Making sense of artificial hands

Exploring Silicone Rubber Skin with Embedded Customizable Shape Capacitive Sensors to Enable Haptic Capabilities on Upper Limb Prosthetics

Commercially available electromechanical prosthetic devices still lack touch-sensing capabilities, and there is a huge gap between research devices and commercially available ones. There is a need for small flexible touch sensors with high accuracy and sensitivity for this type of device. Touch sensors in prosthetic devices are needed for feedback mechanisms to the user and to achieve high dexterity in control schemes for fragile objects. A brief review of prosthetic touch sensors is presented, addressing desirable characteristics for touch sensing. In this paper, a custom shape flexible capacitive touch sensor is designed and characterized, meeting prosthetic sensors needs, such as thickness, power consumption, accuracy, repeatability, and stability. The designed sensor presented the capability to distinguish up to 0.5N steps with good stability. The sensor accomplished a full sensing range between 5N and 100N with reasonable accuracy, and hysteresis analysis achieved an average of 8.8 %. Clinical Relevance- The custom shape capacitive sensors proposed in this paper contribute to the development of tactile sensors for prosthetic devices as more accurate and sensitive sensor interfaces are required to detect and improve manipulating capabilities.

Design and Integration of an Inexpensive Wearable Mechanotactile Feedback System for Myoelectric Prostheses

The aim of this paper was to demonstrate the functionality of an inexpensive mechanotactile sensory feedback system for transhumeral myoelectric prostheses. We summarize the development of a tactile-integrated prosthesis, including 1) evaluation of sensors that were retrofit onto existing commercial terminal devices; 2) design of two custom mechanotactile tactors that were integrated into a socket without compromising suction suspension; 3) design of a modular controller which translated sensor input to tactor output, was wirelessly adjusted, and fit within a prosthetic forearm; and 4) evaluation of the system with a single transhumeral participant. Prosthesis functionality was demonstrated over three test sessions; the participant was able to identify tactor stimulation location and demonstrated a reduction in grasp force with the mechanotactile stimulation. This system offers an inexpensive and modular solution for integration of a mechanotactile sensory feedback system into a prosthetic socket without compromising the suction seal. These principles can be applied in future studies to investigate the direct impact of sensory feedback on tangible outcomes for prosthetic users, thereby reducing barriers to clinical translation.

Control of Prosthetic Hands via the Peripheral Nervous System

This paper intends to provide a critical review of the literature on the technological issues on control and sensorization of hand prostheses interfacing with the Peripheral Nervous System (i.e., PNS), and their experimental validation on amputees. The study opens with an in-depth analysis of control solutions and sensorization features of research and commercially available prosthetic hands. Pros and cons of adopted technologies, signal processing techniques and motion control solutions are investigated. Special emphasis is then dedicated to the recent studies on the restoration of tactile perception in amputees through neural interfaces. The paper finally proposes a number of suggestions for designing the prosthetic system able to re-establish a bidirectional communication with the PNS and foster the prosthesis natural control.

Decellular biological scaffold polymerized with PEDOT for improving peripheral nerve interface charge transfer

Regenerative peripheral nerve interfaces (RPNIs) are for signal transfer between peripheral nerves inside the body to controllers for motorized prosthetics external to the body. Within the residual limb of an amputee, surgical construction of a RPNI connects a remaining peripheral nerve and spare muscle. Nerve signals become concentrated within the RPNI. Currently metal electrodes implanted on the RPNI muscle transfer signals but scarring around metal electrodes progressively diminishes charge transfer. Engineered materials may benefit RPNI signal transfer across the neural interface if they lower the power and charge density of the biologically meaningful signals. Poly3,4-ethylenedioxythiophene (PEDOT) is known to mediate ionic potentials allowing excitation across a critical nerve gap. We hypothesize that the capacity of an interface material to conduct electron mediated current is significantly increased by polymerized coating of PEDOT. SIS was either used plain or after PEDOT coating by electrochemical polymerization. Muscle forces are a direct representation of stimulating current distribution within an RPNI. In situ muscle forces were measured for the same muscle by electrically stimulating: a) the muscle's innervating nerve, b) directly on the muscle, c) on plain SIS laid on the muscle, and d) on SIS polymerized with PEDOT laid on the muscle. Electro-chemically coating PEDOT on SIS resulted in a thin, flexible material. PEDOT coated SIS distributed electrical stimulation more efficiently than SIS alone. Conductive polymer containing biological material allowed ionic signal distribution within the RPNI like muscle at lower charge density.

