Human tactile perception as a standard for artificial tactile sensing—a review

A Face-Shear Mode Piezoelectric Array Sensor for Elasticity and Force Measurement

We present the development of a 6 × 6 piezoelectric array sensor for measuring elasticity and force. The proposed sensor employs an impedance measurement technique, sensing the acoustic load impedance of a target by measuring the electrical impedance shift of face-shear mode PMN-PT (lead magnesium niobate-lead titanate) single crystal elements. Among various modes of PMN-PT single crystals, the face-shear mode was selected due to its especially high sensitivity to acoustic loads. To verify the elasticity sensing performance, gelatin samples with different elastic moduli were prepared and tested. For the force measurement test, different magnitudes of force were loaded to the sensing layer whose acoustic impedance was varied with applied forces. From the experimental results, the fabricated sensor showed an elastic stiffness sensitivity of 23.52 Ohm/MPa with a resolution of 4.25 kPa and contact force sensitivity of 19.27 Ohm/N with a resolution of 5.19 mN. In addition, the mapping experiment of elasticity and force using the sensor array was successfully demonstrated.

Conductive Self-Healing Nanocomposite Hydrogel Skin Sensors with Antifreezing and Thermoresponsive Properties

With growing interest in flexible and wearable devices, the demand for nature-inspired soft smart materials, especially intelligent hydrogels with multiple perceptions toward external strain and temperatures to mimic the human skin, is on the rise. However, simultaneous achievement of intelligent hydrogels with skin-compatible performances, including good transparency, appropriate mechanical properties, autonomous self-healing ability, multiple mechanical/thermoresponsiveness, and retaining flexibility at subzero temperatures, is still challenging and thus limits their application as skinlike devices. Here, conductive nanocomposite hydrogels (NC gels) were delicately designed and prepared via gelation of oligo(ethylene glycol) methacrylate (OEGMA)-based monomers in a glycerol-water cosolvent, where inorganic clay served as the physical cross-linker and provided conductive ions. The resultant NC gels exhibited good conductivity (∼3.32 × 10^-4 S cm^-1, akin to biological muscle tissue) and an autonomously self-healing capacity (healing efficiency reached 84.8%). Additionally, such NC gels displayed excellent flexibility and responded well to multiple strain/temperature external stimuli and subtle human motions in a wide temperature range (from -20 to 45 °C). These distinguished properties would endow such NC gels significant applications in fields of biosensors, human-machine interfaces, and soft robotics.

Recent progress in tactile sensors and their applications in intelligent systems

With the rapid development of intelligent technology, tactile sensors as sensing devices constitute the core foundation of intelligent systems. Biological organs that can sense various stimuli play vital roles in the interaction between human beings and the external environment. Inspired by this fact, research on skin-like tactile sensors with multifunctionality and high performance has attracted extensive attention. An overview of the development of high-performance tactile sensors applied in intelligent systems is systematically presented. First, the development of tactile sensors endowed with stretchability, self-healing, biodegradability, high resolution and self-powered capability is discussed. Then, for intelligent systems, tactile sensors with excellent application prospects in many fields, such as wearable devices, medical treatment, artificial limbs and robotics, are presented. Finally, the future prospects of tactile sensors for intelligent systems are discussed.

Capturing the dynamics of peripersonal space by integrating expectancy effects and sound propagation properties

BACKGROUND

Humans perceive near space and far space differently. Peripersonal space (PPS), i.e. the space directly surrounding the body, is often studied using paradigms based on audiotactile integration. In these paradigms, reaction time (RT) to a tactile stimulus is measured in the presence of a concurrent auditory looming stimulus.

NEW METHOD

We propose here to refine the experimental procedure by disentangling behavioral contributions of the targeted audiotactile integration mechanisms from expectancy effects. To this aim, we added to the protocol a baseline with a fixed sound distance. Furthermore, in order to improve the relevance of the audiotactile integration measures, we took into account sound propagation properties and assessed RTs for logarithmically spaced auditory distances.

RESULTS

Expectation contributed significantly to overall behavioral responses. Subtracting it isolated the audiotactile effect due to the stimulus proximity. This revealed that audiotactile integration effects have to be tested on a logarithmic scale of distances, and that they follow a linear variation on this scale.

COMPARISON WITH EXISTING METHOD(S)

The current method allows cleaner and more pertinent sampling measures for evaluating audiotactile integration phenomena linked to PPS. Furthermore, most of the existing methods propose a sigmoid fitting, which rests on the intuitive framework that PPS is an in-or-out zone. Our results suggest that behavioral effects follow a logarithmic decrease, thus a response graduated in space.

