of the silicon nanoribbon pressure sensor as a function of time (top right). Photograph of experiment using hot and cold glass (middle left). Real-time monitoring of current change (temperature and IR sensor) (middle right). Image of experimental setup for measuring the humidity sensing capabilities of sensor (bottom left). A bar plot indicating the capacitance change in case of dry and wet states (reprinted with permission for Figure 12a,b from Ref.  Copyright 2014 Springer Nature).
a) Schematic illustration showing the stretchable and conformable matrix networks (left). Photographic image of the device (right); ( b) sensing capabilities under various multiple stimuli (pressure, temperature, magnetic, and proximity) (reprinted with permission for Figure 13a,b from Ref.  under CC-BY 4.0 license).
a) Schematic illustration of multimodal E-skin sensor based on graphene material; ( b) circuit diagram of the device; ( c) sensing capabilities of the multimodal e-skin sensor corresponding to various stimuli (hot wind blow, hand touch, and breath) (reprinted with permission for Figure 14a–c from Ref.  Copyright 2016 John Wiley and Sons).
a) Schematic illustration showing the structure of multi-functional e-skin (left) and units (right) including flow, matter, temperature, and pressure sensor; ( b) multiple performance of the fabricated e-skin (reprinted with permission for Figure 15a,b from Ref.  Copyright 2017 John Wiley and Sons).
a) Photograph of the microfluidic diaphragm pressure sensor (left). Illustration showing a layout of the sensing area including tangential and radial sensing components (middle). Circuit diagram of the device using a Wheatstone bridge (right); ( b) Photographic image indicating the tactile sensing glove equipped with the device (top left). Plot showing real-time measurement during the motion of gripping a grape, by using thumb and index finger (bottom left). Photographic image showing the array sensing capabilities, when grasping a bat (right) (reprinted with permission for Figure 16a,b from Ref.  Copyright 2017 John Wiley and Sons).
a) Schematic illustration explaining fabrication process of the waveguide; ( b) output data showing the sensing capabilities of waveguide sensor with respect to different situations including elongation, bending, and pressing force; ( c) sensing abilities of the device related to the various motions (reprinted with permission for Figure 17a–c from Ref.  Copyright 2016 The American Association for the Advancement of Science).
a) Schematic illustration of the measurement setup (left); ( b) plot of pressure variation according to the displacement (smooth and fingerprinted fingers) (top). Output data of power spectra of signals from Fourier transform (bottom) (reprinted with permission for Figure 18a,b from Ref.  Copyright 2009 The American Association for the Advancement of Science); ( c) plot showing the fluctuations (tangential force) with respect to μ/λ (reprinted with permission for Figure 18c from Ref.  Copyright 2011 American Physical Society). ( d) Schematic illustration showing experimental setup and flow by using sensorized finger (reprinted with permission for Figure 18d from Ref.  under CC-BY 4.0 license); ( e) illustration of experimental setup and tools (left), measured force as a function of time at various texture (baking paper, silk, denim, and wood) (right) (reprinted with permission for Figure 18e from Ref.  under CC-BY 4.0 license).
a) Picture of the structure of bio-inspired tactile sensor; ( b) table indicating data of the scratching test from different force directions measured by the bio-inspired tactile sensor; ( c) image of the proposed capacitance architecture to measure a three-axis force (top). Illustration demonstrates the sensing mechanism corresponding to normal and shear force (bottom); ( d) image showing the upper area of forcep with the acoustic cavity; ( e) diagram indicates the sensing principle of the acoustic tactile sensor; ( f) experimental data from the acoustic tactile sensor, when grasping the materials, including rubber and sponge (reprinted with permission for Figure 19d–f from Ref.  Copyright 2017 Springer Nature).
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