E-Glove for Prosthetic Hand Senses Pressure, Temperature, Moisture—and Warms Itself

A conventional prosthetic hand may enable functions such as the ability to grip, but it lacks qualities of softness, warmth, appearance, and sensory perception, including detection of pressure, temperature, and hydration. To improve the cold, unfeeling hand, a team based at Purdue University in collaboration with researchers at the University of Georgia and the University of Texas developed a slip-on flexible electronic glove (e-glove) that adds both sensory capabilities as well as skin-like softness and even warmth.

In the video below, project leader Chi Hwan Lee, an assistant professor at Purdue, provides an overview of the project rationale, fabrication steps, and capabilities:

The e-glove uses thin, flexible electronic sensors and miniaturized standard ICs on standard flexible glove (Fig. 1). It’s connected to a specially designed wristwatch, allowing for real-time display of sensory data and remote transmission to the user for post-data processing.

1. An electronic glove, or e-glove, developed by Purdue University researchers can be worn over a prosthetic hand to provide humanlike softness, warmth, appearance, and sensory perception. (Source: Purdue University)

Fabrication of the e-glove begins with a commercial stretchable nitrile glove, layered with an adhesive layer and active sensing elements, and with a screened-on mesh of silver threads for conductivity (Fig. 2). Other layers were added, including an elastomer silicon layer for skin-like “softness.”

2. A series of optical images for a representative e-glove platform that contains multiple stacked arrays of sensor elements including pressure (left), moisture (middle), and temperature (right) sensors, scale bar is 25 mm; the inset images show an enlarged view of the embedded sensor elements, scale bars are 4 mm (left), 3 mm (middle) and 1 mm (right), respectively (a). Representative electrical characteristics of the embedded sensor elements as a function of externally applied stimuli (b). Optical images of a custom-built wristwatch unit connected to the e-glove system, scale bars are 6 cm (left) and 1 cm (right), respectively (c). Optical image of the embedded internal circuitry in the wristwatch unit, scale bar is 5 mm (d). (Source: Purdue University)

Some of the steps were repeated to stack multiple layers to include different types of sensors. Among these was a capacitive hydration sensor, pressure-sensing layers, electrodes for the recording of electrocardiogram (ECG) and electromyogram (EMG) signals, and temperature sensors. They also incorporated a scheme that uses the stretched conductive mesh for resistive heating of the glove to create a human-like warmth—an asset when shaking hands, for example.

For the wristwatch-like control unit, they used 3D printing and a tiny printed circuit board on which they mounted the microcontroller circuitry, analog components, and multiplexer. The entire structure was attached to commercial wristband using epoxy adhesive.

Among the electronic functions was a 100-μA constant-current source for the sensors, and a 32-channel multiplexer used to switch among sensors while the voltage drop is measured across the elements. The changes in the sensed voltages—corresponding to external stimuli such as pressure, temperature, and more—were measured by a 16-bit analog-to-digital converter, displayed on the control wristwatch unit, and transmitted to an external device (commercial smartphone or tablet) via Bluetooth. The system is powered by a 3.7-V, 350-mAh rechargeable Li-ion polymer battery that provides operation between 15 hours (~71 mW dissipation with continuous display) and 70 hours (~16 mW, on-demand display only).

In addition to detailed finite element analysis (FEA) for mechanical and thermal modeling, they performed both fixture-based and real-world tests using the glove to grasp a baseball, touch a wet diaper, and handle a cup of hot water, all while monitoring the pressure exerted across the whole palm area with an array of 20 pressure sensors (Fig. 3). They also evaluated the “warmth profile” of the glove compared to a human hand.

3. Shown are: Optical image of the e-glove system grasping a baseball, scale bar is 25 mm (a). Results of the recording of pressure (b) Change of conductance as a function of pressure applied for the embedded single sensor element (c). Optical image of the e-glove system touching a wet diaper, scale bar is 5 cm (d). Results of the recording of hydration (e). Results of control measurements by using a commercial hydration sensor (f). Optical image of the e-glove system holding a cup of hot water, scale bar is 5 cm (g). Results of the recording of temperature (h). Results of control measurements by using a commercial infrared (IR) sensor (i). Optical image of electrophysiological (EP) electrodes installed around the thumb of the e-glove system (the inset SEM image highlights the embedded networked Ag nanowire-mesh), scale bars are 4 mm and 600 nm (inset), respectively (j). ECG (top) and EMG (bottom) results measured from the human skin (k). Control measurement results from commercial EP recording electrodes (l). (Source: Purdue University)

“We developed a novel concept of the soft-packaged, sensor-instrumented e-glove built on a commercial nitrile glove, allowing it to seamlessly fit on arbitrary hand shapes,” noted Prof. Lee. “The e-glove is configured with a stretchable form of multimodal sensors to collect various information such as pressure, temperature, humidity, and electrophysiological biosignals, while simultaneously providing realistic human hand-like softness, appearance, and even warmth.”

Full details on the concept, design, modeling, simulation, fabrication, and results are provided in their comprehensive paper “Soft-packaged sensory glove system for human-like natural interaction and control of prosthetic hands,” published in NPG Asia Materials (Springer). The linked Supplementary Information provides further details and results, including a schematic and full bill of materials (BOM), plus links to several videos showing the glove in use.

Further work may even include incorporating “fingerprints” into a next-generation version. Purdue is looking to patent some of the technology and seeking partners to collaborate in clinical trials as well as experts in the prosthetics field to validate the use of the e-glove and to continue optimizing its design.