CONCLUSIONS

The proposed protocol design and method of analysis contribute to sharpen the experimental investigation of the factors influencing and modifying multisensory integration phenomena in the space surrounding the body.

Development of Phantom Material that Resembles Compression Properties of Human Brain Tissue for Training Models

There is a need to quantify and reproduce the mechanical behavior of brain tissue for a variety of applications from designing proper training models for surgeons to enabling research on the effectiveness of personal protective gear, such as football helmets. The mechanical response of several candidate phantom materials, including hydrogels and emulsions, was characterized and compared to porcine brain tissue under similar strains and strain rates. Some candidate materials were selected since their compositions were similar to brain tissue, such as emulsions that mimic the high content of lipids. Others, like silicone, were included since these are currently used as phantom materials. The mechanical response of the emulsion was closer to that of the native porcine brain tissue than the other candidates. The emulsions, created by addition of oil to a hydrogel, were able to withstand compressive strain greater than 40%. The addition of lipids in the emulsions also prevented the syneresis typically seen with hydrogel materials. This allowed the emulsion material to undergo freeze-thaw cycles with no significant change in their mechanical properties.

From finger friction to brain activation: Tactile perception of the roughness of gratings

The formation of tactile perception is related to skin receptors and the cerebral cortex. In order to systematically study the tactile perception from finger friction to the brain response, a 32-channel Brain Products system and two tri-axial force sensors were used to obtain electroencephalograph (EEG) and friction signals during fingers exploring grating surfaces. A finite element finger model was established to analyze the stress changes of the skin receptors during tactile perception. Samples with different grating widths and spaces were chosen. The results indicated that different gratings induced different stress concentrations within skin that stimulated Meissner and Merkel receptors. Skin friction was affected by gratings during the tactile perception. It was also found that P300 evoked by gratings was related with the skin deformation, contact area, friction force, and stress around cutaneous mechanoreceptors. The wider grating width generated larger skin deformation, friction force, and stress, which induced stronger tactile stimulation. The smaller grating spacing generated higher vibration frequency, inducing stronger tactile stimulation. The latency of the P300 peak was related to the difference between the textured target stimulus and the smooth non-target stimulus. This study proofed that there was a relationship between the activation in brain regions, surface friction, and contact conditions of skin during the tactile perception. It contributes to understanding the formation process and cognitive mechanism of tactile perception of different surface textures.

Flexible Pressure-Sensitive Contact Transistors Operating in the Subthreshold Regime

Organic thin-film transistor (TFT)-based pressure sensors have received huge attention for wearable electronic applications such as health monitoring and smart robotics. However, there still remains a challenge to achieve low power consumption and high sensitivity at the same time for the realization of truly wearable sensor systems where minimizing power consumption is significant because of limited battery run time. Here, we introduce a flexible pressure-sensitive contact transistor (PCT), a new type of pressure-sensing device based on organic TFTs for next-generation wearable electronic skin devices. The PCT consists of deformable S/D electrodes integrated on a staggered TFT. The deformable S/D electrodes were fabricated by embedding conducting single-walled carbon nanotubes on the surface of microstructured polydimethylsiloxane. Under pressure loads, the deformation of the electrodes on an organic semiconductor layer leads modulation of drain current from variation in both the channel geometry and contact resistance. By strategic subthreshold operation to minimize power consumption and increase the dominance of contact resistance because of gated Schottky contact, the PCT achieves both ultralow power consumption (order of 10¹ nW) and high sensitivity (18.96 kPa^-1). Finally, we demonstrate a 5 × 5 active matrix PCT array on a 3 μm-thick parylene substrate. The device with ultralow power consumption and high sensitivity on a biocompatible flexible substrate makes the PCT promising candidate for next-generation wearable electronic skin devices.

Design, Motivation and Evaluation of a Full-Resolution Optical Tactile Sensor

Human skin is capable of sensing various types of forces with high resolution and accuracy. The development of an artificial sense of touch needs to address these properties, while retaining scalability to large surfaces with arbitrary shapes. The vision-based tactile sensor proposed in this article exploits the extremely high resolution of modern image sensors to reconstruct the normal force distribution applied to a soft material, whose deformation is observed on the camera images. By embedding a random pattern within the material, the full resolution of the camera can be exploited. The design and the motivation of the proposed approach are discussed with respect to a simplified elasticity model. An artificial deep neural network is trained on experimental data to perform the tactile sensing task with high accuracy for a specific indenter, and with a spatial resolution and a sensing range comparable to the human fingertip.