Microfabricated tactile sensors for biomedical applications: a review

During the last decades, tactile sensors based on different sensing principles have been developed due to the growing interest in robotics and, mainly, in medical applications. Several technological solutions have been employed to design tactile sensors; in particular, solutions based on microfabrication present several attractive features. Microfabrication technologies allow for developing miniaturized sensors with good performance in terms of metrological properties (e.g., accuracy, sensitivity, low power consumption, and frequency response). Small size and good metrological properties heighten the potential role of tactile sensors in medicine, making them especially attractive to be integrated in smart interfaces and microsurgical tools. This paper provides an overview of microfabricated tactile sensors, focusing on the mean principles of sensing, i.e., piezoresistive, piezoelectric and capacitive sensors. These sensors are employed for measuring contact properties, in particular force and pressure, in three main medical fields, i.e., prosthetics and artificial skin, minimal access surgery and smart interfaces for biomechanical analysis. The working principles and the metrological properties of the most promising tactile, microfabricated sensors are analyzed, together with their application in medicine. Finally, the new emerging technologies in these fields are briefly described.

Effect of feedback during virtual training of grip force control with a myoelectric prosthesis

The aim of this study was to determine whether virtual training improves grip force control in prosthesis use, and to examine which type of augmented feedback facilitates its learning most. Thirty-two able-bodied participants trained grip force with a virtual ball-throwing game for five sessions in a two-week period, using a myoelectric simulator. They received either feedback on movement outcome or on movement execution. Sixteen controls received training that did not focus on force control. Variability over learning was examined with the Tolerance-Noise-Covariation approach, and the transfer of grip force control was assessed in five test-tasks that assessed different aspects of force control in a pretest, a posttest and a retention test. During training performance increased while the variability in performance was decreased, mainly by reduction in noise. Grip force control only improved in the test-tasks that provided information on performance. Starting the training with a task that required low force production showed no transfer of the learned grip force. Feedback on movement execution was detrimental to grip force control, whereas feedback on movement outcome enhanced transfer of grip force control to tasks other than trained. Clinical implications of these results regarding virtual training of grip force control are discussed.

Changes in performance over time while learning to use a myoelectric prosthesis

BACKGROUND

Training increases the functional use of an upper limb prosthesis, but little is known about how people learn to use their prosthesis. The aim of this study was to describe the changes in performance with an upper limb myoelectric prosthesis during practice. The results provide a basis to develop an evidence-based training program.

METHODS

Thirty-one able-bodied participants took part in an experiment as well as thirty-one age- and gender-matched controls. Participants in the experimental condition, randomly assigned to one of four groups, practiced with a myoelectric simulator for five sessions in a two-weeks period. Group 1 practiced direct grasping, Group 2 practiced indirect grasping, Group 3 practiced fixating, and Group 4 practiced a combination of all three tasks. The Southampton Hand Assessment Procedure (SHAP) was assessed in a pretest, posttest, and two retention tests. Participants in the control condition performed SHAP two times, two weeks apart with no practice in between. Compressible objects were used in the grasping tasks. Changes in end-point kinematics, joint angles, and grip force control, the latter measured by magnitude of object compression, were examined.

RESULTS

The experimental groups improved more on SHAP than the control group. Interestingly, the fixation group improved comparable to the other training groups on the SHAP. Improvement in global position of the prosthesis leveled off after three practice sessions, whereas learning to control grip force required more time. The indirect grasping group had the smallest object compression in the beginning and this did not change over time, whereas the direct grasping and the combination group had a decrease in compression over time. Moreover, the indirect grasping group had the smallest grasping time that did not vary over object rigidity, while for the other two groups the grasping time decreased with an increase in object rigidity.

CONCLUSIONS

A training program should spend more time on learning fine control aspects of the prosthetic hand during rehabilitation. Moreover, training should start with the indirect grasping task that has the best performance, which is probably due to the higher amount of useful information available from the sound hand.

Sensory feedback in upper limb prosthetics

One of the challenges facing prosthetic designers and engineers is to restore the missing sensory function inherit to hand amputation. Several different techniques can be employed to provide amputees with sensory feedback: sensory substitution methods where the recorded stimulus is not only transferred to the amputee, but also translated to a different modality (modality-matched feedback), which transfers the stimulus without translation and direct neural stimulation, which interacts directly with peripheral afferent nerves. This paper presents an overview of the principal works and devices employed to provide upper limb amputees with sensory feedback. The focus is on sensory substitution and modality matched feedback; the principal features, advantages and disadvantages of the different methods are presented.