The importance of the sense of touch in the medical sciences is nearly impossible to overstate. For example, palpation (examining by touching) is a first-line diagnostic tool in primary care, orthopedics, obstetrics, urology, oncology, and speech pathology. Moreover, touch is a key part of all procedures performed by hand--e.g., setting broken bones and dislocated joints, turning breech babies, and nearly all surgeries. For communities located in urban and rural "healthcare deserts," touch would greatly enhance the value of remote patient visits or drug-store-based diagnostic tests. Despite the attractiveness of virtual touch for remote care, medical training, and robot-assisted surgery, medical haptic technologies are underdeveloped. The reason is that existing systems cannot mimic the texture, softness, wetness, thermal conductivity, tack, and other near-surface properties of biological tissue. The key hypothesis of this project is that to mimic these sensations requires materials that can change their mechanical, electrical, and thermal properties in real time. The approach for doing so is to develop a system of haptic devices, i.e., devices that can stimulate the sense of touch, based on materials that can create sensations that can be transformed dynamically--e.g., rough vs. smooth, hot vs. cold, and sticky vs. slimy. Three types of devices are proposed based on (1) electricity conductive polymers to reproduce the feeling of fine texture, (2) arrays of liquid crystal elastomers that can change their softness in response to light, and (3) thermoplastics that can go from rubbery to stiff with small temperature changes to give the feeling of solidness and elasticity of virtual objects. Leveraging the flexible, wearable nature of these "haptic biomaterials," the investigators will build a prototype haptic glove that will allow a human user to differentiate between virtual objects by touch. By exploring the intersection of very different fields--organic materials and psychology--this project will provide a new toolkit for researchers to understand the tactile sense and mechanical sensing in biological systems more broadly. Research and education will be integrated through the following activities: (1) creation of internships for underrepresented minority students, (2) integration of the results into the investigators' graduate and undergraduate courses, and (3) creation of a video series on YouTube on the science of tactile perception and the results of this project which leverages considerable experience in creating scientific and educational videos.
The long-term goal of this research is to use combinations of haptic devices that exploit multiple effects simultaneously to achieve sensations of hot and cold, hard and soft, rough and smooth, furry and scaly, or sticky and slimy. The focus of this project is on testing the hypothesis that actuators made from stimulus-responsive polymers--"organic actuators"--can supply new types of sensations for biomedical haptic devices unavailable to "off-the-shelf" components. Organic actuators are defined as structures made from polymeric materials whose oxidation state, electrical conductivity, phase behavior, molecular conformation, or packing structure can be altered by an electrical, optical, or thermal stimulus in real time to produce macroscopic effects. The Research Plan is organized under three tasks, each of which generates a tactile sensation using a different physical effect generated by an organic actuator. The FIRST Task is focused on electrical stimulation via spatially resolved electrotactile signals. A stretchable conductive polymer patterned into an array of electrodes generates an electrotactile signal that will be used to measure two-point resolution of stimulation and generate spatially resolved sensations. Studies are designed to test the hypothesis that the small size of the electrodes, along with the ability to address them individually in a purpose-designed multiplexed socket, can be used to produce sensations that translate in the x-y plane to give the sensation of motion. Human subject volunteers will be tested using a double-blind methodology. The SECOND Task is focused on optically-enabled mechanical stimulation created by a liquid-crystal elastomer (LCE) that undergoes a change in shape in response to light to generate sensations of variable softness, texture, and motion at the fingertip. One set of experiments is designed to measure softness thresholds that can be changed in real time by altering the elastic modulus of the LCE with the intensity of irradiation. A second set of experiments will use arrays of LCE microposts that can be moved with illumination to give human subjects the sense of feeling different textures and possibly the sensation of moving interfaces even as the fingertip maintains a fixed position. The THIRD Task is focused on providing thermally-enabled kinesthetic feedback via a thermoplastic polymer embedded into a textile glove. When heated or cooled just above or below its glass transition temperature, the glove will undergo a reversible change from stiff to soft to elicit a kinesthetic response. Control over the temperature of the glove can be achieved by pairing a thermistor that changes its resistance in response to thermal fluctuations, with the thermoelectric devices to stabilize the temperature and therefore the stiffness of the substrate. To achieve a human-machine interface, the glove has been fitted with flex sensors to control a robotic finger on whose tip there is a pressure sensor which, when activated, sends a signal to the thermoelectric devices in the glove to cool (stiffen the finger) and thus provide kinesthetic feedback to the user. Once the thresholds for stiffness required to generate a kinesthetic response are determined, the information gained will be used to design a game in virtual reality that asks participants to grasp objects that appear visually and identify which is solid and which is merely an image. Finally, textural information will be encoded in the solid objects to determine if it is possible for subjects to discriminate between objects by embedding haptic actuators of the type described in previous tasks.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