Repurposed Leather with Sensing Capabilities for Multifunctional Electronic Skin

Electronic skin (e-skin), an important part toward the realization of artificial intelligence, has been developing through comprehending, mimicking, and eventually outperforming skin in some aspects. Most of the e-skin substrates are flexible polymers, such as polydimethylsiloxane (PDMS). Although PDMS was found to be biocompatible, it is not suitable for long-time wearing due to its air impermeability. This study reports a simple and designable leather based e-skin by merging the natural sophisticated structure and wearing comfort of leather with the multifunctional properties of nanomaterials. The leather based e-skin could make leather, "the dead skin," repurposed for its sensing capabilities. This e-skin can be applied in flexible pressure sensors, displays, user-interactive devices, etc. It provides a new class of materials for the development of multifunctional e-skin to mimic or even outshine the functions of real skin.

Biomechanics in Soft Mechanical Sensing: From Natural Case Studies to the Artificial World

Living beings use mechanical interaction with the environment to gather essential cues for implementing necessary movements and actions. This process is mediated by biomechanics, primarily of the sensory structures, meaning that, at first, mechanical stimuli are morphologically computed. In the present paper, we select and review cases of specialized sensory organs for mechanical sensing-from both the animal and plant kingdoms-that distribute their intelligence in both structure and materials. A focus is set on biomechanical aspects, such as morphology and material characteristics of the selected sensory organs, and on how their sensing function is affected by them in natural environments. In this route, examples of artificial sensors that implement these principles are provided, and/or ways in which they can be translated artificially are suggested. Following a biomimetic approach, our aim is to make a step towards creating a toolbox with general tailoring principles, based on mechanical aspects tuned repeatedly in nature, such as orientation, shape, distribution, materials, and micromechanics. These should be used for a future methodical design of novel soft sensing systems for soft robotics.

A wet-chemistry-based hydrogel sensing platform for 2D imaging of pressure, chemicals and temperature

Human skin can perceive pressure, chemical compounds and temperature with a high spatial resolution via specific receptors. Inspired by human skin, we present a wet-chemistry based hydrogel sensing platform for 2D imaging sensitive to specific external stimuli, e.g., pressure, chemicals and temperature. This platform is composed of a hydrogel pyramidal array on a single electrode. Each pyramid serves as a spatially separated reservoir for chemical reactions, enabling independent pixels for sensing without individual electrodes. Depending on the electrochemiluminescence (ECL) electrolyte for specific stimuli, our platform possesses 2D imaging capabilities with high sensitivity for pH and temperature in addition to pressure via the deformation of the viscoelastic hydrogel. This work represents an important step toward the application of sensitive chemical reactions for various external stimuli to biocompatible electronic skins based on hydrogels without addressing circuit for each pixel.

Recent Advances in Tactile Sensing Technology

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.

Flexible Ferroelectric Sensors with Ultrahigh Pressure Sensitivity and Linear Response over Exceptionally Broad Pressure Range

Flexible pressure sensors with a high sensitivity over a broad linear range can simplify wearable sensing systems without additional signal processing for the linear output, enabling device miniaturization and low power consumption. Here, we demonstrate a flexible ferroelectric sensor with ultrahigh pressure sensitivity and linear response over an exceptionally broad pressure range based on the material and structural design of ferroelectric composites with a multilayer interlocked microdome geometry. Due to the stress concentration between interlocked microdome arrays and increased contact area in the multilayer design, the flexible ferroelectric sensors could perceive static/dynamic pressure with high sensitivity (47.7 kPa^-1, 1.3 Pa minimum detection). In addition, efficient stress distribution between stacked multilayers enables linear sensing over exceptionally broad pressure range (0.0013-353 kPa) with fast response time (20 ms) and high reliability over 5000 repetitive cycles even at an extremely high pressure of 272 kPa. Our sensor can be used to monitor diverse stimuli from a low to a high pressure range including weak gas flow, acoustic sound, wrist pulse pressure, respiration, and foot pressure with a single device.

Bioinspired Flexible and Highly Responsive Dual-Mode Strain/Magnetism Composite Sensor

The mimicry of human skin to detect both oncoming and physical-contacting object is of great importance in the fields of manufacturing, artificial robots and vehicles, etc. Herein, a novel bioinspired flexible and highly responsive dual-mode strain/magnetism composite sensor, which works via both contact and contactless modes, is first fabricated by incorporating Fe₃O₄/silicone system into a carbon fiber aerogel (CFA). The distance dependence of magnetic field endorses the CFA/Fe₃O₄/silicone composite possible for spatial sensing due to the introduction of Fe₃O₄ magnetic nanoparticles. As a result, the as-prepared flexible sensor exhibits precise and real-time response not only to direct-contact compression as usual but also to contactless magnetic field in a wide frequency range from 0.1 to 10 Hz, achieving the maximum variance of 68% and 86% in relative electrical resistance, respectively. The contact and contactless sensing modes of the strain/magnetism sensor are clearly demonstrated by recording the speeds of bicycle riding and walking, respectively. Interestingly, this dual-mode composite sensor exhibits the capacity of identifying the contact and contactless state, which is the first report for flexible sensors. The current protocol is eco-friendly, facile, and thought-provoking for the fabrication of multifunctional sensors.

An experimental and numerical study on tactile neuroimaging: A novel minimally invasive technique for intraoperative brain imaging

BACKGROUND

The success of tumour neurosurgery is highly dependent on the ability to accurately localize the operative target, which may shift during the operation. Performing intraoperative brain imaging is crucial in minimally invasive neurosurgery to detect the effect of brain shift on the tumour's location, and to maximize the efficiency of tumour resection.

METHOD

The major objective of this research is to introduce tactile neuroimaging as a novel minimally invasive technique for intraoperative brain imaging. To investigate the feasibility of the proposed method, an experimental and numerical study was first performed on silicone phantoms mimicking the brain tissue with a tumour. Then the study was extended to a clinical model with the meningioma tumour.

RESULTS

The stress distribution on the brain surface has high potential to intraoperatively localize the tumour.

CONCLUSION

Results suggest that tactile neuroimaging can be used to provide non-invasive and real-time intraoperative data on a tumour's features.

Remote tactile sensing system integrated with magnetic synapse

Mechanoreceptors in a fingertip convert external tactile stimulations into electrical signals, which are transmitted by the nervous system through synaptic transmitters and then perceived by the brain with high accuracy and reliability. Inspired by the human synapse system, this paper reports a robust tactile sensing system consisting of a remote touch tip and a magnetic synapse. External pressure on the remote touch tip is transferred in the form of air pressure to the magnetic synapse, where its variation is converted into electrical signals. The developed system has high sensitivity and a wide dynamic range. The remote sensing system demonstrated tactile capabilities over wide pressure range with a minimum detectable pressure of 6 Pa. In addition, it could measure tactile stimulation up to 1,000 Hz without distortion and hysteresis, owing to the separation of the touching and sensing parts. The excellent performance of the system in terms of surface texture discrimination, heartbeat measurement from the human wrist, and satisfactory detection quality in water indicates that it has considerable potential for various mechanosensory applications in different environments.

Tactile Perception of Roughness and Hardness to Discriminate Materials by Friction-Induced Vibration

The human fingertip is an exquisitely powerful bio-tactile sensor in perceiving different materials based on various highly-sensitive mechanoreceptors distributed all over the skin. The tactile perception of surface roughness and material hardness can be estimated by skin vibrations generated during a fingertip stroking of a surface instead of being maintained in a static position. Moreover, reciprocating sliding with increasing velocities and pressures are two common behaviors in humans to discriminate different materials, but the question remains as to what the correlation of the sliding velocity and normal load on the tactile perceptions of surface roughness and hardness is for material discrimination. In order to investigate this correlation, a finger-inspired crossed-I beam structure tactile tester has been designed to mimic the anthropic tactile discrimination behaviors. A novel method of characterizing the fast Fourier transform integral (FFT) slope of the vibration acceleration signal generated from fingertip rubbing on surfaces at increasing sliding velocity and normal load, respectively, are defined as k_v and k_w, and is proposed to discriminate the surface roughness and hardness of different materials. Over eight types of materials were tested, and they proved the capability and advantages of this high tactile-discriminating method. Our study may find applications in investigating humanoid robot perceptual abilities.

Ultratransparent and stretchable graphene electrodes

Two-dimensional materials, such as graphene, are attractive for both conventional semiconductor applications and nascent applications in flexible electronics. However, the high tensile strength of graphene results in fracturing at low strain, making it challenging to take advantage of its extraordinary electronic properties in stretchable electronics. To enable excellent strain-dependent performance of transparent graphene conductors, we created graphene nanoscrolls in between stacked graphene layers, referred to as multilayer graphene/graphene scrolls (MGGs). Under strain, some scrolls bridged the fragmented domains of graphene to maintain a percolating network that enabled excellent conductivity at high strains. Trilayer MGGs supported on elastomers retained 65% of their original conductance at 100% strain, which is perpendicular to the direction of current flow, whereas trilayer films of graphene without nanoscrolls retained only 25% of their starting conductance. A stretchable all-carbon transistor fabricated using MGGs as electrodes exhibited a transmittance of >90% and retained 60% of its original current output at 120% strain (parallel to the direction of charge transport). These highly stretchable and transparent all-carbon transistors could enable sophisticated stretchable optoelectronics.

Bioinspired magnetic reception and multimodal sensing

Several animals use Earth's magnetic field in concert with other sensor modes to accomplish navigational tasks ranging from local homing to continental scale migration. However, despite extensive research, animal magnetic reception remains poorly understood. Similarly, the Earth's magnetic field offers a signal that engineered systems can leverage to navigate in environments where man-made positioning systems such as GPS are either unavailable or unreliable. This work uses a behavioral strategy inspired by the migratory behavior of sea turtles to locate a magnetic goal and respond to wind when it is present. Sensing is performed using a number of distributed sensors. Based on existing theoretical biology considerations, data processing is performed using combinations of circles and ellipses to exploit the distributed sensing paradigm. Agent-based simulation results indicate that this approach is capable of using two separate magnetic properties to locate a goal from a variety of initial conditions in both noiseless and noisy sensory environments. The system's ability to locate the goal appears robust to noise at the cost of overall path length.

Detection of magnetic field properties using distributed sensing: a computational neuroscience approach

Diverse taxa use Earth's magnetic field to aid both short- and long-distance navigation. Study of these behaviors has led to a variety of postulated sensory and processing mechanisms that remain unconfirmed. Although several models have been proposed to explain and understand these mechanisms' underpinnings, they have not necessarily connected a putative sensory signal to the nervous system. Using mathematical software simulation, hardware testing and the computational neuroscience tool of dynamic neural fields, the present work implements a previously developed conceptual model for processing magnetite-based magnetosensory data. Results show that the conceptual model, originally constructed to stimulate thought and generate insights into future physiological experiments, may provide a valid approach to encoding magnetic field information. Specifically, magnetoreceptors that are each individually capable of sensing directional information can, as a population, encode magnetic intensity and direction. The findings hold promise both as a biological magnetoreception concept and for generating engineering innovations in sensing and processing.

The Impact of Simultaneously Applying Normal Stress and Vibrotactile Stimulation for Feedback of Exteroceptive Information

Commercially available prosthetic hands do not convey any tactile information, forcing amputees to rely solely on visual attention. A promising solution to this problem is haptics, which could lead to new prostheses in which tactile information is conveyed between the amputee and the artificial limb. However, the haptic feedback must be optimized so that amputees can use it effectively; and although several studies have examined how specific haptic feedback systems can transmit certain types of tactile information, there has not yet been much research on the effects of superposing two or more types of feedback at the same location, which might prove to be more effective than using a single type of feedback alone. This paper investigates how the simultaneous application of two different types of haptic feedback—vibration and normal stress—impacts the human sensory perception of each separate feedback type. These stimuli were applied to glabrous skin on the forearms of 14 participants. Our experiments tested whether participants experienced more accurate sensory perception, compared to vibration or normal stress alone, when vibration was applied at the same time as the normal stress, at either the same location, or at a different location 6 cm away. Results indicate that although participants' perception of the normal stress diminished when vibration was applied at the same location, the same combination improved their perception of the vibration. Apparently, vibration has a negative impact upon the ability to perceive normal stress, whether applied at the same or a different location; whereas the opposite is true for the effect of normal stress upon the perception of vibration.

Validating a model for detecting magnetic field intensity using dynamic neural fields

Several animals use properties of Earth's magnetic field as a part of their navigation toolkit to accomplish tasks ranging from local homing to continental migration. Studying these behaviors has led to the postulation of both a magnetite-based sense, and a chemically based radical-pair mechanism. Several researchers have proposed models aimed at both understanding these mechanisms, and offering insights into future physiological experiments. The present work mathematically implements a previously developed conceptual model for sensing and processing magnetite-based magnetosensory feedback by using dynamic neural fields, a computational neuroscience tool for modeling nervous system dynamics and processing. Results demonstrate the plausibility of the conceptual model's predictions. Specifically, a population of magnetoreceptors in which each individual can only sense directional information can encode magnetic intensity en masse. Multiple populations can encode both magnetic direction, and intensity, two parameters that several animals use in their navigational toolkits. This work can be expanded to test other magnetoreceptor models.

Modeling of physical human–robot interaction

Enhancement of human performance using an intelligent assist device is becoming more common. In order to achieve effective augmentation of human capacity, cooperation between human and robot must be safe and very intuitive. Ensuring such collaboration remains a challenge, especially when admittance control is used. This paper addresses the issues of transparency and human perception coming from vibration in admittance control schemes. Simulation results obtained with our suggested improved model using an admittance controller are presented, then four models using transfer functions are discussed in detail and evaluated as a means of simulating physical human–robot interaction using admittance control. The simulation and experimental results are then compared in order to assess the validity and limitations of the proposed models in the case of a four-degree-of-freedom intelligent assist device designed for large payload.

Self-Healing, Fully Functional, and Multiparametric Flexible Sensing Platform

A non-biological and flexible self-healing platform has tailored sensitivity toward one or a combination of pressure, strain, gas analytes, and temperature. For demonstration, a complete self-healing device is described in the form of a bendable and stretchable chemiresistor, where every part is self-healing.

Micro/nanostructured surfaces for self-powered and multifunctional electronic skins

We introduce recent advances in the design of bioinspired micro/nanostructures and 2D/3D structures for the enhancement of energy harvesting and multifunctional sensing properties of flexible electronic skins.

Design and Performance of a Low-Cost Telemetric Laparoscopic Tactile Grasper

Tactile feedback is completely lost in laparoscopic surgery, which would provide information about tissue compliance, texture, structural features, and foreign bodies. We developed a system with artificial tactile feedback for laparoscopic surgery that consists of a telemetric tactile laparoscopic grasper, a remote PC with customized software, and a commercial video-mixer. A standard, nonsensorized laparoscopic grasper was customized to allow the integration of a tactile sensor and its electronics. The tactile sensor and the electronics module were designed to be detachable from the instrument. These parts are lightweight and wireless, thus not impeding the use of the device as surgical instrument. The remaining system components used to generate visualization of the tactile data do not influence the workflow in the operating room. The overall system design of the described instrumentation allows for easy implementation in an operating room environment. The fabrication of the tactile sensor is relatively easy and the production costs are low. With this telemetric laparoscopic grasper instrument, systematic preclinical studies can be performed in which surgeons execute surgical tasks that are derived from clinical reality. The experience gained from these investigations could then be used to define the requirements for any further development of artificial tactile feedback systems.

Fingertip skin-inspired microstructured ferroelectric skins discriminate static/dynamic pressure and temperature stimuli

In human fingertips, the fingerprint patterns and interlocked epidermal-dermal microridges play a critical role in amplifying and transferring tactile signals to various mechanoreceptors, enabling spatiotemporal perception of various static and dynamic tactile signals. Inspired by the structure and functions of the human fingertip, we fabricated fingerprint-like patterns and interlocked microstructures in ferroelectric films, which can enhance the piezoelectric, pyroelectric, and piezoresistive sensing of static and dynamic mechanothermal signals. Our flexible and microstructured ferroelectric skins can detect and discriminate between multiple spatiotemporal tactile stimuli including static and dynamic pressure, vibration, and temperature with high sensitivities. As proof-of-concept demonstration, the sensors have been used for the simultaneous monitoring of pulse pressure and temperature of artery vessels, precise detection of acoustic sounds, and discrimination of various surface textures. Our microstructured ferroelectric skins may find applications in robotic skins, wearable sensors, and medical diagnostic devices.

A Wearable Haptic Device Based on Twisting Wire Actuators for Feedback of Tactile Pressure Information

<div class=""abs_img""> <img src=""[disp_template_path]/JRM/abst-image/00270004/12.jpg"" width=""300"" /> A wearable haptic device</div> This paper presents a novel wearable haptic device that provides the user with knowledge of a vertical force, measured at the fingertips, by applying pressure at three different locations on the user’s body. Human prehension and manipulation abilities rely on the ability to convert tactile information into controlled actions, such as the regulation of gripping force. Current upper-limb prosthetics are able to partially replicate the mechanical functions of the human hand, but most do not provide any sensory information to the user. This greatly affects amputees, as they must rely solely on their vision to perform grasping actions. Our device uses a twisted wire actuator to convert rotational motion into linear displacement, which allows the device to remain compact and light-weight. In the past, the main shortcoming of this type of actuator was its limited linear range of motion; but with a slight modification of the principle, we have extended our actuator’s linear range of motion by 40%. In this paper, we present the design of our haptic device, the kinematic and dynamic modelling of the actuator, and the results of the experiments that were used to validate the system’s functionality. </span>

Sensory Feedback Training for Improvement of Finger Perception in Cerebral Palsy

Purpose. To develop and to test a feedback training system for improvement of tactile perception and coordination of fingers in children and youth with cerebral palsy. Methods. The fingers of 7 probands with cerebral palsy of different types and severity were stimulated using small vibration motors integrated in the fingers of a hand glove. The vibration motors were connected through a microcontroller to a computer and to a response 5-button keyboard. By pressing an appropriate keyboard button, the proband must indicate in which finger the vibration was felt. The number of incorrect responses and the reaction time were measured for every finger. The perception and coordination of fingers were estimated before and after two-week training using both clinical tests and the measurements. Results. Proper functioning of the developed system in persons with cerebral palsy was confirmed. The tactile sensation of fingers was improved in five of seven subjects after two weeks of training. There was no clear tendency towards improvement of selective use of fingers. Conclusion. The designed feedback system could be used to train tactile perception of fingers in children and youth with cerebral palsy. An extensive study is required to confirm these findings.

Vibrotactile evaluation: osseointegrated versus socket-suspended transfemoral prostheses

This study investigated detection thresholds of vibrometric stimuli in patients with transfemoral amputation supplied with osseointegrated (OI) and socket-suspended prostheses. It included 17 patients tested preoperatively with socket-suspended prostheses and after 2 yr with OI prostheses and a control group (n = 17) using socket-suspended prostheses, evaluated once. Assessments on the prosthetic and intact feet were conducted at six frequencies (8, 16, 32, 64, 125, and 250 Hz). Furthermore, measurements were conducted to investigate how vibrometric signals are transmitted through a test prosthesis. The results showed that the OI group had improved ability to detect vibrations through the prosthesis at 125 Hz (p = 0.01) at follow-up compared with the preoperative measurement. Compared with the control group, the OI group at follow-up had better ability to detect high frequency vibrations through the prosthesis (125 Hz, p = 0.02; 250 Hz, p = 0.03). The vibrometric signal transmitted through the test prosthesis was reduced at 8, 125, and 250 Hz but was amplified at 16, 32, and 64 Hz. Differences between the OI and the control groups were found in the highest frequencies in which the test prosthesis showed reduction of the vibrometric signal. The study provides insight into the mechanisms of vibration transmission between the exterior and bone-anchored as well as socket-suspended amputation prostheses.

Application of artificial palpation in vascular surgeries for detection of peripheral arterial stenosis

Palpation is one of the applied methods that surgeons usually use during surgery in order to verify the health condition of a tissue/organ. In fact, most of surgical assessments are based on analysis of the force feedback received from tissue/organ via palpation. Although palpation has a key role in efficient progress of surgery operations, it depends very much on the experience and skill of the surgeons. This limits the application of this technique in some cases to a large extent. In this regard, an artificial tactile sensing approach is an innovative technology that tries to make tactile data more available for surgeons, especially in situations where doing the palpation is not possible or is too difficult. In this paper, having considered the present problems of artery bypass surgery in peripheral arterial occlusive disease (PAOD), applicability of a new tactile sensory system capable of detecting arterial stenosis during surgery was evaluated. Presenting the modelling and numerical solution of the problem, it was demonstrated that the artificial tactile sensing approach is not only capable of detecting the presence of an arterial stenosis in an artery, but also its type. Furthermore, it was shown that the new tactile sensory system (previously designed, fabricated and tested in laboratory) is efficiently capable of detecting the simulated artery in the simulated biological tissue as well as diagnosis of the stenosis occurred inside it.

Flexible tactile sensing based on piezoresistive composites: a review

The large expansion of the robotic field in the last decades has created a growing interest in the research and development of tactile sensing solutions for robot hand and body integration. Piezoresistive composites are one of the most widely employed materials for this purpose, combining simple and low cost preparation with high flexibility and conformability to surfaces, low power consumption, and the use of simple read-out electronics. This work provides a review on the different type of composite materials, classified according to the conduction mechanism and analyzing the physics behind it. In particular piezoresistors, strain gauges, percolative and quantum tunnelling devices are reviewed here, with a perspective overview on the most used filler types and polymeric matrices. A description of the state-of-the-art of the tactile sensor solutions from the point of view of the architecture, the design and the performance is also reviewed, with a perspective outlook on the main promising applications.

25th anniversary article: The evolution of electronic skin (e-skin): a brief history, design considerations, and recent progress

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

Optical-based artificial palpation sensors for lesion characterization

Palpation techniques are widely used in medical procedures to detect the presence of lumps or tumors in the soft breast tissues. Since these procedures are very subjective and depend on the skills of the physician, it is imperative to perform detailed a scientific study in order to develop more efficient medical sensors to measure and generate palpation parameters. In this research, we propose an optical-based, artificial palpation sensor for lesion characterization. This has been developed using a multilayer polydimethylsiloxane optical waveguide. Light was generated at the critical angle to reflect totally within the flexible and transparent waveguide. When a waveguide was compressed by an external force, its contact area would deform and cause the light to scatter. The scattered light was captured by a high-resolution camera and saved as an image format. To test the performance of the proposed system, we used a realistic tissue phantom with embedded hard inclusions. The experimental results show that the proposed sensor can detect inclusions and provide the relative value of size, depth, and Young's modulus of an inclusion.

Synthetic and bio-artificial tactile sensing: a review

This paper reviews the state of the art of artificial tactile sensing, with a particular focus on bio-hybrid and fully-biological approaches. To this aim, the study of physiology of the human sense of touch and of the coding mechanisms of tactile information is a significant starting point, which is briefly explored in this review. Then, the progress towards the development of an artificial sense of touch are investigated. Artificial tactile sensing is analysed with respect to the possible approaches to fabricate the outer interface layer: synthetic skin versus bio-artificial skin. With particular respect to the synthetic skin approach, a brief overview is provided on various technologies and transduction principles that can be integrated beneath the skin layer. Then, the main focus moves to approaches characterized by the use of bio-artificial skin as an outer layer of the artificial sensory system. Within this design solution for the skin, bio-hybrid and fully-biological tactile sensing systems are thoroughly presented: while significant results have been reported for the development of tissue engineered skins, the development of mechanotransduction units and their integration is a recent trend that is still lagging behind, therefore requiring research efforts and investments. In the last part of the paper, application domains and perspectives of the reviewed tactile sensing technologies are discussed.

A narrative review on haptic devices: relating the physiology and psychophysical properties of the hand to devices for rehabilitation in central nervous system disorders

PURPOSE

This article provides rehabilitation professionals and engineers with a theoretical and pragmatic rationale for the inclusion of haptic feedback in the rehabilitation of central nervous system disorders affecting the hand.

METHOD

A narrative review of haptic devices used in sensorimotor hand rehabilitation was undertaken. Presented papers were selected to outline and clarify the underlying somatosensory mechanisms underpinning these technologies and provide exemplars of the evidence to date.

RESULTS

Haptic devices provide kinaesthetic and/or tactile stimulation. Kinaesthetic haptics are beginning to be incorporated in central nervous system rehabilitation; however, there has been limited development of tactile haptics. Clinical research in haptic rehabilitation of the hand is embryonic but initial findings indicate potential clinical benefit.

CONCLUSIONS

Haptic rehabilitation offers the potential to advance sensorimotor hand rehabilitation but both scientific and pragmatic developments are needed to ensure that its potential is realized.

A triple-jaw actuated and sensorized instrument for grasping large organs during minimally invasive robotic surgery

BACKGROUND

Secure grasping and effective manipulation of delicate large organs during robotic surgery operations needs especially designed instruments that can enclose a large amount of tissue and feed back the pinch forces.

METHODS

A large organ triple-jaw grasper was instrumented using practical force sensory and actuating systems. A force tracking scheme was proposed to facilitate auto-grasping of large organs during robotic teleoperation surgery. An on-site force commanding/reflecting mechanism was also implemented to use the device as an independent hand-held robotic instrument. The efficacy of the robotic grasper was examined in phantom tests.

RESULTS

The instrument grasped large soft objects effectively and safely with accurately measured and controlled pinch forces. Furthermore, it could characterize the overall mechanical behavior of the grasping objects.

CONCLUSIONS

The instrument designed provides a potential solution for the safe and effective grasping and manipulation of large abdominal organs, either as a hand-held device, or in a teleoperation framework.

Ultrasoft 100 nm thick zero Poisson's ratio film with 60% reversible compressibility

About a 100 nm thick multilayer film of nanoparticle monolayers and polymer layers is shown to behave like cellular-foam with a modulus below 100 KPa. The 1.25 cm radius film adhered to a rigid surface can be compressed reversibly to 60% strain. The more than 4 orders of magnitude lower modulus compared to its constituents is explained by considering local bending in the (nano)cellular structure, similar to cork and wings of beetles. As the rigidity of the polymer backbone is increased in just four monolayers, the modulus of the composite increases by over 70%. Electro-optical map of the strain distribution over the area of compression and increase in modulus with thickness indicates the films have zero Poisson's ratio.

A novel robotic tactile mass detector with application in clinical breast examination

This paper presents a novel tactile sensing robot designed to detect breast lesions with minimum invasiveness to the tissue while providing exact documentation to make therapeutic and surgical decisions. The robot named "Robotic Tactile Breast Mass Identifier (Robo-Tac-BMI) consists of an indentation probe controlled by a robotic system and a visualization interface to manipulate the end-effecter. Geometrical maps of the test points with related tension-relaxation curves are provided during clinical examinations. Utilizing the curves, three functional stiffness parameters are extracted locally for each test point. These parameters are employed to provide objective information to facilitate the surgeon's task in the diagnostic procedure. Computational analysis is proposed for a real breast tissue model to study the capability of artificial tactile sensing in the mass detection. Indications of the mass existence are determined and employed as the basis of the Robo-Tac-BMI design and construction. Clinical trials are executed by the Robo-Tac-BMI on 161 cases. The results show that the robot has the potential to provide tissue mechanical properties unlike the conventional screening modalities carried out either by the surgeon or the imaging techniques which are not quantitative and lack documentation. Sonography with and without mammography is chosen as the "gold standard" tests.